To see the other types of publications on this topic, follow the link: Unsteady Turbulent Flow.
Dissertations / Theses on the topic 'Unsteady Turbulent Flow'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Unsteady Turbulent Flow.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Wu, Jiunn-Chi. "A study of unsteady turbulent flow past airfoils." Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/13091.
Full text
2
Wu, Jiongyang. "Filter-based modeling of unsteady turbulent cavitating flow computations." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0011587.
Full text
3
Xia, Liping. "An experimental and numerical investigation of a turbulent round jet issuing into an unsteady crossflow /." Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19605377.
Full text
4
Gigante, Fabio Antonio. "Time- and frequency-domain turbulent flow analysis of wind turbine unsteady aerodynamics." Thesis, University of Glasgow, 2016. http://theses.gla.ac.uk/7253/.
Full textAbstract:
The main objective of the research work presented in this thesis is the development of a single aerodynamic CFD code for the analysis of complex turbulent flow unsteady aerodynamics such as those encountered in horizontal and vertical axis wind turbines. The finite volume parallel CFD Optimized Structured multi-block Algorithm (COSA) research code solves the Navier-Stokes equations on structured multi-block grids and models turbulence effects with Menter's shear stress transport turbulence model. The novel algorithmic contribution of this research is the successful development of a Harmonic Balance (HB) solver which can reduce the run-time required to compute nonlinear periodic flow fields with respect to the conventional time-domain (TD) approach. The thesis also presents a semi-implicit integration based on LU factorisation and a successfully LAPACK libraries integration to massively improve the computational efficiency of the integration of the HB RANS equations and the turbulence model of Menter. The main computational results of this research are for two low-speed renewable energy applications. The former application is a turbulent unsteady flow analysis of a vertical axis wind turbine working in a low-speed turbulent regime for a wide range of operating conditions. The test case is first solved using the COSA TD turbulent solver to analyse and discuss in great detail the unsteady aerodynamic phenomena occurring in all regimes of this complex device. During the turbine rotation there is a generation of blade vortex shedding and wakes all around the rotor which interacts with the blades itself on the returning side. The most important features of the investigated devices were captured with CFD. In addition, a series of investigations have been conducted to analyse the effects of computational domain refinement, number of time steps per revolution and distance of the farfield boundary from the rotor centre on prediction accuracy. The solution of the turbulent flow solver is validated by comparing torque and power coefficients with experimental data and numerical solutions obtained with a state-of-the-art time-domain of commercial package regularly used by the industry and the Academia worldwide. A detailed selection of results is presented, dealing with the various investigated issues. Afterwards, the COSA HB turbulent solver is used to solve the problem and compare the HB resolution and speed-ups with the TD results. The main motivation for analysing this problem is to highlight the predictive capabilities and the numerical robustness of the developed turbulent HB flow solver for complex realistic problems with a strong nonlinearity and to shed more light on the complex physics of this renewable energy device. The latter application regards the turbulent unsteady flow analysis of horizontal axis wind turbine blade sections in yawed wind regime. The TD and HB turbulent flow analysis of a 164 m-diameter wind turbine rotor is performed. CFD represents an accurate design tool to get a better understanding of the physical behaviour of the flow field past wind turbine rotors and the importance of accurate design is increased as the machines tend to become larger. A study at 30% and at 85% blade section is carried out, allowing the analysis of the unsteady forces acting on two different blade sections. The aim of these analyses is to assess the computational benefits achievable by using the HB method for a common nonlinear flow problem and also to further demonstrate the predictive capabilities of the developed CFD system. The turbulent HB solutions highlight that is possible to obtain an accurate analysis as its TD counterparts can do. Moreover, the results highlight that the turbulent HB solver can compute the hysteresis force cycles of the turbine blade more than 10 times faster than the TD approach. The purpose of proving the turbulent COSA HB capabilities for studying the flow field of wind turbines rotor has been fully achieved and this research represent one of the first turbulent HB RANS applications to the analysis of periodic horizontal axis wind turbine flows, and the first application to vertical axis wind turbine flows.
5
Yu, Chunshui. "Two Dimensional Finite Volume Model for Simulating Unsteady Turbulent Flow and Sediment Transport." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/301662.
Full textAbstract:
The two-dimensional depth-averaged shallow water equations have attracted considerable attentions as a practical way to solve flows with free surface. Compared to three-dimensional Navier-Stokes equations, the shallow water equations give essentially the same results at much lower cost. Solving the shallow water equations by the Godunov-type finite volume method is a newly emerging area. The Godunov-type finite volume method is good at capturing the discontinuous fronts in numerical solutions. This makes the method suitable for solving the system of shallow water equations. In this dissertation, both the shallow water equations and the Godunov-type finite volume method are described in detail. A new surface flow routing method is proposed in the dissertation. The method does not limit the shallow water equations to open channels but extends the shallow water equations to the whole domain. Results show that the new routing method is a promising method for prediction of watershed runoff. The method is also applied to turbulence modeling of free surface flow. The κ - ε turbulence model is incorporated into the system of shallow water equations. The outcomes prove that the turbulence modeling is necessary for calculation of free surface flow. At last part of the dissertation, a total load sediment transport model is described and the model is tested against 1D and 2D laboratory experiments. In summary, the proposed numerical method shows good potential in solving free surface flow problems. And future development will be focusing on river meandering simulation, non-equilibrium sediment transport and surface flow - subsurface flow interaction.
6
夏麗萍 and Liping Xia. "An experimental and numerical investigation of a turbulent round jet issuing into an unsteady crossflow." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31237897.
Full text
7
Qian, Ping. "A numerical study of viscous flows around stalled flat plate wings." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/12059.
Full text
8
Marasli, Barsam. "Spatially traveling waves in a two-dimensional turbulent wake." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184811.
Full textAbstract:
Hot-wire measurements taken in the turbulent wake of a flat plate are presented. Symmetrical and antisymmetrical perturbations at various amplitudes and frequencies were introduced into the wake by small flap oscillations. As predicted by linear stability theory, the sinuous (antisymmetric) mode was observed to be more significant than the varicose (symmetric) mode. When the amplitude of the perturbation was low, the spatial development of the introduced coherent perturbation was predicted well by linear stability theory. At high forcing levels, the wake spreading showed dramatic deviations from the well known square-root behavior of the unforced case. Measured coherent Reynolds stresses changed sign in the neighborhood of the neutral point of the perturbation, as predicted by the linear theory. However, the linear theory failed to predict the disturbance amplitude and transverse shapes close to the neutral point. Some nonlinear aspects of the evolution of instabilities in the wake are discussed. Theoretical predictions of the mean flow distortion and the generation of the first harmonic are compared to experimental measurements. Given the unforced flow and the amplitude of the fundamental wave, the mean flow distortion and the amplitude of the first harmonic are predicted remarkably well.
9
McBrien, Robert K. 1958. "Pressure measurements for periodic fully developed turbulent flow in rectangular interrupted-plate ducts." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65434.
Full text
10
Talha, Tariq. "A numerical investigation of three-dimensional unsteady turbulent channel flow subjected to temporal acceleration." Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/47055/.
Full textAbstract:
Investigation of turbulence response during constant temporal acceleration and deceleration can assist in improving the understanding of turbulence evolution and flow physics. Such flows have potential importance in engineering applications for example the air flow through the main trachea during the breathing cycle experience temporal acceleration and deceleration. The previous experimental and theoretical investigations based on conventional computational fluid dynamics (CFD) modelling could not provide the detailed information about turbulence response in the near-wall region in such types of flows. In particular, the response of near-wall structures has not been studied for turbulent flow with temporal acceleration and deceleration. In the present study, turbulent flows involving temporal acceleration and deceleration has been investigated using DNS and LES. A fully implicit fractional step method is implemented in the present study. The Navier-Stokes equations are discretised using finite volume method. Second-order- implicit Crank-Nicolson method is used for temporal discretisation for the convective and viscous terms. Second-order accuracy of spatial discretisation is achieved using four neighbouring points to calculate velocity gradients. A uniform grid is used in the streamwise and spanwise directions while a non-uniform grid is employed in the wall-normal direction. The numerical implementation has been validated for three test cases. The dynamic subgrid-scale model has been implemented for LES calculations. The LES model implementation has been validated through comparison with benchmark data available in literature. As one of the first DNS of accelerating turbulent flow, this study has produced a comprehensive database of turbulent statistics which can be used for unsteady turbulence modelling and validation. The detailed investigation has substantially enhanced the understanding of turbulence response for such flows. The flow physics has been studied in detail using turbulent kinetic energy budget analysis, vorticity analysis, anisotropy invariant maps and energy spectra. The evolution of new turbulent structures during the acceleration has been investigated using low-speed streaks and λ2 plots and many interesting ow characteristics have been found. The effect of different acceleration rates has been studied using LES. The turbulence propaga- tion in the core region has been studied for different acceleration rates. Turbulent flow subjected to constant temporal deceleration has also been investigated using LES. The effect of different deceleration rates has been also studied. The turbulent flow response to temporal deceleration has been analysed using the rms velocity and vorticity, kinetic energy budget and Reynolds stress anisotropy tensor analysis.
11
Nishad, Kaushal Prasad. "Modeling and unsteady simulation of turbulent multi-phase flow including fuel injection in IC-engines." Phd thesis, TU Prints Technische Universität Darmstadt, 2013. https://tuprints.ulb.tu-darmstadt.de/3421/14/Thesis_Kaushal_Nishad.pdf.
Full textAbstract:
In internal combustion engine (ICE), researchers have to face with stringent environment regulations concerning pollutants while improving engine thermal efficiency, making the engine design a complex task. To meet these requirements, an understanding of the salient features of all the engine processes are very important. Being the primitive process of engine operations, fuel injection influences whole engine cycle via fuel-air mixture preparation, thereby the combustion behavior and subsequently the emission performance. The inhospitable environment inside a combustion chamber makes the experimental investigations more complex and expensive. In contrast, a CFD based investigation can provide comprehensive insight about in-cylinder flow field, spray injection phenomena as encountered in IC-engine.
In the present study, a CFD tool that enables to investigate the real unsteady behavior of realistic engine configuration is developed by coupling Large Eddy Simulation (LES) together with a spray module using the KIVA4-mpi Code. It is based on an Eulerian-Lagrangian framework to describe the spray evolution including primary and secondary atomization. A linear instability sheet atomization (LISA) based sub-model is integrated to represent the primary atomization. The secondary atomization is modeled by an available Taylor analogy break-up (TAB) model. In dense spray region, the droplet-droplet interaction considerably influences the overall spray dynamics. The first novelty of the proposed methodology is to include droplet-droplet interaction processes via an appropriate collision sub-model that is independent of mesh size and type. Thereby, taking account of different regimes, such as bouncing, separation, stretching separation, reflective separation and coalescence. The formation of wall film on hot cylinder surface is a critical process in an IC-engine, since it largely influences the engine performance and emission characteristics. The second novelty of this spray module is the implementation of an improved wall film model that includes the combined effects of droplet kinetic energy and wall temperature into KIVA4-mpi code.
To perform an IC-engine simulation, a good quality mesh generation in ICEM-CFD for an engine geometry is challenging task. The KIVA4-mpi is compatible only with block structured mesh without any use of O-grid. Due to this reason, only certain degree of mesh refinement is possible. This makes it difficult to achieve a good quality fine mesh required for LES simulation. In the present study, a new meshing strategy is proposed to generate suitable mesh for real IC-engine configurations. The new method clearly demonstrates the improvement in resolving the in-cylinder flow structures. First, the simulated results for motored case (no fuel injection and no combustion) are compared with the experimental data for a transparent combustion chamber (TCC) engine configuration from Engine Combustion Network (ECN). Second, to demonstrate the importance of fuel injection sub-models, further simulations are carried out including the evolution of evaporating fuel spray with wall impingement. Third, using the new meshing strategy, simulations are also performed for a real complex canted 4-valve engine configuration. Simulated results are compared well with available experimental data.
12
Ge, Liang. "Numerical Simulation of 3D, Complex, Turbulent Flows with Unsteady Coherent Structures: From Hydraulics to Cardiovascular Fluid Mechanics." Diss., Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-11162004-125756/unrestricted/ge%5Fliang%5F200412%5Fphd.pdf.
Full textAbstract:
Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2005.Yoganathan, Ajit, Committee Member ; Sturm, Terry, Committee Member ; Webster, Donald, Committee Member ; Roberts, Philip, Committee Member ; Sotiropoulos, Fotis, Committee Chair ; Fritz, Hermann, Committee Member. Includes bibliographical references.
13
Mazzacchi, Francesco. "Evaluation of the TAU CFD solver for steady and unsteady turbulent flow analysis of a supercritical wing." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/13370/.
Full textAbstract:
The present work is part of a long-term project aimed at the validation and development of the code in DLR-TAU CFD solver in order to predict the steady and unsteady flow fields, forced and unforced motion and aeroelastic response.
The strategy to validate these methods consists of the identification and quantification of errors in the computational models and the evaluation of the calculation results with the experimental data.
The experimental data were obtained from NASA Langley Transonic Dynamics Tunnel.
The aim is to assess the state-of-the-art Computational Aeroelasticity methods for the prediction of dynamic and static aeroelastic phenomena.
All of this is based on the first and second AIAA Aeroelastic Prediction Workshops, where the (BSCW) Benchmark Supercritical Wing has been chosen as a reference point for these workshops.
The BSCW has a simple geometrical structure, with a rectangular planform and it is considered to be a rigid structure. Three different Test Cases have been determined with different and pre-fixed angles of attack.
The simulations were carried out in the transonic range with Mach numbers between 0.70 $\div$ 0.85 where different flow phenomena may occur and cause serious problems, such as aeroelastic flutter, buffet, and limit cycle oscillations.
The author used the DLR-TAU code implemented by Reynolds-averaged Navier-Stokes (RANS) equations. Several computational setups are implemented and two different types of turbulence models: (SA) Spalart-Allmaras and the (k-$\omega$ SST) Shear Stress Transport.
At the end of this work two different approaches have been compared; the RANS simulations from DLR-Tau and the hybrid from SU2. The latter was carried out by another participant. Both approaches can resolve the largest turbulent structures, but only the hybrid approach can provide significant solutions.
14
Bassit, Megalaa Gorg Abdelmassih. "Numerical and experimental study of steady and unsteady mixed convection flow in a cubical open cavity with the bottom wall heated." Doctoral thesis, Universitat Rovira i Virgili, 2016. http://hdl.handle.net/10803/396082.
Full textAbstract:
En aquest estudi s'analitzen els experiments i simulacions numèriques del flux de convecció mixta en una cavitat cúbica situada a la part inferior d'un canal quadrat. Els nombres de Reynolds en funció de la velocitat mitjana del flux i l'amplada del canal estan en el rang 100≤Re≤1500 i el nombre de Richardson varia entre 0.1≤Ri≤10. La tècnica PIV s'ha utilitzat per a les mesures en un canal d'aigua. Simulacions numèriques Tridimensionals s’han dut a terme amb un codi de volums finits de segon ordre considerant l'aproximació de Boussinesq ja que, per les condicions experimentals utilitzades, la variació de les propietats físiques amb la temperatura no té influència significativa en la topologia general de flux. Per 100≤Re≤1500 i Ri≤0.1 el flux és estacionari i consisteix en un remolí situat a l’interior de la cavitat cúbica que mostra velocitats majors a mesura que augmenta el nombre de Richardson. El flux és no estacionari a Re = 100 i Ri = 10. Prop de les parets laterals es produeixen, de forma alternada, ejeccions de flux, des de l’interior de la cavitat cap al canal, mentre que el flux entra a la cavitat des del canal a través de la part central de la cavitat. S'ha utilitzat una tècnica de mostreig condicional per elucidar l’estructura mitjana de l'evolució del flux turbulent a Ri = 10. S'ha trobat que les ejeccions de flux persisteixen durant tot el rang de Reynolds analitzat. Els números de Nusselt calculats estan d'acord amb els de les correlacions reportades a la literatura, vàlides per cavitats bidimensionalsEn este estudio se analizan los experimentos y simulaciones numéricas del flujo de convección mixta en una cavidad cúbica situada en la parte inferior de un canal de sección cuadrada cuadrado. Los números de Reynolds en función de la velocidad media del flujo y la anchura del canal están en el rango 100≤Re≤1500 y el número de Richardson varía entre 0.1≤Ri≤10. La técnica PIV se ha utilizado para las medidas en un canal de agua. Se han llevado a cabo simulaciones numéricas tridimensionales con un código de volúmenes finitos de segundo orden, considerando la aproximación de Boussinesq ya que, en las condiciones experimentales utilizadas, la variación de las propiedades físicas con la temperatura no tiene influencia significativa en la topología general de flujo. En los rangos 100≤Re≤1500 y Ri≤0.1 el flujo es estacionario y consiste en un remolino situado en el interior de la cavidad cúbica que muestra velocidades mayores a medida que aumenta el número de Richardson. El flujo es no estacionario a Re = 100 y Ri = 10. Cerca de las paredes laterales se producen de forma alternada eyecciones de flujo, desde el interior de la cavidad hacia el canal, mientras que el flujo entra en la cavidad desde el canal a través de la parte central de la cavidad. Se ha utilizado una técnica de muestreo condicional para elucidar la estructura media de la evolución del flujo turbulento a Ri = 10. Se ha encontrado que las eyecciones de flujo persisten durante todo el rango de Reynolds analizado. Los números de Nusselt calculados están de acuerdo con los de las correlaciones reportadas en la literatura, válidas para cavidades bidimensionales.
In this study we analyze experiments and numerical simulations of steady and unsteady mixed convection flow in a cubical cavity located at the bottom of a square channel. The Reynolds numbers based on the mean flow velocity and the channel width are in the range 100≤Re≤1500 and the Richardson numbers vary within 0≤Ri≤10. Particle Image Velocimetry has been used for the measurements in a water channel. Three-dimensional direct numerical simulations have been carried out with a second order finite volume code considering the Boussinesq approximation since, for the experimental conditions considered, the variation of the physical properties with temperature has no significant influence on the overall flow topology. For 100≤Re≤1500 and Ri≤0.1 the flow is steady and it consists in a single roll that exhibits larger velocities as the Richardson number is increased. An unsteady periodic flow is found at Re=100 and Ri=10. Alternate flow ejections from the cavity to the channel occur near the lateral walls while the flow enters the cavity from the channel through the central part of the cavity. A conditional sampling technique has been used to elucidate the evolution of the mean unsteady turbulent flow at Ri=10. It has been found that the alternate flow ejections persist for all the Reynolds analyzed. The computed Nusselt numbers are in general agreement with a previously reported correlation, valid for two dimensional cavities of different aspects ratios.
15
Awasthi, Manuj. "Sound Radiated from Turbulent Flow over Two and Three-Dimensional Surface Discontinuities." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/64158.
Full textAbstract:
Measurements have been performed to understand the sound source mechanism in turbulent boundary layer flow over two and three-dimensional surface discontinuities whose height is smaller than the incoming boundary layer thickness. The work was performed in two different types of boundary layers: a wall-jet flow and a conventional high Reynolds boundary layer. In the wall-jet flow, measurements of far field sound from two-dimensional forward facing steps, gaps with rounded corners and swept forward facing steps with rounded corners were made. The sound from a forward facing step is shown to exhibit effects of non-compactness. Rounding the step corner results in consistent drop in sound levels but the directivity of the sound field remains unchanged. The sound from gaps is dominated by the forward step component and remains unaffected by rounding of the backward step portion. The sound from swept forward facing steps was found to approximately obey an acoustic sweep independence principle up to a sweep angle of 30 deg when the spanwise inhomogeneity in the flow is accounted for using a simple source distribution model. Sweep independence is also observed for steps with corner rounding radii up to 25% of the step height.
The work performed in the high Reynolds number boundary layer included measurements on forward facing steps with rounded corners and a three-dimensional circular embossment with the same height as the forward step. The highest Reynolds number based on discontinuity height achieved in this work was approximately 93,000. The results show that rounding the forward step corner has the same qualitative effect on far field sound as in the wall-jet boundary layer. Quantitatively, for similar boundary layer edge velocity the sound is higher than in the wall-jet flow. The near field measurements show that the separation bubble downstream of the step shrinks as the step corner is rounded while the bubble upstream remains unaffected by it. The unsteady surface force in the lower half of the vertical face of the step was found to be independent of corner rounding. The force on the downstream surface shows similar character within the separation bubble for each rounding but decays faster with increasing downstream distance due to reduced bubble size. The unsteady force measurements were applied to the theory of Glegg et al. (2014) and the resultant of the unsteady forces on the vertical face and downstream surface placed at the top corner of the step is shown to qualitatively describe the far field sound. The acoustic sweep independence principle was applied to the far field sound from the circular embossment and it has been shown that the sound from the three-dimensional geometry can be predicted with reasonable accuracy using sound from a two-dimensional forward step with the same span.Ph. D.
16
Tardu, Sedat. "Ecoulement turbulent instationnaire près d'une paroi : réponse des structures turbulentes : [thèse en partie soutenue sur un ensemble de travaux]." Grenoble 1, 1988. http://www.theses.fr/1988GRE10137.
Full text
17
HUNG, SHI-CHANG. "THE UNSTEADY VISCOUS FLOW OVER A GROOVED WALL: A COMPARISON OF TWO NUMERICAL METHODS (BIOT-SAVART, NAVIER-STOKES)." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183957.
Full textAbstract:
Unsteady two-dimensional laminar flow of an incompressible viscous fluid over a periodically grooved wall is investigated by numerical simulation using two independent finite-difference methods. One is the vorticity-stream function method, and the other involves the vorticity-velocity induction law formulation. The fluid motion is initiated impulsively from rest and is assumed to be spatially periodic in the streamwise direction. The flow field, which includes the time development of the shear layer and the recirculating flow in the zone of separation, is examined in detail during the transient phase to the steady-state condition. The analytical and numerical formulations, which include the implementation of the boundary conditions, are derived in detail. The generation of vorticity at the solid surfaces is modelled differently in the two approaches. This vorticity production plays an important role in determining the surface-pressure distribution and the drag coefficient. Characteristics of the transient solution for a moderate Reynolds number in the laminar range are presented. Included with the graphical results are the temporal development of the constant stream function contours, including the dividing contour between the zone of separation and the main flow, and the constant vorticity contours. These latter contours show the interactions of separated vortices. The flow is found to approach a steady-state condition comprising an undisturbed uniform flow, a nonuniform irrotational flow, a shear layer adjacent to the grooved wall, and a recirculating vortex flow in the groove. Results also include the time development of the surface shear stress, surface pressure, drag coefficient and several typical velocity profiles, which characterize the flow in the recirculating region. Comparisons of the results obtained by the two numerical methods are made during the major development of the flow. The results showing the general features of the flow development including the time development of the shear layer, free shear layer and recirculating vortex flow are in good agreement. However, a significant deviation does exist at early times for the distribution of surface pressure, which accordingly has noticeable effect on the drag coefficient. Nevertheless, the gap between the distributions of surface pressure and drag coefficients dies out gradually as time progresses. The form of the stream function and vorticity contours at the steady state agrees well with those obtained from a recent numerical investigation of the steady flow in grooved channels.
18
Fjällman, Johan. "Unsteady simulations of the turbulent flow in the exhaust system of an IC-engine for optimal energy utilization." Licentiate thesis, KTH, Strömningsfysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-123086.
Full textAbstract:
This licentiate thesis deals with the ow in pipe bends and radial turbines inan internal combustion engine environment. Looking into the engine bay of apassenger car one cannot avoid noticing all the pipe bends and splits. Duringthe development of internal combustion engines the engine manufacturers arestarting to focus more on simulations than on experiments. This is partly becauseof the reduction in cost but also the reduction in turn around time. This isone of the reasons for the need of more accurate and predictive simulations.By using more complex computational methods the accuracy and predictivecapabilities are increased. The downside is that the computational time isincreasing so the long term goal of the project is to use the results to improvethe predictive capability of the lower order methods used by the industry.By comparing experiments, Reynolds Averaged Navier-Stokes (RANS)simulations, and Large Eddy Simulations (LES), the accuracy of the simulationmethods can be established. The advantages of using LES over RANS for the ows under consideration stems from the unsteadiness of the ow in the enginemanifolds. When such unsteadiness overlaps the natural turbulent spectrum,general RANS models cannot handle the problem specic ow. The thesisconsiders this eect on the chosen numerical model. The LES results have beenshown to be more accurate than the RANS simulations both for global meanvalues and for the uctuating components. The LES calculations have provento predict the meanQC 20130603
19
Tian, Geng. "Analysis of the unsteady boundary-layer flow over urban-like canopy using large eddy simulation." Thesis, Ecole centrale de Nantes, 2018. http://www.theses.fr/2018ECDN0062/document.
Full textAbstract:
L’urbanisation croissante fait émerger des enjeux sociétaux et environnementaux relatifs à la pollution atmosphérique et au microclimat urbain. La compréhension des phénomènes physiques de transport de quantité de mouvement, de chaleur et de masse entre la canopée urbaine et la couche limite atmosphérique est primordiale pour évaluer et anticiper les impacts négatifs de l’urbanisation. Les processus turbulents spécifiques à la couche limite urbaine sont étudiés par une approche de simulation des grandes échelles, dans une configuration urbaine représentée par un arrangement de cubes en quinconce. Le modèle de sous-maille de type Smagorinsky dynamique est implémenté pour mieux prendre en compte l’hétérogénéité de l’écoulement et les retours d’énergie des petites vers les grandes structures. Le nombre de Reynolds basé sur la hauteur du domaine et la vitesse de l’écoulement libre est de 50000. L’écoulement est résolu dans les sous-couches visqueuses et le maillage est raffiné dans la canopée. Le domaine est composé de 28 millions de cellules. Les résultats sont comparés à la littérature et aux données récentes obtenues dans la soufflerie du LHEEA. Chaque contribution au bilan d’énergie cinétique turbulente est calculée directement en tout point. Cette information, rare dans la littérature, permet d’étudier les processus dans la sous couche rugueuse. Grâce à ces résultats 3D, l’organisation complexe de l’écoulement moyen (recirculations, vorticité, points singuliers) est analysée en relation avec la production de turbulence. Enfin, une simulation où les obstacles sont remplacés par une force de traînée équivalente est réalisée à des fins d’évaluation de cette approcheThe rapid development of urbanization raises social and environmental challenges related to air pollution and urban climate. Understanding the physical processes of momentum, heat, and mass exchanges between the urban canopy and the atmospheric boundary-layer is a key to assess,predict and prevent negative impacts of urbanization. The turbulent processes occurring in the urban boundary-layer are investigated using computational fluid dynamics (CFD). The unsteady flow over an urban-like canopy modelled by a staggered arrangement of cubes is simulated using large eddy simulation (LES). Considering the highspatial and temporal in homogeneity of the flow, a dynamic Smagorinsky subgrid-scale model is implemented in the code to allow energyback scatter from small to large scales. The Reynolds number based on the domain height and free-stream velocity is 50000. The near-wall viscous sub-layers are resolved and the grid is refined in the canopy resulting in about 28 million grid cells. LES results are assessed by comparison with literature and data recently acquired in the wind tunnel of the LHEEA. The turbulent kinetic energy budget in which all contributions are independently computed is investigated. These rarely available data are used to analyse the turbulent processes in the urban canopy. By taking advantage of the three-dimensionality of the simulated flow, the complex 3D time-averaged organization of the flow (recirculation, vorticesor singular points) is analyzed in relation with production of turbulence. Finally a drag approach where obstacles are replaced by an equivalent drag force is implemented in the same domain and results are compared to obstacle-resolved data
20
Veley, Emma Michelle. "Measurement of Unsteady Characteristics of Endwall Vortices Using Surface-Mounted Hot-Film Sensors." Wright State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=wright1534450563500249.
Full text
21
Dolan, Kevin. "Simulations of Aerosol Exposure from a Dusty Table Source." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1562673613531829.
Full text
22
Nishad, Kaushal Prasad [Verfasser], Johannes [Akademischer Betreuer] Janicka, Amsini [Akademischer Betreuer] Sadiki, and Eva [Akademischer Betreuer] Gutheil. "Modeling and unsteady simulation of turbulent multi-phase flow including fuel injection in IC-engines / Kaushal Prasad Nishad. Betreuer: Johannes Janicka ; Amsini Sadiki ; Eva Gutheil." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2013. http://d-nb.info/1106454650/34.
Full text
23
Adler, Michael C. "On the Advancement of Phenomenological and Mechanistic Descriptions of Unsteadiness in Shock-Wave/Turbulent-Boundary-Layer Interactions." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1553543774661509.
Full text
24
Zidouh, Hamid. "Etude expérimentale du frottement pariétal instationnaire." Valenciennes, 2007. http://ged.univ-valenciennes.fr/nuxeo/site/esupversions/10b7c626-ade1-4620-b77b-d86aeddc29d3.
Full textAbstract:
L’objectif de cette thèse est de déterminer expérimentalement l’évolution temporelle du frottement pariétal instationnaire en présence d’une propagation d’onde de pression. L’écoulement transitoire est obtenu suite à la fermeture brusque d’une vanne située à l’extrémité aval d’une conduite où l’écoulement est initialement permanent. L’étude expérimentale de l’écoulement transitoire est réalisée par vélocimétrie ultrasonore à effet Doppler pour les mesures des profils de vitesse instantanés et par la méthode polarographique pour la détermination du frottement pariétal local. Ces mesures ont permis de mettre en évidence l’effet des ondes de pression sur les profils de vitesse et sur le frottement pariétal. Les résultats ont permis de montrer que l’approche quasi-stationnaire pour la détermination du frottement instationnaire n’est valable que dans le cas où les caractéristiques de l’écoulement varient peu. Lorsque l’écoulement est soumis à de fortes accélérations et décélérations, cette approche n’est plus applicable. Cette étude a permis de confirmer tout en les précisant, certains modèles basés sur l’accélération instantanée. L’analyse des résultats montre que le coefficient empirique de l’accélération instantanée utilisé dans de nombreux modèles dépend intimement de la nature de l’événement transitoire, de l’intensité des accélérations ou des décélérations et du temps et que le frottement instationnaire est en phase avec l’accélération. On montre que l’échelle de temps d’un événement transitoire est un paramètre essentiel dont il faut tenir compte pour une meilleure prédiction du frottement pariétal dans un écoulement instationnaireThe aim of this thesis is to find out experimentally the temporal evolution of unsteady skin friction in the presence of a propagation of pressure wave. The transient flow is obtained downstream sudden valve closure. The experimental study of the transient flow is carried out by Ultrasonic pulsed Doppler velocimetry to measure the instantaneous velocity profiles and by the polarographic method to determine the local skin friction. These measurements made it possible to highlight the effect of the waves of pressure on the velocity profiles and skin friction. The results made it possible to show that the quasi-steady approach to determine the unsteady friction is valid only if the characteristics of the flow vary little. When the flow is subjected to strong accelerations and decelerations, this approach is not applicable. This study made it possible to confirm all while specifying them, certain models based on the instantaneous acceleration. The analysis of the results shows that the empirical coefficient of the instantaneous acceleration used in many models depends closely on the nature of the transient event, of the intensity of accelerations or decelerations and the time. It is shown that the scale of time of a transient event is an essential parameter of which it is necessary to hold account for a better prediction of skin friction in a transient flow
25
Robertson, Francis. "An experimental investigation of the drag on idealised rigid, emergent vegetation and other obstacles in turbulent free-surface flows." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/an-experimental-investigation-of-the-drag-on-idealised-rigid-emergent-vegetation-and-other-obstacles-in-turbulent-freesurface-flows(07165357-67da-461d-a6a2-ed4970e2cb0c).html.
Full textAbstract:
Vegetation is commonly modelled as emergent arrays of rigid, circular cylinders. However, the drag coefficient (CD) of real stems or trunks is closer to that of cylinders with a square cross-section. In this thesis, vegetation has been idealised as square cylinders in laboratory experiments with a turbulence intensity of the order of 10% which is similar to that of typical river flows. These cylinders may also represent other obstacles such as architectural structures. This research has determined CD of an isolated cylinder and cylinder pairs as a function of position as well as the average drag coefficient (CDv) of larger arrays. A strain gauge was used to measure CD whilst CDv was computed with a momentum balance which was validated by strain gauge measurements for a regularly spaced array. The velocity and turbulence intensity surrounding a pair of cylinders arranged one behind the other with respect to mean flow (in tandem) were also measured with an Acoustic Doppler Velocimeter. The isolated cylinder CD was found to be 2.11 in close agreement with other researchers. Under fixed flow conditions CD for a cylinder in a pair was found to be as low as -0.40 and as high as 3.46 depending on their relative positioning. For arrays, CDv was influenced more by the distribution of cylinders than the flow conditions over the range of conditions tested. Mean values of CDv for each array were found to be between 1.52 and 3.06. This new insight therefore suggests that CDv for vegetation in bulk may actually be much higher than the typical value of 1 which is often assumed to apply in practice. If little other information is available, a crude estimate of CDv = 2 would be reasonable for many practical applications. The validity of a 2D realizable k-epsilon turbulence model for predicting the flow around square cylinders was evaluated. The model was successful in predicting CD for an isolated cylinder. In this regard the model performed as well as Large Eddy Simulations by other authors with a significant increase in computational efficiency. However, the numerical model underestimates CD of downstream cylinders in tandem pairs and overestimates velocities in their wake. This suggests it may be necessary to expand the model to three-dimensions when attempting to simulate the flow around two or more bluff obstacles with sharp edges.
26
Moldovan, Stefan Ilie. "Numerical Simulation and Experimental Validation of Fluid Flow and Mass Transfer in an Ammonothermal Crystal Growth Reactor." University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1366033161.
Full text
27
Simon, Bruno. "Effects of tidal bores on turbulent mixing : a numerical and physical study in positive surges." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00965582.
Full textAbstract:
Tidal bores are surge waves propagating upstream rivers as the tide rushes into estuaries. They induce large turbulences and mixing of the river and estuary flow of which effects remain scarcely studied. Herein, tidal bores are investigated experimentally and numerically with an idealised model of positive surges propagating upstream an initially steady flow. The experimental work estimated flow changes and typical turbulent length scale evolution induced by undular bores with and without breaking roller. The bore passage was associated with large free surface and flow velocity fluctuations, together with some variations of the integral turbulent scales. Coherent turbulent structures appeared in the wake of leading wave near the bed and moved upward into the water column during the bore propagation. The numerical simulations were based on previous experimental work on undular bores. Some test cases were realised to verify the accuracy of the numerical methods. The results gave access to the detailed flow evolution during the bore propagation. Large velocity reversals were observed close to the no-slip boundaries. In some configurations, coherent turbulent structures appeared against the walls in the wake of the bore front.
28
Smith, Thomas M. "Unsteady simulations of turbulent premixed reacting flows." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/13097.
Full text
29
Khezzar, Lyes. "Experiments with steady and unsteady confined turbulent flows." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/46926.
Full text
30
Hunt, Alan Ernest. "The behaviour of turbulence in unsteady open channel flow." Thesis, University of Canterbury. Civil Engineering, 1997. http://hdl.handle.net/10092/7722.
Full textAbstract:
An investigation into the behaviour of the turbulence during laboratory simulations of floods in rivers with mild bed slopes was undertaken. Computer control of the flow rate into the flume enabled reproducible flood waves to be generated. To rigorously model the energy gradients in a long channel, an interactive sluice gate control was developed for the downstream end of the flume. Mean flow unsteadiness effects on the turbulence were evaluated by considering different duration hydrographs with similar shapes and magnitudes. The investigation was limited to the longitudinal component of turbulence, as a one-component laser Doppler anemometer was employed for the determination of point velocities. Flow visualisation using a dye plume supplemented velocity data. It was observed that for events having a shorter duration the peak turbulent intensity had a greater magnitude, and occurred relatively earlier on the rising limb of the flood.
The turbulent energy peak coincided with the maximum flow rate divergence. For increasing flow divergence magnitude, which only occurs on the rising limb, the production of turbulence was larger than dissipation, with the transport of turbulence providing an additional sink for turbulent energy. After the depth had peaked the flow experienced pseudo-equilibrium conditions, where the transport mechanism was insignificant and the rate of production approximated dissipation. A feature of the falling limb was a period of inactivity, in which the magnitudes of production and dissipation were at minimum.
A second -5/3 slope region was observed in the energy spectra. The length scale associated with an energy source for this double structure was two orders of magnitude larger than the Kolmogorov dissipation length scale. Decay times for flow structures of this size are similar to the duration of these hydrographs.
It is possible that the unsteady flow created vortex structures that persisted for some time after the flow which generated them had moved downstream. These vortex structures, which provide a turbulence memory mechanism, and the state of pseudo-equilibrium on the falling limb are responsible for residual turbulent energy in the flow throughout the falling limb and immediately following the passing of the flood wave.
In addition, it is suggested that mean flow controls both the production and dissipation of turbulence, with the dissipation of turbulent kinetic energy being controlled by the diffusion of momentum during low speed streaks. The Kolmogorov scale may be interpreted as defining the critical damping condition along these streaks where Reynolds stresses balance viscous forces.
31
Capiaux, Sylvie. "Application et développement de la vélocimétrie par images de particules pour l'étude de la phase d'admission dans les moteurs à allumage commandé." Rouen, 1997. http://www.theses.fr/1997ROUES068.
Full textAbstract:
Le présent travail, effectué dans l'entreprise PSA, en collaboration avec le CORIA par le biais d'une convention CIFRE, vise à implanter la technique de vélocimétrie par images de particules, PIV, à la DRAS (PSA, Vélizy 78). La PIV est une technique bidimensionnelle de mesure de vitesse, qui fournit des champs instantanés de vecteurs vitesse dans un plan matérialisé par une nappe laser. Elle apporte ainsi une vision d'ensemble des structures de l'écoulement que les techniques ponctuelles ne permettent pas d'obtenir. Deux expériences sont mises en œuvre afin de tester la technique d'une part et d'obtenir des informations intéressantes sur l'écoulement en aval d'une culasse de série. La première est un banc statique : un plateau plat doté d'une soupape de série à levée variable, sous lequel est monté un cylindre transparent permettant de visualiser l'écoulement ensemencé de micro gouttelettes d'huile. L'écoulement autour de la soupape et dans le cylindre est créé à l'aide d'une aspiration. La seconde est constituée d'une culasse de série PSA, entrainée par un moteur électrique. La PIV s'avère être un bon outil de diagnostic pour les applications moteur et permet grâce à une méthode de filtrage spatial des champs instantanés d'évaluer les grandes échelles de l'écoulement (>= 7 mm) et la part des fluctuations cycliques. Pour ce faire on utilisera des traitements à l'aide de maillages de taille moyenne (64p*64p) et un taux de recouvrement des mailles de traitement assez élevé (75%). Les images obtenues ici ont l'inconvénient d'être moyennement résolues car les CCD sur le marché il y a 3 ans étaient de petite taille (768 pixels*512 pixels). Elles nécessitent un travail de mise au point conséquent à cause du confinement des cylindres, mais avec l'augmentation des cadences d'acquisition, la dégradation dans le temps d'expérience des images ne sera bientôt plus un problème. L'accès aux plus petites échelles sera possible dans l'avenir avec l'utilisation de cameras plus résolues (Kodak 1000*1000 par ex. ). Nous avons réalisé une étude théorique permettant de quantifier les biais de mesure. Les erreurs sont majoritairement liées à une répartition hétérogène des particules dans les mailles de traitement (mailles moyennes ou grandes et gradients locaux de vitesse au sein des mailles).
32
Birckelbaw, Larry Dean. "High speed aerodynamics of upper surface blowing aircraft configurations." Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/12913.
Full text
33
Mossi, Michele. "Simulation of benchmark and industrial unsteady compressible turbulent fluid flows /." [S.l.] : [s.n.], 1999. http://library.epfl.ch/theses/?nr=1958.
Full text
34
Al-Sharif, Sharaf. "Computation of unsteady and non-equilibrium turbulent flows using Reynolds stress transport models." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/computation-of-unsteady-and-nonequilibrium-turbulent-flows-using-reynolds-stress-transport-models(935dbd20-b049-4b62-9e1c-eebb261675e5).html.
Full textAbstract:
In this work the predictive capability of a number of Reynolds stress transport(RST) models was first tested in a range of non-equilibrium homogeneous flows, comparisons being drawn with existing direct numerical simulation (DNS) results and physical measurements. The cases considered include both shear and normally strained flows, in some cases with a constant applied strain rate, and in others where this varied with time. Models were generally found to perform well in homogeneous shear at low shear rates, but their performance increasingly deteriorated at higher shear rates. This was attributed mainly to weaknesses in the pressure-strain rate models, leading to over-prediction of the shear stress component of the stress anisotropy tensor at high shear rates. Performance in irrotational homogeneous strains was generally good, and was more consistent over a much wider range of strain rates. In the experimental plane strain and axisymmetric contraction cases, with time-varying strain rates, there was evidence of an accelerated dissipation rate generation. Significant improvement was achieved through the use of an alternative dissipation rate generation term, Pε , in these cases, suggesting a possible route for future modelling investigation. Subsequently, the models were also tested in the inhomogeneous case of pulsating channel flow over a wide range of frequencies, the reference for these cases being the LES of Scotti and Piomelli (2001). A particularly challenging feature in this problem set was the partial laminarisation and re-transition that occurred cyclically at low and, to a lesser extent, intermediate frequencies. None of the models tested were able to reproduce correctly all of the observed flow features, and none returned consistently superior results in all the cases examined. Finally, models were tested in the case of a plane jet interacting with a rectangular dead-end enclosure. Two geometric configurations are examined, corresponding a steady regime, and an intrinsically unsteady regime in which periodic flow oscillations are experimentally observed (Mataoui et al., 2003). In the steady case generally similar flow patterns were returned by the models tested, with some differences arising in the degree of downward deflection of the impinging jet, which in turn affected the level of turbulence energy developing in the lower part of the cavity. In the unsteady case, only two of the models tested, a two-equation k-ε model and an advanced RST model, correctly returned purely periodic solutions. The other two RST models, based on linear pressure-strain rate terms, returned unsteady flow patterns that exhibited complex oscillations with significant cycle-to-cycle variations. Unfortunately, the limited availability of reliable experimental data did not allow a detailed quantitative examination of model performance.
35
Thornber, Ben. "Implicit large eddy simulation for unsteady multi-component compressible turbulent flows." Thesis, Cranfield University, 2007. http://hdl.handle.net/1826/2329.
Full textAbstract:
Numerical methods for the simulation of shock-induced turbulent mixing have been
investigated, focussing on Implicit Large Eddy Simulation. Shock-induced turbulent
mixing is of particular importance for many astrophysical phenomena, inertial confinement
fusion, and mixing in supersonic combustion. These disciplines are particularly
reliant on numerical simulation, as the extreme nature of the flow in question makes
gathering accurate experimental data difficult or impossible.
A detailed quantitative study of homogeneous decaying turbulence demonstrates that
existing state of the art methods represent the growth of turbulent structures and the decay
of turbulent kinetic energy to a reasonable degree of accuracy. However, a key observation
is that the numerical methods are too dissipative at high wavenumbers (short
wavelengths relative to the grid spacing). A theoretical analysis of the dissipation of
kinetic energy in low Mach number flows shows that the leading order dissipation rate
for Godunov-type schemes is proportional to the speed of sound and the velocity jump
across the cell interface squared. This shows that the dissipation of Godunov-type
schemes becomes large for low Mach flow features, hence impeding the development
of fluid instabilities, and causing overly dissipative turbulent kinetic energy spectra.
It is shown that this leading order term can be removed by locally modifying the reconstruction
of the velocity components. As the modification is local, it allows the
accurate simulation of mixed compressible/incompressible flows without changing the
formulation of the governing equations. In principle, the modification is applicable to
any finite volume compressible method which includes a reconstruction stage. Extensive
numerical tests show great improvements in performance at low Mach compared
to the standard scheme, significantly improving turbulent kinetic energy spectra, and
giving the correct Mach squared scaling of pressure and density variations down to
Mach 10−4. The proposed modification does not significantly affect the shock capturing
ability of the numerical scheme.
The modified numerical method is validated through simulations of compressible,
deep, open cavity flow where excellent results are gained with minimal modelling
effort. Simulations of single and multimode Richtmyer-Meshkov instability show that
the modification gives equivalent results to the standard scheme at twice the grid resolution
in each direction. This is equivalent to sixteen times decrease in computational
time for a given quality of results. Finally, simulations of a shock-induced turbulent
mixing experiment show excellent qualitative agreement with available experimental
data.
36
Costello, Mark Francis. "A theory for the analysis of rotorcraft operating in atmospheric turbulence." Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/12893.
Full text
37
Song, Tiancheng. "Velocity and turbulence distribution in non-uniform and unsteady open-channel flow /." [S.l.] : [s.n.], 1995. http://library.epfl.ch/theses/?nr=1324.
Full text
38
Wu, Men-Zan B. "Velocity and temperature measurements in a non-premixed reacting flow behind a backward facing step." Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/12045.
Full text
39
Favre-Marinet, Michel. "Structures cohérentes dans un jet rond excité." Grenoble 1, 1986. http://www.theses.fr/1986GRE10061.
Full textAbstract:
Un jet rond est faiblement excite par haut-parleur a la frequence preferentielle du jet permanent. Mesures par anemometrie a fil chaud et a fil froid des champs cinematique et thermique. Par la technique de moyenne de phase on separe les fluctuations periodiques et les fluctuations turbulentes des temperatures et des vitesses. Mise en evidence de la nature tourbillonnaire du mouvement periodique et de la concentration de vorticite dans les structures annulaires. Etude du role joue par les grosses structures dans la diffusion de la chaleur. Comparaison avec la theorie de la stabilite. Etude des interactios entre le mouvement periodique et la turbulence
40
Campioli, Theresa Lynn. "Assessment of Formulations for Numerical Solutions of Low Speed, Unsteady, Turbulent Flows over Bluff Bodies." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/32141.
Full textAbstract:
Two algorithms commonly used for solving low-speed flow fields are evaluated using an unsteady turbulent flow formulation. The first algorithm is the method of artificial compressibility which solves the incompressible Navier-Stokes equations. The second is a preconditioned system for solving the compressible Navier-Stokes equations. Both algorithms have been implemented into GASP Version 4, which is the flow solver used in this investigation. Unsteady numerical simulations of unsteady, 2-D flow over square cylinders are performed with comparisons made to experimental data. Cases studied include both a single-cylinder and a three-cylinder configuration. Two turbulence models are also used in the computations, namely the Spalart-Allmaras model and the Wilcox k-ω (1998) model. The following output data was used for comparison: aerodynamic forces, mean pressure coefficient, Strouhal number, mean velocity magnitude and turbulence intensity. The main results can be summarized as follows. First, the predictions are more sensitive to the turbulence model choice than to the choice of algorithm. The Spalart-Allmaras model overall produced better results with both algorithms than the Wilcox k-ω model. Second, the artificial compressibility algorithm produced slightly more consistent results compared with experiment.Master of Science
41
Ruiz, Anthony. "Unsteady Numerical Simulations of Transcritical Turbulent Combustion in Liquid Rocket Engines." Thesis, Toulouse, INPT, 2012. http://www.theses.fr/2012INPT0009/document.
Full textAbstract:
Ces cinquantes dernières années, la majorité des paramètres de conception des moteurs cryotechniques ont été ajustés en l'absence d'une compréhension détaillée des phénomènes de combustion, en raison des limites des diagnostiques expérimentaux et des capacités de calcul. L'objectif de cette thèse est de réaliser des simulations numériques instationnaires d'écoulements réactifs transcritiques de haute fidélité, pour permettre une meilleure compréhension de la dynamique de flamme dans les moteurs cryotechniques et finalement guider leur amélioration. Dans un premier temps, la thermodynamique gaz-réel et son impact sur les schémas numériques sont présentés. Comme la Simulation aux Grandes Echelles (SGE) comporte des équations filtrées, les effets de filtrages induits par la thermodynamique gaz-réel sont ensuite mis en évidence dans une configuration transcritique type et un opérateur de diffusion artificiel, spécifique au gaz réel, est proposé pour lisser les gradients transcritiques en SGE. Dans un deuxième temps, une étude fondamentale du mélange turbulent et de la combustion dans la zone proche-injecteur des moteurs cryotechniques est menée grâce à la Simulation Numérique Directe (SND). Dans le cas non-réactif, les lâchers tourbillonnaires dans le sillage de la lèvre de l’injecteur jouent un rôle majeur dans le mélange turbulent et provoquent la formation de structures en peigne déjà observées expérimentalement dans des conditions similaires. Dans le cas réactif, la flamme reste attachée à la lèvre de l'injecteur, sans extinction locale, et les structures en peigne disparaissent. La structure de flamme est analysée et différents modes de combustion sont identifiés. Enfin, une étude de flamme-jet transcritique H2/O2, accrochée à un injecteur coaxial avec et sans retrait interne, est menée. Les résultats numériques sont d'abord validés par des données expérimentales pour l'injecteur sans retrait. Ensuite, la configuration avec retrait est comparée à la solution de référence sans retrait et à des données experimentales pour observer les effets de ce paramètre de conception sur l'efficacité de combustionIn the past fifty years, most design parameters of the combustion chamber of Liquid Rocket Engines (LREs) have been adjusted without a detailed understanding of combustion phenomena, because of both limited experimental diagnostics and numerical capabilities. The objective of the present thesis work is to conduct high-fidelity unsteady numerical simulations of transcritical reacting flows, in order to improve the understanding of flame dynamics in LRE, and eventually provide guidelines for their improvement. First real-gas thermodynamics and its impact on numerical schemes are presented. As Large-Eddy Simulation (LES) involves filtered equations, the filtering effects induced by real-gas thermodynamics are then highlighted in a typical 1D transcritical configuration and a specific real-gas artificial dissipation is proposed to smooth transcritical density gradients in LES. Then, a Direct Numerical Simulation (DNS) study of turbulent mixing and combustion in the near-injector region of LREs is conducted. In the non-reacting case, vortex shedding in the wake of the lip of the injector is shown to play a major role in turbulent mixing, and induces the formation of finger-like structures as observed experimentally in similar operating conditions. In the reacting case, the flame is attached to the injector rim without local extinction and the finger-like structures disappear. The flame structure is analyzed and various combustion modes are identified. Finally, a LES study of a transcritical H2/O2 jet flame, issuing from a coaxial injector with and without inner recess, is conducted. Numerical results are first validated against experimental data for the injector without recess. Then, the recessed configuration is compared to the reference solution and to experimental results, to scrutinize the effects of this design parameter on combustion efficiency
42
Harding, Samuel Frederick. "Unsteady velocities of energetic tidal currents : an investigation into dynamic flow effects on lifting surfaces at field and experimental scale." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/8037.
Full textAbstract:
The generation of electricity from tidal currents is an emerging industry with the potential to contribute to the UK energy supply in a predictable and sustainable way. The development of the technology requires the cost effective subsea installation of energy conversion systems in an energetic and challenging marine environment. One concept developed for the fastening of tidal energy converters to the seabed is the Active Gravity Base (AGB), which offers potential reductions in installation cost and time, relative to existing fastening methods. The performance of this concept in response to unsteady flow conditions is explored within this thesis. The dynamic behaviour of a tidal current is driven by a range of factors from gravitational forces of celestial bodies to high-frequency fluctuations of turbulent eddies. The response of the AGB concept to the unsteadiness of tidal currents is herein considered under the two broad time-scales; the directionality of the mean semi-diurnal cycle and the high frequency variations from a given mean flow velocity. The correlation between the direction and velocity of the tidal flow was assessed using hourly averaged data provided by the Admiralty Charts in the northern UK waters. The resulting directionality model was used to predict the performance of the AGB under a range of quasi-steady flow conditions. High frequency velocity measurements of a potential tidal energy site were obtained through collaboration with the University of Washington and the Pacific Northwest National Laboratory. This data was used to estimate the maximum perturbation from the mean velocity that can be expected on an annual basis. An experimental facility was developed within the re-circulating water flume at the University of Edinburgh to examine the dynamic loads generated by controllable two-dimensional flow perturbations. This was successfully achieved using a configuration of twin pitching foils with independent motion control. A relationship between the foil pitch angle and velocity perturbation time series was predicted using a vortex model of the foil wakes. This configuration was shown to be able to generate significant flow fluctuations within the range of reduced frequencies 0:06 ≤ k ≤ 1:9, with a peak gust intensity of Ig = 0:5. The numerical solution was validated against experimental results.
43
Karantonis, Konstantinos. "Modelling and simulation of turbulence in unsteady separated and suddenly-expanded flows." Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/7900.
Full textAbstract:
The scope of this PhD thesis is the simulation of turbulence in time-dependent, separated
and suddenly-expanded channel flows. High-resolution and very high-order numerical
methods have been employed in the framework of Implicit Large Eddy Simulation (ILES)
to elucidate open questions about the physics in flows with sudden expansion.
It is well known that the planar sudden expansion (PSE), despite its simple and symmetric
geometry it produces a very complex behaviour and a distinctly asymmetric flow
pattern ascribed mainly to the Coanda effect. Such flows are encountered in a wide range
of practical engineering applications, such as combustion, hydraulic and fluidic devices,
air ducts, and mixing equipments. It is of great importance, therefore, to understand the
mechanisms that dominate flows with separation and reattachment of the shear layers, as
well as flows with regions of strong reversed motion.
This thesis has for the first time analysed in detail the turbulent kinetic energy budget
(TKEB) for the PSE. This analysis has been extended to examine the influence of Mach
number on each individual component of the TKEB. The resulting data can be used as
reference for further development of turbulence models capable of accurately resolving
the flow behaviour in suddenly-expanded flows.
Cont/d.
44
Lenci, Giancarlo. "A methodology based on local resolution of turbulent structures for effective modeling of unsteady flows." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/106701.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 164-175).
Computational fluid dynamics (CFD) is widely adopted to predict complex flows and to inform the design of advanced engineering systems. In particular, the industry has seen a continuous growth of CFD simulations of turbulent phenomena, which has been made possible by the tremendous reduction achieved in cost per floating point operation. The need for accurate, yet computationally effective, transient methods has drawn particular attention to hybrid turbulence models, seeking to offer significant cost reduction over large-eddy simulation (LES). Despite promising results in academic test cases, the use of hybrid modeling is still scarce in general industrial simulations. Such a low adoption is mainly driven by limitations in the ability to provide accurate, robust, reliable, and grid-convergent solutions. Hybrid models are still far from presenting a viable replacement to unsteady Reynolds-averaged Navier-Stokes (URANS). This work investigates the key weaknesses of current hybrid approaches and develops a novel modeling strategy to overcome selected shortcomings. Hybrid approaches have mostly focused on identifying regions of the flow where LES could be recovered, based for example on a comparison between grid and flow length scales. Conversely, the new approach aims at leveraging the robustness of URANS in suitable flow regions while introducing controlled eddy resolution in regions of poor URANS applicability. This drastic change in strategy focuses on avoiding the frequent failures observed for existing hybrid methods while still enabling the effective resolution of scales. The formulation proposed identifies critical flow regions based on the absolute value of the second invariant of the resolved velocity gradient tensor. The variable retains several useful properties, including the capability to describe scale separation, deformation, shear flow, and coherent structures (thus motivating the name STRUCT adopted for the new approach). The method is implemented into a finite volume, general-purpose CFD solver and tested in unsteady flow applications on URANS-like grids. Results demonstrate the capability of the model to select regions of effective hybrid activation based on local flow variables. In all flow cases tested, the hybrid model activates in areas of strong flow deformation producing large resolved structures in the solution and generating enhanced description of low-frequency phenomena compared to URANS. This observation confirms the powerful consistency between regions of low URANS performance and highly deformed structures, and supports the potential of the STRUCT approach in applications requiring selective spectral information such as fluid-structure interaction analyses. After a controlled evaluation of the model with fixed parameters specified before the simulation, two formulations are proposed to provide full closure: one based on a local averaging operator represented by a truncated Taylor series expansion, and a second one leveraging a Lagrangian differential operator to provide a smooth averaging. Both of those methods aim at providing viable averaged fields as needed by the STRUCT formulation while relying only on local operations for ensuring a low penalty on computational cost in parallel simulations. The former method determines the hybrid activation regions but still relies on a constant coefficient for reducing the modeled turbulent scales. On the other hand, the latter method assigns both conditions automatically. In all simulation results, significant agreement with experimental data is achieved for the first and second central moments of the velocity components. These results illustrate the potential of the STRUCT approach to provide accurate LES-like predictions with a computational cost only about 10% higher than that of URANS while orders of magnitude lower than LES. The generality of the STRUCT approach is confirmed in applied work extending its applicability to real flow cases. The controlled STRUCT approach demonstrates significant grid consistency properties while preventing strong error increase as the grid is coarsened beyond URANS convergence. The STRUCT methodology has the potential to revert to URANS in conditions of poor hybrid model applicability while future work can design LES retrieval at the fine-grid limit. Due to those robust properties and to the safe fail-to-URANS rationale, the STRUCT concept has the potential to achieve through future tests and developments a reliable enhancement over URANS.
by Giancarlo Lenci.
Ph. D.
45
Taheri, Arash. "Detached eddy simulation of unsteady turbulent flows in the draft tube of a bulb turbine." Doctoral thesis, Université Laval, 2015. http://hdl.handle.net/20.500.11794/27061.
Full textAbstract:
Les aspirateurs de turbines hydrauliques jouent un rôle crucial dans l’extraction de l’énergie disponible. Dans ce projet, les écoulements dans l’aspirateur d’une turbine de basse chute ont été simulés à l'aide de différents modèles de turbulence dont le modèle DDES, un hybride LES/RANS, qui permet de résoudre une partie du spectre turbulent. Déterminer des conditions aux limites pour ce modèle à l’entrée de l’aspirateur est un défi. Des profils d’entrée 1D axisymétriques et 2D instationnaires tenant compte des sillages et vortex induits par les aubes de la roue ont notamment été testés. Une fluctuation artificielle a également été imposée, afin d’imiter la turbulence qui existe juste après la roue. Les simulations ont été effectuées pour deux configurations d’aspirateur du projet BulbT. Pour la deuxième, plusieurs comparaisons avec des données expérimentales ont été faites pour deux conditions d'opération, à charge partielle et dans la zone de baisse rapide du rendement après le point de meilleur rendement. Cela a permis d’évaluer l'efficacité et les lacunes de la modélisation turbulente et des conditions limites à travers leurs effets sur les quantités globales et locales. Les résultats ont montrés que les structures tourbillonnaires et sillages sortant de la roue sont adéquatement résolus par les simulations DDES de l’aspirateur, en appliquant les profils instationnaires bidimensionnels et un schéma de faible dissipation pour le terme convectif. En outre, les effets de la turbulence artificielle à l'entrée de l’aspirateur ont été explorés à l'aide de l’estimation de l’intermittence du décollement, de corrélations en deux points, du spectre d'énergie et du concept de structures cohérentes lagrangiennes. Ces analyses ont montré que les détails de la dynamique de l'écoulement et de la séparation sont modifiés, ainsi que les patrons des lignes de transport à divers endroits de l’aspirateur. Cependant, les quantités globales comme le coefficient de récupération de l’aspirateur ne sont pas influencées par ces spécificités locales.Draft tubes play a crucial role in elevating the available energy extraction of hydroturbines. In this project, turbulent flows in the draft tube of a low-head bulb turbine were simulated using, among others, an advance hybrid LES/RANS turbulent model, called DDES, which can resolve portions of the turbulent spectrum. Providing appropriate inflow boundary conditions for such models is a challenging issue. In this regard, different inflow boundary conditions were tested, including axisymmetric 1D profiles, and unsteady 2D inflow profiles that take runner blade wakes and vortices into account. Artificial fluctuation at the inlet section of the draft tube was also included to mimic the turbulence existing after the runner. Simulations were conducted for two draft tube configurations of the BulbT project. For one of them, intensive comparisons with experimental data were done for two operating conditions, one at part load and another in the sharp drop-off portion of the efficiency hill after the best efficiency point. This allowed to assess the effectiveness and shortcomings of the adopted turbulence modeling and boundary conditions through their effects on the global and local quantities. The results showed that the runner-related vortical structures and wakes are appropriately resolved using stand-alone DDES simulation of the draft tube flows. This is achieved by applying unsteady 2D inflow profiles along with adopting low dissipation scheme for the convective term. Furthermore, the effects of applying artificial turbulence at inlet were explored using separation intermittency, two-point correlation, energy spectrum and Lagrangian coherent structure concepts. These analyses revealed that the type of inflow boundary conditions modifies the details of the flow and separation dynamics as well as patterns of the transport barriers in different regions of the draft tube. However, the global quantities such as recovery coefficient are not influenced by these local features.
46
Ma, Ruolong. "Unsteady Turbulence Interaction in a Tip Leakage Flow Downstream of a Simulated Axial Compressor Rotor." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/28060.
Full textAbstract:
The unsteady behavior of a tip leakage flow downstream of a simulated axial compressor rotor has been studied. The Virginia Tech low speed linear cascade wind tunnel was adapted to model the unsteady tip leakage flow produced by a rotor operating in the vortical wakes of a set of stator vanes. The cascade, consisting of 8 GE rotor B blades, has adjustable tip gap, inlet angle of 65.1 degrees, turning angle of 11.8 degrees and solidity of 1.076. The cascade Reynolds number, based on blade chord, was 393,000. A moving end wall was used to simulate the relative motion between rotor and casing, and vortex generators attached to the moving end wall were used to produce an idealized periodic unsteady vortical inflow similar to that shed by the junction of a row of inlet guide vanes.
Measurements of the vortical inflow to the cascade produced by the generators and of the mean blade loading at the mid span are presented. The periodic and aperiodic behavior of the tip leakage flow downstream of the cascade, produced by this vortical disturbance, is also presented using phase and time averaged 3-component turbulence and pressure fluctuation measurements. These measurements are made for tip gap from 0.83% to 3.3% chord and streamwise locations from 0.772% to 1.117% blade spacing axially downstream of the cascade.
The phase averaged inflow measurements reveal that the inflow produced by the vortex generators consists of a pair asymmetric counter-rotating vortices embedded in a thin (4.6% chord) endwall boundary layer. The vortices extend some 7.4% chord from the end wall. Their strength is about two orders smaller than the typical circulation of the tip leakage vortices produced by the cascade.
Phase averaged single point three component hot-wire measurements downstream of the cascade reveal that the vortical inflow is, however, capable of producing significant large scale fluctuations in the size, strength, structure and position of the tip leakage vortex. These effects increase in magnitude with increase of tip gap. For small tip gaps these effects appear to be due to simple superposition between the inflow vortices and the tip leakage vortex. However for larger tip gaps these effects appear primarily a consequence of the inflow vortices interfering with the shedding of circulation from the blade tip. The fact that the circulation fluctuation is consistent with the inviscid unsteady loading prediction suggests that the inviscid response may be a major mechanism for generating the tip leakage unsteadiness.
Although there is large periodic fluctuation in the tip leakage flow disturbed by the inflow, there is a larger aperiodic component. Two point correlation measurements and linear stochastic estimation are used to reveal the structure of this aperiodic part for a tip gap of 3.3% chord. The aperiodic fluctuation, containing most of the turbulence energy, is found appearing to be organized structures in large scale, and making the estimated instantaneous velocity field significantly different from the phase averaged periodic velocity field.
Phase averaged pressure fluctuation measurements made using a microphone in the tip leakage vortex downstream of the cascade reveal that there are significant periodic fluctuating pressure waves and intense mean square fluctuation of the aperiodic fluctuating pressure. They are consistent with the measured periodic flow and aperiodic flow field respectively. These microphone measurements are validated using fluctuating pressure gradient estimates determined from the hot-wire measurements.Ph. D.
47
Ozturk, Burak. "Combined effects of Reynolds number, turbulence intensity and periodic unsteady wake flow conditions on boundary layer development and heat transfer of a low pressure turbine blade." [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1150.
Full text
48
Seddighi-Moormani, Mehdi. "Study of turbulence and wall shear stress in unsteady flow over smooth and rough wall surfaces." Thesis, University of Aberdeen, 2011. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=166096.
Full textAbstract:
Flows over hydraulically smooth walls are predominant in turbulence studies whereas real surfaces in engineering applications are often rough. This is important because turbulent flows close to the two types of surface can exhibit large differences. Unfortunately, neither experimental studies nor theoretical studies based on conventional computational fluid dynamics (CFD) can give sufficiently accurate, detailed information about unsteady turbulent flow behaviour close to solid surfaces, even for smooth wall cases. In this thesis, therefore, use is made of a state of the art computational method “Direct Numerical Simulation (DNS)” to investigate the unsteady flows. An “in-house” DNS computer code is developed for the study reported in this thesis. Spatial discretization in the code is achieved using a second order, finite difference method. The semi-implicit (Runge-Kutta & Crank-Nicholson) time advancement is incorporated into the fractional-step method. A Fast Fourier Transform solver is used for solving the Poisson equation. An efficient immersed Boundary Method (IBM) is used for treating the roughness. The code is parallelized using a Message Passing Interface (MPI) and it is adopted for use on a distributed-memory computer cluster at University of Aberdeen as well as for use at the UK’s national high-performance computing service, HECToR. As one of the first DNS of accelerating/decelerating flows over smooth and rough walls, the study has produced detailed new information on turbulence behaviours which can be used for turbulence model development and validations. The detailed data have enabled better understanding of the flow physics to be developed. The results revealed strong non-equilibrium and anisotropic behaviours of turbulence dynamics in such flows. The preliminary results on the rough wall flow show the response of turbulence in the core and wall regions, and the relationship between the axial and the other components are significantly different from those in smooth wall flows.
49
Pont, Grégoire. "Self adaptive turbulence models for unsteady compressible flows Modèles de turbulence auto-adaptatifs pour la simulation des écoulements compressibles instationnaires." Thesis, Paris, ENSAM, 2015. http://www.theses.fr/2015ENAM0008/document.
Full textAbstract:
Cette thèse est principalement dédiée à la simulation des écoulements massivement décollés dans le domaine spatial. Nous avons restreint notre étude aux écoulements d'arrière-corps, pour lesquels ces décollements sont imposés par des changements brutaux de la géométrie. Dans le domaine spatial, le caractère fortement compressible des écoulements rencontrés impose l'utilisation de schémas numériques robustes. D'un autre coté, la simulation fine de la turbulence impose des schémas d'ordre élevé et peu dissipatifs. Ces deux spécifications, apparemment contradictoires, doivent pourtant coexister au sein d'une même simulation. Les modèles de turbulence ainsi que les schémas de discrétisation sont indissociables et leur couplage doit impérativement être considéré. Les schémas numériques doivent garder leur précision formelle dans des géométries complexes et des maillages très irréguliers imposés par le contexte industriel. Cette étude analyse le schéma de discrétisation utilisé dans le code de calcul FLUSEPA développé par Airbus Defence & Space. Ce schéma est robuste et précis pour des écoulements avec chocs et il présente une faible sensibilité au maillage (l'ordre 3 étant conservé même sur des maillages fortement perturbés). Malheureusement, le schéma possède une trop faible résolvabilité liée à un niveau de dissipation trop élevé pour envisager des simulations hybrides RANS/LES. Pour pallier à cet inconvénient, nous nous sommes penchés vers une solution basée sur un recentrage conditionnel et local : dans les zones dominées par des structures tourbillonnaires, une fonction analytique assure un recentrage local lorsque la stabilité numérique le permet. Cette condition de stabilité assure le couplage entre le schéma et le modèle. De cette manière, les viscosités laminaire et tourbillonnaire sont les seules à jouer un rôle dans les régions dominées par la vorticité et servent aussi à stabiliser le schéma numérique. Cette étude présente de plus une comparaison qualitative et quantitative de plusieurs modèles hybrides RANS/LES, à égalité de maillage et de schéma utilisés Pour cela, un certain nombre d'améliorations (notamment de leur capacité à résoudre les instabilités de Kelvin-Helmohlotz sans retard), proposées dans la littérature ou bien introduites dans cette thèse, sont prises en compte. Les applications numériques étudiées concernent des géométries allant de la marche descendante au lanceur spatial complet à échelle réduiteThis thesis is mainly dedicated to the simulation of massively separated flows in the space domain. We restricted our study to afterbody flows, where the separation is imposed by abrupt geometry changes. In the space domain, highly compressible flows require the use of robust numerical schemes. On the other hand, the simulation of turbulence imposes high-order low dissipative numerical schemes. These two specifications, apparently contradictory, must coexist within the same simulation. The coupling between turbulence models and discretization schemes is of the utmost importance and must be considered. Numerical schemes should keep their formal accuracy on complex geometries and on very irregular meshes imposed by the industrial context. In this research, we analyze the discretization scheme implemented in the FLUSEPA solver, developed by Airbus Defence & Space. Such a scheme is robust and accurate for flows with shocks and exhibits a low sensitivity to the grid (the third order of accuracy being ensured, even on highly irregular grids). Unfortunately, the scheme possesses a too low resolvability related to a too high numerical dissipation for RANS/LES simulations. To circumvent this problem, we considered a conditional and local re-centering strategy: in regions dominated by vortical structures, an analytic function provides local re-centering when a numerical stability condition is satisfied. This stability condition ensures the coupling between the numerical scheme and the model. In this way, only the turbulent and the laminar viscosities play a role in regions dominated by vorticity, and also allow to stabilize the numerical scheme. This study provides also a qualitative and quantitative assessment of several hybrid RANS/LES models, using the same grids and discretization scheme. For this purpose some recent improvements (improving their ability to trigger the Kelvin-Helmohlotz instabilities without delay), proposed in the litterature or suggested in this work, are taken into account. Numerical applications include geometrical configurations ranging from a backward facing step to realistic launcher configurations
50
Sanders, Darius Demetri. "CFD Modeling of Separation and Transitional Flow in Low Pressure Turbine Blades at Low Reynolds Numbers." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/29303.
Full textAbstract:
There is increasing interest in design methods and performance prediction for turbine engines operating at low Reynolds numbers. In this regime, boundary layer separation may be more likely to occur in the turbine flow passages. For accurate CFD predictions of the flow, correct modeling of laminar-turbulent boundary layer transition is essential to capture the details of the flow. To investigate possible improvements in model fidelity, both two-dimensional and three-dimensional CFD models were created for the flow over several low pressure turbine blade designs. A new three-equation eddy-viscosity type turbulent transitional flow model originally developed by Walters and Leylek was employed for the current RANS CFD calculations. Flows over three low pressure turbine blade airfoils with different aerodynamic characteristics were simulated over a Reynolds number range of 15,000-100,000, and predictions were compared to experiments. The turbulent transitional flow model sensitivity to inlet turbulent flow parameters showed a dependence on free-stream turbulence intensity and turbulent length scale. Using the total pressure loss coefficient as a measurement of aerodynamic performance, the Walters and Leylek transitional flow model produced adequate prediction of the Reynolds number performance in the Lightly Loaded blade. Furthermore, the correct qualitative flow response to separated shear layers was observed for the Highly Loaded blade. The vortex shedding produced by the separated flow was largely two-dimensional with small spanwise variations in the separation region. The blade loading and separation location was sufficiently predicted for the Aft-Loaded L1A blade flowfield. Investigations of the unsteady flowfield of the Aft-Loaded L1A blade showed the shear layer produced a large separation region on the suction surface. This separation region was located more downstream and significantly reduced in size when impinged upon by the upstream wakes, thus improving the aerodynamic performance consistent with experiments. For all cases investigated, the Walters and Leylek transitional flow model was judged to be sufficient for understanding the separation and transition characteristics, and superior to other widely-used turbulence models in accuracy of describing the details of the transitional and separated flow. This research characterized and assessed a new model for low Reynolds number turbine aerodynamic flow prediction and design improvement.Ph. D.