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1
Bardot, Leon. "Explosive volcanism on Santorini : palaeomagnetic estimation of emplacement temperatures of pyroclastics." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360162.
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Lazzarini, Lorenzo. "Numerical modeling of a hot-wire anemometer in turbulent flows." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/17957/.
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The present thesis deals with the numerical modeling of an hot wire anemometer inside a turbulent channel flow at Re_tau=180 with heat transfer. There are two main approaches when studying turbulence: one could follow an experimental path or a numerical approach could be pursued. Experiments showed some issues when measuring turbulence with hot wire anemometry, spatial and temporal filtering are two examples of such problems. In the present work, numerical simulations were performed in order to validate a code that model a hot-wire probe inside a turbulent channel flow.
Direct Numerical Simulation (DNS) solved through a spectral code were used to build such model, due to their high level of precision and resolution. A validation process was performed starting from Kim & Moin experience and Kasagi studies related to DNS of channel flow with passive scalar. Following this path we implement inside our code a line source of heat mimicking the hot-wire behaviour. While simulations were running we collected statistics in order to know the values regarding turbulence fluctuations throughout the entire channel.
We obtained a new data-set coming from DNS and spectral element method with not only just a passive scalar but a precise implementation of an hot-wire probe.
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Kirk, Daniel Robert 1975. "Aeroacoustic measurement and analysis of transient supersonic hot nozzle flows." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/29883.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1999.Includes bibliographical references (p. 195-199).
A transient testing technique for the study of jet noise was investigated and assessed. A shock tunnel facility was utilized to produce short duration, 10-20 millisecond, under expanded supersonic hot air jets from a series of scaled nozzles. The primary purpose of the facility is to investigate noise suppressor nozzle concepts relevant to supersonic civil transport aircraft applications. The shock tube has many strengths; it is mechanically simple, versatile, has low operating costs, and can generate fluid dynamic jet conditions that are comparable to aircraft gas turbine engine exhausts. Further, as a result of shock heating, the total temperature and pressure profiles at the nozzle inlet are uniform, eliminating the noise associated with entropy non-uniformities that are often present in steady state, vitiated air facilities. The primary drawback to transient testing is the brief duration of useful test time. Sufficient time must be allowed for the nozzle flow and free jet to reach a quasi-steady-state before acoustic measurements can be made. However, if this constraint is met, the short run times become advantageous. The test articles are only exposed to the high temperature flow for a fraction of a second, and can be constructed of relatively inexpensive stereo-lithography or cast aluminum. A comparison between shock tunnel transient noise data and steady-state data is presented to ascertain the usefulness of the technique to make acoustic measurements on scaled nozzles. Three types of nozzles are compared in the assessment effort: (1) a series of 0.64 - 1.9 cm exit diameter small-scale round nozzles that can be operated at transient and cold-flow steady-state conditions at the MIT facility for in-house comparison, (2) a series of 5.1 - 10.2 cm exit diameter ASME standard axisymmetric nozzles, and (3) a 1/1 2th scale version of a modern mixer-ejector nozzle. Scaled versions of nozzles (2) and (3) were tested at Boeing's steady-state low speed aeroacoustic facility for comparison to the transient shock tube noise data. The assessment establishes the uncertainty bounds on sound pressure level measurements over the range of frequency bands, nozzle pressure ratios (1.5 - 4.0), total temperature ratios (1.5 - 3.5), and nozzle scales for which the facility can be employed as a substitute and/or as a complimentary mode of investigation to steady-state hot-flow test facilities. Far-field narrowband spectra were obtained at directivity angles from 65 to 145 degrees and the data were extrapolated to full-scale flight conditions consistent with FAR-36 regulations. Nozzle pressure ratio and total temperature ratio were repeatable to within ± 1 percent of desired conditions. The constraint of short test duration is shown to be alleviated through the use of multiple runs to reduce the uncertainty associated with making transient acoustic measurements. Sound pressure level versus frequency trends with nozzle pressure ratio and directivity angle are shown to be comparable between the steady-state and transient noise data for all three nozzle types. The small scale nozzles exhibited agreement to within ± 1 - 2 dB over a full-scale frequency range of 50 - 1250 Hz. The ASME nozzle results demonstrated that the transient noise data replicates the Boeing steady-state data to within 2 - 3 dB on SPL versus full-scale frequency from 250 - 6300 Hz, as well as OASPL and PNL versus directivity angle. The magnitude of EPNL values are shown to agree to within 1 - 3 dB depending on test condition and nozzle scale. The mixer-ejector model exhibited agreement with the steady-state noise data to within 2 - 5 dB over a frequency range of 500 - 6300 Hz for all directivity angles. OASPL and PNL versus directivity angle noise data exhibited agreement with magnitude to within 1 - 4 dB. Steady-state trends with MAR, azimuthal angle, and EPNL were also present in the transient noise data.
by Daniel Robert Kirk.
S.M.
4
Laurantzon, Fredrik. "Flow Measuring Techniques in Steady and Pulsating Compressible Flows." Licentiate thesis, KTH, Mekanik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-26344.
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This thesis deals with flow measuring techniques applied on steady and pulsatingflows. Specifically, it is focused on gas flows where density changes canbe significant, i.e. compressible flows. In such flows only the mass flow ratehas a significance and not the volume flow rate since the latter depends onthe pressure. The motivation for the present study is found in the use of flowmeters for various purposes in the gas exchange system for internal combustionengines. Applications can be found for instance regarding measurements of airflow to the engine, or measurements of the amount of exhaust gas recirculation.However the scope of thesis is wider than this, since the thesis aims toinvestigate the response of flow meters to pulsating flows. The study is mainlyexperimental, but it also includes an introduction and discussion of several inindustry, common flow measuring techniques.The flow meters were studied using a newly developed flow rig, designedfor measurement of steady and pulsating air flow of mass flow rates and pulsefrequencies typically found in the gas exchange system of cars and smallertrucks. Flow rates are up to about 200 g/s and pulsation frequencies from 0 Hz(i.e. steady flow) up to 80 Hz. The study included the following flow meters:hot-film mass flow meter, venturi flowmeter, Pitot tube, vortex flowmeter andturbine flowmeter. The performance of these meters were evaluated at bothsteady and pulsating conditions. Furthermore, the flow under both steady andpulsating conditions were characterized by means of a resistance-wire basedmass flow meter, with the ability to perform time resolved measurements ofboth the mass flux ρu, and the stagnation temperature T0.Experiments shows that, for certain flow meters, a quasi-steady assumptionis fairly well justified at pulsating flow conditions. This means that thefundamental equations describing the steady flow, for each instant of time,is applicable also in the pulsating flow. In the set-up, back-flow occurred atcertain pulse frequencies, which can result in highly inaccurate output fromcertain flow meters, depending on the measurement principle. For the purposeof finding means to determine when back flow prevails, LDV measurementswere also carried out. These measurements were compared with measurementsusing a vortex flow meter together with a new signal processing technique basedon wavelet analysis. The comparison showed that this technique may have apotential to measure pulsating flow rates accurately.Descriptors: Flow measuring, compressible flow, steady flow, pulsating flow,hot-wire anemometry, cold-wire anemometry.QC 20101208
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Sigfrids, Timmy. "Hot wire and PIV studies of transonic turbulent wall-bounded flows." Licentiate thesis, KTH, Mechanics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1577.
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The compressible turbulent boundary layer developing over atwo-dimensional bump which leads to a supersonic pocket with aterminating shock wave has been studied. The measurements havebeen made with hot-wire anemometry and Particle ImageVelocimetry (PIV).
A method to calibrate hot-wire probes in compressible ow hasbeen developed which take into account not only the ow velocitybut also the inuence of the Mach number, stagnation temperatureand uid density. The calibration unit consists of a small jetow facility, where the temperature can be varied. The hot wiresare calibrated in the potential core of the free jet. The jetemanates in a container where the static pressure can becontrolled, and thereby the gas density. The calibration methodwas verfied in the at plate zero pressure gradient turbulentboundary layer in front of the bump at three different Machnumbers, namely 0.3, 0.5 and 0.7. The profiles were alsomeasured at different static pressures in order to see theinuence of varying density. Good agreement between the profilesmeasured at different pressures, as well as with the standardlogarithmic profile was obtained.
The PIV measurements of the boundary layer ow in front ofthe 2D bump showed good agreement with the velocity profilesmeasured with hotwire anemometry. The shock wave boundary layerinteraction was investigated for an inlet Mach number of 0.69.A lambda shock wave was seen on the downstream side of thebump. The velocity on both sides of the shock wave as measuredwith the PIV was in good agreement with theory. The shock wavewas found to cause boundary layer separation, which was seen asa rapid growth of the boundary layer thickness downstream theshock. However, no back ow was seen in the PIV-data, probablybecause the seeding did not give enough particles in theseparated region. The PIV data also showed that the shock wavewas oscillating, i.e. it was moving approximately 5 mm back andforth. This distance corresponds to about five boundary layerthicknesses in terms of the boundary layer upstream theshock.
Descriptors:Fluid mechanics, compressible ow,turbulence, boundary layer, hot-wire anemometry, PIV, shockwave boundary layer interaction, shape factor.
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Fiorini, Tommaso. "Hot wire manufacturing and resolution effects in high Reynolds number flows." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/5217/.
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Lo studio della turbolenza è di fondamentale importanza non solo per la fluidodinamica teorica ma anche perchè viene riscontrata in una moltitudine di problemi di interesse ingegneristico. All'aumentare del numero di Reynolds, le
scale caratteristiche tendono a ridurre le loro dimensioni assolute. Nella fluidodinamica sperimentale già da lungo tempo si è affermata l'anemometria a filo caldo, grazie
ad ottime caratteristiche di risoluzione spaziale e temporale. Questa tecnica, caratterizzata da un basso costo e da una relativa semplicità, rende possibile la realizzazione di sensori di tipo artigianale, che hanno il vantaggio di poter essere relizzati in dimensioni inferiori. Nonostante l'ottima risoluzione spaziale degli hot-wire, infatti, si può verificare, ad alto
numero di Reynolds, che le dimensioni dell'elemento sensibile siano superiori a quelle delle piccole scale. Questo impedisce al sensore di risolvere correttamente le strutture più piccole.
Per questa tesi di laurea è stato allestito un laboratorio per la costruzione di sensori a filo caldo con filo di platino. Sono in questo modo stati realizzati diversi sensori dalle dimensioni caratteristiche inferiori a quelle dei sensori disponibili commercialmente. I sensori ottenuti sono quindi stati testati in un getto turbolento, dapprima confrontandone la risposta con un sensore di tipo commerciale, per verificarne il corretto funzionamento. In seguito si sono eseguite misure più specifiche e limitate ad alcune particolari zone all'interno del campo di moto, dove è probabile riscontrare effetti di risoluzione spaziale. Sono stati analizzati gli effetti della dimensione fisica del sensore sui momenti statistici centrali, sugli spettri di velocità e sulle funzioni di densità di probabilità.
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Beirutty, Mohammad Hussein. "Development of a hot-wire measurement technique for moderate intensity three-dimensional flows /." Thesis, Connect to this title online; UW restricted, 1987. http://hdl.handle.net/1773/7074.
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Farrar, B. "Hot-film anemometry in dispersed oil-water flows : Development of a hot-film anemometer based measurement technique for detailed studies of complex two-phase flows and its application.........bubbly water-kerosene and water-air flows." Thesis, University of Bradford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234685.
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Ondore, Faustin Alloise. "An experimental and numerical investigation of turbulent flows in a square duct with 90deg bend." Thesis, Brunel University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286693.
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Lai, Huanxin. "Simulation of two-phase bubbly flows : an inert bubble introduced into a hot liquid." Thesis, Nottingham Trent University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271735.
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Malizia, Fabio. "A numerical study of temperature effects on hot wire measurements inside turbulent channel flows." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/5221/.
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A way to investigate turbulence is through experiments where hot wire measurements are performed. Analysis of the in turbulence of a temperature gradient on hot wire measurements is the aim of this thesis work. Actually - to author's knowledge - this investigation is the first attempt to document, understand and ultimately correct the effect of temperature gradients on turbulence statistics.
However a numerical approach is used since instantaneous temperature and streamwise velocity fields are required to evaluate this effect. A channel flow simulation at Re_tau = 180 is analyzed to make a first evaluation of the amount of error introduced by temperature gradient inside the domain. Hot wire data field is obtained processing the numerical
flow field through the application of a proper version of the King's law, which connect voltage, velocity and temperature.
A drift in mean streamwise velocity profile and rms is
observed when temperature correction is performed by means of centerline temperature. A correct mean velocity pro�le is achieved correcting temperature through its mean value at each wall normal position, but a not negligible error is still present into rms. The key point to correct properly the sensed velocity from the hot wire is the knowledge of the instantaneous temperature field. For this purpose
three correction methods are proposed.
At the end a numerical simulation at Re_tau =590 is also evaluated in order to confirm the results discussed earlier.
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Diehl, Steven. "The Hot Interstellar Medium in Normal Elliptical Galaxies." Ohio University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1149262336.
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Kalpakli, Athanasia. "Experimental study of turbulent flows through pipe bends." Licentiate thesis, KTH, Linné Flow Center, FLOW, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-93316.
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This thesis deals with turbulent flows in 90 degree curved pipes of circular cross-section. The flow cases investigated experimentally are turbulent flow with and without an additional motion, swirling or pulsating, superposed on the primary flow. The aim is to investigate these complex flows in detail both in terms of statistical quantities as well as vortical structures that are apparent when curvature is present. Such a flow field can contain strong secondary flow in a plane normal to the main flow direction as well as reverse flow. The motivation of the study has mainly been the presence of highly pulsating turbulent flow through complex geometries, including sharp bends, in the gas exchange system of Internal Combustion Engines (ICE). On the other hand, the industrial relevance and importance of the other type of flows were not underestimated. The geometry used was curved pipes of different curvature ratios, mounted at the exit of straight pipe sections which constituted the inflow conditions. Two experimental set ups have been used. In the first one, fully developed turbulent flow with a well defined inflow condition was fed into the pipe bend. A swirling motion could be applied in order to study the interaction between the swirl and the secondary flow induced by the bend itself. In the second set up a highly pulsating flow (up to 40 Hz) was achieved by rotating a valve located at a short distance upstream from the measurement site. In this case engine-like conditions were examined, where the turbulent flow into the bend is non-developed and the pipe bend is sharp. In addition to flow measurements, the effect of non-ideal flow conditions on the performance of a turbocharger was investigated. Three different experimental techniques were employed to study the flow field. Time-resolved stereoscopic particle image velocimetry was used in order to visualize but also quantify the secondary motions at different downstream stations from the pipe bend while combined hot-/cold-wire anemometry was used for statistical analysis. Laser Doppler velocimetry was mainly employed for validation of the aforementioned experimental methods. The three-dimensional flow field depicting varying vortical patterns has been captured under turbulent steady, swirling and pulsating flow conditions, for parameter values for which experimental evidence has been missing in literature.QC 20120425
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Örlü, Ramis. "Experimental study of passive scalar mixing in swirling jet flows." Licentiate thesis, KTH, Mechanics, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4142.
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Despite its importance in various industrial applications there is still a lack of experimental studies on the dynamic and thermal field of swirling jets in the near-field region. The present study is an attempt to close this lack and provide new insights on the effect of rotation on the turbulent mixing of a passive scalar, on turbulence (joint) statistics as well as the turbulence structure.
Swirl is known to increase the spreading of free turbulent jets and hence to entrain more ambient fluid. Contrary to previous experiments, which leave traces of the swirl generating method especially in the near-field, the swirl was imparted by discharging a slightly heated air flow from an axially rotating and thermally insulated pipe (6 m long, diameter 60 mm). This gives well-defined axisymmetric streamwise and azimuthal velocity distributions as well as a well-defined temperature profile at the jet outlet. The experiments were performed at a Reynolds number of 24000 and a swirl number (ratio between the angular velocity of the pipe wall and the bulk velocity in the pipe) of 0.5.
By means of a specially designed combined X-wire and cold-wire probe it was possible to simultaneously acquire the instantaneous axial and azimuthal velocity components as well as the temperature and compensate the former against temperature variations. The comparison of the swirling and non-swirling cases clearly indicates a modification of the turbulence structure to that effect that the swirling jet spreads and mixes faster than its non-swirling counterpart. It is also shown that the streamwise velocity and temperature fluctuations are highly correlated and that the addition of swirl drastically increases the streamwise passive scalar flux in the near field.
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Schmidt, Olaf. "Heat transfer and evaporation in spray cooling of hot gas flows, including the effect of nozzle design." Thesis, Middlesex University, 2001. http://eprints.mdx.ac.uk/13382/.
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This study investigates the influence of spray nozzle internal geometry on heat transfer performance and the resultant power requirements. An experimental apparatus was designed and built, which allowed for close control of the heat transfer from air to water and the required energy for droplet production. The apparatus allowed for simultaneous measurements of heat transfer rate from the gas to the spray droplets and the pumping power requirements for the sprayed liquid. A spray chamber was constructed in the form of a Perspex cylinder, 372 mm internal diameter and 372 mm height, mounted on its vertical axis. Thermocouples, humidity sensors, and pressure sensors were used to measure the temperature difference of the air and water, the humidity difference of the air, and the pressure drop across the nozzle. The spray nozzles have been installed at the centre of the upper cover plate directed along the cylinder axis. The heat and mass transfer process was carried out in a counter current flow. Two different nozzle designs were the subject of this investigation. The pressure swirl nozzle works on liquid pressure alone. Droplet formation and size is influenced by changes of the internal geometry and liquid pressure. An effervescent two fluid atomiser with internal mixing was tested. The influence of changes in gas bubble and exit orifice geometry on droplet size and formation was investigated. Analysis of the heat transfer process is based on the energy balance for the whole cylinder. This analysis allows for the determination of the nozzle with the best performance characteristics. From the required energy to produce the droplets and the rate of heat transfer, a new equation for the index of energy performance, was defined. A Laser Doppler Analyser was used to determine the droplet size and velocity for the low pressure nozzles and this data was compared with the existing theory. The droplet distribution of the spray nozzles was determined for various configuration. The measured droplet size was below the calculated droplet size using the derived equations from the literature. Photographs of the spray angle at different liquid pressures were taken for digital analysis. The spray angle showed reasonable agreement with the literature. A three dimensional numerical model was designed to simulate the heat transfer process inside the spray chamber using PHOENICS, a Computational Fluid Dynamics (CFD) software. The software modelled the heat and mass transfer inside the spray chamber. This model then allowed for the testing of different droplet distributions, formations, and their influence on the heat transfer process. In order to validate the results, the necessary variables such as the gas mass flow, liquid mass flow rate, droplet size, spray angle and scatter, hot air inlet temperature, were obtained from the experimental data. The result of the simulation is the air outlet temperature and humidity of the spray chamber. The internal 3D flow field is solved with the Lagrangian and Eulerian equation including the disturbance, solved with the k-epsilon turbulence model, created by the spray droplets. Four different pressure swirl configurations were simulated. Every configuration had five different pressure points. Every pressure point was simulated individually in order to find out if the numerical simulation software was able to predict the correct result for different liquid mass flow rates without altering the boundary setting and parameters. The heat transfer process was found to depend on the droplet size and distribution produced by the spray nozzle. A comparison of the experimental data with the simulation results demonstrated the accuracy of the CFD model. The temperature accuracy was ±5.9% and for the humidity ±12% on average for all simulations. It was found that the heat transfer of the effervescent atomiser depends on the mass ALR and that the highest heat transfer was measured when it was operating with an ALR of 0.1. The tested effervescent atomiser was found to be strongly influenced by the atomising air, an effectiveness of 93% achieved. The change of the internal geometries had no significant influence on the heat transfer rates. The change of the internal geometry, especially the exit orifice diameter, had a strong influence on the pressure swirl nozzle performance, which started at 85% and reached a maximum of 95%. It was found that the pressure requirement for the 4.7 mm exit orifice was only 20% of the pressure requirement of the 2.5 mm exit orifice in order to achieve the same cooling performance. The pressure swirl needed for all flow rates approximately 20 times less energy to achieve the same cooling as the effervescent nozzle.
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GUPTA, VIPUL KUMAR. "EFFECTS OF HOT STREAK MANAGEMENT ON SURFACE TEMPERATURE OF FIRST-STAGE TURBINE USING LINEARIZED METHOD." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin996854670.
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Fabbiane, Nicolò. "Adaptive and model-based control in laminar boundary-layer flows." Licentiate thesis, KTH, Mekanik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-154052.
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In boundary-layer flows it is possible to reduce the friction drag by breaking the path from laminar to turbulent state. In low turbulence environments, the laminar-to-turbulent transition is dominated by local flow instabilities – Tollmien-Schlichting (TS) waves – that exponentially grows while being con- vected by the flow and, eventually, lead to transition. Hence, by attenuating these disturbances via localised forcing in the flow it is possible to delay farther downstream the onset of turbulence and reduce the friction drag. Reactive control techniques are widely investigated to this end. The aim of this work is to compare model-based and adaptive control techniques and show how the adaptivity is crucial to control TS-waves in real applications. The control design consists in (i) choosing sensors and actuators and (ii) designing the system responsible to process on-line the measurement signals in order to compute an appropriate forcing by the actuators. This system, called compen- sator, can be static or adaptive, depending on the possibility of self-adjusting its response to unmodelled flow dynamics. A Linear Quadratic Gaussian (LQG) regulator is chosen as representative of static controllers. Direct numerical simulations of the flow are performed to provide a model for the compensator design and test its performance. An adaptive Filtered-X Least-Mean-Squares (FXLMS) compensator is also designed for the same flow case and its per- formance is compared to the model-based compensator via simulations and experiments. Although the LQG regulator behaves better at design conditions, it lacks robustness to small flow variations. On the other hand, the FXLMS compensator proved to be able to adapt its response to overcome the varied conditions and perform an adequate control action. It is thus found that an adaptive control technique is more suitable to delay the laminar-to-turbulent transition in situations where an accurate model of the flow is not available.I det tunna gränsskikt som uppstår en yta, kan friktionen minskas genom att förhindra omslag från ett laminärt till ett turbulent flöde. När turbulensnivån är låg i omgivningen, domineras till en början omslaget av lokala instabiliteter (Tollmien-Schlichting (TS) v ågor) som växer i en exponentiell takt samtidigt som de propagerar nedströms. Därför, kan man förskjuta omslaget genom att dämpa TS vågors tillväxt i ett gränsskikt och därmed minska friktionen.Med detta mål i sikte, tillämpas och jämförs två reglertekniska metoder, nämligen en adaptiv signalbaserad metod och en statiskt modellbaserad metod. Vi visar att adaptivitet är av avgörande betydelse för att kunna dämpa TS vågor i en verklig miljö. Den reglertekniska konstruktionen består av val av givare och aktuatorer samt att bestämma det system som behandlar mätsignaler (on- line) för beräkning av en lämplig signal till aktuatorer. Detta system, som kallas för en kompensator, kan vara antingen statisk eller adaptiv, beroende på om det har möjlighet till att anpassa sig till omgivningen. En så kallad linjär regulator (LQG), som representerar den statiska kompensator, har tagits fram med hjälp av numeriska simuleringar of strömningsfältet. Denna kompensator jämförs med en adaptiv regulator som kallas för Filtered-X Least-Mean-Squares (FXLMS) både experimentellt och numeriskt. Det visar sig att LQG regulatorn har en bättre prestanda än FXLMS för de parametrar som den var framtagen för, men brister i robusthet. FXLMS å andra sidan, anpassar sig till icke- modellerade störningar och variationer, och kan därmed hålla en god och jämn prestanda.Man kan därmed dra slutsaten att adaptiva regulatorer är mer lämpliga för att förhala omslaget fr ån laminär till turbulent strömning i situationer då en exakt modell av fysiken saknas.
QC 20141020
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Odemark, Ylva. "Wind-turbine wake flows - Effects of boundary layers and periodic disturbances." Doctoral thesis, KTH, Strömningsfysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-144475.
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The increased fatigue loads and decreased power output of a wind turbine placed in the wake of another turbine is a well-known problem when building new wind-power farms and a subject of intensive research. These problems are caused by the velocity gradients and high turbulence levels present in the wake of a turbine. In order to better estimate the total power output and life time of a wind-power farm, knowledge about the development and stability of wind-turbine wakes is crucial. In the present thesis, the flow field around small-scale model wind turbines has been investigated experimentally in two wind tunnels. The flow velocity was measured with both hot-wire anemometry and particle image velocimetry. To monitor the turbine performance, the rotational frequency, the power output and the total drag force on the turbine were also measured. The power and thrust coefficients for different tip-speed ratios were calculated and compared to the blade element momentum method, with a reasonable agreement. The same method was also used to design and manufacture new turbine blades, which gave an estimate of the distribution of the lift and drag forces along the blades. The influence of the inlet conditions on the turbine and the wake properties was studied by subjecting the turbine to both uniform in flow and different types of boundary layer in flows. In order to study the stability and development of the tip vortices shed from the turbine blades, a new experimental setup for phase-locked measurements was constructed. The setup made it possible to introduce perturbations of different frequencies and amplitudes, located in the rear part of the nacelle. With a newly developed method, it was possible to characterize the vortices and follow their development downstream, using only the streamwise velocity component. Measurements were also performed on porous discs placed in different configurations. The results highlighted the importance of turbine spacings. Both the measurements on the turbine and the discs were also used to compare with large eddy simulations using the actuator disc method. The simulations managed to predict the mean velocity fairly well in both cases, while larger discrepancies were seen in the turbulence intensity.QC 20140424
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Vallée, Christophe. "Dynamics of the free surface of stratified two-phase flows in channels with rectangular cross-sections." Forschungszentrum Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-86493.
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Stratified two-phase flows were investigated at different test facilities with horizontal test sections in order to provide an experimental database for the development and validation of computational fluid dynamics (CFD) codes. These channels were designed with rectangular cross-sections to enable optimal observation conditions for the application of optical measurement techniques. Consequently, the local flow structure was visualised with a high-speed video camera, delivering data with high-resolution in space and time as needed for CFD code validation.
Generic investigations were performed at atmospheric pressure and room temperature in two air/water channels made of acrylic glass. Divers preliminary experiments were conducted with various measuring systems in a test section mounted between two separators. The second test facility, the Horizontal Air/Water Channel (HAWAC), is dedicated to co-current flow investigations. The hydraulic jump as the quasi-stationary discontinuous transition between super- and subcritical flow was studied in this closed channel. Moreover, the instable wave growth leading to slug flow was investigated from the test section inlet. For quantitative analysis of the optical measurements, an algorithm was developed to recognise the stratified interface in the camera frames, allowing statistical treatments for comparison with CFD calculation results.
The third test apparatus was installed in the pressure chamber of the TOPFLOW test facility in order to be operated at reactor typical conditions under pressure equilibrium with the vessel atmosphere. The test section representing a flat model of the hot leg of the German Konvoi pressurised water reactor (PWR) scaled at 1:3 is equipped with large glass side walls in the region of the elbow and of the steam generator inlet chamber to allow visual observations. The experiments were conducted with air and water at room temperature and maximum pressures of 3 bar as well as with steam and water at boundary conditions of up to 50 bar and 264°C. Four types of experiments were performed, including generic test cases as well as transient validation cases of typical nuclear reactor safety issues. As an example, the co-current flow experiments simulate the two-phase natural circulation in the primary circuit of a PWR. The probability distribution of the water level measured in the reactor pressure vessel simulator was used to characterise the flow in the hot leg. Moreover, the flooding behaviour in this conduit was investigated with dedicated counter-current flow limitation experiments. A comparison of the flooding characteristics with similar experimental data and correlations available in the literature shows that the channel height is the characteristic length to be used in the Wallis parameter for channels with rectangular cross-sections. Furthermore, for the analysis of steam/water experiments, condensation effects had to be taken into account. Finally, the experimental results confirm that the Wallis similarity is appropriate to scale flooding in the hot leg of a PWR over a large range of pressure and temperature conditions.
Not least, different examples of comparison between experiment and simulation demonstrate the possibilities offered by the data to support the development and validation of CFD codes. Besides the comparison of qualitative aspects, it is shown exemplarily how to treat the CFD results in order to enable quantitative comparisons with the experiments.
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Xavier, Carla Marques. "Análise experimental e numérica de escoamentos turbulentos em canais compostos empregando simulação de grandes escalas e método dos elementos finitos." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2013. http://hdl.handle.net/10183/105032.
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Este trabalho apresenta um estudo experimental e numérico de escoamentos em canais compostos. Simulação de grandes escalas e método dos elementos finitos, em paralelo com medições utilizando anemômetros de fio quente em um canal aerodinâmico são realizadas. Canais compostos estão presentes em muitas aplicações de engenharia. Dispositivos eletrônicos, trocadores de calor, reatores nucleares, canais de irrigação e planícies de inundação são alguns dos desafios enfrentados pela engenharia. A combinação de simulação de grandes escalas e o método dos elementos finitos para a investigação de escoamentos turbulentos pode ser de grande importância para o estudo dos escoamentos na engenharia. No caso dos escoamentos através dos canais compostos, publicações neste tema são ainda raros. Os principais objetivos deste trabalho são: analisar o escoamento de um fluido viscoso, incompressível e isotérmicas em um canal composto, empregando um código de computação tridimensional apresentado por Petry em 2002, que realiza simulação de grandes escalas com o método dos elementos finitos, para comparar os resultados numéricos com os resultados experimentais do escoamento turbulento em um canal composto cuja geometria é exactamente reproduzida pela malha numérica, para verificar a validade do método numérico e o comportamento de modelos em escala subgrade para reproduzir o fluxo no canal composto investigado; e comparar a eficácia dos esquemas Taylor-Galerkin e dois passos para analisar os resultados. O canal investigado consiste em um canal principal com seção transversal retangular, conectado a uma fenda retangular estreita. No código numérico, o modelo clássico de Smargorinsky é comparado com o modelo dinâmico de viscosidade turbulenta, inicialmente proposto por Germano et al. 1991. A segunda filtragem do processo dinâmico é feita através dos elementos finitos independentes propostos por Petry, 2002. Para a implementação do algoritmo, o método dos elementos finitos é usado, Taylor-Galerkin e esquemas dois passos são usados para a discretização no tempo e no espaço e de ligação das equações governantes. O domínio computacional é discretizadas por intermédio de elementos lineares hexaédricos. Os resultados obtidos a partir simulações de grandes escalas, usando o modelo clássico de Smagorinsky e o modelo dinâmico de submalha; mostram o desenvolvimento de uma camada de cisalhamento na direção principal do escoamento com características dinâmicas regidas pelos perfis de velocidade média. Os resultados da simulação mostraram boa concordância com os dados experimentais dos perfis de velocidade média, intensidade de turbulência e tensão de cisalhamento turbulenta. Em geral, o modelo dinâmico com o esquema de duis passos foi mais eficiente para reproduzir estruturas turbulentas, em comparação com o modelo Smagorinsky e o esquema Taylor-Galerkin particularmente ao longo da região da fenda do canal.This work presents an experimental and numerical study of turbulent flows in compound channels. Large eddy simulation and finite element method in parallel with hot wires measurements in an aerodynamic channel are employed. Compound channels are present in many engineering applications like in electronic devices, heat exchangers, nuclear reactors and irrigation channels and flooding plains are some of the challenges faced by mechanical engineering. The combination of large eddy simulation and the finite element method for the investigation of turbulent flows can be of great relevance to the study of engineering flows. In the case of flows through compound channels, publications in this subject are still rare. The main objectives in this work are: to analyze the flow of viscous, incompressible and isothermal fluids in a compound channel; employing a three-dimensional computation code presented by Petry, 2002, which performs large eddy simulation with the finite element method; to compare the numerical results with experimental results of the turbulent flow in a compound channel whose geometry is exactly reproduced by the numerical mesh; to check the validity of the numerical method and the behavior of subgrid scale models to reproduce the flow in the compound channel investigated and compare the efficacy of the Taylor-Galerkin and Two-Steps schemes in analyzing the results. The compound channel investigated consists of a rectangular channel connected to a rectangular shaped slot. In the numerical code, Smargorinsky´s classical model is compared to the dynamic model of turbulent viscosity, initially proposed by Germano et al. The second filtering of the dynamic process is made through the independent finite elements proposed by Petry, 2002. For the implementation of the algorithm, the finite element method is used, Taylor- Galerkin and Two-Steps schemes are used for discretization in time and space and to link governing equations. The computational domain is discretized by means of linear hexahedrical elements. The results obtained from large eddy simulations, using the classical model of Smagorinsky and the Dynamic subgrid scale model show the development of a shear layer in the main direction of flow with dynamic characteristics governed by the mean velocity profiles. The simulation results showed good agreement compared to experimental data, and analysis of the profiles of mean velocity, turbulence intensities and turbulent shear stress. In general, dynamic model with the two-steps scheme was more able to reproduce turbulent structures in comparison with the Smagorinsky model with Taylor-Galerkin scheme, particularly along the channel slot.
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Ouyang, Xutong. "Exploring the attributes relevant to accidents between vehicles and unprotected road users, taking Stockholm as an example." Thesis, KTH, Geoinformatik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-278990.
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Traffic accidents is one of the major causes of fatalities and economic loss around the world. Thus, there is an urgent need for a better understanding about the factors that contribute to accidents so that the accidents can be prevented in the future. The research objective of this thesis is to analyze the traffic accidents between vehicles and unprotected road users (pedestrians and bicycles) in Stockholm, finding spatial distribution patterns, related attributes and examining relationships between accidents and a number of vehicle flows. The data is first analyzed with general statistical analysis to examine the basic characteristics. There is no apparent trend of change among the number of accidents per year, while the numbers of accidents happening from May to October is higher than the rest of the year except for July due to less traffic during holiday period. Most traffic accidents occur in overcast weather, on a dry road surface, or during the day. In the spatial analysis part of the thesis, Global Moran’s I is used to detect whether there is an attribute-related spatial distribution pattern. Hot spot analysis is then applied on the clustered attributes to find significant hot and cold spots over the study area. The conclusions are that road surface conditions and occurrence time during day/night are two related factors that influence traffic accidents while weather is not considered a related attribute since the accidents distribute randomly in terms of weather, of which it is difficult to obtain temporally-aligned, detailed local information for further analysis. Different parameters are selected and discussed during the process. When calculating the distance between two accidents in traffic accident analysis, Manhattan distance is more appropriate than Euclidean distance since traffic accidents are restricted to the road network. The distance band determines scales of analysis tools, with 50 meters on an intersection and 500 meters for a larger region in Stockholm. Most hot spots arise at intersections and roundabouts where different types of traffic flows meet each other. The result of the relationships between traffic accidents and different types of vehicle flows shows that the correlation coefficients between number of traffic accidents and traffic flows are low, meaning that there is no obvious correlation between them, which is also proved by the scatter plots. Poisson regression model is applied on the traffic accident data. As a result, high-risk and low-risk areas in Stockholm are pointed out. Some are consistent with the hot-spot analysis result.
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Kledy, Michel. "Développement d'une méthode de mesure des champs de vitesse et de température liquide en écoulement diphasique bouillant en conditions réacteurs ou simulantes." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI035.
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Ce travail de thèse constitue une contribution à la caractérisation des écoulements diphasiques bouillants convectifs à haute pression rencontrés dans les réacteurs à eau sous pression (REP) ou dans des conditions simulantes.La première partie présente un modèle bi-dimensionnel permettant de décrire le développement d'un écoulement bouillant dans une conduite circulaire (régime à bulle). La modélisation proposée est basée sur les équations locales stationnaires du mélange homogène fermées à l'aide d'un modèle de relaxation thermodynamique. Une confrontation des résultats avec les données expérimentales issues de la banque de donnée DEBORA a ensuite montré que si le modèle était capable de rendre compte de manière satisfaisante des résultats expérimentaux, les mécanismes de transport radiaux de la turbulence ainsi que de la vapeur étaient encore mal modélisés.La seconde partie de l'étude traite du développement de la thermo-anémométrie dans l'installation expérimentale DEBORA, afin de mesurer de manière colocalisée les champs de vitesse et de température liquide ainsi que le taux de vide en écoulement diphasique bouillant. La procédure expérimentale repose sur l'utilisation de sondes anémométriques classiques (sonde à film DANTEC@ 70 µm de diamètre, sonde à fil 2.5µm de 2.5 de diamètre) fonctionnant successivement à différentes surchauffes et pilotées à l'aide d'un anémomètre à courant constant. Des mesures ont d'abord été réalisées en écoulement monophasique chauffé, puis une procédure de discrimination phasique a été développée et a permis de fournir des premières mesures en écoulement bouillant. Ces dernières ont alors été comparées aux résultats du modèleThis study is a contribution to the comprehension of high pressure boiling flows relative to PWR.The first part exposes a two-dimensional unsteady state model in order to predict the development of a boiling flow in a circular pipe. The local mixture balanced equations are used with a relaxation model to close the vapor production rate (local homogeneous relaxation model). The results obtained from the comparison with the data bank DEBORA reveal a good qualitative agreement. Nerveless, the model is currently unable to correctly describe radial transports of turbulence and vapor fraction from the heated wall to the center of the pipe.The second part deals with the use of hot wire anemometry in experimental loop DEBORA to provide radial distributions of mean liquid velocity, mean liquid temperature and void fraction in a boiling flow. Classical hot wire probes are used (DANTEC@ hot film and hot wire probes) and are driven at different overheats using a constant current anemometer. Some measurements are first performed in single phase heated flows. Then, a phase identification procedure is developed, and some boiling flow measurements are obtained and compared with the model
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Pandey, Manoj Kumar. "A Hop-by-Hop Architecture for Multicast Transport in Ad Hoc Wireless Networks." Diss., CLICK HERE for online access, 2009. http://contentdm.lib.byu.edu/ETD/image/etd3119.pdf.
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Örlü, Ramis. "Experimental studies in jet flows and zero pressure-gradient turbulent boundary layers." Doctoral thesis, KTH, Mekanik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10448.
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This thesis deals with the description and development of two classical turbulent shear flows, namely free jet and flat plate turbulent boundary layer flows. In both cases new experimental data has been obtained and in the latter case comparisons are also made with data obtained from data bases, both of experimental and numerical origin. The jet flow studies comprise three parts, made in three different experimental facilities, each dealing with a specific aspect of jet flows. The first part is devoted to the effect of swirl on the mixing characteristics of a passive scalar in the near-field region of a moderately swirling jet. Instantaneous streamwise and azimuthal velocity components as well as the temperature were simultaneously accessed by means of combined X-wire and cold-wire anemometry. The results indicate a modification of the turbulence structures to that effect that the swirling jet spreads, mixes and evolves faster compared to its non-swirling counterpart. The high correlation between streamwise velocity and temperature fluctuations as well as the streamwise passive scalar flux are even more enhanced due to the addition of swirl, which in turn shortens the distance and hence time needed to mix the jet with the ambient air. The second jet flow part was set out to test the hypothesis put forward by Talamelli & Gavarini (Flow, Turbul. & Combust. 76), who proposed that the wake behind a separation wall between two streams of a coaxial jet creates the condition for an absolute instability. The experiments confirm the hypothesis and show that the instability, by means of the induced vortex shedding, provides a continuous forcing mechanism for the control of the flow field. The potential of this passive mechanism as an easy, effective and practical way to control the near-field of interacting shear layers as well as its effect towards increased turbulence activity has been shown. The third part of the jet flow studies deals with the hypothesis that so called oblique transition may play a role in the breakdown to turbulence for an axisymmetric jet.For wall bounded flows oblique transition gives rise to steady streamwise streaks that break down to turbulence, as for instance documented by Elofsson & Alfredsson (J. Fluid Mech. 358). The scenario of oblique transition has so far not been considered for jet flows and the aim was to study the effect of two oblique modes on the transition scenario as well as on the flow dynamics. For certain frequencies the turbulence intensity was surprisingly found to be reduced, however it was not possible to detect the presence of streamwise streaks. This aspect must be furher investigated in the future in order to understand the connection between the turbulence reduction and the azimuthal forcing. The boundary layer part of the thesis is also threefold, and uses both new data as well as data from various data bases to investigate the effect of certain limitations of hot-wire measurements near the wall on the mean velocity but also on the fluctuating streamwise velocity component. In the first part a new set of experimental data from a zero pressure-gradient turbulent boundary layer, supplemented by direct and independent skin friction measurements, are presented. The Reynolds number range of the data is between 2300 and 18700 when based on the free stream velocity and the momentum loss thickness. Data both for the mean and fluctuating streamwise velocity component are presented. The data are validated against the composite profile by Chauhan et al. (Fluid Dyn. Res. 41) and are found to fulfil recently established equilibrium criteria. The problem of accurately locating the wall position of a hot-wire probe and the errors this can result in is thoroughly discussed in part 2 of the boundary layer study. It is shown that the expanded law of the wall to forth and fifth order with calibration constants determined from recent high Reynolds number DNS can be used to fix the wall position to an accuracy of 0.1 and 0.25 l_ * (l_* is the viscous length scale) when accurately determined measurements reaching y+=5 and 10, respectively, are available. In the absence of data below the above given limits, commonly employed analytical functions and their log law constants, have been found to affect the the determination of wall position to a high degree. It has been shown, that near-wall measurements below y+=10 or preferable 5 are essential in order to ensure a correctly measured or deduced absolute wall position. A number of peculiarities in concurrent wall-bounded turbulent flow studies, was found to be associated with a erroneously deduced wall position. The effect of poor spatial resolution using hot-wire anemometry on the measurements of the streamwise velocity is dealt with in the last part. The viscous scaled hot-wire length, L+, has been found to exert a strong impact on the probability density distribution (pdf) of the streamwise velocity, and hence its higher order moments, over the entire buffer region and also the lower region of the log region. For varying Reynolds numbers spatial resolution effects act against the trend imposed by the Reynolds number. A systematic reduction of the mean velocity with increasing L+ over the entire classical buffer region and beyond has been found. A reduction of around 0.3 uƬ, where uƬ is the friction velocity, has been deduced for L+=60 compared to L+=15. Neglecting this effect can lead to a seemingly Reynolds number dependent buffer or log region. This should be taken into consideration, for instance, in the debate, regarding the prevailing influence of viscosity above the buffer region at high Reynolds numbers. We also conclude that the debate concerning the universality of the pdf within the overlap region has been artificially complicated due to the ignorance of spatial resolution effects beyond the classical buffer region on the velocity fluctuations.QC 20100820
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Sun, Yanxia 1976. "Hot-wire sensing of a micro-jet flow." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/89335.
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Cutbill, Sue. "A study of the turbulent flow of a high speed Coanda jet." Thesis, Durham University, 1998. http://etheses.dur.ac.uk/4743/.
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This thesis presents an experimental investigation into a compressible turbulent wall jet issuing from a slot, and flowing over a surface with streamwise curvature, followed by a plane wall recovery region. The purpose of this data was to provide suitable test cases to aid in the design and validation of turbulence models used for curved flow situations in computational fluid dynamics. The presence of streamwise curvature provides an extra rate of strain to the flow which effects both the mean flow field and the turbulence structure. The effects of curvature are dependent on the ratio of the slot width to the radius of curvature. The effects are increased with the magnitude of this ratio. Hot film anemometry was used to measure the mean flow and Reynolds stresses under six different flow regimes. Four experiments were performed using a constant slot to radius ratio, and the supply pressure ratio was varied. Two further experiments were performed at a constant pressure ratio, but at differing slot to radius ratios. In all cases, the extra rate of strain was found to increase the jet growth and velocity decay rates beyond those of a plane wall jet. 'History effects' were apparent where there was a change from flow with streamwise wall curvature to that without. The turbulence structure was found to require a finite distance along the recovery section before it reverts to a plane wall turbulence structure. The presence of the extra rate of strain, and the history effects at sudden changes in surface curvature, make strong demands on any turbulence model. Various turbulence models have been tested, and although no one turbulence model has proved robust enough for all flow situations, a number of models have been identified to provide superior performance under certain conditions. The use of a higher order numerical scheme has also been found to reduce the effects of numerical diffusion, leading to improvements in the predictions of the flow shock cell structure and the breakaway performance of the jet.
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Gelwick, Katrina D. "Full of Hot Air: Heat Flow at the Medicine Lake Volcano Hot Spot, Modoc County, California." Oberlin College Honors Theses / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1398936533.
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Ruh, Christian. "Performance of boiling and hot sparged agitated reactors." Thesis, University of Surrey, 1997. http://epubs.surrey.ac.uk/844300/.
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In this dissertation the power draw, the mass transfer and the liquid mixing behaviour of boiling and hot sparged stirred tank reactors (STRs) were investigated. The power draw characteristics of six different impellers were studied under varying operating conditions and expressed in terms of the relative power draw, RPD. Generally the impellers showed considerably higher power draw in hot gassed than in comparable cold conditions. The main phenomenon in hot systems, the evaporation of liquid into a gas bubble suddenly exposed to it, was investigated experimentally. The growth of nitrogen and air bubbles in hot water was found to be very fast and be completed typically within milliseconds after their exposure to the liquid. This was confirmed by studies applying acoustic bubble sizing techniques which were carried out together with Richard Manasseh from CSIRO, Melbourne, Australia. Experimental studies of the gas-liquid mass transfer in hot sparged STRs were carried out using a tank of 450 mm in diameter agitated by a 180 mm Rushton turbine. Experiments involving the temperature kinetics in an air-water system and absorption and desorption of ammonia were used to determine gas and also some liquid side mass transfer coefficients. The gas side coefficients kga were found to be typically in the order of 0.01 s-1. An enhancement of the liquid side mass transfer was also observed. Both Fick and Stefan-Maxwell models were employed to express gas side mass transfer coefficients. The models predict there will be a decrease of the coefficients at high concentrations. In the hot sparged tank the temperature is essentially uniform throughout the STR. Liquid mixing times have been measured for various boil-off and sparging rates. No significant deviations from the single phase or the cold gassed mixing times in this equipment were recorded.
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Al-Hajeri, Mohammad Hamad. "Characterization of the fluid flow associated with ceramic candle filters." Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323258.
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Lanspeary, Peter V. "Establishing very low speed, disturbance-free flow for anemometry in turbulent boundary layers." Title page, contents and summary only, 1997. http://web4.library.adelaide.edu.au/theses/09PH/09phl295.pdf.
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Thesis (Ph. D.)--University of Adelaide, Dept. of Mechanical Engineering, 1998?System requirements for accompanying computer disks: IBM-compatible computer. Other requirements: Fortran and/or C Compiler. Includes bibliographical references (p. 315-330).
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Salomonsson, Sebastian. "Exploring NAT Host Counting Using Network Traffic Flows." Thesis, Karlstads universitet, Institutionen för matematik och datavetenskap (from 2013), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-55261.
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Hosder, Serhat. "Unsteady Skin-Friction Measurements on a Maneuvering Darpa2 Suboff Model." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/33582.
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Steady and unsteady flow over a generic Suboff submarine model is studied. The skin-friction magnitudes are measured by using hot-film sensors each connected to a constant temperature anemometer. The local minima in the skin-friction magnitudes are used to obtain the separation locations. Steady static pressure measurements on the model surface are performed at 10° and 20° angles of attack. Steady and unsteady results are presented for two model configurations: barebody and sail-on-side case. The dynamic plunge-pitch-roll model mount (DyPPiR) is used to simulate the pitchup maneuvers. The pitchup maneuver is a linear ramp from 1° to 27° in 0.33 seconds. All the tests are conducted at ReL=5,500,000 with a nominal wind tunnel speed of 42.7±1 m/s. Steady results show that the flow structure on the leeward side of the barebody can be characterized by the crossflow separation. In the sail-on-side case, the separation pattern of the non-sail region follow the barebody separation trend closely. The flow on the sail side is strongly affected by the presence of the sail and the separation pattern is different from the crossflow separation. The flow in the vicinity of the sail-body junction is dominated by the horseshoe type separation. Unsteady results of the barebody and the non-sail region of the sail-on-side case show significant time lags between unsteady and steady crossflow separation locations. These effects produce the difference in separation topology between the unsteady and steady flowfields. A first-order time lag model approximates the unsteady separation locations reasonably well and time lags are obtained by fitting the model equation with the experimental data. The unsteady separation pattern of the sail side does not follow the quasi-steady data with a time lag and the unsteady separation structure is different from the unsteady crossflow separation topology observed for the barebody and the non-sail region of the sail-on-side case.Master of Science
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García, Fernández Víctor Gerardo. "Constitutive relations to model the hot flow of commercial purity copper." Doctoral thesis, Universitat Politècnica de Catalunya, 2004. http://hdl.handle.net/10803/6043.
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Se ha llevado a cabo un estudio con el fin de observar diferencias en el comportamiento de fluencia en caliente de los cobres refinados al fuego con una pureza de 99.9%, dicho estudio ha permitido proponer modelos para predecir la curva esfuerzo-deformación y para predecir el tamaño de grano recristalizado dinámicamente. Los cobres refinados al fuego con una pureza de 99.9% se caracterizan por tener una composición residual de varios otros elementos, en algunos casos hasta 1000ppm. En los cobres con por lo menos 99.9% de pureza que tengan pocos elementos residuales, las diferencias observadas durante la fluencia en caliente se atribuyen a las interacciones entre átomos disueltos y dislocaciones, específicamente las interacciones con oxígeno intersticial. En el cobre electrolítico, el cual contiene principalmente altos contenidos de oxigeno, las diferencias de fluencia se atribuyen a cantidades cada vez mayores de partículas de Cu2O. Este trabajo más bien demuestra que las diferencias de esfuerzo encontradas en cobres refinados al fuego con una pureza de 99.9% son debidas a la cantidad de oxígeno residual, el cual forma finos precipitados a temperaturas intermedias que refuerzan la matriz metálica. A pesar del bajo contenido en oxígeno en los cobres estudiados (26-62ppm) se han caracterizado precipitados de Cu2O y se han utilizado teorías del endurecimiento por precipitación que han indicado que los precipitados de Cu2O eran los responsables del incremento en resistencia. Las interacciones entre átomos de oxígeno y dislocaciones son poco probables que causen un retro esfuerzo adicional a temperaturas superiores a los 600º C, en donde se ha llevado a cabo este trabajo. Se han comprimido tres cobres con 26, 46 y 62ppm de oxígeno a unas velocidades de deformación de 0.3s-1, 0.1s-1, 0.03s-1, 0.01s-1, 0.003s-1 y 0.001s-1 y a unas temperaturas desde 600º C hasta 950º C en intervalos de 50º. En este trabajo se presenta evidencia de cómo bajos contenidos de oxígeno en cobres 99.9% puros pueden afectar el comportamiento esfuerzo-deformación y el tamaño de grano recristalizado dinámicamente.Además de haber encontrado el elemento y el mecanismo responsable del retro esfuerzo adicional también se presenta un algoritmo matemático para estudiar y predecir las oscilaciones de esfuerzo durante la recristalización dinámica de pico múltiple. Intentos anteriores utilizando Modelos Computarizados de Monte Carlo, Modelos de Autómatas Celulares o Modelos Matemáticos para la Recristalización Dinámica (DRX) no predicen las oscilaciones de esfuerzo de materiales reales y su tiempo de computo los hace inviables para procesos de simulación industrial. El nuevo Modelo de Avrami con Coseno Amortiguado para la DRX es capaz de predecir la transición de DRX de pico simple a DRX de pico múltiple. Además el nuevo modelo define el esfuerzo de estado estable sin tener que escoger un valor de una curva experimental que posiblemente no haya alcanzado un estado estable. Otra contribución del nuevo modelo es que demuestra que las oscilaciones son completamente predecibles en términos de la velocidad de deformación y la temperatura, una característica que antes se había dicho ser improbable. El nuevo modelo para la DRX junto con un modelo modificado de Voce-Kocks para la restauración dinámica han sido exitosamente implementados para predecir la fluencia en caliente.
Adicionalmente a las anteriores contribuciones este trabajo también da a conocer la relación que tiene el tamaño de grano recristalizado con la temperatura y la velocidad de deformación. Se asume que los cobres 99.9% puros, como los estudiados, tenderán a un tamaño de grano de estado estable el cual cuando esté a temperatura ambiente determinará las propiedades mecánicas del producto forjado.
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Abele, Hanns, Georg Kodek, and Guido K. Schaefer. "Hot Tips Turned Flops: Liability for Unsuitable Investment Advice - An Integrated Approach." Fondazione Gerardo Capriglione Onlus and Regent¿s University of London, 2015. http://epub.wu.ac.at/4769/1/Hot_Tips_Turned_Flops.pdf.
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This paper develops a new analytical framework for assessing losses from unsuitable investment advice, integrating both legal and economic aspects. First, a core of legal concepts for assessing losses is identified that is common to most jurisdictions. These include negligence in advice, causation as examined by the but-for-test, and the loss caused by the unsuitable advice.
Building upon these legal concepts, five economic tests are developed for analyzing the causal chain from improper advice to financial loss. If the tests show that the advice was unsuitable, the investor did not know about it, the investment violated his risk patterns, and the assets most likely chosen with suitable advice would have performed better, an economic proof for establishing liability is provided, thus supporting legal assessments of losses. Several new analytical tools are suggested to substantiate the analysis. As a major conclusion, it is shown that proving liability for unsuitable investment advice gets more difficult, the more financially sophisticated an investor is.
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Seidel, T., and M. Beyer. "Two-phase flow experiments in a model of the hot leg of a pressurised water reactor." Helmholtz-Zentrum Dresden-Rossendorf, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-85349.
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In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at FZD. The hot leg model is operated in the pressure chamber of the TOPFLOW test facility, which is used to perform high-pressure experiments under pressure equilibrium with the inside atmosphere of the chamber. This technique makes it possible to visualise the two-phase flow through large windows, also at reactor-typical pressure levels. In order to optimise the optical observation possibilities, the test section was designed with a rectangular cross-section.
Experiments were performed with air and water at 1.5 and 3.0 bar at room temperature as well as with steam and water at 15, 30 and 50 bar and the corresponding saturation temperature (i.e. up to 264°C). The total of 194 runs are divided into 4 types of experiments covering stationary co-current flow, counter-current flow, flow without water circulation and transient counter-current flow limitation (CCFL) experiments.
This report provides a detailed documentation of the experiments including information on the experimental setup, experimental procedure, test matrix and on the calibration of the measuring devices. The available data is described and data sheets were arranged for each experiment in order to give an overview of the most important parameters. For the cocurrent flow experiments, water level histograms were arranged and used to characterise the flow in the hot leg. In fact, the form of the probability distribution was found to be sensitive to the boundary conditions and, therefore, is useful for the CFD comparison.
Furthermore, the flooding characteristics of the hot leg model plotted in terms of the classical Wallis parameter or Kutateladze number were found to fail to properly correlate the data of the air/water and steam/water series. Therefore, a modified Wallis parameter is proposed, which takes the effect of viscosity into account.
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Herbach, Clauß-Michael, Peter Gippner, H. G. Ortlepp, and W. Wagner. "The binary decay of hot heavy nuclei: fission, evaporation, and also flow?" Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-31564.
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Ahrens, Denise [Verfasser]. "NOx-Formation in Reacting Premixed Jets in Hot Cross Flow / Denise Ahrens." München : Verlag Dr. Hut, 2015. http://d-nb.info/1077404093/34.
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Herbach, Clauß-Michael, Peter Gippner, H. G. Ortlepp, and W. Wagner. "The binary decay of hot heavy nuclei: fission, evaporation, and also flow?" Forschungszentrum Rossendorf, 1996. https://hzdr.qucosa.de/id/qucosa%3A21983.
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Zhao, Zhiling. "Investigations into Hot-Tip Scanning Electrochemical Microscopy and Redox Flow Battery Applications." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1563098472286652.
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Alex, Alvisi, and Perez Adalberto. "Analysis of wall-mounted hot-wire probes." Thesis, KTH, Strömningsmekanik och Teknisk Akustik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-289564.
Full textAbstract:
Flush-mounted cavity hot-wire probes have been around since two decades, but have typically not been applied as often compared to the traditional wall hot-wires mounted several wire diameters above the surface. While the latter suffer from heat conduction from the hot wire to the substrate in particular when used in air flows, the former is belived to significantly enhance the frequency response of the sensor. The recent work using a cavity hotwire by Gubian et al. (2019) came to the surprising conclusion that the magnitute of the fluctuating wall-shear stress τ+w,rms reaches an asymptotic value of 0.44 beyond the friction Reynolds number Re τ ∼ 600. In an effort to explain this result, which is at odds with the majority of the literature, the present work combines direct numerical simulations (DNS) of a turbulent channel flow with a cavity modelled using the immersed boundary method, as well as an experimental replication of the study of Gubian et al. in a turbulent boundary layer to explain how the contradicting results could have been obtained. It is shown that the measurements of the mentioned study can be replicated qualitatively as a result of measurement problems. We will present why cavity hot-wire probes should neither be used for quantitative nor qualitative measurements of wall-bounded flows, and that several experimental short-comings can interact to sometimes falsely yield seemingly correct results.
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Henderson, April K. "Gifted flows : engaging narratives of hip hop and Sāmoan diaspora /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2007. http://uclibs.org/PID/11984.
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Neumeister, William D. "Hot-Wire Anemometer for the Boundary Layer Data System." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/830.
Full textAbstract:
Hot-wire anemometry has been routinely employed for laboratory measurements of turbulence for decades. This thesis presents a hot-wire anemometer suitable for use with the Boundary Layer Data System (BLDS). BLDS provides a unique platform for in- flight measurements because of its small, self-contained, robust design and flexible architecture. Addition of a hot-wire anemometer would provide BLDS with a sensor that could directly measure flow velocity fluctuations caused by turbulence. Hot-wires are commonly operated in constant-temperature mode for high frequency response, but require a carefully tuned bridge. The constant-voltage anemometer (CVA) uses a simple op-amp circuit to improve frequency response over constant-current operation. Due to its balance between ease of operation and performance, a CVA system built for this project was tested with a 3.8 micron diameter, platinum-coated tungsten probe. The CVA was calibrated in a steady jet and a power-law curve fit accurately represented the calibration data. The CVA successfully measured velocity fluctuations in a turbulent jet, as well as in laminar and tripped turbulent boundary layers over a flat plate in a 110 MPH wind tunnel. CVA frequency response was investigated using a thermal/electrical model, controlled oscillation in a steady flow, and with a square wave test; these three methods showed agreement. The CVA is selected for integration with BLDS.
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Dixon, Teresa Joan. "The effect of microstructure in the advances of hot rolling of steel." Thesis, University of Sheffield, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286885.
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Zhang, Xiang. "Dimensional analysis based CFD modelling for power transformers." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/dimensional-analysis-based-cfd-modelling-for-power-transformers(49cac27d-38b9-4f23-a6ec-b5106422420c).html.
Full textAbstract:
Reliable thermal modelling approaches are crucial to transformer thermal design and operation. The highest temperature in the winding, usually referred to as the hot-spot temperature, is of the greatest interest because the insulation paper at the hot-spot undergoes the severest thermal ageing, and determines the life expectancy of the transformer insulation. Therefore, the primary objective of transformer thermal design is to control the hot-spot temperature rise over the ambient temperature within certain limit. For liquid-immersed power transformers, the hot-spot temperature rise over the ambient temperature is controlled by the winding geometry, power loss distribution, liquid flow rate and liquid properties. In order to obtain universally applicable thermal modelling results, dimensional analysis is adopted in this PhD thesis to guide computational fluid dynamics (CFD) simulations for disc-type transformer windings in steady state and their experimental verification. The modelling work is split into two parts on oil forced and directed (OD) cooling modes and oil natural (ON) cooling modes. COMSOL software is used for the CFD simulation work For OD cooling modes, volumetric oil flow proportion in each horizontal cooling duct (Pfi) and pressure drop coefficient over the winding (Cpd) are found mainly controlled by the Reynolds number at the winding pass inlet (Re) and the ratio of horizontal duct height to vertical duct width. The correlations for Pfi and Cpd with the dimensionless controlling parameters are derived from CFD parametric sweeps and verified by experimental tests. The effects of different liquid types on the flow distribution and pressure drop are investigated using the correlations derived. Reverse flows at the bottom part of winding passes are shown by both CFD simulations and experimental measurements. The hot-spot factor, H, is interpreted as a dimensionless temperature at the hot-spot and the effects of operational conditions e.g. ambient temperature and loading level on H are analysed. For ON cooling modes, the flow is driven by buoyancy forces and hot-streak dynamics play a vital role in determining fluid flow and temperature distributions. The dimensionless liquid flow and temperature distributions and H are all found to be controlled by Re, Pr and Gr/Re2. An optimal design and operational regime in terms of obtaining the minimum H, is identified from CFD parametric sweeps, where the effects of buoyancy forces are balanced by the effects of inertial forces. Reverse flows are found at the top part of winding passes, opposite to the OD results. The total liquid flow rates of different liquids for the same winding geometry with the same power loss distribution in an ON cooling mode are determined and with these determined total liquid flow rates, the effects of different liquids on fluid flow and temperature distributions are investigated by CFD simulations. The CFD modelling work on disc-type transformer windings in steady state present in this PhD thesis is based on the dimensional analyses on the fluid flow and heat transfer in the windings. Therefore, the results obtained are universally applicable and of the simplest form as well. In addition, the dimensional analyses have provided insight into how the flow and temperature distribution patterns are controlled by the dimensionless controlling parameters, regardless of the transformer operational conditions and the coolant liquid types used.
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Harper, Ronald Jett. "A measurement system for turbulence properties in a three- dimensional flow using a data logger." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/53074.
Full textAbstract:
An analysis is presented for hot wire/film anemometer measurement of mean velocities and turbulent stresses in a three dimensional flow field with a predominant flow direction. The experimental data can be taken with an automated traverse under the control of a digital data acquisition system which has been modified for this particular application.Master of Science
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Rahim, Amir. "Effect of nozzle guide vane shaping on high pressure turbine stage performance." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:35274ff0-0ea7-47bc-adc3-388f136b9555.
Full textAbstract:
This thesis presents a computational fluid dynamic (CFD) study of high pressure gas turbine blade design with different realistic inlet temperature and velocity boundary conditions. The effects of blade shaping and inlet conditions can only be fully understood by considering the aerodynamics and heat transfer concurrently; this is in contrast to the sequential method of blade design for aerodynamics followed by cooling. The inlet boundary conditions to the NGV simulations are governed by the existence of discrete fuel injectors in the combustion chamber. An appreciation of NGV shaping design under engine realistic inflow conditions will allow for an identification of the correct three dimensional shaping parameters that should be considered for design optimisation. The Rolls-Royce efficient Navier-Stokes solver, HYDRA, was employed in all computational results for a transonic turbine stage. The single passage unsteady method based on the Fourier Shape Correction is adopted. The solver is validated under both rich burn (hot steak only) and the case with swirl inlet profiles for aerothermal characteristics; good agreement is noted with the validation data. Post processing methods were used in order to obtain time-averaged results and blade visualisations. Subsequently, a surrogate design optimisation methodology using machine learning combined with a Genetic Algorithm is implemented and validated. A study of the effect of NGV compound lean on stage performance is carried out and contrasted for uniform and rich burn inlets, and subsequently for lean burn. Compound lean is shown to produce a tip uploading at the rotor inlet, which is beneficial for rich burn, but detrimental for lean burn. It is also found that for rich burn, fluid driving temperature is more dominant than HTC in determining rotor blade heat transfer, the opposite sense to the uniform inlet. Also, for a lean burn inlet, there is another role reversal, with HTC dominating fluid driving temperature in determining heat transfer. A novel NGV design methodology is proposed that seeks to mitigate the combined effects of inlet hot streak and swirling flow. In essence, the concept two NGVs in a pair are shaped independently of each other, thus allowing the inlet flow non uniformity to be suitably accommodated. Finally, two numerical NGV optimisation studies are undertaken for the combined hot streak and swirl inlet for two clocking positions; vane impinging and passage aligned. Due to the prohibitive cost of unsteady CFD simulations for an optimisation strategy, a suitable objective function at the NGV exit plane is used to minimise rotor tip heat flux. The optimised shape for the passage case resulted in the lowest tip heat flux distribution, however the optimum shape for the impinging case led to the highest gain in stage efficiency. This therefore suggests that NGV lean and clocking position should be a consideration for future optimisation and design of the HP stage.
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Imayama, Shintaro. "Studies of the rotating-disk boundary-layer flow." Doctoral thesis, KTH, Strömningsfysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-158973.
Full textAbstract:
The rotating-disk boundary layer is not only a simpler model for the study of cross-flow instability than swept-wing boundary layers but also a useful simplification of many industrial-flow applications where rotating configurations are present. For the rotating disk, it has been suggested that a local absolute instability, leading to a global instability, is responsible for the small variation in the observed laminar-turbulent transition Reynolds number however the exact nature of the transition is still not fully understood. This thesis aims to clarify certain aspects of the transition process. Furthermore, the thesis considers the turbulent rotating-disk boundary layer, as an example of a class of three-dimensional turbulent boundary-layer flows. The rotating-disk boundary layer has been investigated in an experimental apparatus designed for low vibration levels and with a polished glass disk that gave a smooth surface. The apparatus provided a low-disturbance environment and velocity measurements of the azimuthal component were made with a single hot-wire probe. A new way to present data in the form of a probability density function (PDF) map of the azimuthal fluctuation velocity, which gives clear insights into the laminar-turbulent transition region, has been proposed. Measurements performed with various disk-edge conditions and edge Reynolds numbers showed that neither of these conditions a↵ect the transition process significantly, and the Reynolds number for the onset of transition was observed to be highly reproducible. Laminar-turbulent transition for a ‘clean’ disk was compared with that for a disk with roughness elements located upstream of the critical Reynolds number for absolute instability. This showed that, even with minute surface roughness elements, strong convectively unstable stationary disturbances were excited. In this case, breakdown of the flow occurred before reaching the absolutely unstable region, i.e. through a convectively unstable route. For the rough disk, the breakdown location was shown to depend on the amplitude of individual stationary vortices. In contrast, for the smooth (clean-disk) condition, the amplitude of the stationary vortices did not fix the breakdown location, which instead was fixed by a well-defined Reynolds number. Furthermore, for the clean-disk case, travelling disturbances have been observed at the onset of nonlinearity, and the associated disturbance profile is in good agreement with the eigenfunction of the critical absolute instability. Finally, the turbulent boundary layer on the rotating disk has been investigated. The azimuthal friction velocity was directly measured from the azimuthal velocity profile in the viscous sublayer and the velocity statistics, normalized by the inner scale, are presented. The characteristics of this three-dimensional turbulent boundary-layer flow have been compared with those for the two-dimensional flow over a flat plate and close to the wall they are found to be quite similar but with rather large differences in the outer region.QC 20150119
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Zhao, Yongjun. "The cooling of a hot steel plate by an impinging water jet." Access electronically, 2005. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20060316.150622/index.html.
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Kojok, Ali Tarraf. "Hot jet ignition delay characterization of methane and hydrogen at elevated temperatures." Thesis, Pro Quest, 2017. https://doi.org/10.7912/C2CH35.
Full textAbstract:
Indiana University-Purdue University Indianapolis (IUPUI)This study contributes to a better understanding of ignition by hot combustion gases which finds application in internal combustion chambers with pre-chamber ignition as well as in wave rotor engine applications. The experimental apparatus consists of two combustion chambers: a pre chamber that generates the transient hot jet of gas and a main chamber which contains the main fuel air blend under study. Variables considered are three fuel mixtures (Hydrogen, Methane, 50\% Hydrogen-Methane), initial pressure in the pre-chamber ranging from 1 to 2 atm, equivalence ratio of the fuel air mixture in the main combustion chamber ranging from 0.4 to 1.5, and initial temperature of the main combustion chamber mixture ranging from 297 K to 500 K. Experimental data makes use of 4 pressure sensors with a recorded sampling rate up to 300 kHz, as well as high speed Schlieren imaging with a recorded frame rate up to 20,833 frame per seconds. Results shows an overall increase in ignition delay with increasing equivalence ratio. High temperature of the main chamber blend was found not to affect hot jet ignition delay considerably. Physical mixing effects, and density of the main chamber mixture have a greater effect on hot jet ignition delay.
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Seidel, Tobias, Christoph Vallée, Dirk Lucas, Matthias Beyer, and Darlianto Deen. "Two-phase flow experiments in a model of the hot leg of a pressurised water reactor." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-33535.
Full textAbstract:
In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at FZD. The hot leg model is operated in the pressure chamber of the TOPFLOW test facility, which is used to perform high-pressure experiments under pressure equilibrium with the inside atmosphere of the chamber. This technique makes it possible to visualise the two-phase flow through large windows, also at reactor-typical pressure levels. In order to optimise the optical observation possibilities, the test section was designed with a rectangular cross-section.
Experiments were performed with air and water at 1.5 and 3.0 bar at room temperature as well as with steam and water at 15, 30 and 50 bar and the corresponding saturation temperature (i.e. up to 264°C). The total of 194 runs are divided into 4 types of experiments covering stationary co-current flow, counter-current flow, flow without water circulation and transient counter-current flow limitation (CCFL) experiments.
This report provides a detailed documentation of the experiments including information on the experimental setup, experimental procedure, test matrix and on the calibration of the measuring devices. The available data is described and data sheets were arranged for each experiment in order to give an overview of the most important parameters. For the cocurrent flow experiments, water level histograms were arranged and used to characterise the flow in the hot leg. In fact, the form of the probability distribution was found to be sensitive to the boundary conditions and, therefore, is useful for the CFD comparison.
Furthermore, the flooding characteristics of the hot leg model plotted in terms of the classical Wallis parameter or Kutateladze number were found to fail to properly correlate the data of the air/water and steam/water series. Therefore, a modified Wallis parameter is proposed, which takes the effect of viscosity into account.