Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session A29: Turbulence Simulations |
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Chair: Lian-ping Wang, University of Delaware Room: Georgia World Congress Center B401 |
Sunday, November 18, 2018 8:00AM - 8:13AM |
A29.00001: Dynamics of the decay of an isolated sphere of turbulence Ke Yu, Timothy E Colonius, Dale I. Pullin We perform direct numerical simulation and large eddy simulation of an initially spherical region of turbulence evolving in free space. The computations are preformed with a lattice Green’s function method, which allows the exact free-space boundary conditions to be imposed on a compact vortical region. The initial condition is spherically windowed, forced, isotropic turbulence. We study the statistics of the decaying region of turbulence as a function of radius and time. The boundary develops intermittency and features occasional ejections of vortex rings. |
Sunday, November 18, 2018 8:13AM - 8:26AM |
A29.00002: Near wall patch representation of wall bounded turbulence Sean Carney, Bjorn Engquist, Robert D Moser Wall bounded turbulent flows at high Re are characterized by the separation of scales between the near-wall eddies and the larger structures farther away from the wall. It is well known that there is a near-wall autonomous cycle of self-sustaining mechanisms whose existence does not depend on the outer layer (Jimenez et al., JFM Vol. 389). In addition, there is evidence that the large scale structures in the outer layer modulate the inner layer turbulence (Marusic et al., Science Vol. 329). Lastly, recent work by Lee et al. (JFM Vol. 774) suggests that the small-scale dynamics of the near-wall region are Re independent. With these works in mind, we formulate numerical simulations of near-wall turbulence in a small domain localized to the boundary, whose size scales in viscous units. The primary goal is to accurately capture the small scales in the near-wall region, which we assess by comparing our statistics to those of a posteriori filtered DNS. To mimic the environment in which the small-scale near-wall turbulence evolves, our formulation accounts for the flux of mean momentum and turbulent kinetic energy through the upper boundary of the domain. We discuss the degree to which our formulation successfully describes near-wall dynamics, and its utility in a wall-modeled LES. |
Sunday, November 18, 2018 8:26AM - 8:39AM |
A29.00003: Generalized quasi-linear simulation of plane Poiseuille flow Colleen B. Kellam, Brandon P Montemuro, Steven Tobias, Gregory Chini Quasi-linear (QL) simulations of shear-driven turbulence have gained popularity in recent years. Under the QL approximation, each flow field is decomposed into a suitable (e.g. streamwise) mean plus fluctuation component, and fluctuation/fluctuation nonlinearities are retained only where they feed back upon the mean fields. Marston et al. (Phys. Rev. Lett., 116, 2016) introduced the generalized quasi-linear (GQL) approximation to improve the accuracy of QL simulations relative to full direction numerical simulations (DNS). The GQL reduction is achieved by separating the flow variables into low and high modes via a spectral filter rather than by decomposition into a strict mean and fluctuations. Nonlinear coupling among the high modes is retained only where this coupling projects onto the dynamics of the low modes, which are allowed to undergo fully nonlinear interactions. Here, the accuracy and efficiency of GQL simulations of turbulent channel flow are evaluated relative to DNS and to QL simulations. Remarkably, retention of only a few low GQL modes is shown to increase accuracy dramatically. To increase computational efficiency, sideband truncations, in which only a localized band of high modes is retained, are explored. |
Sunday, November 18, 2018 8:39AM - 8:52AM |
A29.00004: On the convergence of statistics in simulations of stationary turbulent flows Yasaman Shirian, Jeremy Horwitz, Ali Mani When performing computational simulation of any statistically stationary chaotic phenomenon, before reporting statistics, it is important to ensure that the simulations are time-converged. This condition is needed for rigorous reporting of the mean quantities by allowing a fair estimation of statistical error. In this work we consider homogeneous and isotropic turbulence as a model problem to investigate statistical convergence over finite simulation times. Specifically, we investigate the time integration requirements that allow meaningful reporting of the statistical error associated with finiteness of the temporal domain. We present our results in the context of the law of large numbers and central limit theorem. Given these two consideration we address two key questions: 1) How long should a simulation be performed in terms of large eddy time so that sufficient data samples are collected? 2) What is the appropriate range of sampling frequency in large eddy time units? |
Sunday, November 18, 2018 8:52AM - 9:05AM |
A29.00005: Comparative Analysis of Hybrid Turbulence Models Ryan Kelly, Harry Aquino, Aleksandar Jemcov A numerical study was performed to evaluate two dynamic hybrid models (DHM). The two DHM's investigated are based upon Speziale's damping function and a function based on the turbulent kinetic energy spectrum. Each model computes a sub-filter turbulent viscosity defined by combining a local effective filter length scale with a standard two-equation turbulent viscosity formulation. The efficiency of the DHM is attributed to the dynamic calculation of the sub-filter cutoff length scale. Evaluation of the hybrid turbulence models was performed by simulating backward facing step using three varying grid resolutions. All simulations were executed using the open source solver CAELUS. Effectiveness of each model was established using experimental measurements along with LES and DNS solutions available in the literature. Additionally, DES, DDES, and IDDES simulations were executed to show consistency with current hybrid models. It was shown that the dynamic hybrid turbulence models demonstrated a consistency the existing hybrid models in the fine grid limit as well as an increase in model effectiveness as the grid was coarsened. |
Sunday, November 18, 2018 9:05AM - 9:18AM |
A29.00006: Numerical characterization of the von-Kármán swirling flow with a moving Immersed Boundary Method M. Houssem Kasbaoui, Fabrizio Bisetti We conduct simulations of the von-Kármán flow at various Reynolds numbers. The flow is driven by blades mounted on counter-rotating top and bottom disks in a cylindrical enclosure. The configuration results in highly anisotropic turbulence with persistent large-scale coherent structures. The simulation strategy relies on a low mach flow solver coupled with a moving immersed boundary method. We vary the Reynolds number from 55 to 4000 by increasing the rotation rate of the disks. In the laminar regime, the flow exhibits an axisymmetric steady state. As we increase the Reynolds number, the flow symmetries break down and an anisotropic turbulent flow eventually establishes. |
Sunday, November 18, 2018 9:18AM - 9:31AM |
A29.00007: Spiral vortex structure and energy spectrum in the Super Typhoon Masaki Matsui, Kiyosi Horiuti This study aims to elucidate the detailed structure of Super Typhoon using numerical data generated by Cloud Resolving Storm Simulator (SFA0457). In typhoons, tube in core region (eye) is wrapped by spiralling vortex sheets (rain bands). In homogeneous turbulence (HT), similar spiral vortex was identified (Horiuti and Tamaki 2013), whose vorticity along the sheet is either parallel (Mode 1) or perpendicular (Mode 3) to the tube. Mode 1 and 3 induce -5/3 and −7/3 energy spectrum, respectively. In SFA0457, it is shown that vertical and horizontal vorticities dominate in the eye and rain band regions, respectively. Formation of this Mode 3 configuration is similar to HT. Stagnation flow caused by dual sheets converges to form recirculating flow, which stretches the sheets. Vortex tube is formed by axial straining and lowering of pressure. By differential rotation, neighboring vortex sheets such as rain front are entrained by tube and form spiral turns. The energy spectrum is extracted by scaling of velocity field induced by the tube. Azimuthal velocity obeys power-law of the distance from the center as u_{}_{θ } ∼ r^{- -β} (Pirozzoli 2012). In SFA0457, β≈1/3 and the slope in energy spectrum is determined as (-3+2β=) -7/3, which is consistent with the spectrum induced by Mode 3 spiral vortex. |
Sunday, November 18, 2018 9:31AM - 9:44AM |
A29.00008: Subgrid scale structure of turbulence subject to surface wave straining Kuanyu Chen, Minping Wan, Lian-Ping Wang, Shiyi Chen |
Sunday, November 18, 2018 9:44AM - 9:57AM |
A29.00009: Abstract Withdrawn Direct numerical simulations of turbulent Couette-Poiseuille flows (CP-flows) are performed to examine the effects of the moving wall on the turbulent characteristics. As the moving wall velocity on the top wall systematically increases, the mean shear rate (thus, friction Reynolds number) on both walls increases and the logarithmic layer is established on the top wall, whereas it is shortened on the bottom wall. Furthermore, inspection of the turbulent intensities and Reynolds shear stress shows that the turbulent activity increases near the moving wall and decreases near the stationary wall with an increase of the Reynolds number. Comparison of the energy spectrum with dataset from turbulent Poiseuille flows at similar Reynolds numbers suggests that the unique features in the CP-flows dominantly come from the shift of the wall-normal location for the zero mean shear to the bottom wall. The increase of the negatively signed shear layer on the top wall leads to active development of large-scale motions in the outer layer, whereas it is not on the bottom wall. |
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