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 PB: Turbulence Simulations IV |
Hide Abstracts |
Chair: J. M. McDonough, University of Kentucky Room: 001B |
Tuesday, November 25, 2008 11:35AM - 11:48AM |
PB.00001: A robust non-dissipative all-mach number scheme for unstructured grids Suman Muppidi, Krishnan Mahesh We are interested in simulations of high speed external flows, and those in scramjet like geometries (of which supersonic jets in crossflow are an example). We are therefore developing an algorithm that solves the compressible equations on unstructured grids using a predictor-corrector approach, a novel scaling for pressure, and a characteristic filter based shock-capturing. Hou and Mahesh (J. Comp. Phys., vol 205) formulated an all-Mach number approach to solve compressible flows on structured grids, that this work has extended to unstructured grids. The attraction of this method is that the compressible Navier Stokes equations naturally revert to Zero-Mach number equations in the incompressible limit (the discrete energy equation results in the divergence-free condition at zero Mach number), avoiding the stiffness in the equations without preconditioning or artificial compressibility. The shock capturing scheme employed in the present algorithm was developed by Park and Mahesh (AIAA paper, 2007-722) for unstructured grids, and is implemented as a predictor-corrector approach. This ensures that shock-capturing is active only in regions of discontinuity, avoiding any dissipation in regions away from shocks. This feature improves the overall accuracy of the simulations. We will present issues regarding the algorithm, its implementation, and some example results/simulations. [Preview Abstract] |
Tuesday, November 25, 2008 11:48AM - 12:01PM |
PB.00002: Numerical simulation of the thermal effect of a laser--induced plasma on isotropic turbulence Shankar Ghosh, Krishnan Mahesh The interaction of a laser--induced plasma with isotropic turbulence is studied using numerical simulations. The simulations use air as the working fluid and assume local thermodynamic equilibrium. The numerical method is fully spectral and uses a shock capturing scheme in a corrector step. Turbulent Reynolds number $ Re_\lambda = 30 $ and fluctuation Mach numbers $M_t = 0.001$ and $0.3$ are considered. $M_t$ of $0.001$ is chosen to correspond to low speed experiments (e.g. Comte--Bellot and Corrsin 1971). Here, the shock wave propagates on a much faster time--scale compared to the turbulence evolution. The turbulence ahead of the shock is therefore almost frozen. At $M_t$ of $0.3$ the time--scales of the shock wave are comparable to that of the background. In both cases, the mean flow has a significant effect on the turbulence. The effect of the turbulence on the time scale of shock formation and the shock velocity and distortion is studied. The turbulence experiences strong compression due to the shock wave and strong expansion in the core. Turbulence intensities are enhanced and suppressed due to the effects of compression and expansion respectively. This behavior is spatially inhomogeneous and non--stationary in time. Spatial and one--point temporal statistics are discussed. Also kinetic energy budgets are computed and will be discussed. [Preview Abstract] |
Tuesday, November 25, 2008 12:01PM - 12:14PM |
PB.00003: DNS of Decaying Compressible Turbulence Using Gas Kinetic Scheme Wei Liao, Yan Peng, Li-Shi Luo, Robert Rubinstein We apply the gas-kinetic scheme to direct numerical simulation of decaying compressible turbulence. We compute the kinetic energy $K(t)$, dissipation rate $\varepsilon(t)$, probability density functions (PDFs) of the two-point longitudinal velocity difference, shocklet strength, and local Mach number. Our results reveal the following features of decaying compressible turbulence: (1) With the initial Taylor microscale Reynolds number $\mbox{Re}_\lambda$ fixed, increase of initial turbulent Mach number $\mbox{Ma}_{\rm t}$ leads to an increase of the dissipation rate $\varepsilon$ at the initial stage; (2) Change of $\mbox{Ma}_{\rm t}$ has little effect on $K(t)$ and the long-time asymptotics of $\varepsilon(t)$; (3) At the lower $\mbox{Ma}_{\rm t}$ ($\approx 0.1$), intermittency persists, while at the higher $\mbox{Ma}_{\rm t}$ ($\approx 0.5$), intermittency quickly dissipates, \emph{i.e.}, the PDF of the two-point longitudinal velocity difference becomes Gaussian independent of the separation distance $\delta r$; and (4) the PDF's of both shock strength and the local Mach number all appear to follow scaling laws. [Preview Abstract] |
Tuesday, November 25, 2008 12:14PM - 12:27PM |
PB.00004: Direct simulation of a turbulent channel with wire in cross flow Reetesh Ranjan, Carlos Pantano, Paul Fischer, Andrew Siegel We present results from a direct numerical simulation study of turbulent channel flow across a thin, cylindrical wire. This model mimics flow through the wire-wrapped fuel pins typical of most fast neutron reactor designs. Mean fow develops both along the wire and across the wire, leading to the formation of a turbulent cross-flow regime in the channel. The friction Reynolds number in the axial direction is approximately 303. Cross-flow friction Reynolds numbers ranging from 0 to 115 are examined for several wire-diameter to channel height ratios. The numerical method uses spectral elements in the plane perpendicular to the wire axis and a Fourier decomposition in the direction of the axis of the wire. The simulations use up to 78 million collocation points and were performed at the Argonne Leadership BG/P supercomputer. The flow field statistics are investigated, including mean flow, turbulence statistics and instantaneous flow structures. Shear stress distributions on the walls, and in particular along the recirculation zones behind the wire, are also investigated. Implications of these results for large-eddy simulation of turbulent flows with recirculation will be discussed. [Preview Abstract] |
Tuesday, November 25, 2008 12:27PM - 12:40PM |
PB.00005: Lattice Boltzmann and Pseudo-Spectral Methods for Decaying Turbulence Li-Shi Luo, Yan Peng, Wei Liao, Lian-Ping Wang We conduct a comparison of the lattice Boltzmann and the pseudo-spectral methods for DNS of decaying turbulence in a 3D periodic cube. We use a mesh size of $128^3$ and the Taylor micro-scale Reynolds number $24.35 \leq \mbox{Re}_\lambda \leq 72.37$. All simulations are carried out to $t \approx 30 \tau_0$, where $\tau_0$ is the turbulence turnover time. We compare instantaneous velocity $\mathbf{u}$ and vorticity $\mathbf{\omega}$ fields, the energy $K(t)$, the energy spectrum $E(k,\, t)$, the dissipation rate $\varepsilon(t)$, the rms pressure fluctuation $\delta p(t)$, the pressure spectrum $P(k,\, t)$, the skewness, and flatness. Our results show that the LB method compares well with the PS method in terms of accuracy and efficiency: the flow fields and all the statistical quantities, except $\delta p(t)$ and $P(k,\, t)$, obtained from the two methods agree well with each other when the initial flow field is adequately resolved by both methods. Our results indicate that the LB method resolution requirement is $\eta_0 / \delta x \geq 1.0$, where $\eta_0$ and $\delta x$ are the initial Kolmogorov length and the grid spacing, respectively. [Preview Abstract] |
Tuesday, November 25, 2008 12:40PM - 12:53PM |
PB.00006: Lagrangian triangle and tetrad statistics in isotropic turbulence Jason F. Hackl, P.K. Yeung, Brian L. Sawford, Michael S. Borgas We study the displacement statistics of three- and four-particle clusters extracted from direct numerical simulations of three-dimensional isotropic turbulence at Reynolds numbers ranging from \(R_{\lambda} \approx 240\) to 650. These statistics determine the third and fourth moments, respectively, of scalar concentration fields. Our focus is on the nature of non-Gaussian dynamics expressed via the shape factors \(I_i=g_i/R^2,(i=1,2,3)\) which are defined in terms of the eigenvalues \(g_i\) of the moment-of-inertia tensor and the radius of gyration \(R\), which represents the linear size of the cluster. Shape factors computed from clusters with initial sizes in the inertial sub-range approach constant values at intermediate times. The average values obtained, \(\langle I_1 \rangle \approx 0.83\), \(\langle I_2 \rangle \approx 0.16\) and \(\langle I_3 \rangle \approx 0.015\) for four-particle clusters, are insensitive to Reynolds number in the present data range, possibly indicating an approach to self-similar inertial sub-range behavior. These results differ from their respective Gaussian values of 0.75, 0.22 and 0.03. High-order statistics conditioned on cluster size are used to explore the nature and origins of these departures from Gaussian behavior and guide development of maximum-entropy theories of cluster shape. [Preview Abstract] |
Tuesday, November 25, 2008 12:53PM - 1:06PM |
PB.00007: Direct Numerical Simulation of Instabilities in MHD Duct Flows Maxime Kinet, Sergei Molokov, Xavier Albets, Bernard Knaepen Magnetohydrodynamics (MHD) --- which governs the flow of an electrically conducting fluid in presence of a magnetic field --- has applications in the steel industry (where magnetic fields are used to damp or to stir the turbulent motions) and in nuclear fusion devices (i.e. tokamaks). There, the liquid lithium, used as coolant, undergoes the effect of the plasma-confining magnetic field. When a magnetic field is applied perpendicularly to a rectangular duct whose walls are electrically conducting, the Lorentz force strongly modifies the the flow and gives rise to an M shaped velocity profile with two strong jets in the vicinity of the walls parallel to the magnetic field. Because of the important shear they generate, those jets are unstable at sufficiently high Reynolds number. Using Direct Numerical Simulations, we compute the critical Reynolds number as a function of the wall conductivity and the strength of the magnetic field. The frequency and form of the corresponding instabilities are also studied. Finally, turbulence statistics and mean velocity profiles in the fully developed regime are discussed. [Preview Abstract] |
Tuesday, November 25, 2008 1:06PM - 1:19PM |
PB.00008: Direct and Large-Eddy Simulation of Turbulent Flow in a Plane Asymmetric Diffuser by the Spectral Element Method Johan Ohlsson, Philipp Schlatter, Paul F. Fischer, Dan S. Henningson Turbulent flow in a plane asymmetric diffuser is simulated by the spectral element method (SEM) as a direct numerical simulation (DNS) and with large-eddy simulation (LES) using an adapted version of the dynamic Smagorinsky model. The SEM, which is a high-order numerical method, has opened the possibility to accurately simulate fluid phenomena known to be very sensitive to numerical discretization errors, e.g. flows exhibiting separation. In addition, SEM exhibits favorable parallelization properties. Due to the development of tools for numerical stabilization specific for SEM, SEM is now suitable for turbulence simulations at moderate to high Reynolds numbers. Results from investigations on the influence of such stabilization tools are presented. For the turbulent diffuser flow case, results are presented for Re=4,500 and Re=9,000 (based on bulk velocity and channel half-height) and compared to results by Herbst et al. (2007). Quantities of interest include e.g. the size of the separation bubble and turbulent stresses. [Preview Abstract] |
Tuesday, November 25, 2008 1:19PM - 1:32PM |
PB.00009: Large-eddy simulations of flow around a circulation control airfoil Seonghyeon Hahn, Karim Shariff Circulation control, proposed in NASA's Cruise Efficient Short Take-off and Landing (CESTOL) concept, has the potential to increase air-traffic throughput and reduce the noise footprint. Circulation control obtains a substantial increase in lift coefficient by using a wall-jet that blows tangentially on a rounded (Coanda) surface deflected at the trailing edge. The flow has proven to be difficult to reliably predict using Reynolds-averaged models. We undertake large-eddy simulations to better understand underlying mechanisms and create a database for modelers. Simulations are patterned after Novak et al.'s (1987) experiment, which, despite its faults, is the best documented to date. A Reynolds number of 10\^{}6 and two cases with low and high blowing are considered using Stanford's unstructured solver CDP. The upper surface begins with laminar to turbulent transition following a region of weak shear stress. Then strong favorable pressure gradient as the jet slot is approached leads to a raised log-law. There exists a region over the Coanda surface where the mean flow development collapses very well in wall-jet similarity coordinates, indicating that a portion of the near-wall region maintains classical wall-jet characteristics. At the present time, the lower surface has delayed transition due to lack of tripping in the simulations and considerable discrepancies with the experiments for second-order statistics. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700