Thèses : « Boundary Layer Wind Tunnel (BLWT) »

1

Grossir, Guillaume. « Longshot hypersonic wind tunnel flow characterization and boundary layer stability investigations ». Doctoral thesis, Universite Libre de Bruxelles, 2015. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209044.

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The hypersonic laminar to turbulent transition problem above Mach 10 is addressed experimentally in the short duration VKI Longshot gun tunnel. Reentry conditions are partially duplicated in terms of Mach and Reynolds numbers. Pure nitrogen is used as a test gas with flow enthalpies sufficiently low to avoid its dissociation, thus approaching a perfect gas behavior. The stabilizing effects of Mach number and nosetip bluntness on the development of natural boundary layer disturbances are evaluated over a 7 degrees half-angle conical geometry without angle of attack.

Emphasis is initially placed on the flow characterization of the Longshot wind tunnel where these experiments are performed. Free-stream static pressure diagnostics are implemented in order to complete existing stagnation point pressure and heat flux measurements on a hemispherical probe. An alternative method used to determine accurate free-stream flow conditions is then derived following a rigorous theoretical approach coupled to the VKI Mutation thermo-chemical library. Resulting sensitivities of free-stream quantities to the experimental inputs are determined and the corresponding uncertainties are quantified and discussed. The benefits of this different approach are underlined, revealing the severe weaknesses of traditional methods based on the measurement of reservoir conditions and the following assumptions of an isentropic and adiabatic flow through the nozzle. The operational map of the Longshot wind tunnel is redefined accordingly. The practical limits associated with the onset of nitrogen flow condensation under non-equilibrium conditions are also accounted for.

Boundary layer transition experiments are then performed in this environment with free-stream Mach numbers ranging between 10-12. Instrumentation along the 800mm long conical model includes flush-mounted thermocouples and fast-response pressure sensors. Transition locations on sharp cones compare favorably with engineering correlations. A strong stabilizing effect of nosetip bluntness is reported and no transition reversal regime is observed for Re_RN<120000. Wavelet analysis of wall pressure traces denote the presence of inviscid instabilities belonging to Mack's second mode. An excellent agreement with Linear Stability Theory results is obtained from which the N-factor of the Longshot wind tunnel in these conditions is inferred. A novel Schlieren technique using a short duration laser light source is developed, allowing for high-quality flow visualization of the boundary layer disturbances. Comparisons of these measurement techniques between each other are finally reported, providing a detailed view of the transition process above Mach 10.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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Clifton, Andrew James. « Wind tunnel investigations of boundary layer conditions before and during snow drift / ». Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17165.

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Bertholds, Alexander. « CFD Simulations of the New University of Sydney Boundary Layer Wind Tunnel ». Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-166945.

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Using Computational Fluid Dynamics Simulations, the flow in the new University of Sydney closed circuit wind tunnel has been analyzed prior to the construction of the tunnel. The objective was to obtain a uniform flow in the test section of the wind tunnel while keeping the pressure losses over the tunnel as low as possible. This was achieved by using several flow-improving components such as guide vanes, screens, a honeycomb and a settling chamber. The guide vanes were used in the corners and in the diverging part leading into the settling chamber, giving a significant improvement of the flow as they prevent it from taking undesired paths. The settling chamber is used to decelerate the flow before it is accelerated when leaving the settling chamber, a process which reduces the turbulence in the flow. Screens were used in the settling chamber to further improve the flow by imposing a pressure drop which evens out differences in the flow speed and reduces the turbulence. The honeycomb, which is situated in the end of the settling chamber, makes the flow more uniform by forcing it to go in only one direction. A uniform flow was obtained using three screens and one honeycomb together with the guide vanes and the settling chamber.

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Mazur, Zachary Thomas Lyn. « Calibration and Baseline Flow Surveys of a Reconstructed Boundary-Layer Wind Tunnel ». Youngstown State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1597422848793191.

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Wu, Jie [Verfasser]. « Boundary-layer Instability Experiments in a Tandem Nozzle Supersonic Wind Tunnel / Jie Wu ». Aachen : Shaker, 2015. http://d-nb.info/106904864X/34.

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Tirtey, Sandy C. « Characterization of a transitional hypersonic boundary layer in wind tunnel and flight conditions ». Doctoral thesis, Universite Libre de Bruxelles, 2009. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210367.

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Laminar turbulent transition is known for a long time as a critical phenomenon influencing the thermal load encountered by hypersonic vehicle during their planetary re-entry trajectory. Despite the efforts made by several research laboratories all over the world, the prediction of transition remains inaccurate, leading to oversized thermal protection system and dramatic limitations of hypersonic vehicles performances. One of the reasons explaining the difficulties encountered in predicting transition is the wide variety of parameters playing a role in the phenomenon. Among these parameters, surface roughness is known to play a major role and has been investigated in the present thesis.

A wide bibliographic review describing the main parameters affecting transition and their coupling is proposed. The most popular roughness-induced transition predictions correlations are presented, insisting on the lack of physics included in these methods and the difficulties encountered in performing ground hypersonic transition experiments representative of real flight characteristics. This bibliographic review shows the importance of a better understanding of the physical phenomenon and of a wider experimental database, including real flight data, for the development of accurate prediction methods.

Based on the above conclusions, a hypersonic experimental test campaign is realized for the characterization of the flow field structure in the vicinity and in the wake of 3D roughness elements. This fundamental flat plate study is associated with numerical simulations for supporting the interpretation of experimental results and thus a better understanding of transition physics. Finally, a model is proposed in agreement with the wind tunnel observations and the bibliographic survey.

The second principal axis of the present study is the development of a hypersonic in-flight roughness-induced transition experiment in the frame of the European EXPERT program. These flight data, together with various wind tunnel measurements are very important for the development of a wide experimental database supporting the elaboration of future transition prediction methods.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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Blanco, Mark Richard. « Design and Qualification of a Boundary-Layer Wind Tunnel for Modern CFD Validation Experiments ». Youngstown State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1559237473563483.

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Fonti, Elio. « Measurements of aircraft wake vortices in ground proximity within an atmospheric boundary layer wind tunnel ». Thesis, Cranfield University, 2010. http://dspace.lib.cranfield.ac.uk/handle/1826/5635.

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The vortex wake characteristics of aircraft during landing and take-off are of interest in connection with both the safety of following aircraft penetrating the vortex and the dispersion of engine exhaust plumes. A series of measurements were carried out in an Atmospheric Boundary Layer Wind Tunnel (ABLWT) to identify and characterise both the mean and turbulent flow field of a pair of wake vortices in ground proximity. Cont/d.

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Petersen, Graciana [Verfasser], et Bernd [Akademischer Betreuer] Leitl. « Wind tunnel modelling of atmospheric boundary layer flow over hills / Graciana Petersen. Betreuer : Bernd Leitl ». Hamburg : Staats- und Universitätsbibliothek Hamburg, 2013. http://d-nb.info/1031280405/34.

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Petersen, Graciana Verfasser], et Bernd [Akademischer Betreuer] [Leitl. « Wind tunnel modelling of atmospheric boundary layer flow over hills / Graciana Petersen. Betreuer : Bernd Leitl ». Hamburg : Staats- und Universitätsbibliothek Hamburg, 2013. http://nbn-resolving.de/urn:nbn:de:gbv:18-60540.

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Galbraith, Daniel S. « Computational Fluid Dynamics Investigation into Shock Boundary Layer Interactions in the “Glass Inlet” Wind Tunnel ». University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1322053278.

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Joseph, Liselle AnnMarie. « Transition Detection for Low Speed Wind Tunnel Testing Using Infrared Thermography ». Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/78145.

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Transition is an important phenomenon in large scale, commercial, wind tunnel testing at low speeds because it is an excellent indicator of an airfoil performance. It is difficult to estimate transition through numerical techniques because of the complex nature of viscous flow. Therefore experimental techniques can be essential. Over the transition region the rate of heat transfer shows significant increases which can be detected using infrared thermography. This technique has been used predominantly at high speeds, on small models made of insulated materials, and for short test runs. Large scale testing has not been widely undertaken because the high sensitivity of transition to external factors makes it difficult to detect. The present study records the process undertaken to develop, implement and validate a transition detection system for continual use in the Virginia Tech Stability Wind Tunnel: a low speed, commercial wind tunnel where large, aluminium models are tested. The final system developed comprises of two high resolution FLIR A655sc infrared cameras; four 63.5-mm diameter circular windows; aluminium models covered in 0.8-mm silicone rubber insulation and a top layer of ConTact© paper; and a series of 25.4-mm wide rubber silicone fiberglass insulated heaters mounted inside the model and controlled externally by experimenters. This system produces images or videos of the model and the associated transition location, which is later extracted through image processing methods to give a final transition location in percentage chord. The system was validated using two DU96-W-180 airfoils of different chord lengths in the Virginia Tech Stability Wind Tunnel, each tested two months apart. The system proved to be robust and efficient, while not affecting the airfoil performance or any other system in use in the wind tunnel. Transition results produced by the system were compared to measurements obtained from pressure data and stethoscope tests as well as the numerical predictions of XFOIL. The transition results from all four methods showed excellent agreement with each other for the two models, for at least two Reynolds numbers and for several angles of attack on both suction and pressure side of the model. The agreement of data obtained under such different conditions and at different times suggests that the infrared thermography system efficiently and accurately detects transition for large aluminium models at low speeds.
Master of Science

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Horton, Damien. « Development of an Infrared Thermography System to Measure Boundary Layer Transition in a Low Speed Wind Tunnel Testing Environment ». DigitalCommons@CalPoly, 2021. https://digitalcommons.calpoly.edu/theses/2287.

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The use of infrared thermography for boundary layer detection was evaluated for use in the Cal Poly Low Speed Wind Tunnel (LSWT) and recommendations for the successful use of this technique were developed. In cooperation with Joby Aviation, an infinite wing model was designed, manufactured and tested for use in the LSWT. The wing was designed around a custom airfoil profile specific for this project, where the nearly-flat pressure gradient at a zero pitch angle would delay the chordwise onset of boundary layer transition. Steady-state, RANS numerical simulations predicted the onset of transition to occur at 0.75 x/c for the design Reynolds Number condition of 6.25x105. The wing was manufactured from 3D printed aluminum, with a wall thickness of 0.125 inches and a chord length of 13.78 inches. Two central rows of static pressure taps were used, each with 12 functional chordwise locations. The taps were able to generate strong correlation to the numerically predicted pressure coefficient distribution. The use of an infrared camera visualized and confirmed the presence of boundary layer transition at the chordline location anticipated by the early simulations. To do so, the model was pre-heated such that the differential cooling properties of laminar and turbulent flow would generate a clear temperature gradient on the surface correlating to boundary layer transition. Adjustment of the model’s pitch angle demonstrated a change in the onset location of boundary layer transition during the infrared testing. The change of onset location was seen to move forward along the chordline as the aerodynamic angle of attack was increased. Testing with a Preston Tube system allowed for the interpolation of local skin friction coefficient values at each static tap location. Application of both laminar and turbulent empirical assumptions, when compared to numerical expectations, allowed for the qualitative assessment of boundary layer transition onset. Overall, the wing model developed for this research proved capable of producing quality and repetitive results for the experimental goals it was designed to meet. The model will next be used in continued tests which will further explore the use of infrared thermography.

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Hobson-Dupont, Maximillian. « The development of a small scale wind tunnel simulating the atmospheric boundary layer in support of a stochastic wind model ». Thesis, San Jose State University, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1593083.

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There has been much success in atmospheric boundary layer simulation with medium sized closed-circuit wind tunnels with test section dimensions of approximately 1 x 1 m. However, smaller, blower-type wind tunnels are more common in university laboratories due to the lower cost and smaller space requirements. A small size, open flow wind tunnel with a 1 x 1 foot test section was modified to simulate the atmospheric boundary layer with a combination of upstream spires and cubic roughness elements. The primitive spire geometry detailed in the literature was found to yield poor agreement with the power law velocity profile of interest, and a novel iterative algorithm was developed to produce nonlinear spire geometry. The geometry generated by the algorithm was tested in the wind tunnel and found to simulate the desired velocity profile based on a Hellman exponent of 0.20 with a high degree of agreement, having a maximum velocity error of 4%. This confirmed the suitability of small-sized wind tunnels for simulating the atmospheric boundary layer.

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James, Ralph William. « The effect of boundary layer blowing in the corner region of a linear compressor cascade wind tunnel ». Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-05092009-040547/.

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Mallor, Fermin. « Enabling high-fidelity measurements of turbulent boundary layer flow over wing sections in the MTL wind tunnel ». Thesis, KTH, Mekanik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-264842.

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A reinforced fiber-glass model of a NACA 4412 wing profile is designed and set-up in the Minimum Turbulence Level (MTL) wind tunnel facility at KTH. The model has 65 pressure taps orifices, and the set-up includes two mounting panels designed to allow for particle image velocimetry (PIV) and hot wire anemometry (HWA) measurements of the boundary layer (to be performed in a future campaign). In a first experimental campaign pressure scans are conducted at three angles of attack of interest (5,10 and 12 degrees), and at four different Reynolds numbers based on chord length and inflow velocity (200,000, 400,000, 1,000,000, and 1,640,000). The preliminary results show good agreement with DNS and LES data, however, the effective angle of attack of the wing is affected by the interference of the test section. In order to obtain proper flow conditions for future campaigns inside the test section, wall inserts are designed using 2D k-omega SST simulations. The side-walls are streamlined and the final geometry is corrected to account for the boundary-layer growth over them. The inserts are shown to avoid early separation near the trailing edge at higher angles of attack (10 and 12 degrees), but the 2D simulations fail to capture the aforementioned angle-of-attack issue affecting the pressure distributions. Future extensions of the present insert design should include both 3D simulations of the test-section and a robust optimization procedure to prescribe the resulting pressure distribution.
En NACA 4412 vingprofilsmodel av förstärkt glasfiber utformas och installeras enligt Minimum Turbulence Level (MTL) i vindtunnelanläggningen på KTH. Modellen har 65 tryckluftsöppningar, och uppsättningen innehåller två monteringspaneler som är utformade för att möjliggöra mätningar av particle image velocimetry (PIV) and hot wire anemometry (HWA) hos gränsskiktet (som ska utföras i en framtida kampanj). I en första experimentell kampanj utförs tryckskanningar vid tre anfallsvinklar av intresse (5, 10, och 12 grader) samt vid fyra olika Reynolds-nummer (200 000, 400 000, 1 000 000 och 1 640 000). De preliminära resultaten visar god överensstämmelse med DNS- och LES-data, men den effektiva anfallsvinkeln på vingen påverkas av störningar från testsektionen. För att tillhandahålla korrekta flödesförhållanden för framtida kampanjer i testdelen är vägginsatser konstruerade med 2D k-omega SST-simuleringar. Sidoväggarna är strömlinjeformade och den slutliga geometrin korrigeras för att ta hänsyn till gränsiktets tillväxt. Insatserna undviker den tidig separation som sker nära bakkanten vid högre anfallsvinklar (10 och 12 grader), men 2D-simuleringarna misslyckades med att fånga det ovan nämnda anfallsvinkelproblemet som påverkar tryckfördelningarna.

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Goliber, Matthew Robert. « Pressure distribution on the roof of a model low-rise building tested in a boundary layer wind tunnel ». [Ames, Iowa : Iowa State University], 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1473211.

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Roepke, Joshua. « AN EXPERIMENTAL INVESTIGATION OF A GOLDSCHMIED PROPULSOR ». DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/939.

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A wind tunnel investigation of an axisymmetric bluff body, known as a Goldschmied propulsor, was completed. This model conceptually combines boundary layer control and boundary layer ingestion into a single complementary system that is intended to use energy to reduce the axial force on the body by eliminating separation and increasing the pressure recovery aft of the body’s maximum thickness. The goal of the current project was to design, fabricate, and fully document the performance of a wind tunnel model incorporating the Goldschmied propulsor concept and complete an examination of its aerodynamic performance. The investigation took place at California Polytechnic State University, San Luis Obispo in the Aerospace Engineering Department’s subsonic 3ft by 4ft wind tunnel. The model is 38.5 inches in length and 13.5 inches in diameter with a discrete suction slot at 85% of the body length and an embedded propulsor that provides the suction flow, expelling it out of the model’s aft end. The experiment included measurements of surface pressure, total axial force, suction mass flow rate, fan thrust, fan torque, fan speed, and input fan power. The size of the suction slot and amount of input fan power were the main test variables in the 54 data point test matrix that was completed at a length Reynolds number of 1.34 million and a tunnel speed of 66 ft/s (20 m/s). The model was able to achieve fully attached flow on the aftbody with as little as 100W of input power and a net positive (forward) axial force coefficient of 0.12 with as little as 200W of input power. The model was also able to achieve a peak axial pressure force coefficient of 0.005 in the forward direction with an input power of 500W and a slot gap of 1.6% of the body length. A slightly lower axial pressure force coefficient of 0.0045 was achieved with only 200W of input power and a slot gap of 0.7% of the body length. The peak axial pressure force for most tested slot gaps occurred at about 200W of input power, and a slot gap of 0.7% of the body length resulted in the best overall performance for most input power settings. Two different suction slot configurations, a simple gap and a cusp, were tested, and no significant performance differences were seen between them. The pressure coefficient data showed similar trends as test data from 1956 of a similar model at higher Reynolds number, but it did not show complete agreement. Despite these positive aspects of the investigation, a simple power based comparison between the collected data and a conventional non-integrated propulsor does not show a performance improvement for the Goldschmied propulsor.

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Hussain, Ali. « The Effect of Spanwise Location of an Active Boundary Layer Fence on Swept Wing Performance ». The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555516043121521.

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Ebenhoch, Raphael. « Simplified modeling of wind-farm flows ». Thesis, KTH, Strömningsfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-177309.

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Abstact: In order to address the wind-industry's need for a new generation of more advanced wake models, which accurately quantify the mean flow characteristics within a reasonably CPU-time, the two-dimensional analytical approach by Belcher et al. (2003) has been extended to a three-dimensional wake model. Hereby, the boundary-layer approximation of the Navier-Stokes equations has been linearized around an undisturbed baseflow, assuming that the wind turbines provoke a small perturbation of the velocity field. The conducted linearization of the well established actuator-disc theory brought valuable additional insights that could be used to understand the behavior (as well as the limitations) of a model based on linear methods. Hereby, one of the results was that an adjustment of the thrust coecient is necessary in order to get the same wake-velocity field within the used linear framework. In this thesis, two different datasets from experiments conducted in two different wind-tunnel facilities were used in order to validate the proposed model against wind-farm and single-turbine cases. The developed model is, in contrary to current engineering wake models, able to account for effects occurring in the upstream flow region. The measurement, as well as the simulations, show that the presence of a wind farm affects the approaching flow even far upstream of the first turbine row, which is not considered in current industrial guidelines. Despite the model assumptions, several velocity statistics above wind farms have been properly estimated, providing insight about the transfer of momentum inside the turbine rows. Overall, a promising preliminary version of a wake model is introduced, which can be extended arbitrarily depending on the regarded purpose.

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Di, Giovanni Antonio [Verfasser], Christian [Akademischer Betreuer] Stemmer, Wolfgang [Gutachter] Schröder et Christian [Gutachter] Stemmer. « Roughness-Induced Transition in a Hypersonic Capsule Boundary Layer under Wind-Tunnel and Reentry Conditions / Antonio Di Giovanni ; Gutachter : Wolfgang Schröder, Christian Stemmer ; Betreuer : Christian Stemmer ». München : Universitätsbibliothek der TU München, 2020. http://d-nb.info/1211725227/34.

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Wittwer, Adrián Roberto. « Simulação do vento atmosférico e dos processos de dispersão de poluentes em túnel de vento ». reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2006. http://hdl.handle.net/10183/8684.

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O estudo experimental dos processos de dispersão atmosférica de poluentes permite a análise de problemas específicos e a avaliação dos modelos teórico-numéricos. Os custos da experimentação de campo conduzem à realização de estudos de laboratório em modelos reduzidos. Este trabalho tem por objetivo principal a reprodução dos ventos atmosféricos e dos processos de dispersão em escala reduzida em túnel de vento. Foram estabelecidos os requerimentos gerais de modelagem para os diversos problemas relacionados com o estudo experimental da dispersão de poluentes atmosféricos, incluindo a simulação da camada limite atmosférica e da fonte de emissão. A partir desta análise, foram desenvolvidos e avaliados diversos modelos experimentais dos ventos turbulentos na camada limite atmosférica neutral utilizando velocidades médias muito baixas que permitam cumprir os requerimentos de semelhança do processo de dispersão. As simulações incluem ventos turbulentos sobre terrenos homogêneos a diferentes escalas. Na avaliação experimental foram utilizados dados da literatura e comparações diretas com resultados de campo para a condição de atmosfera em estabilidade neutra. Foram estudados escoamentos turbulentos mais complexos nas proximidades de um modelo simples de uma edificação e em um entorno urbano não homogêneo. Para os estudos da difusão atmosférica, foi estabelecida a prioridade da modelagem de problemas locais de dispersão. Foi modelada uma fonte de emissão pontual de baixa altura representativa de uma chaminé que permita a modificação das condições de empuxo da pluma. A análise do processo de dispersão e das concentrações foi realizada considerando diversas configurações que incluem a fonte de emissão isolada num escoamento homogêneo, a consideração dos efeitos da esteira próxima ao modelo de uma edificação, e finalmente de um terreno urbano não homogêneo. Foram determinadas as concentrações médias e as flutuações de concentração na pluma. Estes resultados permitiram obter os campos de concentração e, a partir das funções de densidade de probabilidade e funções de densidade espectral, analisar as zonas de intermitência no campo de concentração. Comparações com resultados da literatura e com modelos teóricos complementam o estudo realizado. É dada ênfase na análise das flutuações de concentração e na intermitência dos processos de dispersão, dada a importância do seu conhecimento para o desenvolvimento de modelos bem como à escassa informação experimental na bibliografia. Os resultados deste trabalho permitem estabelecer a viabilidade da simulação da camada atmosférica neutral e dos estudos de dispersão em túnel de vento, determinando vantagens e limitações dos modelos reduzidos. A influência das características do escoamento turbulento, das configurações próximas do terreno e das características da emissão no processo de dispersão foi estudada. Finalmente, são analisadas as condições de intermitência associadas aos escoamentos turbulentos e, em particular, aos campos de concentração próximos a uma fonte de emissão.
The experimental study of the pollutant dispersion processes allows the analysis of specific problems as well as the evaluation of theoretical models. The costs related to full scale measurements make the experimental studies over reduced scaled models a better research tool. This work has the aim of modeling some kinds of atmospheric winds and related dispersion processes in wind tunnels. The general modeling laws related to the experimental study of pollutants dispersion were followed, including the boundary layer simulation and the emission source. Several experimental models of the turbulent winds in neutral boundary layers were developed and evaluated by using very low wind velocities, allowing the fulfillment of the similitude laws of the dispersion process. The simulations include turbulent winds over homogeneous terrains at different scales. Literature data were used in the experimental evaluation as well as direct comparisons with field results for the atmosphere under neutral stability conditions. Also, more complex turbulent flows were studied in the close proximities of a simple building model in a non homogeneous surrounding. For the atmospheric diffusion studies, it was decided to model local dispersion situations. A single, punctual type of emission source was modeled, representing the conditions at a low height chimney and allowing the modification of the plume buoyancy conditions. The analysis of the dispersion process and concentrations was performed under several configurations including the isolated source emission in a homogeneous flow, the consideration of the wake effects close to a building model, and finally of a non homogeneous urban terrain. The mean and fluctuating components of the plume concentration were obtained. These results allowed the characterization of the concentration fields. From the probability and spectral density functions it was possible to analyze the intermittence of the concentration field. Comparisons with literature results and with theoretical models complement the study. Special care is taken in the analysis of the fluctuations of the concentration and in the intermittence of the dispersion processes, due to its importance to the development of theoretical models as well as the lack of experimental information in the open literature.

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Wisda, David Martin. « Noise from a Rotor Ingesting Inhomogeneous Turbulence ». Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/52986.

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On-blade hot wire anemometry measurements as well as far field sound measurements at several receiving angles have been previously made for a rotor partially embedded in a boundary layer. The inflow distortion effect on the rotor angle of attack distribution was determined directly from the on-blade measurements, and was found to minimally affect the angle of attack at the blade tips and lower the angle attack in the rotor disk plane as the radial location moves towards the hub. A narrow, sharp increase in angle of attack as the rotor blades approached the wall was also observed, indicating blade interaction with flow reversal. The haystacking pattern, or spectral humps that appear at multiples of the blade passage frequency, was studied for a wide range of advance ratios. At high advance ratios, evidence of vortex shedding from the blade trailing edges was observed. For low advance ratios, the haystacks narrowed, became more symmetric and increased in number. A method of determining the average acoustic signature of an eddy passage through a rotor was developed from time delay aligning multiple microphone signals and eddy passages detected using the continuous wavelet transform. It was found that the eddy passage signatures were similar to a cosine wave with a Gaussian window. It was also found that normalized timescales obtained directly from the eddy passage signatures remained somewhat constant with advance ratio, but increases slightly for fixed free stream velocities with increasing rotor RPM. For advance ratios less than 0.6, the eddy passage signatures were dominated by a tonal component due to rotor ingestion of misaligned flow caused by a boundary layer separation at the wall. This indicates that flow reversal known as the Pirouette Effect is interacting with the rotor blades.
Master of Science

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Mattuella, Jussara Maria Leite. « Avaliação em túnel de vento do comportamento da camada limite atmosférica em terrenos complexos ». reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/85643.

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A estrutura do vento varia de acordo com as características do terreno e com a rugosidade da superfície terrestre, desacelerando proporcionalmente sua intensidade de acordo com a proximidade do solo, o que determina a constituição da camada limite atmosférica (C.L.A.). As características do escoamento sobre e no entorno de características topográficas obtusas tais como morros são de grande interesse em muitas aplicações, especialmente aquelas ligadas à engenharia de vento. Esta pesquisa foca a investigação da C.L.A. sobre terrenos complexos, analisando a estrutura do escoamento turbulento, a separação e a recomposição do mesmo. Para tanto, dois métodos são empregados e comparados na presente investigação para identificar a influência da orografia complexa sobre o escoamento do vento: padrões ou códigos de carga de vento e análises experimentais em túnel de vento. Nove modelos experimentais de morros isolados, sendo quatro simétricos bidimensionais, quatro simétricos tridimensionais e um assimétrico, todos com a consideração de dois tipos de terreno, categoria I – plano e categorias III-IV – medianamente rugosas são analisados. A partir de uma simulação experimental da camada limite em túnel de vento, é possível parametrizar os efeitos do vento sobre terrenos complexos (MILLER, 1995). A definição de variáveis, tais como: o perfil de velocidade do vento, a intensidade de turbulência, os efeitos topográficos na velocidade do vento constituem-se em elementos fundamentais para cálculos estruturais de edificações situadas no entorno. Foram desenvolvidas simulações experimentais no túnel de vento de camada limite Prof. Joaquim Blessmann, da Universidade Federal do Rio Grande do Sul. Na superfície do modelo assimétrico, na radial principal do mesmo, foram localizados nove perfis de medição, contendo cada um, vinte alturas de investigação. Os demais modelos tiveram como foco de análise o cume dos mesmos, também com perfis definidos nas mesmas alturas. As medições da velocidade do vento e da intensidade da turbulência foram procedidas por um sistema de anemometria de fio quente. Os dados obtidos em túnel de vento foram confrontados com expressões empíricas calculadas para os mesmos pontos segundo cinco códigos ou padrões de carga de vento, pontuando também as correlações entre os mesmos e entre estes com a norma brasileira NBR 6123 (1988). Os modelos, códigos ou padrões analisados foram: Jackson e Hunt (1975) e Davenport, Surry e Lemelin (1988), models e as normas a seguir nominadas:Norma Brasileira: cargas de vento em Edificações - NBR 6123 (1988); European Standard:Eurocode1: Basis of Design and Actions on Structures, CEN TC 250: 2002; Australian/New Zealand Standard: Minimum Design Loads on Structures, AS/NZS 1170.2: 2002; Architectural Institute of Japan AIJ: 2004; American Society of Civil Engineering Standard, ASCE 7-95 (ASCE 7-95), Minimum Design Loads for Buildings and Other Structures;National Building Code of Canada, 2005, (NRCC 2005). Além do estudo comparativo acerca da resposta estimada pelos códigos nominados, esta pesquisa constitui-se em um banco de dados de medições em pontos localizados nos morros nominados, em túnel de vento. O comparativo entre os padrões mostra a inexistência de uma harmonização entre os mesmos para a consideração dos parâmetros a serem empregues para o cálculo de cargas de vento. Estas diferenças na definição dos parâmetros básicos para o carregamento de vento em estruturas determinam grandes dificuldades na unificação de formatos recomendados na previsão das cargas de vento. Comparativamente aos dados experimentais, os padrões, em geral, mostram-se conservadores para os dois tipos de morros analisados, simétrico e assimétrico, para os dois tipos de terreno, tanto considerando-se análises em 2D ou 3D.
The structure of the wind varies with the characteristics of the terrain and roughness land surface, slowing its intensity proportionally according to the surrounding terrain, which determines the onset of boundary layer (ABL). The characteristics of the flow over and around topographic features such as hills are of great interest in many applications, especially those related to wind engineering. From an experimental simulation of the boundary layer wind tunnel, it is possible to parameterize the effects of wind over complex terrain (MILLER, 1995). The definition of variables, such as the profile of wind speed, the turbulence intensity, the topographic effects on wind speed are key elements in structural calculations for buildings situated around the area. This research focuses on the investigation of the ABL complex terrain conditions, analyzing the structure of turbulent flow and characterization of separation and reattachment of the flow. Experimental simulations were developed in the wind tunnel of the atmospheric boundary layer Prof. Joaquim Blessmann, Federal University of Rio Grande do Sul in nine models of hills, four symmetrical two-dimensional, four- symmetrical threedimensional and one asymmetrical, all considering two types of terrain, category I - plan and Category III-IV- moderately rough. The surface of the asymmetric model was measured in nine profiles ploted on the main radial of the hill, with twenty heights each, and the other models were examined at top of the hill. The measurements were performed with a system of hot wire anemometry to measure the wind velocity and intensity of turbulence. The identification of the data obtained in the wind tunnel were confronted with empirical expressions for the same points, in order to establish the correlations between patterns and among these with NBR 6123 (1988). Two models and five codes of wind loads are analyzed: Jackson and Hunt (1975) and e Davenport, Surry e Lemelin (1988) Models and Brazilian Association of Technical Standards: Wind Load on Buildings, NBR 6123 (1988); European Standard: Eurocode1: Basis of Design and Actions on Structures, CEN TC 250: 2002; Australian/New Zealand Standard: Minimum Design Loads on Structures, AS/NZS 1170.2: 2002; Architectural Institute of Japan AIJ: 2004; American Society of Civil Engineering Standard, ASCE 7-95 (ASCE 7-95), Minimum Design Loads for Buildings and Other Structures; National Building Code of Canada, 2005, (NRCC 2005) codes. This study focuses not only the comparison of the response estimated by international codes nominees, but also a data bank of wind tunnel data to validate this tool based on empirical expressions. The comparison of the patterns shows a lack of consideration for international harmonization of the parameters to be employed for the calculations of wind loads. These differences in defining the basic parameters for the wind loading on structures determines difficulties to unify the formats recommended in the prediction of wind loads. Compared to the experimental data, the patterns will generally show up conservative for both types of mounts analyzed, symmetrical and asymmetrical, for both types of terrain, both considering 2D or 3D.

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Martinez, Hugo. « Contribution à la modélisation du transport éolien de particules : mesures de profils de concentration en soufflerie diphasique ». Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10032.

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Ce travail traite de l'utilisation des outils de modelisations physique et numerique dans le domaine du transport eolien de differentes particules. La modelisation physique en soufflerie diphasique et la theorie de la couche limite turbulente ont permis de reproduire les conditions de transport in situ. Dans le cadre de cette approche, nous avons concu et mis en place un dispositif optique de visualisation laser, et une chaine de prise et de traitement d'images pour la determination des profils de concentration massique de l'ecoulement charge. La phase transitoire qui mene vers la saturation est etudiee. L'influence des caracteristiques des particules sur les profils de concentration est aussi analysee. Cette technique de mesure non intrusive donne des resultats tres encourageants par rapport aux profils prevus par la theorie, et permet d'obtenir un nombre de points de mesure tres important. Une simulation numerique basee sur les lois de conservation de la mecanique des fluides est presentee. L'interaction entre l'ecoulement et le lit de particules est prise en compte par l'intermediaire d'un flux massique determine experimentalement, grace a un dispositif optique (diode laser) qui permet de mesurer l'evolution de l'epaisseur du lit de particules. Ces observations experimentales donnent lieu a une analyse du phenomene de ripples observe lors de l'evolution temporelle de l'epaisseur du lit. Une premiere simulation par le code flow3d (cfds-aea technology, angleterre) indique une bonne reproduction des champs de vitesses. Cependant, meme si les ordres de grandeur pour les profils de concentration sont corrects dans les premiers millimetres, ce code numerique ne permet pas d'obtenir une diffusion verticale suffisante des particules. Une seconde approche numerique permet de resoudre l'equation de conservation de la masse solide dans la zone de suspension, et donne une distribution spatiale de la concentration tres proche de la distribution experimentale

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Sanz, Rodrigo Javier. « On antarctic wind engineering ». Doctoral thesis, Universite Libre de Bruxelles, 2011. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209953.

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Antarctic Wind Engineering deals with the effects of wind on the built environment. The assessment of wind induced forces, wind resource and wind driven snowdrifts are the main tasks for a wind engineer when participating on the design of an Antarctic building. While conventional Wind Engineering techniques are generally applicable to the Antarctic environment, there are some aspects that require further analysis due to the special characteristics of the Antarctic wind climate and its boundary layer meteorology.

The first issue in remote places like Antarctica is the lack of site wind measurements and meteorological information in general. In order to complement this shortage of information various meteorological databases have been surveyed. Global Reanalyses, produced by the European Met Office ECMWF, and RACMO/ANT mesoscale model simulations, produced by the Institute for Marine and Atmospheric Research of Utrecht University (IMAU), have been validated versus independent observations from a network of 115 automatic weather stations. The resolution of these models, of some tens of kilometers, is sufficient to characterize the wind climate in areas of smooth topography like the interior plateaus or the coastal ice shelves. In contrast, in escarpment and coastal areas, where the terrain gets rugged and katabatic winds are further intensified in confluence zones, the models lack resolution and underestimate the wind velocity.

The Antarctic atmospheric boundary layer (ABL) is characterized by the presence of strong katabatic winds that are generated by the presence of surface temperature inversions in sloping terrain. This inversion is persistent in Antarctica due to an almost continuous cooling by longwave radiation, especially during the winter night. As a result, the ABL is stably stratified most of the time and, only when the wind speed is high it becomes near neutrally stratified. This thesis also aims at making a critical review of the hypothesis underlying wind engineering models when extreme boundary layer situations are faced. It will be shown that the classical approach of assuming a neutral log-law in the surface layer can hold for studies of wind loading under strong winds but can be of limited use when detailed assessments are pursued.

The Antarctic landscape, mostly composed of very long fetches of ice covered terrain, makes it an optimum natural laboratory for the development of homogeneous boundary layers, which are a basic need for the formulation of ABL theories. Flux-profile measurements, made at Halley Research Station in the Brunt Ice Shelf by the British Antarctic Survery (BAS), have been used to analyze boundary layer similarity in view of formulating a one-dimensional ABL model. A 1D model of the neutral and stable boundary layer with a transport model for blowing snow has been implemented and verified versus test cases of the literature. A validation of quasi-stationary homogeneous profiles at different levels of stability confirms that such 1D models can be used to classify wind profiles to be used as boundary conditions for detailed 3D computational wind engineering studies.

A summary of the wind engineering activities carried out during the design of the Antarctic Research Station is provided as contextual reference and point of departure of this thesis. An elevated building on top of sloping terrain and connected to an under-snow garage constitutes a challenging environment for building design. Building aerodynamics and snowdrift management were tested in the von Karman Institute L1B wind tunnel for different building geometries and ridge integrations. Not only for safety and cost reduction but also for the integration of renewable energies, important benefits in the design of a building can be achieved if wind engineering is considered since the conceptual phase of the integrated building design process.

Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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Demarco, Giuliano. « Simulações em laboratório de escoamentos em meios estratificados ». Universidade Federal de Santa Maria, 2013. http://repositorio.ufsm.br/handle/1/3916.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico
In the present thesis, two distinct scientific problem in fluid mechanics are studied using laboratory observation techniques. In the first of them, a tank was used to simulate microburst propagation. In the experimental set-up, the flow was driven by combined impinging jet and density perturbations forcing with the aim of determining their relative influence on the overall microburst behaviour and, in particular, the initiation and structural evolution of the resulting vortex. These results were compared with those reported in previous simulation works. Such comparisons showed that the laboratory model may satisfactorily reproduce relevant aspects of a microburst. An expression for the characteristic microburst propagation velocity was derived, accounting for the combined effects of forced velocity and flotation forces generated by the density difference. The vortex structure is largely affected by the forcing type. The succession of vortex is best defined when a large density perturbation is combined with a weak jet impingement. The opposite configuration causes a main vortex to be succeeded by a wake where vortex structures are not clearly defined. In the second part, experiments were conducted in a wind tunnel above a cooled surface with the aim of determining the influence of the thermal stratification on turbulence-related quantities. The experimental apparatus consists of an aluminum plate inserted at the bottom surface of the test section, which is then cooled until 5ºC, so that a stably stratified surface is formed. As wind speeds increase, such a stable layer is soon destroyed. Data show that quantities such as temperature, variances, dissipation rates and turbulent fluxes are substantially reduced when a stratification is present. On the other hand, third and fourth order statistical moments, as well as the mean wind speed are very slightly affected by the stratification.
Neste trabalho, dois problemas científicos distintos de mecânica dos fluídos são estudados utilizando-se técnicas de observação em laboratório. no primeiro deles, utilizou-se observações em tanque para simular microbursts. O escoamento foi induzido através da combinação de dois processos definidos como jato incidente e perturbações de densidade, com o objetivo de determinar a sua influência sobre o comportamento de forma geral do microbursts e, em particular, o começo e a evolução estrutural dos vórtices resultantes. Estes resultados foram comparados com trabalhos anteriores. Uma expressão para a velocidade característica de propagação do microburst foi obtida, representando os efeitos combinados de velocidade forçada e as forças de perturbação gerados pela diferença de densidade, cujas previsões estão em boa concordância com os dados experimentais. A estrutura do vórtice é em grande parte afetada pelo tipo de forçante. A sucessão de vórtices é melhor definida quando a influência da perturbação de densidade se destaca sobre a de jato incidente. A configuração oposta provoca um vórtice principal a ser sucedido por uma esteira, no qual as estruturas dos vórtices não são claramente definidas. Em uma segunda etapa, experimentos foram realizados em túnel de vento sobre uma superfície resfriada para verificar- se a influência da estratificação térmica sobre quantidades associadas a um escoamento turbulento. No aparato experimental, uma placa de alumínio foi inserida na superfície inferior da seção de testes e resfriada até atingir uma temperatura de 5ºC, com o objetivo de verificar a formação de uma camada limite térmica estável e a influência da mesma sobre as grandezas analisadas. É possível observar a formação de uma camada estratificada, e logo destruída conforme os valores de vento aumentam. Os dados analisados, mostram uma redução substancial nos casos de vento mais fraco para as grandezas como temperatura, variâncias, taxas de dissipação e fluxos turbulentos. Por outro lado, momentos estatísticos de terceira e quarta ordem, assim como a velocidade média do vento foram pouco afetados pela estratificação.

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北村, 圭一, Keiichi KITAMURA, 啓伺小澤, Hiroshi OZAWA, 勝祥花井, Katsuhisa HANAI, 浩一森, Koichi MORI, 佳朗中村 et Yoshiaki NAKAMURA. « 極超音速TSTOにおける衝撃波干渉・境界層剥離を伴う流れ場の解析 ». 日本航空宇宙学会, 2008. http://hdl.handle.net/2237/13872.

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Vecina, Tanit-Daniel Jodar. « Investigação da camada limite atmosférica simulada em túnel de vento no topo de morros utilizando dinâmica dos fluídos computacional (CFD) ». reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/158347.

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O formato do perfil de velocidades do vento varia de acordo com as características locais da superfície terrestre e de rugosidade do terreno, parâmetros que definem o perfil da Camada-Limite Atmosférica (CLA). As características do escoamento do ar atmosférico sobre e ao redor de acidentes geográficos, tais como morros e colinas, são de grande interesse para aplicações relacionadas à Engenharia de Turbinas e Parques Eólicos. No topo de morros, ocorre a aceleração do vento, fenômeno que pode representar um fator decisivo para a instalação de aerogeradores. Este trabalho dedica-se ao estudo do comportamento da CLA como função da inclinação e rugosidade superficial da elevação, fazendo uso da Dinâmica de Fluidos Computacional (CFD) para construir perfis de velocidade do vento e de intensidade de turbulência. O problema de fechamento das Equações Médias de Reynolds (RANS) é contornado com o uso do modelo de turbulência k-ω SST; os resultados numéricos obtidos são comparados com dados experimentais medidos em túnel de vento sobre modelos em escala dos morros. São testados oito modelos de morros com declives que variam de 25° a 64° para dois tipos de categorias de terreno, em 2D e 3D, e são aplicados dois códigos analíticos para representar o perfil de velocidades de entrada. Resultados numéricos para os perfis de velocidade apresentam diferença inferior a 4% em relação aos respectivos dados obtidos experimentalmente. Os perfis de intensidade de turbulência apresentam diferença máxima na casa dos 7% em comparação aos dados experimentais, o que é explicado pelo fato de que não é possível inserir o perfil de entrada de intensidade de turbulência nas simulações numéricas. Em alternativa, foi usado um valor constante resultado da média dos valores dos perfis usados no túnel de vento. Os modelos de morro em 3D apresentam maior concordância nos resultados de velocidade que os modelos em 2D e que ademais quanto maior é a inclinação do morro maior é a concordância com as medições experimentais.
The shape of the wind velocity profile changes according to local features of terrain shape and roughness, which are parameters responsible for defining the Atmospheric Boundary Layer (ABL) profile. Air flow characteristics over and around landforms, such as hills, are of considerable importance for applications related to Wind Farm and Turbine Engineering. The air flow is accelerated on top of hills, which can represent a decisive factor for Wind Turbine placement choices. The present work focuses on the study of ABL behavior as a function of slope and surface roughness of hill-shaped landforms, using the Computational Fluid Dynamics (CFD) to build wind velocity and turbulent intensity profiles. Reynolds-Averaged Navier-Stokes (RANS) equations are closed using the SST k-ω turbulence model; numerical results are compared to experimental data measured in wind tunnel over scale models of the hills under consideration. Eight hill models with slopes varying from 25° to 64° were tested for two types of terrain categories in 2D and 3D, and two analytical codes are used to represent the inlet velocity profiles. Numerical results for the velocity profiles show differences under 4% when compared to their respective experimental data. Turbulent intensity profiles show maximum differences around 7% when compared to experimental data, this can be explained by not being possible to insert inlet turbulent intensity profiles in the simulations. Alternatively, constant values based on the averages of the turbulent intensity at the wind tunnel inlet were used. The 3D models present greater concordance in the speed results than the 2D models and that in addition the greater the slope of the hill, the greater the agreement with the experimental measurements.

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Murray, Henry Hall IV. « Turbulence and Sound Generated by a Rotor Operating Near a Wall ». Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/71332.

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Acoustic and aerodynamic measurements have been carried out on a rotor operating in a planar turbulent boundary layer near a wall for a variety of thrust conditions and yaw angles with respect to the inflow. At the highest thrust condition a strong flow reversal in the wall-rotor tip gap was observed. Average velocity fields filtered by the angular position of the rotor show that the flow reversal is fed by jets of fluid that tend to form below the blade as it passes by the wall. Instantaneous velocity measurements show the presence of strong vortices in the tip gap. These vortices were characterized and found to be both stronger and more numerous on the downstroke side of the tip gap. Additionally, vortices with the same handedness as the bound circulation in the blade were more numerous and only located on the downstroke side of the tip gap. Those with the opposite handedness were found to be only located on the upstroke side. Unexpectedly strong far-field acoustic response at the blade passage frequency at this highest thrust condition and is believed to be due to an interaction of the blade tip with these vortices. At moderate thrust, when the rotor was yawed toward the downstroke side the far field acoustic response at the blade passage frequency was found to increase. The opposite was true as it was yawed toward the upstroke side. At the highest thrust, however the unyawed rotor had the strongest blade passage frequency response which is believed to be due to stronger vortex-tip interaction in this case.
Master of Science

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Poette, Christopher. « La fragmentation du paysage : impact sur l'écoulement atmosphérique et la stabilité au vent des peuplements forestiers ». Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0387/document.

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A l’heure actuelle, seuls des facteurs locaux, stationnels, sont considérés pour le calcul des risques liés au vent alors que le vent qui aborde un peuplement forestier est affecté par les surfaces sur lesquelles il vient de passer ; les lisières en particulier jouent un rôle important sur l’écoulement atmosphérique, en contribuant à générer de la turbulence. Dans un paysage fragmenté, constitué d’une mosaïque de surfaces de différentes hauteurs et rugosités, la multiplicité des lisières est ainsi susceptible d’avoir des effets cumulatifs perceptibles à l’échelle régionale, qui pourraient contribuer de manière significative à la fragilité des massifs face à des tempêtes. Certains niveaux de fragmentation semblent susceptibles de conduire à un accroissement des risques en cas de vent violent. Bien que la région de lisière a été étudiée de manière approfondie dans le passé en raison de leur importance pour la détermination des vitesses de vent, des niveaux de turbulence et des échanges entre l’atmosphère et la canopée, il n’y a aucune étude de l’impact de lisières multiples ou de la fragmentation des forêts sur les caractéristiques de la couche limite à l’échelle du paysage. Quelques rares études laissent penser que la fragmentation du paysage pourrait moduler de manière significative la structure turbulente de la couche limite atmosphérique mais ces études concernent des réseaux de brisevents plutôt qu’un ensemble de parcelles forestières. On cherche par conséquent à caractériser les champs de vent et de turbulence pour ces différentes configurations. Pour ce faire, une expérimentation en soufflerie à été réalisée, visant à caractériser l’écoulement sur des maquettes de paysage présentant cinq degrés de fragmentation (L = ~ 5, ~ 10, ~15, ~20, ~30h, où L est la distance entre deux patchs de forêts régulièrement espacés et h est la hauteur de la canopée). Un cas homogène a également été simulé et sert ici de référence. Pour le modèle de canopée choisi, ces expérimentations montrent que l’énergie cinétique turbulente présente dans la basse atmosphère ne passe pas par un maximum pour une valeur de l’espacement intermédiaire comme il était supposé à l’origine. Le cas homogène est la configuration la plus rugueuse. Pour de grands espacements l’influence d’une parcelle ne se fait guère sentir sur la suivante et lorsqu’ils sont faibles l’écoulement ne "ressent" guère les clairières et présente des caractéristiques semblables au cas homogène. Nous avons également évalué un modèle atmosphérique de type "simulation des grandes échelles" à l’aide des données présentées précédemment. Le modèle est capable de reproduire les grandes caractéristiques de la turbulence telles que les vitesses de vent horizontales et verticales, l’énergie cinétique turbulente, les contraintes de Reynolds et les coefficients d’asymétrie horizontale et verticale en tous points du domaine. Cela nous a permis de confirmer la validité des calculs numériques et de simuler l’écoulement sur une plus large gamme de paysages fragmentés. Les résultats démontrent l’importance de l’indice foliaire pour le calcul de la rugosité effective sur une succession de patchs de forêt
At present only the characteristics of a forest stand and its immediate environment are taken into account in calculating forest wind risk. However, it is known that the wind is strongly affected by the surfaces over which it has previously flowed. Forest edges in particular play an important role in determining the characteristics of the atmospheric flow by generating increased turbulence, triggering the formation of coherent tree scale structures. In a fragmented landscape, consisting of surfaces of different heights and roughness, the multiplicity of edges may have cumulative effects at the regional scale leading to increased forest damage during storms. Flow changes in the atmospheric boundary-layer across surface roughness changes have received extensive study in the past because of their importance in determining velocities, turbulence levels and exchange between the atmosphere and biosphere or ground. There have also been a number of studies across single forest edges both in the field, wind-tunnels and computer models. However, there have been no studies of flow across multiple forest edges or the impact of forest fragmentation on the characteristics of the boundary-layer. The only studies on multiple surface changes have been wind-tunnel examination of the flow though and across multiple wind-breaks. In this thesis we show results from a series of wind tunnel experiments on a range of levels of forest fragmentation. Five gap spacings (L = ~ 5, ~ 10, ~15, ~20, ~30h, where L is the length of the gap and h is the canopy height) were investigated using 3D laser doppler velocimetry in order to assess the effects of fragmented landscapes on mean and turbulent wind characteristics. The fragmentation was two-dimensional with the transition between forest and gaps only being along the wind direction and the forest and gaps were continuous perpendicular to the wind direction. The wind speeds and turbulence characteristics are compared against measurements from a single forest edge in the wind tunnel, which acts as a reference. No enhancement of turbulence formation at a particular level of fragmentation was observed but there was a consistent pattern of wind speed and turbulence back from the first edge of each simulation with the horizontal velocity at tree top increasing and the turbulent kinetic energy decreasing as gap size increased. We also compare mean wind speeds (U and W) and turbulence characteristics (variance in u, v, and w; skewness in U, V, and W; Reynold’s stress, and TKE) at all points in the experimental measurement domain of the wind tunnel with Large Eddy Simulation (LES) results, which allows us to confirm the validity of the LES calculations and to conduct a wider range of experiments than was possible in the wind-tunnel. The results demonstrate the importance of the frontal area index or roughness density of elements (in this case trees) in determining the nature of the flow and the effective roughness of the overall surface. They also show that as the gaps between forest blocks increases the flow transitions (at a gap size between 10 to 15 tree heights) from flow comparable to that over a continuous forest to flow across a set of isolated forest blocks

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Sheng, Risheng. « Application de l’approche de simulation des grandes échelles à l’évaluation des charges de vent sur les structures ». Thesis, Ecole centrale de Nantes, 2017. http://www.theses.fr/2017ECDN0030/document.

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Des bâtiments de grande hauteur sont construits avec un poids et un amortissement structurel de plus en plus faibles en lien avec l'évolution des techniques de construction et des matériaux. La connaissance des charges de vent dynamiques est un enjeu important pour la conception des grands bâtiments afin de garantir leur sécurité structurelle. L'objectif de cette thèse est d’évaluer la capacité de la simulation numérique des grandes échelles (LES) à prédire les charges de vent sur les structures et d’étudier l'influence des conditions d’entrée d’une simulation LES sur ces charges. Des expériences ont été menées à échelle réduite dans la soufflerie atmosphérique NSA du CSTB afin de documenter l’écoulement atmosphérique modélisé, de caractériser son interaction avec un bâtiment et les charges de vent statiques et dynamiques résultantes. Le sillage du bâtiment a été caractérisé grâce à des mesures PIV. Les efforts globaux et les pressions locales ont été mesurés par une balance et des prises de pression à haute fréquence. Ces expériences en soufflerie ont permis de développer un générateur de conditions amont (GCA) pour la simulation LES, visant à reproduire les principales caractéristiques de la turbulence dans la couche limite. La base de données constituée a également permis de qualifier les résultats des simulations LES réalisées avec le code OpenFOAM dans la configuration de l’expérience. L’utilisation du nouveau GCA et d’un générateur dégradé qui ne respecte pas toutes les caractéristiques de l'écoulement a permis de montrer la nécessité de bien reproduire les caractéristiques du vent incident pour accéder aux charges dynamiques sur le bâtiment
High-rise buildings are built with increasingly low weight and structural damping in relation to the evolution of construction techniques and materials. The understanding of dynamic wind loads is an important issue for the design of high-rise buildings in order to guarantee their structural safety. The objective of the present work is to assess the ability of large eddy simulation (LES) to predict wind loads on structures and to investigate the influence of the inflow boundary conditions of a LES simulation on these loads. Experiments were carried out at a small scale in the NSA atmospheric wind tunnel of CSTB to document the modeled atmospheric boundary layer, to characterize its interaction with a building and the resulting static and dynamic wind loads. The wake flow around the building has been characterized by PIV measurements. Global and local wind loads were measured by a high frequency force balance and high frequency pressure taps. These wind tunnel experiments allowed for the development of an inflow turbulence generator for the LES simulation,which was aimed at reproducing the main characteristics of turbulence in the boundary layer. The database also made it possible to assess the quality of the results of the LES simulations carried out with the OpenFOAM code in the same configuration as the experiment. The use of both the new turbulence generator and a degraded one that does not account for all the characteristics of the flow has made it possible to show the necessity to reproduce the characteristics of the upstream wind flow in order to access the dynamic wind loads on the building

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Blackman, Karin. « Interactions multi-échelles entre la basse atmosphère et la canopée urbaine ». Thesis, Ecole centrale de Nantes, 2017. http://www.theses.fr/2017ECDN0028.

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La couche limite urbaine est caractérisée par la présence de structures cohérentes complexes, telles que des structures de grande échelle à basse vitesse, et par des processus turbulents intermittents de balayage et d’éjection, responsables du transport de masse, de chaleur et de quantité de mouvement. Ces structures sont bien identifiées qualitativement mais leurs interactions avec les petites structures induites par la présence de la canopée urbaine sont encore mal connues. Afin d'étudier ces interactions, des écoulements de couche limite se développant sur des parois rugueuses sont étudiés en soufflerie. Le signal à petite échelle n'étant pas résolu temporellement, l'estimation stochastique linéaire est utilisée pour décomposer le champ de vitesse en grandes et petites échelles. On confirme que les structures à grande échelle dans la couche limite influencent les petites échelles proches de la rugosité à travers un mécanisme non linéaire similaire à une modulation d'amplitude. On montre également que la modification de la géométrie des éléments de rugosité entraîne une modification de cette interaction non linéaire dans la couche cisaillée. Le bilan complet de l'énergie cinétique turbulente (TKE), incluant la dissipation, est calculé à l'aide d'un modèle LE-PIV et démontre que les structures à petite échelle dans la couche de cisaillement sont importantes pour la production, le transport et la dissipation de l'énergie. Enfin, la décomposition triple du bilan de TKE confirme que la relation non linéaire qui existe entre les structures à grande échelle et les petites échelles proches de la rugosité est liée au transfert d'énergie entre ces structures
The urban boundary layer consists of complex coherent structures, such as large-scale low momentum regions and intermittent turbulent sweeps and ejections, which are responsible for the transport of heat, momentum and pollution. Although these structures have been well identified, their quantitative relationship with the flow inside the canopy is still unknown. Wind tunnel modelling of flow over simplified rough terrain consisting of either three-dimensional or twodimensional roughness elements are able to reproduce these structures and are used to investigate the nonlinear relationship between large-scale momentum regions and small-scales induced by the presence of the roughness. As the temporally resolved small-scale signalis not available Linear Stochastic Estimation is used to decompose the flow into large and small-scales and confirm that the large-scale structures within the overlying boundary layer influence the small-scales close to the roughness through a non-linear mechanism similar to amplitude modulation. Changing terrain configuration from 3D to 2D roughness results in a modification of the non-linear relationship closer to the shear layer that develops near the top of the obstacles. The full turbulent kinetic energy (TKE) budget including dissipation is calculated using an LE-PIV model and demonstrates that small-scale structures within the shear layer are important to the production, transport and dissipation of energy. Finally, triple decomposition of theTKE budget confirms that the non-linear relationship that exists between large-scale momentum regions and small-scales close to the roughness is related to energy transfer between these structures

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ORLANDO, MAURIZIO. « Indagine Sperimentale ed Analisi Numerica degli Effetti di Interferenza Indotti dal Vento su Due Torri di Raffreddamento Adiacenti ». Doctoral thesis, 1999. http://hdl.handle.net/2158/676032.

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Le torri di raffreddamento a tiro naturale sono strutture a guscio in c.a. dalla forma iperbolica, utilizzate nelle centrali termoelettriche e nucleari come dispositivi di raffreddamento. Se due o più torri sono situate l’una accanto all’altra o nelle vicinanze di altri edifici, lo stato di sollecitazione indotto su di esse dal vento può essere molto diverso da quello di una torre isolata. Infatti in queste situazioni il flusso che le investe è modificato dalle strutture circostanti e, pertanto, la loro risposta strutturale subisce variazioni significative rispetto al caso isolato. Il fenomeno è noto come interferenza. Il presente lavoro ha come obbiettivo la caratterizzazione degli effetti di interferenza su due torri adiacenti identiche, al variare della distanza reciproca e della direzione del vento. Lo studio si compone di due parti: la prima, di carattere sperimentale, descrive i campi di pressione registrati nella galleria del vento a strato limite sviluppato del CRIACIV sul modello rigido di una torre isolata e delle due torri in gruppo; la seconda espone i risultati di analisi computazionali, eseguite con i dati sperimentali, per valutare gli effetti di interferenza sulla risposta strutturale. I risultati ottenuti per le torri in gruppo sono stati confrontati con quelli della torre isolata, utilizzando un "fattore di interferenza", già introdotto da altri ricercatori, ed uno "pseudo-fattore di raffica". Infine è stato fatto un confronto con le prescrizioni di alcune Normative Europee.

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Bor-Yann, Pan, et 潘伯彥. « Generation of Boundary Layer Flows in A Wind Tunnel ». Thesis, 1999. http://ndltd.ncl.edu.tw/handle/39772998861264731143.

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碩士
國立中興大學
土木工程學系
87
Human behavior are always within hundreds meters near the earth surface. Atmosphere within this region is called the atmospheric boundary layer flow. Because of the increasing pollution sources and number of high-rise buildings, and higher demands of human living quality, it becomes more important to carry out researches on atmospheric characteristics. The study concentrates on generation of atmospheric boundary flows in an open wind tunnel. The outcomes would be used as the basis of future experiments involving atmospheric boundary layer flows. In the study, triangular vortex generators and proper roughness elements, suggested by Irwin(1981), are adopted to simulate three different types of boundary layer flows, corresponding respectively to those in the rural, suburban and urban terrains . After the resulting mean and fluctuating velocity profiles are measured, the effects from the selection of the arrangements are assessed.

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Lo, Kuoshien, et 羅國憲. « A Study on Wind Tunnel Boundary Layer Generation with ». Thesis, 2003. http://ndltd.ncl.edu.tw/handle/67681704040814364596.

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碩士
國立高雄應用科技大學
土木工程與防災科技研究所
91
ABSTRACT Almost all buildings and civil engineering structures stand in the earth ground boundary layer. To stimulate this condition, we must generate boundary layer in the wind tunnel’s test section. Two types of boundary layer generators could be used : elliptical or triangular. For the sake of easy working, we took the triangular type. According to Irwin’s study, the desired wind velocity profile should be located downstream the triangular boundary layer generator at a distance 6 times the height of boundary layer generator. In this study we tried to shorten the distance with punched triangular boundary layer generator. We stimulated two types of wind velocity profile, α=0.12 and α=0.36. In each condition we tried two value of boundary layer height, 30cm and 40cm. Also, we changed the fan speed of the wind tunnel. The area of the punched generators should be larger than that of non-punched generators to compensate the area of holes. The results show that the punched generators will generate better wind velocity profile in most cases. But the gradient wind velocity decreases in most cases too. This unexpected phenomenon should be studied at the next step.

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Farrell, Thomas Elmer Miller L. Scott. « Development of a new boundary layer control technique for automotive wind tunnel testing ». Diss., 2005. http://il.proquest.com/products_umi/dissertations.

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Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering.
"December 2005." Title from PDF title page (viewed on April 22, 2007). Thesis adviser: L. Scott Miller. UMI Number: AAT 1436555 Includes bibliographic references (leaves 50-51).

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Farrell, Thomas Elmer. « Development of a new boundary layer control technique for automotive wind tunnel testing ». Thesis, 2005. http://hdl.handle.net/10057/760.

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Many different boundary layer control techniques are used in ground vehicle aerodynamic testing including suction, blowing, ground-boards, and rolling roads. In this paper an alternative boundary layer control method is discussed. Low momentum flow in the boundary layer can be energized using circulation from a rotating cylinder protruding through the floor. A comparison study shows that this application, if effective, may be a more cost-efficient solution than current road vehicle boundary layer control techniques. A pilot tunnel test was performed in the WSU Boundary Layer Tunnel with the results showing a boundary layer profile with an initial momentum thickness of 0.098 in. could be reduced by 40-45% with rotational velocities of approximately 5000rpm. Following this successful test, a full scale test performed in the WSU Walter H. Beech Memorial Wind Tunnel demonstrated the feasibility of the concept. An initial momentum thickness of 0.1445 in. was reduced 29% with a rotational velocity of 3900rpm. The results found seem to indicate this technique would be a very viable option provided certain aspects including cylinder balance, sizing, and rotational velocity could be optimized in future testing.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering.
"December 2005."

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Tzeng, Yu-ting, et 曾鈺婷. « Field measurements and wind tunnel investigation on the characteristics of atmospheric boundary layer ». Thesis, 2011. http://ndltd.ncl.edu.tw/handle/10388765580135443437.

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碩士
淡江大學
土木工程學系碩士班
99
The population is growing rapidly in Taiwan, and as a result the geographical area encapsulating the population is decreasing dramatically. This is forcing people to use space more efficiently, and this was reflected by constructing tall, multi-storey buildings. Therefore, it is often common to see a lot of tall buildings in modern and congested cities. However, according to reinforcing of wind, tall buildings are of exceptional height and relatively low mass. These two characteristics have their advantages and disadvantages. Since Taiwan is located in the subtropical zone, it has northeast monsoon in the winter and typhoons in the summer, so people have to be extremely considerate when it comes to designing tall buildings in such conditions. It is critically important that they understand the causes and effects of wind power on the buildings’ physical structures. For example, tall constructions are stiffer than low ones; however they suffer more pressure from wind. The main objective of this research is to discuss the different characteristics of atmospheric boundary layer between Taipei city and Danshui. It also focuses on the comparison between the wind tunnel experiments and field measurement. It includes characteristics of atmospheric boundary layer, wind profile, turbulence intensity, turbulence length scale, turbulence spectrum, gust factor, and coherence function. According to the experiment result, it shows that the average intensity of wind velocity have some effects on the wind profile figure under a strong wind circumstance; the turbulence intensity decrease steadily when there is an increase on the average intensity of wind velocity. On the other hand, the turbulence length scale expands while the average intensity of wind velocity increases. The Von-Karman spectrum density function represent the recommended figure of local’s normal wind characteristics. Different level of height of Coherence Function satisfied Davenport’s recommended figure. Under the accurate reduced scale conditions, both the Practical situation model and wind tunnel investigation have similar outcome after comparing the result of the Characteristics of wind field and Field measurement.

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Kuo, Ting-Wei, et 郭庭瑋. « Wind tunnel investigation on the different topography of characteristics of atmospheric boundary layer ». Thesis, 2011. http://ndltd.ncl.edu.tw/handle/38362739898722682801.

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碩士
淡江大學
土木工程學系碩士班
99
Before, we only have three typical terrain’s roughness blocks. If we want to know a real topography’s wind feature, we have to make a reduced scale’s model to simulate it. But it will be waste human resources and spend a lot of time and money. So if we can find some way to use roughness blocks to simulate the real topography, it will be more efficiently. On the other hand, in the field measurement we can’t got the information of the turbulence. If we successfully use the way to simulate terrain, we can got more information of terrain. The results show that we can use the mean height of the build and density of the terrain to simulate the real topography. In roughness block’s experiment, we successfully simulate the wind profile, turbulence intensity and turbulence length scale.

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Chiang, Yun-yu, et 蔣昀祐. « A Study on Simulating the Atmospheric Boundary Layer Formation in Small Low Speed Wind Tunnel - Take Wind Tunnel in CYUT as an example ». Thesis, 2011. http://ndltd.ncl.edu.tw/handle/01371503964218027149.

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碩士
朝陽科技大學
建築及都市設計研究所
99
Wind tunnel laboratory in Architecture Department of CYUT is arranged for simulating the wind field in urban environment and building surroundings for research and experiments. It is planned to offer reference for site and buildings location arrangement when under design and planning. To do the urban design, architectural design, green design, structure, disaster prevention, building physical condition and equipment design, wind tunnel experiment practice is important for students to understand the wind field changing in the environment by using model simulation. It is helpful to realize the actual situation in the environment to do the urban planning and building design. Main in research is to establish the simulating atmospheric boundary layer in wind tunnel according to the different site conditions. The wind field will be affected by various site localities like seashore, plain, suburb, and urban type of terrain to form different shape of atmospheric boundary layer. Passive devices such as spires, barriers, and roughness elements were implemented in the tunnel for the simulations. We try to use different size of passive devices and spacing to generate our exclusive atmospheric boundary layer in our low speed, small size wind tunnel. These results will be judged to correct the drift or partly drift from the theory profile line of the atmospheric boundary layer by changing the size and spacing of passive devices. Finally, we will have a suitable atmospheric boundary layer which fit the theory profile line as the achievement. These wind profile will be suitable for the experiment and relevant researches. The purposes of this research are trying to can build up our wind tunnel experiment simulation abilities effectiveness and efficiency in order to help students to understand the wind effects in the environment and promote cooperation of academic circle and the field. Also these will help us to construct the data base for offering references to other researches.

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Chien-EnHuang et 黃健恩. « Analysis and Measurements of Wakes from Multi-blade Turbines in a Boundary-Layer Wind Tunnel ». Thesis, 2018. http://ndltd.ncl.edu.tw/handle/s2g82w.

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碩士
國立成功大學
工程科學系
106
An experiment was carried out to study complex turbulence in the wakes originated from stand-alone 2, 3 and 4-blade wind turbines placed in the turbulent boundary-layer wind tunnel (turbulence intensity of 10% at the hub height) with two conditions:(1) the measurements in the vertical plane, and (2) the measurements in the horizontal plane when the turbine works in +20°,-20° and 0° yaw angle conditions. The calibration-free Cobra Probe was used to measure the three instantaneous velocity components in the wakes from the stand-alone turbine. Turbulence key statistics are analyzed and presented, including time-averaged velocity, turbulence intensity, momentum flux, and power spectrum. Besides, we use the BEM theory to predict the streamwise wind velocity to compare with the results of the measurements at the downwind position X/D=1 in the turbulence (the data obtained from this experiment) and uniform incoming flow (the data duplicate from the reference, Lyu (2017)[1]). The results of the measurements indicate that the distribution of time-averaged velocity declines immediately downstream of the turbine models and then recovers with the wake-wise direction. The turbulence intensity has a strong enhancement at the tip-levels in the near-wake region. Momentum flux demonstrates how the kinetic energy of the flow is transported to recover the velocity deficit in the wakes. In particular, the wakes of the statistics are deflected to the side when the turbine works in a yaw angle condition, and the maximum of the key turbulence statistics are in the four-blade turbine case. The plots of the energy spectrum from the results are close to the inertial subrange with a global slope of -5/3 to confirm further the measured device is reliable. The comparisons of the prediction from the BEM theory and the measurements in the turbulence and uniform inflow conditions demonstrate that the wind velocity deficit recovers faster in the turbulence case because of the turbulence mixing, and the BEM theory can be used to predict the approximate value of the wind velocity in the near wake.

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Kuester, Matthew. « Acoustics in the Klebanoff-Saric Wind Tunnel : Background Identification, Forcing, and Active Control ». Thesis, 2012. http://hdl.handle.net/1969.1/ETD-TAMU-2012-05-10731.

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Low disturbance wind tunnels, such as the Klebanoff–Saric Wind Tunnel (KSWT), offer an ideal environment to study boundary layer transition. In particular, the leading-edge receptivity of sound can be measured by creating acoustic disturbances that interact with the leading edge of a model to create Tollmien–Schlichting Waves. The magnitude and composition (sound, turbulence) of the background disturbances can affect these experiments, so the background disturbances should be minimized and documented thoroughly. The purpose of this thesis is to document the background acoustic signature of the KSWT and describe infrastructure upgrades for acoustic receptivity experiments. The measurements presented in this thesis will support future receptivity measurements in the KSWT. Microphone measurements revealed several important acoustic features in the tunnel. Cross correlations showed that two sources of low-frequency unsteadiness (the extended diffuser and corner two) create large pressure fluctuations that dominate the pressure spectrum. Directional separation of waves in the test section revealed that motor and blade passing noise travels primarily upstream into the test section. Finally, the acoustic treatments in the plenum are effective at removing sound from the tunnel. A wall of speakers was installed in the plenum to enable acoustic receptivity experiments. The speakers create both the primary downstream traveling waves and reflected upstream traveling waves in the test section. An adaptive closed loop control system was installed to reduce the amplitude of the reflected waves during acoustic forcing. Although the performance of the control system is frequency dependent, the technique was implemented successfully. The reduction in the diffuser reflection will increase the quality of future acoustic receptivity experiments in the KSWT.

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Hofferth, Jerrod William. « Boundary-Layer Stability and Transition on a Flared Cone in a Mach 6 Quiet Wind Tunnel ». Thesis, 2013. http://hdl.handle.net/1969.1/150990.

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A key remaining challenge in the design of hypersonic vehicles is the incomplete understanding of the process of boundary-layer transition. Turbulent heating rates are substantially higher than those for a laminar boundary layer, and large uncertainties in transition prediction therefore demand conservative, inefficient designs for thermal protection systems. It is only through close collaboration between theory, experiment, and computation that the state of the art can be advanced, but experiments relevant to flight require ground-test facilities with very low disturbance levels. To enable this work, a unique Mach 6 low-disturbance wind tunnel, previously of NASA Langley Research Center, is established within a new pressure-vacuum blow-down infrastructure at Texas A&M. A 40-second run time at constant conditions enables detailed measurements for comparison with computation. The freestream environment is extensively characterized, with a large region of low-disturbance flow found to be reliably present for unit Reynolds numbers Re < 11×10^6 m-1. Experiments are performed on a 5º half-angle flared cone model at Re = 10×10^6 m-1 and zero angle of attack. For the study of the second-mode instability, well-resolved boundary-layer profiles of mean and fluctuating mass flux are acquired at several axial locations using hot-wire probes with a bandwidth of 330 kHz. The second mode instability is observed to undergo significant growth between 250 and 310 kHz. Mode shapes of the disturbance agree well with those predicted from linear parabolized stability equation (LPSE) computations. A 17% (40 kHz) disagreement is observed in the frequency for most-amplified growth between experiment and LPSE. Possible sources of the disagreement are discussed, and the effect of small misalignments of the model is quantified experimentally. A focused schlieren deflectometer with high bandwidth (1 MHz) and high signal-to-noise ratio is employed to complement the hot-wire work. The second-mode fundamental at 250 kHz is observed, as well as additional harmonic content not discernible in the hot-wire measurements at two and three times the fundamental. A bispectral analysis shows that after sufficient amplification of the second mode, several nonlinear mechanisms become significant, including ones involving the third harmonic, which have not hitherto been reported in the literature.

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St, Hill Simon. « Drag reduction of cube-van through boundary-layer control : wind tunnel experiments and prototype road tests ». Thesis, 1993. http://hdl.handle.net/2429/2358.

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Due to increasing fuel cost and emphasis on energy conservation as well as pollution control, there has been considerable interest in improving propulsive efficiency of road vehicles. Reduction in aerodynamic resistance is one aspect of it. Although aerodynamically contoured automobiles has become a standard design practice. Trucks have changed little over the past three decades. The thesis presents results of an organized and extensive wind tunnel test-program, complemented by full-scale road tests, aimed at assessing the effectiveness of two boundary-layer control procedures for reduction of the pressure drag of a cube-van. Wind tunnel results, obtained using 1/6th scale models, at a subcritical Reynolds number of 105, suggest that both the Moving Surface Boundary-layer Control (MSBC) as well as the tripping of the boundary-layer using fences reduce the pressure drag coefficient. Although both the concepts are promising, application of the entirely passive fence procedure appears more attractive from an economic consideration as well as the ease of implementation. The road tests with a full-size cube-van substantiated the trends indicated by the fence data although the actual drag reduction observed was lower (yet quite significant, = 16.6%) than that predicted by the wind tunnel tests. This may be attributed to a wide variety of factors including the differences in the geometry (models; fences and their orientation),operating conditions (Reynolds number; yaw; wind variations in magnitude and direction; turbulence; road boundary-layer; road surface condition), and measurement errors. However, the objective of the study was to assess potential of the concepts which, indeed, is quite promising. Fuel consumption results also substantiated the drag reduction trend. As expected they depend on the gearing condition and hence no general expression applicable to all speed ranges is available. As anticipated the data show a rapid increase in the fuel consumption efficiency at the top end of the speed range. It is concluded that fences can lead to a significant improvement in drag reduction and fuel consumption when applied to flat-faced trucks if positioned correctly. They represent a more elegant, versatile, and cheaper alternative to the 'nose cones' and deflectors available in the market. It is recommended that further road tests should be conducted using both boundary-layer control devices.

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Ho, Kuo Ching, et 郭敬和. « The Wind Tunnel to Study The Correlations of Surface Wind Pressure of High Rise Building in Turbulent Boundary Layer Flow ». Thesis, 2002. http://ndltd.ncl.edu.tw/handle/06745190856225647867.

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碩士
國立海洋大學
河海工程學系
90
The experiments are conducted on the wind tunnel to study the correlations of surface wind pressure of high rise building in the urban terrain type of neutral turbulent boundary layer flow. The geometric scale of 1/500 of square prismatic model is used in the wind tunnel experiment. Results show that the simulated neutral turbulent boundary layer flow is good in comparison with Counihan’s field data and Von Karman spectrum equation. In the present study, the probability density function (PDF) of fluctuating wind pressure is presented. The wind pressure spectrum and cross spectrum for different measured surface taps are also presented. Wind attack angles on the building surface pressure variations are measured and analyzed.

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47

Manu, K. V. « Experiments on the Late Stages of Boundary Layer Transition ». Thesis, 2013. http://hdl.handle.net/2005/3285.

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In canonical boundary layer transition, a uniform laminar flow perturbed by 2-d T-S waves develops downstream into 3-d waves, which eventually break down with turbulent spots appearing. Previous experimental studies have established that this kind of development is absent, is by-passed, in transition induced by free-stream turbulence or surface roughness. However a common, characteristic feature of the late, three-dimensional stage is the prevalence of streamwise vorticity and streaks. Isolated and multiple streamwise vortices are present in both, canonical transition and bypass transition. This thesis de-scribes an experimental study of the late stages of boundary layer transition after a single or a pair of streamwise vortices have formed. The present work can be considered both as a study of transition induced by surface roughness and as a study of the late stages of transition in general. The experiments were made on a zero-pressure-gradient boundary layer in a low speed wind tunnel. Various hill configurations, mounted on a flat plate, were used to create isolated and multiple streamwise vortices. Particle image velocimetry (PIV) and hot-wire anemometry used for measurements. Numerical simulations of the initial laminar stage were carried out to understand the vortex formation at the edge of the hills. Computations have shown that the streamwise vorticity induced by the spanwise asymmetry of the hill rolls up into a single streamwise vortex. The streamwise vortex causes high speed fluid to be brought close to the wall and low speed fluid to move away. In turn, streamwise velocity profiles acquire inflections in both the spanwise and wall-normal directions. Previous studies have concluded that the inviscid instability of inflectional profiles are essential, or at least common, precursors to transition. Another view of the structure of bypass transition induced involves a secondary instability of streaks that can be sinuous or varicose. These two types follow from instabilities of the inflectional spanwise and wall-normal profiles of the streamwise velocity, respectively. However the present study confirms that the occurrence of inflections is not sufficient for transition. The first series of experiments were with smooth Gaussian shaped hills that spanned one-half of the tunnel. Two hill shapes were taken, steep and shallow. Isolated streamwise vortices formed by the side of the hill. Hill heights were less than that of the incoming boundary layer, and they were mounted within the subcritical part of the boundary layer. At low free stream speeds, streaks formed, with inflectional wall-normal and spanwise velocity profiles, but without effecting transition. The necessary conditions for inviscid instability Rayleigh’s inflexion-point theorem and Fjortoft’s theorem are satisfied for these low-speed non-transitional cases. Transition observed at higher speeds show two kinds of development. With the steep hill, the streamwise vortex is not too close to the plate and it exhibits oscillations over some distance before flow breaks down to turbulence; streamwise velocity signals exhibited the passage of a wave packet which intensified before break-down to turbulence. This dominant mode persists far downstream from the hill even while the flow breaks down and frequency content grows over a range of scales. With the shallow hill, the breakdown develops continuously without such a precursor stage; there was a broad range of frequencies present immediately downstream of the hill. For the steep hill the maximum fluctuation is observed on the upwash side of the vortex. With the shallow hill, the fluctuation level is maximum at the location between low and high speed streak. Features of breakdown to transition caused by these single streamwise vortices are found to be similar to those in transition by other causes such as surface roughness, freestream turbulence etc. With the steep hill, the growth of fluctuations(urms, the peak levels of streamwise velocity component fluctuations) is remarkably similar to that in the K-type transition. Unlike in freestream induced transition, the initial growth of u2 rms,max with downstream distance was not linear. Profiles of urms/urms,max vs. y/δ∗where δ∗,is the displacement thickness is partially matching with the optimal disturbances, for the steep hill case. The phase velocity matches as in previous measurements of roughness induced transition. The flow exhibits the breakup of a shear layer near the outer edge of the boundary layer into successive vortices. This breakdown pattern resembles to those in the recent numerical simulations. The passing frequency of these vortices scales with freestream velocity, similar to that in single-roughness induced transition. Quadrant analysis of streamwise and wall-normal velocity fluctuations show large ejection events in the outer layer. The difference in the route to transition between the steep and shallow hills was considered to the relative proximity of the initial streamwise vortex to the flat plate and its interaction with the wall. To examine this conjecture, two configurations were prepared to produce two types of counter-rotating streamwise vortices. One is a hill that span the tunnel except for a short gap, and the other, its complement, is a short span hill. The short-gap hill produce a pair of vortices with the common flow directed away from the wall. This resulted in a separation bubble that formed a short distance downstream and breakdown to turbulence. The short-span hill configuration seems to have a stabilizing effect. With the short gap hill, transition occurs for lower freestream speeds than with the isolated vortices considered before. Also, the breakdown location is further downstream when the gap is larger. The initial velocity profiles look similar for transitional and non-transitional flow cases, and are inflectional, which clearly indicates that inflectional instabilities are not effective here. A separation index was computed to identify unsteadiness of the separated flow region. The separation is itself steady, where as the reattachment is unsteady. Fluctuations grow near this reattachment zone. The unsteadiness of the reattachment coexists with the appearance of strong fluctuations and transition. It is likely that the this last stage of breakdown results when the shear layer, lifted up by the separation bubble, breaks down near the edge of the boundary layer and the consequent unsteadiness is in the reattachment also. Coherent cat’s-eye-like patterns were observed in a longitudinal, plane normal to the wall. With isolated vortices sinuous oscillations and with stream-wise vortex pairs varicose oscillations were observed in wall-parallel planes. In both cases passing frequency of these vortices scales with freestream velocity. Λ-type vortices were identified in spanwise plane with counter-rotating legs. These experiments have identified some possible roles of streamwise vortices in the last stages of boundary layer transition. Vortices may undergo their own instability in the background shear layer, evident as oscillations, if they are not too close to the wall. Otherwise the breakdown is without such a stage. Wall interaction of these vortices seems to be a necessary last stage. Inflectional instability is not indicated. Wall interaction that results in separation results in break-down in the unsteady reattachment zone. Breakdown coexists with the reattachment and not at separation, even though it may be the separating shear layer that breaks down.

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48

Freels, Justin Reed. « An Examination of Configurations for Using Infrared to Measure Boundary Layer Transition ». Thesis, 2012. http://hdl.handle.net/1969.1/ETD-TAMU-2012-08-11476.

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Infrared transition location estimates can be fast and useful measurements in wind tunnel and flight tests. Because turbulent boundary layers have a much higher rate of convective heat transfer than laminar boundary layers, a difference in surface temperature can be observed between turbulent and laminar regions of an airfoil at a different temperature than the free stream air temperature. Various implementations of this technique are examined in a wind tunnel. These include using a heat lamp as an external source and circulating fluid inside of the airfoil. Furthermore, ABS plastic and aluminum airfoils are tested with and without coatings such as black paint and surface wraps. The results show that thermal conduction within the model and surface reflections are the driving issues in designing an IR system for detecting transition. Aluminum has a high thermal diffusivity so is a poor choice for this method. However, its performance can be improved using an insulating layer. Internal fluid circulation was far more successful than the heat lamp because it eliminates the reflected IR due to the heat lamp. However, using smooth surface wraps can mitigate reflection issues caused by the heat lamps by reducing the scatter within the reflection, producing an IR image with fewer contaminating reflections.

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49

Huang, Cheng-Wen, et 黃政文. « Wind tunnel study on the flow and dispersion characteristics for a turbulent boundary layer flow over two consecutive embankments with different spaces ». Thesis, 2010. http://ndltd.ncl.edu.tw/handle/01057697019547843189.

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碩士
國立臺灣海洋大學
河海工程學系
98
The wind tunnel experiments were conducted to study the flow and dispersion characteristics for a turbulent boundary layer flow over two consecutive embankments with different spaces. The upwind slope angle and down slope angle of the embankment was the same. Two slope angles of 27o and 45o were adopted. Two consecutive embankments were arranged with spaces of 0L, L, 2L, and 3L. Here L is the top surface length of the embankment. The flow and dispersion characteristics included the mean velocity, turbulence intensity, Reynolds stress, and dispersion parameters. Effects of the embankment slope angles and spaces between the two embankments on the flow and dispersion were investigated in the study.

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50

(10721112), Joshua Craig Ownbey. « Preliminary Design of a High-Enthalpy Hypersonic Wind Tunnel Facility and Analysis of Flow Interactions in a High-Speed Missile Configuration ». Thesis, 2021.

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An approach for designing a high-enthalpy wind tunnel driven by exothermic chemical reactions was developed. Nozzle contours were designed using CONTUR, a program implementing the method of characteristics, to design nozzle contours at various flow conditions. A reacting mixture including nitrous oxide has been identified as the best candidate for providing clean air at high temperatures. The nitrous oxide has a few performance factors that were considered, specifically the combustion of the gas. Initial CFD simulations were performed on the nozzle and test region to validate flow characteristics and possible issues. Initial results show a fairly uniform exit velocity and ability to perform testing. In a second phase of the work, two generic, high-speed missile configurations were explored using numerical simulation. The mean flow was computed on both geometries at 0 and 45 roll and 0, 1, and 10 angle of attack. The computations identified complex flow structures, including three-dimensional shock/boundary-layer interactions, that varied considerably with angle of attack.

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Thèses sur le sujet « Boundary Layer Wind Tunnel (BLWT) »

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