Thèses : « Experimental roughness »

1

Kalogeropoulos, Elias. « Experimental investigation of roughness effects on centrifugal compressor performance ». Thesis, University of Sussex, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326927.

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Petry-Johnson, Travis T. « Experimental investigation of spur gear efficiency ». Connect to resource, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1209585550.

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Hu, Jin. « Experimental and theoretical investigation of roughness effects on thin laminar fluid films ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ27957.pdf.

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4

Brackbill, Tim. « Experimental investigation on the effects of surface roughness on microscale liquid flow / ». Online version of thesis, 2008. http://hdl.handle.net/1850/6136.

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5

Fouflias, Dimitrios. « An experimental and computational analysis of compressor cascades with varying surface roughness ». Thesis, Cranfield University, 2009. http://dspace.lib.cranfield.ac.uk/handle/1826/7029.

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This thesis presents a CFD and experimental analysis associated with the parameter compressor fouling and a CFD analysis associated with the parameter on-line compressor washing of industrial gas turbines. On-line compressor washing is very popular and quite effective in the industrial gas turbine operational scheme. Many companies apply on-line washing with the engine running at normal speed so as to avoid downtime periods for off-line cleanings that could cause significant economic drawbacks. At this thesis vital parameters affecting compressor cleaning of an industrial gas turbine were examined and combined in such a way so as to provide adequate coverage of the frontal inlet guide vane area which is critical for effective cleaning. The parameters investigated were water injection nozzle position, inclination with respect to the engine centerline, injection velocity and nozzle spray angles. However, before applying compressor washing, compressor fouling comes into consideration. For this purpose a compressor cascade tunnel (test rig) was designed and come into operation in order to examine different levels of fouling. The cascade test rig involved as well a washing kit for future cleaning of the cascade blades. This work related to the cascade design released a lot of information about designing suction type compressor cascade test rigs by analysing the flow inside the cascade rig computationally and three-dimensionally via CFD tools. The results in terms of the quality of flow obtained for the current test rig were also compared with modified versions of the test rig, one which involved a bigger plenum area behind the cascade test section and one involving the current rig running in a blowing type mode. The CFD results coming out from the compressor cascade tunnel for the different fouling levels, were analysed in terms of mass flow capacity and polytropic efficiency reduction due to fouling by using Howell’s theory (1945) and they were used as inputs for running performance simulation in terms of an industrial gas turbine engine using the performance simulation code Turbomatch. Therefore, a correlation between cascade fouling and real engine uniformly stage spread fouling was achieved. At high levels fouling where the 254 microns roughness height takes place, the nondimensional air mass flow reduction can reach levels of 1.6% and the drop in compressor efficiency can touch the value of 5%. The CFD results obtained after running all the simulation scheme for the different roughness levels, were compared to the actual experimental results coming from running the compressor cascade rig with the same fouling scheme of roughness. Applying Howell’s theory (1945), the fouled cascade was correlated to a uniformly fouled stage and a real industrial gas turbine. This time input in the Turbomatch code was the percentage deterioration in compressor efficiency calculated from correlated cascade data. This deterioration reaches a high level of 11 % when the fouling particle size is 254 microns.

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Olsson, Niklas, et Christian Selberg. « Numerical simulation and experimental validation of a manufactured wing profile ». Thesis, Högskolan Väst, Avdelningen för Industriell ekonomi, Elektro- och Maskinteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-14287.

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The background for this thesis originates from a study of the flow characteristics for an airfoil of the type NACA0018. The aim for this thesis was to evaluate how the characteristics of the flow over the NACA0018 profile depend on surface roughness. Airfoils were manufactured in Aluminum by Computer Numerical Control-milling and in polylactide polymer using a 3D-printer, where some of the profile surfaces were postprocessed with sandpaper in various grain sizes. The surface roughness of the profiles was evaluated in a 3D optical profilometer using white light interferometry from Filmetrics. By that technique 3D surface plots were created. The manufactured airfoils were tested in a wind tunnel where the achieved data was made dimensionless for comparative purposes. The computational fluid dynamics simulations were performed in Ansys Fluent and compared against the wind tunnel data as well as with the data from a previously made study at htw saar. The results from the wind tunnel tests show that the surface roughness has an effect on the flow characteristic of the airfoil, where different angles of stall were observed in the comparison. The difference for the dimensionless numbers coefficient of lift and drag show that the manufactured aluminum airfoil performs better compared to the 3D-Printed airfoil in this study. It has a higher performance mean value for both of these coefficients in a span of angles between 0 and 30 degrees. When compared, the results from the simulations and wind tunnel experiments do match in some cases, where the dimensionless coefficients and stall angle coheres. Further studies based on this report are recommended, where small geometric changes to the profile could be tested and validated.

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Wen, Quan. « An experimental investigation of inner surface roughness on friction factor for horizontal micro-tubes ». Thesis, University of Macau, 2010. http://umaclib3.umac.mo/record=b2493677.

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Lundberg, Staffan. « Experimental investigations in wood machining related to cutting forces, sawdust gluing, and surface roughness ». Licentiate thesis, Luleå tekniska universitet, Matematiska vetenskaper, 1994. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17499.

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Plogmann, Benjamin [Verfasser]. « Experimental investigations on roughness initiated instability and transition in airfoil boundary layers / Benjamin Plogmann ». München : Verlag Dr. Hut, 2015. http://d-nb.info/1079768254/34.

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Tee, Boon Tuan. « An experimental study of the response of turbulent boundary layers to changes in roughness ». Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610435.

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Leite, Sueli Souza [UNESP]. « Avaliação de desempenho no processo de lixamento de madeiras das espécies Pinus elliottii e Corymbia citriodora ». Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/137956.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
O lixamento da madeira envolve inúmeras variáveis as quais influenciam na qualidade superficial da peça produzida, tornando-se por isso, um processo complexo. Atua de forma imprescindível nas indústrias, principalmente fabricantes de móveis, painéis, molduras, esquadrias e dentre outras. Entretanto, é tratado de forma empírica, prejudicando a qualidade do produto e elevando os custos de produção, visto que é, um dos processamentos mais caros na indústria de madeira. Sabido disto, este trabalho, teve por objetivo combinar um conjunto de fatores para padronizar o processo de lixamento. Para isto, seguiu o planejamento experimental de Taguchi, método baseado em conceitos estatísticos, responsável por diagnosticar o conjunto de fatores que propiciam o alcance da qualidade do produto final. A experimentação realizou-se em relação a uma matriz ortogonal L8, criando assim, oito condições diferentes de lixamento, repetindo-as três vezes cada, totalizando em 24 ensaios. Variou os níveis dos seguintes fatores: granulometria, grão abrasivo, sentido do lixamento e espécie da madeira, com o intuito de analisar o comportamento dos parâmetros: emissão sonora, potência, rugosidade, taxa de remoção e temperatura no decorrer do processo. Por meio da análise de variância (ANOVA), concluiu-se que o comportamento dos parâmetros foram influênciados pelos fatores estipulados, os quais interferiram na qualidade superficial da madeira.
The sanding of wood involves numerous variables which influence the surface quality of the produced piece, becoming therefore a complex process. It is a crucial process in industries, particularly manufacturers such as furniture, panels, moldings, frames and others. However, the process is trated empirically, decreasing the product quality and increasing production costs, since it is one of the most expensive processes in the wood industry. According to this, this paper, aimed to standardize a set of factors to achieve the best surface finish of the wood. For this, the following experimental design Taguchi method based on statistical concepts, responsible for diagnosing the set of factors that promote the achievement of the quality of the final product. The experiment was performed in relation to a matrix L8 orthogonal matrix, creating eight different conditions sanding, repeating three times each, totaling in 24 trials. Varied levels of the following factors: particle size, abrasive grain, sense of sanding and timber species, in order to analyze the parameters of behavior, noise emission, power, roughness, temperature and removal rate in the process. Through analysis of variance (ANOVA), it was concluded that the behavior parameters were influenced by prescribed factors which interfere in the surface quality of the wood.

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Turner, Stephen Edward. « Gas flow and heat transfer in microchannels : an experimental investigation of compressibility, rarefaction, and surface roughness / ». View online ; access limited to URI, 2003. http://0-wwwlib.umi.com.helin.uri.edu/dissertations/dlnow/3115639.

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13

Miller, Mark A. « Experimental Characterization of Roughness and Flow Injection Effects in a High Reynolds Number Turbulent Channel ». UKnowledge, 2013. http://uknowledge.uky.edu/me_etds/26.

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A turbulent channel flow was used to study the scaling of the combined effects of roughness and flow injection on the mean flow and turbulence statistics of turbulent plane Poiseuille flow. It was found that the additional momentum injected through the rough surface acted primarily to enhance the roughness effects and, with respect to the mean flow, blowing produced similar mean flow effects as increasing the roughness height. This was not found to hold for the turbulence statistics, as a departure from Townsend’s hypothesis was seen. Instead, the resulting outer-scaled streamwise Reynolds stress for cases with roughness and blowing deviated significantly from the roughness only condition well throughout the inner and outer layers. Investigation into this phenomena indicated that suppression of the large-scale motions due to blowing may have been contributing to this deviation.

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Guegan, Johan. « Experimental investigation into the influence of roughness on friction and film thickness in EHD contacts ». Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/53388.

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The roughness of machined surfaces such as those in bearings and gears is characterized by asperities which cover a wide spectrum of wavelengths and heights. When the height of the asperities becomes comparable to the lubricant film thickness, the roughness is known to influence friction and wear behaviour. This thesis reports an experimental investigation into the effect of roughness on the film thickness and friction in EHD contact. This work focuses on the particular roughness case of ridges oriented parallel to the rolling-sliding direction, such as the ones produced on raceways during the manufacturing process of rolling element bearings. To carry-out this research a ball-on disk test rig was used to model the contact between the ball and the ring of a ball bearing. The disks were made of glass to enable the lubricant film thickness to be measured through an optical technique based on optical interferometry. The ball specimens were made of AISI 52100 steel and they were roughened with a cutting tool, resulting in longitudinally oriented roughness ridges showing a dominant wavelength and amplitude. The friction was measured through a torque meter attached to the ball shaft. A duo-chromatic system using two LEDs was developed in order to be able to measure the film thickness over a wider range of film thickness. A novel procedure was also introduced to enable the film thickness in rough EHD contacts to be measured accurately. The film thickness and the friction produced by specimens with various amplitude and wavelength were measured under pure rolling and rolling-sliding conditions. The roughness was found to have a big influence on both film build-up and friction. In particular, under the same operating condition, a rough specimen will generate a thinner minimum film and a higher friction compared to a smooth specimen. At the top of the asperities, a micro-EHD film was found to form. As suggested by friction and pressure measurements, the conditions in this micro film are severe enough to reach the limiting shear stress of the lubricant.

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15

Baumann, Martin John. « An experimental investigation of the aerodynamic effects of roughness consisting of arrays of depressions in surfaces ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0007/MQ43336.pdf.

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Yamaguchi, Keiko. « Improved ice accretion prediction techniques based on experimental observations of surface roughness effects on heat transfer ». Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/14148.

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Baumann, Martin John Carleton University Dissertation Engineering Mechanical and Aerospace. « An Experimental investigation of the aerodynamic effects of roughness consisting of arrays of depressions in surface ». Ottawa, 1999.

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18

Lindberg, Eskil. « Vehicle Disc Brake Roughness Noise : Experimental Study of the Interior Noise andVibro-Acoustic Modelling of Suspension Systems ». Licentiate thesis, KTH, MWL Strukturakustik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-39554.

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Prediction of vehicle disc brake roughness noise is a non-trivial challenge. In fact, neither the source mechanisms, nor the transfer paths are so far well understood. Traditionally, disc brake noise problems are studied as part of the friction-induced noise field, where the source is considered to be a more or less local phenomenon related to the brake disc and brake pad. However, for the roughness noise of interest here this viewpoint is not adequate when attempting to solve the interior noise problem since the transfer of vibro-energy from the brake into the vehicle body is a crucial aspect and plays an important role in the understanding and solution to the problem. The vibroacoustic energy transfer associated with the brake roughness noise is a problem where geometrical complexity and material combinations, including rubber bushings, pose an intricate modelling problem. Additionally, system altering effects from moving parts and loadings are important, e.g. due to the steering or brake systems. In addition, the source mechanisms themselves must also be understood to be able to solve the problem. The current work constitutes a combined experimental and theoretical investigation, aiming at an increased understanding of the source, the transfer paths and how they are a affected by change in the operational state. The experimental study of the vehicle disc brake roughness noise, is based on measurements conducted in a laboratory using a complete passenger car. It is found that the interior noise is a structural-borne broadband noise event well correlated to vehicle speed and brake pressure. The results suggest that the friction source may be divided into vibrations created in the sliding direction and vibrations created normal to the contact plane, where the sliding direction levels appear to be proportional to brake pressure according to Coulomb’s friction law; the vibration level in the normal direction of the contact plane on the other hand has behaviour proportional to Hertz contact theory. The measurements also indicate that the brake force created carried by the suspension system when braking will also alter the vibro-acoustic response of the system. To facilitate the theoretical simulations, an approach for modelling of the suspension system is developed. The vibro-acoustic transfer path model developed is using a modal based on the Craig-Bampton method where a restriction on the coupling modes is suggested. The approach suggested uses undeformed coupling interfaces, to couple structures of fundamentally different stiffness such as may be the case in a vehicle suspension system where for instance rubber bushings are combined with steel linking arms. The approach show great potential inreducing computational cost compared to the classical Craig-Bampton method.
QC 20110913

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Thein, Myint. « Experimental investigation of flow resistance and velocity distributions in a rectangular channel with large bed-roughness elements ». Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/19580.

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Huebbe-Walker, Sylvia. « An experimental study of the effects of roughness and curvature on heat transfer in turbulent boundary layers ». Thesis, University of Sussex, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296591.

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Alfama, Marco. « Theoretical and experimental investigation of the heat transfer and pressure drop optimisation on textured heat transfer surfaces ». Diss., University of Pretoria, 2017. http://hdl.handle.net/2263/62792.

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Modern nuclear reactors still use Zirconium-4 Alloy (Zircaloy®) as the cladding material for fuel elements. A substantial amount of research has been done to investigate the boiling heat transfer behind the cooling mechanism of the reactor. Boiling heat transfer is notoriously difficult to quantify in an acceptable manner and many empirical correlations have been derived in order to achieve some semblance of a mathematical model. It is well known that the surface conditions on the heat transfer surface plays a role in the formulation of the heat transfer coefficient but on the other hand it also has an effect on the pressure drop alongside the surface. It is therefore necessary to see whether there might be an optimum surface roughness that maximises heat transfer and still provides acceptably low pressure drop. The purpose of this study was to experimentally measure pressure drop and heat transfer associated with vertical heated tubes surrounded by flowing water in order to produce flow boiling heat transfer. The boiling heat transfer data was used to ascertain what surface roughness range would be best for everyday functioning of nuclear reactors. An experimental set-up was designed and built, which included a removable panel that could be used to secure a variety of rods with different surface roughnesses. The pressure drop, surface temperature, flow rate and heat input measurements were taken and captured in order to analyse the heat transfer and friction factors. Four rods were manufactured with different roughnesses along with a fifth rod, which remained standard. These rods were tested in the flow loop with water in the upward flow direction. Three different system mass flow rates were used: 0kg/s, 3.2kg/s and 6.4kg/s. Six repetitions were done on each rod for the tests; the first repetition was not used in the results since it served the purpose to deaerate the water in the flow loop. The full range of the power input was used for each repetition in the tests. For the heat transfer coefficient at a system mass flow rate of 3.2kg/s, satisfactory comparisons were made between the test results and those found in literature with an average deviation of 14.53%. At 6.4kg/s system mass flow rate the comparisons deviated on average 55.45%. The velocity of the fluid in the test section was calculated from the pressure drop and was validated using separate tests. The plain rod, with no added roughness, was found to be the optimal surface roughness which is what is used in industry today. The flow loop was in need of a couple of redesigns in order to produce more accurate results. Future work suggestions include adding more rods in the test section in order to investigate the nature of heat transfer in a rod bundle array as well as implementing all the suggested changes listed in the conclusion.
Dissertation (MEng)--University of Pretoria, 2017.
Mechanical and Aeronautical Engineering
MEng
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BATISTA, Cláudia da Silva. « Estudo teórico e experimental do fluxo de sólidos particulados em silos verticais ». Universidade Federal de Campina Grande, 2009. http://dspace.sti.ufcg.edu.br:8080/jspui/handle/riufcg/1815.

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Este trabalho teve por objetivo principal apresentar um estudo teórico e experimental da vazão mássica e do fluxo de produtos granulares para subsidiar o projeto estrutural em silos. Foi desenvolvido um modelo matemático para predizer a vazão de descarregamento para distintos produtos. Estudou-se as características físicas e de fluxo de cinco produtos granulares: painço, areia fina e três farelos de milho, e avaliou-se o comportamento do fluxo das partículas em um silo cilíndrico, equipado com fundo plano e tremonhas de 30 e 45 de inclinação com a vertical; diferentes orifícios de descarga, 3,5 e 5 cm de diâmetro; e três rugosidades das paredes, 0,06, 6,56 e 11,9 m. Concluiu-se que a rugosidade da parede, para a faixa estudada, não influenciou na vazão de descarregamento, para todos os produtos. As maiores vazões de descarregamento no silo foram registradas para a areia e as menores foram observadas para o farelo de milho M1, cuja razão aproximada foi de 2,5 para as diversas formas de descarregamento. As maiores vazões de descarga foram observadas quando o diâmetro do orifício de saída foi de 5 cm chegando a um valor de 1,35 kg/s. As menores vazões de descarregamento dos produtos foram registradas quando se utilizou a tremonha com inclinação de 30 com o valor de 0, 16 kg/s para o produto que apresentou as menores vazões, farelo de milho M1.O fenômeno “slip stick” foi verificado para as diferentes granulometrias do farelo de milho, sendo mais intenso para o M2. O modelo proposto apresentou ajuste razoável em relação aos dados experimentais.
This work was aimed at presenting a theoretical and experimental study of the mass flow and the flow of granular products to support the structural design of silos. We developed a mathematical model to predict the flow of discharge for different products. We studied the physical characteristics and flow of five granular products: millet, fine sand and three meals of corn, and evaluated the flow behavior of particles in a cylindrical silo, equipped with flat bottom hoppers 30 and 45 inclination to the vertical, different discharge outlets, 3.5 and 5cm in diameter and three m.roughness of the walls, 0.06, 6.56 and 11.9 It was concluded that the roughness of the wall, in the range studied did not influence the flow of discharge for all products. The highest rates of discharge were recorded in the silo for sand and the lowest was observed for the corn bran M1, whose approximate ratio was 2.5 for the various forms of discharge. The highest rates of discharge were observed when the diameter of the exit hole was 5 cm reaching a value of 1.35 kg / s. The lowest flow rate of discharge of the products were recorded when using the to the value of 0, 16 kg/s for the product hopper with an inclination of 30 that had the lowest flow rates, corn bran M1.O phenomenon "slip stick" was observed for different particle size of corn bran, being more intense for the M2. The proposed model presented a reasonable adjustment in relation to the experimental data.

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Puckert, Dominik [Verfasser]. « Experimental Investigation on Global Instability and Critical Reynolds Number in Roughness-Induced Laminar-to-Turbulent Transition / Dominik Puckert ». München : Verlag Dr. Hut, 2019. http://d-nb.info/1181515130/34.

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Silva, Alessandro Alves da. « Efeitos topográficos em espectros RBS ». Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-09042008-142058/.

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A medida da rugosidade de uma superfície costuma produzir resultados que dependem da metodologia empregada. A microscopia eletrônica de varredura, SEM, a microscopia de força atômica, AFM e a perfilometria são algumas das técnicas costumeiramente empregadas na caracterização de superfícies rugosas. Esse trabalho explora a e desenvolve o uso da espectrometria de retroespalhamento Rutherford, RBS, para medir e quantificar a rugosidade de uma superfície. Quatro diferentes amostras com rugosidade periódica e controlada (duas retangulares e duas senoidais) com razão de aspecto suficientemente grande que produzam efeitos mensuráveis por RBS, foram produzidas por interferometria óptica. Os espectros RBS experimentais foram convertidos em rugosidade rms e comparados com resultados de SEM e AFM. Medir rugosidade através de RBS permite inspecionar uma área (da ordem de alguns mm2) e profundidades muito maiores que as acessíveis por AFM, apesar de ainda limitados pela resolução em energia intrínseca da metodologia RBS.
Measuring the roughness of a surface use to produce results which depend on the employed methodology. Scanning Electronic Microscopy, Atomic Force Microscopy, profilometry, are some of the techniques used to characterize surface roughness. This work explores and develops the use of Rutherford Backscattering Spectrometry to measure and quantify the roughness of a surface. Four different samples with controlled and periodic surface profiles (two rectangular waved, and two sinusoidal), with enough aspect ratio to, give measurable effects in an RBS analysis, were produced by optical interferometry to test and verify the proposed methodology. The experimental RBS spectra were converted into rms roughness and compared to SEM and AFM measurements. Measuring roughness by RBS enables one to inspect a much bigger area (of the order of some mm2) and with more depth resolution, than by using an AFM, yet still limited by the experimental intrinsic energy resolution of the RBS methodology.

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Li, Pingju. « An Experimental Investigation of Velocity Distribution and Head Loss of Oscillatory Flow in a Rectangular Duct with Sand Roughness ». Doctoral thesis, Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-300.

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Frequency and amplitude dependency of velocity distribution and head loss of oscillatory flow in a rectangular duct have been studied experimentally with a model tunnel system.

Tests were carried out with the duct of both smooth and rough walls. The smooth wall was made of Plexiglas. Sand roughness was used for the rough wall. Velocity, pressure and differential pressure of stationary flow, pure oscillatory flow and combined oscillatory flow were measured. The combined oscillatory flow was classified as oscillation dominant flow, stationary dominant flow, and oscillation-and-stationary balanced flow. Various oscillating frequencies, amplitudes and steady flow percentages were tested for oscillatory flows. The oscillating frequencies tested were varied from 0.01 Hz to 1.00 Hz. Oscillatory amplitude and stationary part were varied from 10 to 100%. Velocity of the flow was measured with a 2D PIV (Particle Image Velocimetry) and a 2D LDV (Laser Doppler Velocimetry) respectively at different test stages. The maximum mainstream velocity was ranged from 0.05 m/s to 1.1 m/s. Data of pressure variations along the tunnel were collected with differential pressure sensors. Flow rate and instant wall pressures at multiple points along the test tunnel were measured simultaneously. The static pressure in the test tunnel was about 1.0 mWC. The differential pressure along the tunnel was less than 20 mmWC per meter.

Examples of velocity distribution in the test rig from LDV measurement are presented, for both stationary flow and oscillatory flow. The dimensionless velocity distributions of stationary flow are in good agreement with the universal velocity distribution law. Deviations are obvious between the velocity distributions of oscillatory flow and the universal velocity distribution law, when the measured velocity is scaled to dimensionless by friction velocity from Clauser chart. Examples of PIV velocities of different flow regimes are presented in the forms of velocity profile and velocity waveform. Generally, the velocity distributions are in good agreement with the results from LDV, in agreement with the normal turbulent velocity distribution in a duct, if the velocity magnitude is not too small. Dimensionless velocity profiles at various phase angles of the same oscillatory flow regime have quite consistent distribution. The annular effect is observed in some cases. Its occurrence depends on the complex actions of oscillating frequency, amplitude and stationary flow percentage. The velocity waveform confirms the characteristics of mass oscillation of the flow. No significant phase shift is displayed between the velocity waveform of the boundary and centreline in most cases tested. The vertical velocity, which is normal to the mainstream, is quite small and has similar features to the mainstream velocity.

The velocity profiles got from both LDV and PIV show that the flows in the test tunnel were typical turbulence, with typical velocity distribution of turbulence. No transition between laminar and turbulence is observed even at the turning point of oscillation.

Pressure variations measured along the tunnel of different flow regimes are presented. The accelerative heads of oscillatory flow are calculated. The friction head losses along the tunnel are evaluated. The dependencies of pressure variation and friction head loss on oscillatory frequency and amplitude are investigated for both pure oscillatory flow and combined oscillatory flow. It is proven that the friction head loss of oscillatory flow increases along with the increase of frequency if the mean flow rate is kept constant. The peak friction head loss increases along with the increase of oscillatory amplitude. Comparison of pressure variation and friction head loss between stationary flow and oscillatory flow shows that the friction head loss of unsteady flow is much bigger than that of steady flow. This is in good agreement with the expectancy based on the experimental results of laminar flow. The head loss of pure oscillatory flow was greater than that of the stationary flow for dozens or more times for various flow regimes running at equivalent flow rate. The ratio of head loss of combined oscillatory flow to stationary flow running at equivalent flow rate is smaller than that of pure oscillatory flow to stationary flow, several times to dozen times. In general, the frequency dependency of head loss on oscillatory frequency and amplitude is clear, though the measuring length is only 9 metres and the absolute magnitude of pressure variation is less than 0.20 mWC.

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Sharma, Vivek Inder. « Experimental investigation of effects of surface roughness, wettability and boiling-time on steady state and transient CHF for nanofluids ». Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/76924.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 239-248).
Critical Heat Flux (CHF) is one of the primary design constraints in a nuclear reactor. Increasing the CHF of water can enhance the safety margins of the current fleet of Light Water Reactors (LWRs) and/or increase their power output. It has been shown that a suspension of nanoparticles called nanofluids in DI water enhances the CHF of water significantly. During boiling, nanoparticles in the nanofluid develop a coating on the heater surface, which is porous and hydrophylic, leading to a higher CH{F compared to water. One of the primary objectives of this thesis is to conduct an experimental investigation of the effects of three parameters (i.e. initial roughness, initial wettability and boiling time) on the steady-state CHF of nanofluids. Experiments with DI water served as the base case for CHF values, and experiments with nanofluid were done analyze their effects on CHF. Metallic heaters made of SS304 oriented vertically in a pool of test-fluid are used for experiments. The nanofluid used in the experiments has 0.01 v% ZnO nanoparticles in DI water. Multiple experiments were done to measure CHF of DI water (base-case) and test nanofluid for varied initial surface roughness (Ra), surface wettability and different preboiling times. Results indicate that compared to water, nanofluids enhanced CHF by an average of 77% (ranging from 25% to 150% for different surface and experimental conditions). It was also observed that the effect of nanofluids in increasing CHF was less pronounced if the initial heaters contained a superhydrophilic surface coating before use with nanofluids as opposed to the initial heaters being bare and uncoated. Additionally, the thickness of the nanocoating appeared to plateau after approximately 30 - 40 minutes of boiling time, and additional pre-boiling times of up to 8 hours did not have any effect on nanocoating development or CHF. The other objective of this work is to assess the applicability of nanofluids to accident scenarios in nuclear reactors, which are accompanied by rapid power transients. Such situations are simulated by rapidly increasing heat flux through the heater elements from 0 to CHF in short time frames of 1, 10 and 100 s. It was observed that for nanofluid tests, nanocoatings started to generate on the heater surface in as short time frames as 10 and 100 s, and the nanocoatings enhanced CHF, compared to DI water, by approximately 20%. However, for 1 s tests, nanofluids did not enhance the CHF, and nanocoatings were not detected at the heater surface. Additionally, pre-boiling the heater surfaces in the nanofluid caused a CHF enhancement for all three rates of power increase.
by Vivek Inder Sharma.
Ph.D.

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Cali, Serdal. « An Experimental Study On Single Crystal Diamond Turning Of Optical Quality Silicon ». Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/2/12609235/index.pdf.

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Silicon is commonly used in infrared (IR) imaging systems. The surface quality is an important issue in optics manufacturing since surface roughness affects optical performance of imaging systems. Surface quality of an optical component is determined by number of factor, including cutting parameters
cutting speed, depth of cut and feed in radial direction. In this thesis, an experimental study has been performed to investigate the relation between cutting parameters and average roughness of the surface of silicon. In the experiments, silicon specimens, which have a diameter of 50 mm, were face turned by using a 2-axis CNC single point diamond turning machine. The specimens were machined by using either constant spindle speed or constant cutting speed. Two different tools with rake angles of -15 degrees and -25 degrees were used. The attained surfaces were measured by using a white light interferometer, which has a resolution of 0.1nm. The experiments were designed according to the factorial design method, considering cutting parameters. The effects of cutting parameters and tool rake angles on surface quality of silicon were observed. The best average surface roughness obtained was about 1 nm which is quite better than the acceptable average surface roughness level of 25 nm.

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Chaudhury, Kreteeka. « An Experimental Investigation of the Impact of Engineered Surface Processes on Efficiency of Spur Gears ». The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1556553897979376.

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Nanetti, Marco. « Experimental Study on Friction between Saline Ice and Steel ». Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amslaurea.unibo.it/57/.

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Understanding the interaction of sea ice with offshore structures is of primary importance for the development of technology in cold climate regions. The rheological properties of sea ice (strength, creep, viscosity) as well as the roughness of the contact surface are the main factors influencing the type of interaction with a structure. A device was developed and designed and small scale laboratory experiments were carried out to study sea ice frictional interaction with steel material by means of a uniaxial compression rig. Sea-ice was artificially grown between a stainless steel piston (of circular cross section) and a hollow cylinder of the same material, coaxial to the former and of the same surface roughness. Three different values for the roughness were tested: 1.2, 10 and 30 μm Ry (maximum asperities height), chosen as representative values for typical surface conditions, from smooth to normally corroded steel. Creep tests (0.2, 0.3, 0.4 and 0.6 kN) were conducted at T = -10 ºC. By pushing the piston head towards the cylinder base, three different types of relative movement were observed: 1) the piston slid through the ice, 2) the piston slid through the ice and the ice slid on the surface of the outer cylinder, 3) the ice slid only on the cylinder surface. A cyclic stick-slip motion of the piston was detected with a representative frequency of 0.1 Hz. The ratio of the mean rate of axial displacement to the frequency of the stick-slip oscillations was found to be comparable to the roughness length (Sm). The roughness is the most influential parameter affecting the amplitude of the oscillations, while the load has a relevant influence on the their frequency. Guidelines for further investigations were recommended. Marco Nanetti - seloselo@virgilio.it

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Apsilidis, Nikolaos. « Experimental Investigation of Turbulent Flows at Smooth and Rough Wall-Cylinder Junctions ». Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/71713.

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Junction flows originate from the interaction between a fluid moving over a wall with an obstacle mounted on the same surface. Understanding the physics of such flows is of great interest to engineers responsible for the design of systems consisting of wall-body junctions. From aerodynamics to turbomachinery and electronics to bridge hydraulics, a number of phenomena (drag, heat transfer, scouring) are driven by the behavior of the most prominent feature of junction flows: the horseshoe vortex system (HVS). Focusing on turbulent flows, the complex dynamics of the HVS is established through its unsteadiness and non-uniformity. The fundamentals of this dynamically-rich phenomenon have been described within the body of a rapidly-expanding literature. Nevertheless, important aspects remain inadequately understood and call for further scrutiny. This study emphasized three of them, by investigating the effects of: model scale, wall roughness, and bed geometry. High-resolution experiments were carried out using Particle Image Velocimetry (PIV). Statistical analyses, vortex identification schemes, and Proper Orthogonal decomposition were employed to extract additional information from the large PIV datasets. The time-averaged topology of junction flows developing over a smooth and impermeable wall was independent of the flow Reynolds number, Re (parameter that expresses the effects of scale). On the contrary, time-resolved analysis revealed a trend of increasing vorticity, momentum, and eruptions of near-wall fluid with Re. New insights on the modal dynamics of the HVS were also documented in a modified flow mechanism. Wall roughness (modeled with a permeable layer of crushed stones) diffused turbulence and vorticity throughout the domain. This effect manifested with high levels of intermittency and spatial irregularity for the HVS. Energetic flow structures were also identified away from the typical footprint of the HVS. Finally, a novel implementation of PIV allowed for unique velocity measurements over an erodible bed. It was demonstrated that, during the initial stages of scouring, the downflow at the face of the obstacle becomes the dominant flow characteristic in the absence of the HVS. Notwithstanding modeling limitations, the physical insight contributed here could be used to enhance the design of systems with similar flow and geometrical characteristics.
Ph. D.

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Helvey, Jacob. « Experimental Investigation of Wall Shear Stress Modifications due to Turbulent Flow over an Ablative Thermal Protection System Analog Surface ». UKnowledge, 2015. http://uknowledge.uky.edu/me_etds/57.

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Modifications were made to the turbulent channel flow facility to allow for fully developed rough quasi-2D Poiseuille flow with flow injection through one surface and flow suction through the opposing surface. The combination of roughness and flow injection is designed to be analogous to the flow field over a thermal protection system which produces ablative pyrolysis gases during ablation. It was found that the additional momentum through the surface acted to reduce skin friction to a point below smooth-wall behavior. This effect was less significant with increasing Reynolds number. It was also found that the momentum injection modified the wake region of the flow.

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Marsh, Richard. « Experimental analysis of oil based cavitation peening in air ». Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/43602.

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Oil Jet Cavitation Peening in Air (OPA) is capable of inducing compressive residual stress in standard aerospace materials. This paper demonstrates the process capabilities of OPA on Al 2024-T3. Specifically, changes in the workpiece residual stress, microhardness, mass loss and surface roughness are investigated as a function of the control parameters for the system. Additionally, the paper identifies a method to monitor the process in situ through the use of high frequency acoustic emission sensors. The results indicate the OPA process is capable of generating residual stresses comparable to those of standard shot peening, up to 60% of the yield strength of the material, at similar depths, around 300 µm. Finally, the acoustic emission signal may be utilized to monitor the process, specifically in predicting the microhardness and mass loss of the system.

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Lindberg, Eskil. « A Vibro-Acoustic Study of Vehicle Suspension Systems : Experimental and Mathematical Component Approaches ». Doctoral thesis, KTH, MWL Strukturakustik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-121575.

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The objective of the present work is to study the vehicle suspension as a vibro-acoustic system of high complexity, consisting of many sub-systems with fundamentally different acoustical properties. In a parallel numerical and experimental modelling effort, important contributions to the understanding of its behaviour have been achieved. These findings are based on a balance between component investigations and global modelling of the complete system; they have been formulated for the transmission of both tyre-road excitation and friction-induced vibrations in the brake system. Initially an experimental study was conducted on a full vehicle test rig studying the broadband interior brake noise problem of, here named, roughness noise. The purpose of the study was twofold: first, to determine if the transmission from the source to the interior of the vehicle was structure-borne; second, to study the complexity of the suspension as a vibro-acoustic system. Parameters a_ecting the vibro-acoustic source were varied to gain understanding of the source mechanisms. This experimental study laid the foundation of the first part of this thesis (paper A) and provided the directions for the second part, the development of a mathematical modelling approach (paper B and C). In these two papers, methods for analysing the complex vibro-acoustic transfer of structure-borne sound in a vehicle suspension system were developed. The last part was then focussed on the wheel rim influence on the vibro-acoustic behaviour (paper D) of the suspension system. As a whole, the work clearly demonstrates that it is possible to conduct component studies of subsystems in the vehicle suspension system; and from these component studies it is possible draw conclusions that very well may avoid severe degradations in the interior noise of future vehicle generations.

QC 20130503

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Marchand, Jean-Baptiste. « Experimental Analysis and Numerical Simulation of Foil Sections for Tidal Turbine Application ». Thesis, Paris, ENSAM, 2014. http://www.theses.fr/2014ENAM0038.

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Dans un contexte de développement des énergies renouvelables, les énergies marines suscitent un grand intérêt. Parmi elles, les courants de marée paraissent constituer une ressource intéressante du fait de la densité de l'eau de mer et de la possibilité de prévoir les oscillations de marée à un endroit donné. Pour une turbine à axe vertical et en accord avec le partenaire industriel, les contraintes à l'échelle de la section de pale incluent la bidirectionnalité de l'écoulement, l'état de surface ainsi que la turbulence amont. La première partie du travail présentée ici s'est donc attachée à étudier deux solutions permettant de répondre à la bidirectionnalité de l'écoulement à l'échelle d'une section de pale. Un profil bidirectionnel spécifique a ainsi été comparé à un NACA 0015 en écoulement directe et inversé. La seconde partie s'est attachée à caractériser l'effet de la rugosité de surface et de la turbulence amont sur les propriétés d'un profil unidirectionnel spécifiquement développé pour les turbines à axe horizontal. Les deux sujets ont été abordés sur des profils académiques 2D, au travers d'une approche expérimentale originale et d'étude numériques. Des calculs tout turbulents et avec prise en compte de la transition ont été comparés à des mesures d'effort par balance, couplés à des observations de l'écoulement par PIV. Le foil bidirectionnel ainsi que le foil NACA en écoulement direct et inversé ont montrés des comportements singuliers qui pénalisent leurs performances dans l'optique d'une utilisation en tant que section de pale. A partir d'une valeur seuil, la hauteur de la rugosité de surface a montré engendrer un changement profond de la nature de l'écoulement autour du foil unidirectionnel. Finalement, il a été observé que la turbulence amont modifiait modérément les propriétés de ce type de foils, mais de façon moins significative à l'échelle de la pale
In a context of development of renewable energies, there is a growing interest in marine energies. Among them, tidal currents are promising due to the density of seawater and the predictability of tidal oscillations at a given location. For horizontal axis tidal turbines and according to the industrial partner, constraints at the blade section scale include bi-directionality of the flow, surface roughness and upstream turbulence. The first part of the present work studied two solutions to achieve bi-directionality of the flow at the blade section scale. A specific bi-directional hydrofoil was compared to a NACA 0015 in forward and reversed flow. The second part focussed on the effect of surface roughness and upstream turbulence on a unidirectional blade section designed for current turbines. Both studies were carried out on academic two-dimensional hydrofoils, using both numerical investigation and a specifically developed experimental approach. Computations using fully turbulent and transition models were compared to balance force measurements coupled with PIV flow observations. The bidirectional foil as well as the NACA foil in forward and reversed flow, showed specific behaviours that could considerably reduce their performances for a use as a tidal turbine rotor. Roughness height was also observed to deeply change the foil properties, beyond a critical height. Finally, upstream turbulence resulted in moderate performance changes, less significant at the machine scale

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Nyantekyi-Kwakye, Baafour. « Experimental investigation on the flow characteristics of three-dimensional turbulent offset jets ». Taylor and Francis Group, 2015. http://hdl.handle.net/1993/31626.

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An experimental study was designed to investigate the effect of different parameters on the development and structure of turbulent 3D offset jets. The present investigation considered the effects of offset height ratio, expansion ratio, surface roughness and rib placement on the flow dynamics of a turbulent 3D offset jet. The velocity measurements were performed using an acoustic Doppler velocimetry (ADV) and particle image velocimetry (PIV). Measurements were conducted within the symmetry and lateral planes. For the PIV technique, the measurements in the symmetry and lateral planes were conducted over a streamwise range of 0 ≤ x/bo ≤ 80 and 12 ≤ x/bo ≤ 60, respectively (where bo is the nozzle height). Likewise, velocity measurements using the ADV technique were conducted over a range of 4 ≤ x/bo ≤ 45 in both the symmetry and lateral planes. The velocity measurements were analyzed using both one-point and multi-point statistics. The one-point statistics included profiles of the mean velocities, Reynolds stresses and some of the budget terms in the turbulent kinetic energy transport equation. The quadrant analysis technique was used to investigate the dominant events that contribute towards the Reynolds shear stress. The two-point correlation analysis was used to investigate how the turbulence quantities are correlated. Information obtained from the two-point correlation analysis was also used to investigate the inclination of vortical structures within the inner and outer shear layers of the 3D offset jet. The direction of the positive mean shear gradient played an active role in the inclination of these vortical structures within the inner and outer shear layers. The reattachment process resulted in the breakdown of these structures within the developing region. Similarly, various length scales were estimated from these structures. The proper orthogonal decomposition was used to examine the distribution of the turbulent kinetic energy within the offset jet flow. Also, the dynamic role of the large scale structures towards the turbulent intensities, turbulent kinetic energy and Reynolds shear stress was investigated.
October 2016

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Collier, Christopher Thomas. « Experimental and computational investigation into light scattering by atmospheric ice crystals ». Thesis, University of Hertfordshire, 2015. http://hdl.handle.net/2299/16359.

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An investigation was carried out into light scattering by Gaussian rough ice crystals. Gaussian rough crystal geometries were generated using roughness parameters derived from mineral dust grains, which have been reported to be suitable proxies for rough ice crystals. Light scattering data for these geometries was computed using the discrete dipole approximation (DDA) method. Phase functions, 2D scattering patterns, degree of linear polarisation patterns and asymmetry parameters were computed for smooth, moderately rough and highly rough crystals with a variety of orientations and size parameters. A sodium fluorosilicate ice analogue crystal with three partially roughened prism facets was created using focused ion beam (FIB) milling and 2D scattering patterns were collected from it using the small ice detector (SID) 3 cloud probe. It was found that roughness reduces features in the phase function compared to scattering by smooth hexagonal prisms, particularly when the roughness features were horizontally much larger than the wavelength. However, the most effective roughness model also takes account of horizontal features whose size is closer to that of the wavelength. Horizontal features smaller than the wavelength have very little effect.

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Schneck, Fabiana. « Efeitos da rugosidade de substratos, distúrbios físicos e organismos pastejadores na estruturação de assembleias de algas bênticas e na biomassa perifítica em um riacho subtropical : uma abordagem experimental ». reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/49267.

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Os estudos apresentados nesta tese tiveram como objetivo compreender aspectos da organização de assembleias de algas bênticas em riachos. Foi avaliado especificamente o efeito da heterogeneidade de habitat na escala de rugosidade de substratos e sua interação com distúrbios hidrológicos e organismos pastejadores (grazers). Utilizou-se uma abordagem experimental in situ com substratos lisos e rugosos (com fendas) constituindo os tratamentos. Os experimentos foram conduzidos no Rio do Marco, um riacho de quarta ordem na região dos Campos de Cima da Serra, em São José dos Ausentes, Rio Grande do Sul. Após uma introdução geral acerca do assunto são apresentados os capítulos com os estudos. O Capítulo 1 avaliou os efeitos da rugosidade de substratos sobre a riqueza de espécies, densidade, composição e padrões de distribuição de assembleias de algas bênticas. Assembleias em substratos rugosos foram mais ricas que assembleias em substratos lisos, porém esse resultado diferiu entre grupos com diferentes formas de vida, assim como as diferenças na composição de espécies, indicando que somente alguns grupos foram beneficiados pela ocorrência de refúgios em substratos rugosos. Observou-se também que diferenças na composição da assembleia entre substratos lisos e rugosos resultaram de aninhamento e substituição de espécies. No Capítulo 2 foi testada a hipótese de que substratos rugosos abrigam assembleias mais persistentes que substratos lisos. Os resultados encontrados confirmaram esta hipótese e foram atribuídos ao efeito da rugosidade per se após a exclusão de alguns fatores de confundimento, como estabilidade física dos substratos e diferenças na riqueza de espécies. Concluiu-se que o mecanismo mais plausível para explicar a maior persistência em substratos rugosos é a maior disponibilidade de refúgios em relação a substratos lisos. O objetivo do Capítulo 3 foi avaliar o efeito da rugosidade de substratos sobre assembleias de algas frente a um distúrbio hidrológico experimental, testando especificamente se a resistência e a resiliência de algas é maior em substratos rugosos que em substratos lisos e se a resposta de diferentes formas de vida é distinta. Os resultados indicaram que a rugosidade de substratos não apresenta efeitos pronunciados sobre a resistência e a resiliência de algas bênticas. Porém, grupos de algas com distintas formas de vida diferiram quanto à resistência e resiliência, de forma que o padrão observado está relacionado a atributos biológicos que conferem habilidades para suportar distúrbios. Os resultados deste estudo em conjunto com os resultados obtidos no Capítulo 2 e resultados obtidos por outros autores permitiram que fosse proposto que a importância da heterogeneidade de habitas e de refúgios é mediada pela intensidade de distúrbios. No Capítulo 4 foram avaliados os efeitos independentes e as interações de rugosidade de substratos, peixes pastejadores e tipos de mesohabitats (corredeiras e remansos) sobre a biomassa algal, matéria orgânica e peso seco total. O efeito de peixes pastejadores não foi mediado pelos mesohabitats, sendo que a exclusão de peixes causou aumento nas três variáveis resposta, independente do tipo de mesohabitat. Por outro lado, houve uma interação entre mesohabitats e substratos para determinar o acúmulo de peso seco total, sendo que substratos rugosos acumularam maior quantidade de material em remansos que em corredeiras, enquanto substratos lisos acumularam quantidades similares entre os dois tipos de mesohabitats. Já a biomassa algal e matéria orgânica apresentaram maior acúmulo nos substratos rugosos em relação aos lisos, independente do mesohabitat. Os resultados encontrados indicam que a perda de organismos pastejadores pode afetar o acúmulo de biomassa algal e material orgânico, importantes recursos alimentares em riachos. Finalmente, na última seção são apresentadas as considerações finais.
The studies presented in this thesis aimed at understanding some aspects of the organization of benthic algal assemblages in streams. Specifically, the studies evaluated the effect of habitat heterogeneity on the scale of substrate roughness and its interaction with hydrological disturbances and grazing organisms. An experimental in situ approach was used, in which the treatments were constituted by smooth and rough (with crevices) substrates. The experiments were conducted in the Marco River, a fourth-order stream at the region of Campos de Cima da Serra, São José dos Ausentes, Rio Grande do Sul, Brazil. After a general introduction on the subjects of this thesis, the chapters with the studies are presented. The Chapter 1 describes a study to evaluate the effects of substrate roughness on species richness, density, composition and distribution patterns of benthic algal assemblages. Algal assemblages on rough substrates were richer than on smooth substrates, but this result differed among algal life forms. Similarly, results on species composition also differed among life forms, indicating that only some groups were benefited by the occurrence of refuges on rough substrates. It was also observed that differences in the composition of assemblages between rough and smooth substrates resulted from nestedness and turnover. The Chapter 2 describes a study in which was tested the hypothesis that rough substrates harbor more persistent assemblages than smooth substrates. The results confirmed this hypothesis and were attributed to the effect of roughness per se after the exclusion of some confounding factors, such as the physical stability of substrates and differences in species richness. It was concluded that the most plausible mechanism that could explain the higher persistence in rough substrates is the greater availability of refuges in relation to smooth substrates. The main aim of the study described in Chapter 3 was to evaluate the effect of substrate roughness on algal assemblages in the face of an experimental hydrological disturbance. Specifically, it was tested if the resistance and resilience of algae is higher on rough than on smooth substrates and if algal life forms differ in their response to disturbance. The results indicated that substrate roughness had no pronounced effects on benthic algal resistance and resilience. However, algal life forms differ in their resistance and resilience, and the observed pattern was mostly related to biological traits that confer abilities to support disturbances. The results of this study, in addition to the results obtained in Chapters 1 and 2, allowed us to suggest that the importance of habitat heterogeneity and refuges is mediated by the intensity of disturbances. The Chapter 4 describes a study that evaluated the independent and interacting effects of substrate roughness, grazing fish and mesohabitats (pools and riffles) on algal biomass, organic matter and total dry mass accrual. The effect of grazers was not mediated by mesohabitats, and their exclusion caused an increase in the three response variables, regardless of mesohabitat. On the other hand, mesohabitats and substrates interacted to determine the accrual of total dry mass, since rough substrates accumulated greater amounts of dry mass in pools than in riffles, while smooth substrates accumulated similar amounts in both mesohabitats. Algal biomass and organic matter showed greater accrual on rough than on smooth substrates, independently of mesohabitat. These results indicate that the loss of grazers may affect the accrual of algal biomass and organic matter, which are important food resources in streams. Finally, in the last section are presented the concluding remarks.

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York, David Christopher. « Studies of thermal transpiration ». Thesis, University of York, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323501.

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SANTOS, HAMILTA de O. « Caracterização de camisas de cilindro em ligas Al-Si hipereutéticas e investigação do comportamento de corrosão em meio de condensado sintético automotivo ». reponame:Repositório Institucional do IPEN, 2006. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11425.

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Made available in DSpace on 2014-10-09T12:51:46Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T14:08:49Z (GMT). No. of bitstreams: 0
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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40

Рапута, М. В. « Чисельне та експериментальне дослідження впливу шорсткості поверхні на характеристики лабіринтних ущільнень ». Master's thesis, Сумський державний університет, 2018. http://essuir.sumdu.edu.ua/handle/123456789/72180.

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У роботі виконано чисельне та експериментальне дослідження впливу шорсткості поверхні на характеристики лабіринтних ущільнень
В работе выполнено численное и экспериментальное исследование влияния шероховатости поверхности на характеристики лабиринтных уплотнений.
A numerical and experimental study of the effect of surface roughness on the characteristics of labyrinth seals was performed.

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Chevalier, Eric. « Les surfaces à marches des cristaux d'hélium 4 ». Université Joseph Fourier (Grenoble), 1994. http://www.theses.fr/1994GRE10150.

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Le travail presente dans ce memoire est une mesure experimentale des proprietes des surfaces a marches, surfaces faiblement desorientees par rapport a l'axe cristallographique c, des cristaux d'helium-4, a partir des ondes de fusion-cristallisation. Nous montrons pour la premiere fois, l'existence d'un passage entre le regime rugueux et le regime a marches en fonction de l'angle. Nous le mettons en evidence par la mesure independante des deux composantes transverses et longitudinales du tenseur de rigidite de surface. Dans le regime a marches, nous avons non seulement montre que l'interaction repulsive entre les marches cristallines est bien proportionnelle a l'inverse de la distance entre marches au carre, mais avons aussi mesure a la fois la contribution entropique et elastique de cette interaction

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42

Al-Maaitah, Ayman Adnan. « Effect of roughness element on the stability of boundary layers ». Thesis, Virginia Tech, 1986. http://hdl.handle.net/10919/45741.

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The instability of flows around hump and dip imperfections is investigated. The mean flow is calculated using interacting boundary layers, thereby accounting for viscous/inviscid interaction and separation bubbles. Then, the two-dimensional linear instability of this flow is analyzed, and the amplification factors are computed. Results are obtained for several height/width ratios and locations. The theoretical results have been used to correlate the experimental results of Greening and Walker. The observed transition locations are found to correspond to amplification factors varying between 7.4 and 10, consistent with previous results for flat plates. The method accounts for Tollmien-Schlichting waves, the shear layer instability, and their interaction. Separation is found to increase significantly the amplification factor.
Master of Science

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43

Soriano, i. Fradera Jordi. « Roughness experiments of viscous fluid interfaces in disordered Hele-Shaw cells ». Doctoral thesis, Universitat de Barcelona, 2003. http://hdl.handle.net/10803/669591.

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Se presenta un trabajo experimental sobre el crecimiento de interficies rugosas en medios desordenados. El experimento consiste en una celda de Hele-Shaw en cuya placa inferior se han distribuido una serie de obstáculos de cobre que hacen la función de desorden congelado. Un aceite de silicona es inyectado por uno de los extremos de la celda desplazando el aire inicialmente presente. El frente es estable por contraste de viscosidad pero se hace rugoso debido a la presencia del desorden. Los experimentos realizados se pueden clasificar en dos grupos principales según el tipo de mecanismo utilizado para la inyección del aceite: A- Velocidad constante y B- Presión constante. Para el Caso A- se han realizado multitud de experimentos variando la velocidad del fluido, el espaciado entre placas en la celda de Hele-Shaw y la configuración del desorden. Se ha observado que cuando la velocidad promedio del aceite es alta y/o la longitud de correlación del desorden en la dirección de crecimiento es baja (desorden débil), entonces el escalamiento de las fluctuaciones de la interfície sigue el escalamiento dinámico de Family-Vicsek, con un exponente de crecimiento de beta=0,50 independiente de la velocidad promedio de la interface, espaciado entre placas y configuración del desorden. También se ha estudiado del exponente de rugosidad, encontrando dos regímenes, alfa-1 a escalas pequeñas y alfa-2 a escalas grandes, con unos valores que dependen de la velocidad promedio, el espaciado entre placas y la configuración del desorden. Para velocidades grandes se obtienen un valor límite de alfa 1=1,3 y alfa 2=0 independientemente de los parámetros experimentales. También se ha caracterizado el punto de crossover entre alfa-1 y alfa-2, el cual escala con la velocidad con un exponente 0.5, de acuerdo con predicciones teóricas.

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44

Vigueras, Zuniga Marco Osvaldo. « Analysis of gas turbine compressor fouling and washing on line ». Thesis, Cranfield University, 2007. http://hdl.handle.net/1826/2448.

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This work presents a model of the fouling mechanism and the evaluation of compressor washing on line. The results of this research were obtained from experimental and computational models. The experimental model analyzed the localization of the particle deposition on the blade surface and the change of the surface roughness condition. The design of the test rig was based on the cascade blade arrangement and blade aerodynamics. The results of the experiment demonstrated that fouling occurred on both surfaces of the blade. This mechanism mainly affected the leading edge region of the blade. The increment of the surface roughness on this region was 1.0 μm. This result was used to create the CFD model (FLUENT). According to the results of the CFD, fouling reduced the thickness of the boundary layer region and increased the drag force of the blade. The model of fouling was created based on the experiment and CFD results and was used to calculate the engine performance in the simulation code (TURBOMATCH). The engine performance results demonstrated that in five days fouling can affect the overall efficiency by 3.5%. The evaluation of the compressor washing on line was based on the experimental tests and simulation of the engine performance. This system demonstrated that it could recover 99% of the original blade surface. In addition, this system was evaluated in a study case of a Power Plant, where it proved itself to be a techno-economic way to recover the power of the engine due to fouling. The model of the fouling mechanism presented in this work was validated by experimental tests, CFD models and information from real engines. However, for further applications of the model, it would be necessary to consider the specific conditions of fouling in each new environment.

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ROGER, JEAN-PAUL. « Contributions a l'etude des surfaces, interfaces et films minces par la methode mirage ». Paris 6, 1988. http://www.theses.fr/1988PA066509.

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Detection in situ d'un depot metallique sur une electrode rugueuse avec une sensibilite d'une fraction de couche monoatomique; analyse et modelisation des effets de rugosite pour des surfaces metalliques, caracterisation optique et thermique de couches minces semiconductrices et mise en evidence d'une absorption de surface

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Yi, Okson. « Investigation of factors affecting the sticking of insects on aircraft wing surfaces ». Thesis, Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/53200.

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This aircraft industry is concerned with the increase of drag on planes due to the sticking of insects on critical airfoil areas. The objectives of the present study were to investigate the effects of surface energy and elasticity on the number of insects sticking onto the polymer coatings on a modified aircraft wing and to determine the mechanism by which insects stick onto surfaces during a high-Velocity impact. Analyses including scanning electron microscopy (SEM), electron spectroscopy for chemical analysis (ESCA) and contact angle measurements of uncoated and polymer-coated aluminum surfaces have been performed. An air-gun was designed to accelerate insects to high speeds and impact them onto modified wing surfaces in a laboratory environment. A direct relation between the number of insects sticking on a sample and its surface energy was obtained. Since the sticky liquid from a burst-open insect will not spread on the low energy surface, it will ball up providing poor adhesion between the insect debris and the surface. The incoming air How can easily blow oH' the insect debris thus reducing the number of insects that remain stuck on the surface. Also a direct relation between the number of insect sticking onto sample surfaces and their moduli of elasticity was obtained. The deceleration of an insect impacting onto an elastomer reduces in proportional to the modulus of elasticity of the material. As a consequence, the rate of change of momentum is lower and the force and pressure exerted on the body of the insect is reduced if it impacts onto a material with a low modulus of elasticity. This lessens the chance of bursting the i insect exoskeleton.
Master of Science

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Siochi, Emilie J. « A fundamental study of the sticking of insect residues to aircraft wings ». Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/101264.

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The aircraft industry has long been concerned with the increase of drag on airplanes due to fouling of the wings by insects. The present research studied the effects of surface energy and surface roughness on the phenomenon of insect sticking. Aluminum plates of different roughnesses were coated with thin films of polymers with varying surface energies. The coated plates were attached to a custom jig and mounted on top of an automobile for insect collection. Contact angle measurements, x-ray photoelectron spectroscopy and specular reflectance infrared spectroscopy were used to characterize the surfaces before and after the insect impact experiments. Scanning electron microscopy showed the topography of insect residues on the exposed plates. Moments were calculated in order to find a correlation between the parameters studied and the amount of bugs collected on the plates. An effect of surface energy on the sticking of insect residues was demonstrated.
M.S.

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Santos, Hamilta de Oliveira. « Caracterização de camisas de cilindro em ligas Al-Si hipereutéticas e investigação do comportamento de corrosão em meio de condensado sintético automotivo ». Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-18052012-091151/.

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No presente trabalho quatro ligas Al-Si hipereutéticas, três das quais foram produzidas por conformação por \"spray\" e a outra por fundição, foram caracterizadas quanto a textura, dureza, microestrutura e resistência à corrosão em meio de condensado sintético automotivo (CSA). Duas das ligas conformadas por \"spray\" foram retiradas de camisas de cilindro e a outra de um pré-formado obtido em laboratório. A conformação por \"spray\" envolve a atomização de uma liga e a deposição de gotículas em um substrato, antes mesmo que todas se encontrem no estado sólido. Este processo permite a obtenção de materiais que se caracterizam por uma microestrutura livre de macrossegregações e bastante refinada, implicando melhor trabalhabilidade a quente. A caracterização da microestrutura das quatro ligas hipereutéticas revelou a presença de porosidades na liga obtida em laboratório, e microestrutura com distribuição homogênea de precipitados primários nas três ligas conformadas por \"spray\". A microestrutura de uma das ligas apresentou-se muito diferenciada, com a presença de eutético, sugerindo que esta foi fabricada por fundição. Nas camisas de cilindro foram feitas medidas de rugosidade, e em todas as ligas foram realizados ensaios de microdureza. A liga conformada por \"spray\" e obtida em laboratório foi laminada a quente e a frio. Foram realizados também estudos de textura, para tentar estabelecer uma correlação entre todas as ligas quanto ao processo de fabricação. A avaliação da textura indicou que a presença de fases de silício primário, finamente distribuídas impedem o aparecimento de texturas típicas de deformação de ligas de alumínio, mesmo após severas deformações, como as necessárias para a transformação de pré-formados em tubos que originam as camisas de cilindro. As medidas de rugosidade indicaram características próprias do acabamento superficial usado para a produção das camisas, por brunimento ou por ataque químico. Os ensaios de microdureza apresentaram variações de acordo com as rotas de fabricação sendo que a liga eutética apresentou os maiores valores de microdureza em comparação às ligas conformadas por \"spray\". Todas as ligas foram avaliadas quanto a resistência à corrosão por ensaios de espectroscopia de impedância eletroquímica em dois meios, CSA com pH 3,3 e CSA com pH 11. As quatro ligas hipereutéticas estudadas apresentaram mecanismo de corrosão similar em condensado sintético automotivo (CSA) pH 3,3. Em todas ocorreu o ataque intenso da matriz de alumínio e as partículas de silício primário atuaram como regiões catódicas. A liga 2 apresentou maior resistência à corrosão entre todas as ligas ensaiadas, tanto em CSA pH 3,3 como em pH 11. Neste último meio, uma camada de produtos de corrosão formou-se sobre todas as ligas, e os resultados indicaram mecanismos diferentes para o ataque da matriz de Al e para o crescimento da camada depositada na superfície das ligas estudadas. O ataque da matriz da liga 2 neste meio foi aparentemente mais lento do que sobre as demais ligas, com a formação de uma camada mais compacta de produtos de corrosão, estabelecendo um controle por difusão dos processos interfaciais para maiores períodos de ensaio. A camada formada sobre as demais ligas neste meio apresentou-se mais defeituosa, e nestas ocorreu também menor controle da velocidade das reações interfaciais por processos difusionais.
In the present study four hypereutectic Al-Si alloys, three produced by spray forming and one by casting, were characterized for microhardness, roughness, microstructure, texture and corrosion resistance in a synthetic automotive condensed solution (SACS). Two of the spray formed alloys tested were obtained from cylinder liners and the other was laboratory made. Spray forming involves alloy atomization and droplets deposition on a substrate, previous to the solidification of all of the droplets. This process favours the production of materials with a fine microstructure free of macrosegregation that is related to improved hot workability. The microstructure characterization of the four alloys revealed the presence of porosities in the laboratory made alloy. All the three alloys produced by spray forming showed a homogeneous distribution of primary precipitates. The microstructure of one of the alloys showed eutectic microstructure, indicating that this alloy was fabricated by casting. In the cylinder liners, the surface roughness was measured and the microhardness of all the alloys was also evaluated. Furthermore, the laboratory made alloy was hot and cold rolled. Texture determinations were carried out to investigate the correlation between the alloy type and their fabrication process. The texture investigation indicated that the fine distribution of primary silicon phase in the alloy hindered the development of texture typical of aluminium alloys deformation, even after severe mechanical work, such as those used in the conversion of pre-formed in cylinder liners. The surface roughness results indicated typical characteristics of the surface finishing used, honing or chemical etching. The microhardness results were dependent on the fabrication process used, with higher microhardness associated to the eutectic alloy comparatively to the spray formed ones. All hypereutectic alloys were tested for corrosion resistance using electrochemical impedance spectroscopy in two electrolytes, SACS with pH 3.3 and SACS with pH 11. The four tested alloys showed similar corrosion mechanisms in the acid electrolyte (SACS pH 3.3). The intense attack of the aluminium matrix occurred in ali tested alloys and the primary silicon phase was unattacked and appeared as emerging from the surface after corrosion immersion test. The primary silicon particles acted as cathodic sites. The alloy 2 showed the highest corrosion resistance among the tested alloys in both electrolytes, SACS pH 3.3 and SACS pH 11. In this last medium, a layer of corrosion products formed on all the alloys, and the results indicated different mechanisms for the aluminium matrix corrosive attack and growth of the deposited layer on the alloys surface. The kinetics of aluminium matrix attack was apparently slower in the alloy 2 than for the other alloys, resulting in the formation of a more compact layer of corrosion products, leading to diffusion controlled interfacial processes for longer test periods. The layer of corrosion products on the other three alloys (1, 3, and 4) had more defects and for these alloys diffusional controlled interfacial processes were not as significant as for alloy 2.

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Celik, Kazim Arda. « Development Of A Methodology For Prediction Of Surface Roughness Of Curved Cavities Manufactured By 5-axes Cnc Milling ». Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608368/index.pdf.

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The surface quality is identified by surface roughness parameters. The average surface roughness (Ra) is used in this study, as it is the most commonly used roughness parameter in the industry. A particular curved cavity of a forging die is selected for the experimental study. Different milling methods are tested. The comparison studies are conducted between 3-axes and 5-axes milling, linear and circular tool path strategies and down and up milling. According to the experimental study, appropriate method is determined for the milling of a particular curved cavity of a forging die. The experimental analysis based on design of experiments (DOE) has been employed by considering cutting speed, feed per tooth and stepover parameters. Multiple linear regression technique is used by which a mathematical formula has been developed to predict the Ra values for milling parameters. The results of the mathematical formula are controlled by conducting test experiments and good correlations are observed between the results of the formula and the results of test experiments.

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Webb, Joshua J. « The Effect of Particle Size and Film Cooling on Nozzle Guide Vane Deposition ». The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1313528110.

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