Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session AA: Turbulent Boundary Layers: DNS & LES |
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Chair: Huidan Yu, Los Alamos National Laboratory Room: 001A |
Sunday, November 23, 2008 8:00AM - 8:13AM |
AA.00001: Chasing eddies and their wall signature in turbulent boundary layers at Mach 3 through 10 Stephan Priebe, Izaak Beekman, M. Pino Martin We use a direct numerical simulation database of turbulent boundary layers,\footnote{Martin, M.P., JFM, vol. 570, pp. 347- 364, 2006}$^,$\footnote{Martin, M.P., AIAA Paper 2004-2337}$^,$\footnote{Beekman \& Martin, APS DFD08} statistical tools,\footnote{Brown \& Thomas, Phys. Fluids, vol. 20, pp243-251, 1977} scientifically-rooted packet-pattern recognition,\footnote {Ringuette, Wu \& Martin, JFM, vol. 594, pp. 59-69, 2008} and validated visualization algorithms\footnote{O'Farrell, C. Senior Thesis, Princeton University 2008} to identify hairpin packets and their wall signature. We investigate the variation of time scales and length scales associated with coherent structures and the role of hairpin packets on the generation of skin friction, wall-pressure loading and heat transfer. [Preview Abstract] |
Sunday, November 23, 2008 8:13AM - 8:26AM |
AA.00002: Wall turbulence without walls Yoshinori Mizuno, Javier Jimenez Direct numerical simulations are presented of isolated logarithmic layers without an underlying buffer zone. They are implemented by enforcing artificial boundary conditions within the logarithmic layer which are synthesized from values from the interior of the flow. As an example, simulations of a half-channel employing this technique are discussed. The results exhibit logarithmic mean velocity profiles, and velocity fluctuation intensities that are similar to those obtained by the full DNS of half or full channels. Those results strongly suggest that the formation of a logarithmic layer is not overly dependent on the presence of a near-wall region, and that such a flow can exist by itself. The technique enables us to perform conceptual experiments to clarify what is essential to the logarithmic layer. For example, preliminary results show that the logarithmic layer cannot be created only by a non-uniform shear, and requires a spatial gradient of the scales of the fluctuations. Somewhat surprisingly, some simulations result in K\'arm\'an constants fairly different from $\kappa=0.4$, providing clues to what determines $\kappa$ in real wall turbulence. [Preview Abstract] |
Sunday, November 23, 2008 8:26AM - 8:39AM |
AA.00003: Direct numerical simulations of reacting boundary layers Lian Duan, M. Pino Martin Direct numerical simulations (DNS) of turbulent boundary layers\footnote{Mart\'in \& Candler, Phys. Fluids, vol. 10, pp. 11715-1724, 1998}\footnote{Mart\'in \& Candler, AIAA Paper 2001- 2717} show that there is a strong coupling between temperature fluctuation and chemical composition. Small temperature fluctuations result in large fluctuations in the chemical composition of the gas. The maximum fluctuation levels occur when the reactions are exothermic, right at the surface, where the coupling with the surface chemistry is important. In this work, we conduct DNS of reacting turbulent boundary layers, including non-catalytic, partially catalytic and fully catalytic wall conditions, and we explore the feedback mechanisms between the surface reactions at the wall, near-wall gas phase chemistry, and turbulent boundary layer. [Preview Abstract] |
Sunday, November 23, 2008 8:39AM - 8:52AM |
AA.00004: Effect of heat transfer on turbulent boundary layers Izaak Beekman, M. Pino Martin We use direct numerical simulation to gather a database of hypersonic turbulent boundary layers at different flow conditions varying heat transfer. A statistical description of the data is given, including the effect of wall-temperature condition on fluctuation levels, Reynolds stresses, energy and vorticity budgets, Reynolds analogies, skin friction, wall- pressure loading, and entrainment. Additionally, the turbulence structure is visualized and characterized. [Preview Abstract] |
Sunday, November 23, 2008 8:52AM - 9:05AM |
AA.00005: LES of Turbulent Channel Flow at Large $Re_{\tau}$ Daniel Chung, Dale Pullin Large-eddy simulation (LES) of turbulent channel flow will be discussed. A special near-wall, subgrid-scale (SGS) model is developed based on wall-normal averaging of the streamwise momentum equation and local inner scaling combined with an extended form of the stretched-vortex, subgrid-scale (SGS) model. The latter incorporates production of Reynolds shear stress produced by the winding of streamwise momentum by near-wall, attached, SGS vortices. This then allows calculation of an instantaneous slip velocity that is then used as a ``virtual-wall'' boundary condition for the LES within the log region. A K\'arm\'an-like constant is calculated dynamically as part of the LES. With this closure, LES of turbulent channel flow will be presented for $Re_{\tau}$ in the range $2\,\times 10^3$ -- $2\,\times 10^7$. [Preview Abstract] |
Sunday, November 23, 2008 9:05AM - 9:18AM |
AA.00006: Comparison between turbulent boundary layers and channels from direct simulation Javier Jimenez, Sergio Hoyas, Mark P. Simens, Yoshinori Mizuno Results are presented from a new simulation of the ZPG turbulent boundary layer at $Re_{\theta}=1000-2100$, and compared to turbulent channels at similar Reynolds numbers. Even the low order statistics differ between the two flows, including within the buffer layer. The pressure and the transverse velocity fluctuations are stronger in boundary layers, even if the wall-parallel scales derived from the spectra and the two-point correlations are similar in both cases. On the other hand, the streamwise fluctuation intensities are roughly similar in both flows, but their scales are shorter and narrower in boundary layers. The differences are traced to an excess of turbulent energy production in the outer part of the boundary layer, compared to channels, associated with the stronger wake component of the mean velocity profile. Most of this excess is compensated by stronger pressure fluctuations and by the pressure-strain term, which redistribute the energy to the transverse components. The differences persist in higher Reynolds numbers experiments, suggesting caution in mixing results from different flows when documenting,for example, Reynolds number effects. [Preview Abstract] |
Sunday, November 23, 2008 9:18AM - 9:31AM |
AA.00007: Simulations of High-Reynolds Number Turbulent Boundary Layers Philipp Schlatter, Qiang Li, Geert Brethouwer, Arne V. Johansson, Dan S. Henningson Direct and large-eddy simulations (DNS and LES) of spatially developing turbulent boundary layers under zero pressure gradient up to relatively high Reynolds numbers ($Re_{\theta}$ = 3000 and above) are performed. The computational quantities include the velocity plus passive scalar fields at Prandtl numbers between 0.2 and 2. The inflow is located at $Re_{\delta^*}$ = 450, a position where natural transition to turbulence can be expected. In addition to fully-resolved DNS, several carefully validated and promising subgrid-scale closures shall be applied together with a well-resolved, spectral numerical method. The results are extensively compared to available measurements, e.g. the ones obtained by \"Osterlund et al. (1999). Additionally, quantities difficult or impossible to measure, e.g. pressure fluctuations and complete Reynolds stress budgets, shall be presented. The goal of the project is to provide the research community with reliable numerical data for high- Reynolds number, spatially evolving wall-bounded turbulence. In addition, it shall be shown that with today's computer power Reynolds numbers relevant for industrial application can be within reach for DNS/LES. [Preview Abstract] |
Sunday, November 23, 2008 9:31AM - 9:44AM |
AA.00008: Analysis of vortical structures in highly compressible turbulent boundary layers Matteo Bernardini, Sergio Pirozzoli, Francesco Grasso The coherent vortical structures in spatially developing supersonic turbulent boundary layers are analyzed by means of direct numerical simulation of the compressible Navier-Stokes equations. Three Mach numbers, M=2,4,6 are investigated to get some insight into the effect of flow compressibility on the size, orientation, and strength of the structures. To capture even the finest scale structures a very small grid spacing is used, corresponding to 4.5 wall units both in the streamwise and the spanwise directions. For all test conditions the same qualitative behavior is observed: consistent with incompressible dynamics, the near-wall layer is found to consist of quasi-streamise vortices strongly associated with meandering, low-speed streaks. In the outer layer, the vortex orientation statistics are consistent with the occurrence (at least in statistical sense) of ring-like vortices oriented at a shallow angle with respect to the wall plane. Good scaling of the vortex with wall properties is observed, even for the stronger Mach numbers. The analysis of the dilatation field show the onset of turbulence shocklets starting at M=4. Shocklets are found to be more intense in the very-near wall region, and to be statistically associated with sweeps of high-momentum fluid towards the wall. [Preview Abstract] |
Sunday, November 23, 2008 9:44AM - 9:57AM |
AA.00009: ABSTRACT WITHDRAWN |
Sunday, November 23, 2008 9:57AM - 10:10AM |
AA.00010: Statistical properties for homogeneous isotropic turbulence and turbulent channel flows using a coherent structure function Hiromichi Kobayashi, Yasuhiro Tominaga, Taisuke Kubota, Mamoru Tanahashi, Toshio Miyauchi Coherent structures in turbulence are usually extracted by the second invariant of a velocity gradient tensor. Coherent fine scale eddies can be scaled by the Kolmogorov microscale and the rms of the velocity fluctuation, and the scaling is universal in homogeneous isotropic turbulence, turbulent channel flows and turbulent mixing layers. On the other hand, a coherent structure function is defined as the second invariant normalized by the magnitude of the velocity gradient tensor. The coherent structure function $F_{CS}$ extracts the statistical properties of turbulent flow fields, and has been successfully used to a local subgrid-scale model for complex geometries. Since the $F_{CS}$ has distinct upper and lower limits, it may be convenient to use $F_{CS}$ rather than the second invariant whose magnitude depends on Reynolds number. The statistical properties of $F_{CS}$ are shown with outstanding DNS databases for homogeneous isotropic turbulence and turbulent channel flows. [Preview Abstract] |
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