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15
SIMSON–A PseudoSpectral Solver for Incompressible Boundary Layer Flow
, 2007
"... This is software which is distributed freely on a limited basis; it comes with no guarantees whatsoever. Problems can be reported to henning@mech.kth.se, but no action is promised. If results obtained by using the programs included in the Simson distribution are published the authors would like an a ..."
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Cited by 12 (3 self)
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This is software which is distributed freely on a limited basis; it comes with no guarantees whatsoever. Problems can be reported to henning@mech.kth.se, but no action is promised. If results obtained by using the programs included in the Simson distribution are published the authors would like an acknowledgment, e.g. in the form of referencing this code manual. The front page image is a visualization of laminarturbulent transition induced by ambient freestream turbulence convected above a flat plate, i.e. socalled bypass transition (Brandt et al., 2004). The largeeddy simulation used to generate the image (Schlatter et al., 2006) is performed with Simson using the ADMRT subgridscale model (Schlatter et al., 2004), further postprocessed using the program lambda2 and rendered using OpenDX. Low and high speed streaks are visualized with blue and red isocontours, respectively; green and yellow isocontours indicate the λ2 vortex identification criterion (Jeong & Hussain, 1995). The flow is from lower left to upper right. This user guide is compiled from revision 1047. ISBN 9789171788382
Reynolds stress budgets in Couette and boundary layer flows
"... Introduction The development of cheap, powerful, computers has lead to wide use of CFD codes for the prediction of turbulent flows. These codes almost always use turbulence models to try to capture the characteristics of the turbulent flow, and the prediction is no better than the weakest link in c ..."
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Cited by 5 (1 self)
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Introduction The development of cheap, powerful, computers has lead to wide use of CFD codes for the prediction of turbulent flows. These codes almost always use turbulence models to try to capture the characteristics of the turbulent flow, and the prediction is no better than the weakest link in computational chain. Often the weakest link is the turbulence model. But to develop better turbulence models one must have data to compare them against. In the early days of turbulence modelling one had to rely on indirect methods to test the various closure models. Experimentaldi#5LG%% in measuring pressure and velocity with su# cient resolution did not make direct comparisons possible. With the development of highspeed supercomputers, and new algorithms, Orszag (1969, 1970); Kreiss & Oliger (1972); Basdevant (1983), it became possible to simulate turbulent flows directly without resorting to large eddy simulations or turbulence models. Now it became possible to evaluate any desira
Direct Numerical Simulation of a separated channel flow with a smooth profile
, 2008
"... A direct numerical simulation (DNS) of a channel flow with one curved surface was performed at moderate Reynolds number (Reτ = 395 at the inlet). The adverse pressure gradient was obtained by a wall curvature through a mathematical mapping from physical coordinates to Cartesian ones. The code, using ..."
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Cited by 4 (2 self)
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A direct numerical simulation (DNS) of a channel flow with one curved surface was performed at moderate Reynolds number (Reτ = 395 at the inlet). The adverse pressure gradient was obtained by a wall curvature through a mathematical mapping from physical coordinates to Cartesian ones. The code, using spectral spanwise and normal discretization, combines the advantage of a good accuracy with a fast integration procedure compared to standard numerical procedures for complex geometries. The turbulent flow slightly separates on the profile at the lower curved wall and is at the onset of separation at the opposite flat wall. The thin separation bubble is characterized with a reversal flow fraction. Intense vortices are generated near the separation line on the lower wall but also at the upper wall. Turbulent normal stresses and kinetic energy budget are investigated along the channel.
Scaling of the velocity profile in strongly drag reduced turbulent flows over an oscillating wall
 International Journal of Heat and Fluid Flow
, 2014
"... Abstract Scaling analysis of the velocity profiles in strongly drag reduced flows reveals that the slope of the logarithmic part depends on the amount of drag reduction (DR). Unlike DR due to polymeric fluids, the slope changes gradually and can be predicted by the analysis. Furthermore, the interc ..."
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Abstract Scaling analysis of the velocity profiles in strongly drag reduced flows reveals that the slope of the logarithmic part depends on the amount of drag reduction (DR). Unlike DR due to polymeric fluids, the slope changes gradually and can be predicted by the analysis. Furthermore, the intercept of the profiles is found do vary linearly with the DR. Two velocity scales are utilized: the reference (undisturbed) and the actual friction velocity. The theory is based on the assumption that the nearwall linear region is only governed by the actual friction velocity, while the outer part is governed by the reference friction velocity. As a result, logarithmic part is influenced by both velocity scales and the slope of the velocity profile is directly linked to the DR. The theoretically obtained results are verified by data from six previously performed direct numerical simulations (DNSs) of boundary layers over spatial and temporal wall oscillations, with a wide range of resulting DR. The theory is further supported by data from numerous investigations (DNSs as well as experiments) of wallbounded flows forced by various forms of oscillating wallmotion. The assumption that the outer part is unaffected by the actual friction velocity limits the validity of the proposed loglaw to flows not fully adapted to the imposed wall forcing, hence the theory provides a measure of the level of adjustment. In addition, a fundamental difference in the applicability of the theory to spatially developing boundary flow and infinite channel flow is discussed.
19b. TELEPHONE NUMBER
"... a. REPORT 16. SECURITY CLASSIFICATION OF: Unsteady flow separation during dynamic stall often leads to unacceptably large vibra tory loads and acoustic noise, and limit forward flight speeds and maneuverability. To gain a quantitative understanding of the unsteady separation process, largeeddy sim ..."
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a. REPORT 16. SECURITY CLASSIFICATION OF: Unsteady flow separation during dynamic stall often leads to unacceptably large vibra tory loads and acoustic noise, and limit forward flight speeds and maneuverability. To gain a quantitative understanding of the unsteady separation process, largeeddy simula tion (LES) of turbulent flow over a pitching airfoil at realistic Reynolds and Mach numbers is performed. Numerical stability at high Reynolds number simulation is maintained us ing an unstructuredgrid LES technology, which obeys higherorder conservation principles and employs a globalcoefficient subgridscale turbulence model. A hybrid implicitexplicit timeintegration scheme is employed to
Annual Research Briefs 2012
"... DNS and modeling of a turbulent boundary layer with separation and reattachment over a range of ..."
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DNS and modeling of a turbulent boundary layer with separation and reattachment over a range of
LargeEddy Simulation of the Flatplate Turbulent Boundary Layer at High Reynolds numbers
, 2012
"... iii To my family iv Acknowledgements I would like to first express my deepest gratitude to my advisor, Professor Dale Pullin, who provided a chance to work on exciting and fulfilling research projects. I sincerely appreciate his incredible patience in teaching me the fundamental process of research ..."
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iii To my family iv Acknowledgements I would like to first express my deepest gratitude to my advisor, Professor Dale Pullin, who provided a chance to work on exciting and fulfilling research projects. I sincerely appreciate his incredible patience in teaching me the fundamental process of research in the computational fluid dynamics of turbulence. I am also grateful for his understanding my pursuing a minor in Applied & Computational Mathematics, which helped me expand my intellectual horizon. Being honored to be one of his students, I could not have asked for a better advisor. I also gratefully acknowledge the helpful comments and suggestions on my thesis from the members of my thesis committee, Professors Beverley McKeon, Tim Colonius, and Anthony Leonard. I was fortunate to participate in a fruitful collaborative effort on extending the capabilities of largeeddy simulations (Chapters 4 and 5) with Professor Ivan Marusic and Dr. Romain Mathis from the University of Melbourne. I learned much from our discussions, especially the nuances of experimental research. Thanks also go to Professor Andrew Ooi, who most generously provided computational resources at the Victorian Life Sciences Computation Initiative (VLSCI), and Zambri Harun who provided experimental measurements of the adversepressuregradient turbulent boundary layer (Chapter 5). Life at Caltech was fascinating, thanks to my fellow graduate students at GALCIT and former and current members in the Allen Puckett Laboratory of Computational Fluid Dynamics; I thank Andrew, Alejandro, Geoff, Jack, Manuel, Namiko, Richard, and Yue for their friendships and many
FACULTE DES SCIENCES ET DE GENIE
"... Experimental study of the turbulence structures in a boundary layer subjected to a strong adverse pressure gradient Thèse présentée à la Faculté des études supérieures de l'Université Laval dans le cadre du programme de doctorat génie mécanique pour l'obtention du grade de Philosophiae Doc ..."
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Experimental study of the turbulence structures in a boundary layer subjected to a strong adverse pressure gradient Thèse présentée à la Faculté des études supérieures de l'Université Laval dans le cadre du programme de doctorat génie mécanique pour l'obtention du grade de Philosophiae Doctor (Ph.D.)