Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session Q18: Compressible Turbulence |
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Chair: Ivan Bermejo-Moreno, USC Room: 400 |
Tuesday, November 26, 2019 7:45AM - 7:58AM |
Q18.00001: Compressibility Effects in High Speed Turbulent Shear Layers — Revisited Kristen Matsuno, Sanjiva Lele In the past few decades, several models have been proposed to capture the consequences of compressibility on turbulence in shear flows. However, current explanations of reduced growth rates and alterations to turbulence structure with increasing Mach number remain somewhat incomplete, and comprehensive theory and modeling is elusive. In this work, compressible mixing layers over a range of convective Mach numbers ($M_c \in [0.2,2.0]$) and free-stream density ratios ($\frac{\rho_2}{\rho_1}=[\frac{1}{7},1,7]$) are directly simulated and compared to previous work. Using this database, the effect of $M_c$ on key mechanisms in the evolution of turbulent kinetic energy (TKE) such as the pressure-dilatation correlation and the baropycnal work term are presented. The well-known effects of increasing compressibility on turbulent lengthscales and anisotropy are also demonstrated. Fluctuating velocity fields are decomposed into solenoidal and dilatational components via a Helmholtz decomposition, and resulting Reynolds stress components display cancellations in the transverse direction. Pressure fluctuations are analyzed to characterize acoustic communication across vortical structures. [Preview Abstract] |
Tuesday, November 26, 2019 7:58AM - 8:11AM |
Q18.00002: Investigating the dynamics of vorticity and strain rate in compressible turbulent flows Nishant Parashar, Sawan S Sinha, Mohammad Danish, Balaji Srinivasan We examine the effect of compressibility on vorticity and strain rate dynamics for compressible turbulent flows. For this, we employ direct numerical simulations of decaying compressible isotropic turbulent flows. A Lagrangian particle tracker is used to identify the influence of compressibility on vorticity-strain rate dynamics. Time correlations between the instantaneous vorticity vector and the strain-rate eigenvector system are calculated using the Lagrangian history of fluid particles. We show that while the statistics obtained are independent of turbulent Mach number, they are found to be significantly influenced by the locally normalized dilatation rate. Further, we study the time correlations conditioned on local flow topologies (based on invariants of the velocity gradient tensor) as well. We find that the influence of dilatation rate is predominantly associated with rotation dominated flow topologies (unstable-focus-compressing and stable-focus-stretching). At last, we provide a physical explanation of all these observations by tracking the moment of inertia and angular momentum history of tetrahedral fluid elements. [Preview Abstract] |
Tuesday, November 26, 2019 8:11AM - 8:24AM |
Q18.00003: Influence of compressibility on lifetimes of topologies in turbulent flows Sawan Sinha, Nishant Parashar, Balaji Srinivasan Flow field topologies are categorized based on the nature of eigenvalues of the local velocity gradient tensor. Physically, these topologies are suggestive of the relative importance of the local strain-rate and the rotation rate-tensors. The question that how long a given topology lasts in a turbulent flow field is of fundamental importance in geophysical and astrophysical flows. It has been reported in literature that while in the former, this quest is linked to the process of raindrop formation, in the latter, the question finds its significance in context of star formations. While some earlier attempts have been made to estimate the lifetimes of topologies using surrogate methods like the conditional mean trajectories (CMT), in this work we take a more direct approach and accurately estimate topology lifetimes using well resolved direct numerical simulation data in conjugation with a Lagrangian particle tracker. In particular, we investigate and explain how initial turbulent Mach number and local dilatation rate tends to influence the lifetimes of various topologies in a compressible turbulent flow field. Finally, some modeling implications of these findings are also presented. [Preview Abstract] |
Tuesday, November 26, 2019 8:24AM - 8:37AM |
Q18.00004: Multiscale analysis of passive scalar transfer in compressible isotropic turbulence Jianchun Wang, Minping Wan, Chenyue Xie, Qinmin Zheng, Xiaoning Wang, Jian Teng, Lian-Ping Wang, Shiyi Chen Inter-scale transfer of a passive scalar in stationary compressible isotropic turbulence is studied by numerical simulations at a Taylor Reynolds number of approximately 250, and at turbulent Mach numbers of 0.4 and 1.0. The -5/3 scaling behavior is identified for the fluctuation spectrum of passive scalar, with the Obukhov-Corrsin constant close to that of a passive scalar spectrum in incompressible turbulence. The average subgrid-scale (SGS) flux of passive scalar normalized by the total dissipation rate is close to 1 in the inertial range. It is shown by Helmholtz decomposition that the SGS flux of passive scalar is dominated by the solenoidal mode of velocity field. Moreover, the effect of local compressibility on the SGS flux of passive scalar is investigated by conditional averaging with respect to the filtered velocity divergence. A discrete approximate deconvolution model (DADM) is proposed to reconstruct the SGS flux of passive scalar from the filtered flow fields. Numerical results show that the SGS flux of passive scale reconstructed by DADM is in good agreement with the real SGS flux of passive scalar. [Preview Abstract] |
Tuesday, November 26, 2019 8:37AM - 8:50AM |
Q18.00005: Solenoidal scaling laws for compressible mixing John Panickacheril John, Diego A Donzis, Katepalli R Sreenivasan Mixing of passive scalars in compressible turbulence does not obey the same classical Reynolds number scaling as its incompressible counterpart. In this work we first show from a large database of direct numerical simulations that even the solenoidal part of the velocity field fails to follow the classical incompressible scaling when the forcing includes a substantial dilatational component. Though the dilatational effects on the flow remain significant, our main results are that both the solenoidal energy spectrum and the passive scalar spectrum scale assume incompressible forms, and that the scalar gradient aligns with the most compressive eigenvalue of the solenoidal part, provided that only the solenoidal components are used for scaling in a consistent manner. Minor modifications to this result are also pointed out, in particular the interaction of scalar field with the dilatational part of flow field. Two parameters that are found to be important in compressible mixing are the ratio of dilatational to solenoidal rms velocities and the turbulent Mach number, whose role in mixing will also be discussed. [Preview Abstract] |
Tuesday, November 26, 2019 8:50AM - 9:03AM |
Q18.00006: Reproducing the local characteristics of compressible turbulent flows at a low cost: derivation and application Guillaume Beardsell, Guillaume Blanquart When performing Direct Numerical Simulations (DNS) of highly turbulent reacting flows, it is often prohibitively expensive to simulate complete flow geometries. For example, simulations of turbulence-flame interactions usually do not capture the full combustor, and instead focus on a specific portion of the domain, e.g. the region around the flame front. However, by doing so, one misses turbulent kinetic energy injection due to shear by the large scales. In the present work, we include these large-scale contributions, e.g., from experimental data, and we solve for the small-scale components only. The resulting equations are the same as the original compressible Navier-Stokes equations, except for the introduction of additional terms involving the large-scale flow features, which appear as forcing terms. This approach allows us to achieve high turbulent Reynolds numbers while keeping the computational cost reasonable. We have already applied this strategy to incompressible flows, but not to compressible ones, where special care must be taken regarding the energy equation. Using the finite-difference solver NGA, we apply this framework to simulations of homogeneous turbulence and premixed flames. We provide comparisons with results obtained with other forcing schemes. [Preview Abstract] |
Tuesday, November 26, 2019 9:03AM - 9:16AM |
Q18.00007: The Interaction of a Homogeneous Field of Acoustic Waves with a Shock Wave Yuchen Liu, Lian Duan Direct numerical simulations (DNS) and linear interaction analysis (LIA) are used toexamine the significant flow characteristics associated with a homogeneous field ofacoustic waves passing through a nominally normal shock wave. The full-fledgednonlinear simulations and the linear analysis are enabled by a pre-cursor numericaldatabase of boundary-layer acoustic radiation that provides incident acoustic fields withhigh degree of physical realism and applicability. The research contributes to thefundamental understanding of the interaction of a shock wave with a field of turbulenceby characterizing its behaviors in the pure dilatational limit and complements existingstudies of shock/turbulence interaction with a vorticity-dominated incident turbulentfield. [Preview Abstract] |
Tuesday, November 26, 2019 9:16AM - 9:29AM |
Q18.00008: Tracking of flow structures in shock-turbulence interaction Jonas Buchmeier, Alexander Bussmann, Xiangyu Gao, Ivan Bermejo-Moreno A tracking algorithm is applied to study the time evolution of flow structures, defined as isosurfaces of a field of interest. Correspondences between structures in consecutive time steps are found in a higher dimensional feature space, which includes a geometric signature of the structures, in addition to their spatial information. To allow for larger tracking steps, constraints are used to reject correspondences based on physical realizability. Accepted correspondences are used to dynamically build a graph describing the evolution and interactions of structures over time. Complex split-merge interactions resulting from large tracking steps are handled based on confidence indicators obtained from the search, physical properties and history of the involved structures. The graph is then queried to retrieve statistical information on the evolution of the structures. The algorithm is applied to a shock-capturing DNS of shock-turbulence interaction ($Re_{\lambda}=40$; $M_t=0.1,0.4$; $M=1.5,3.0$). Passive scalar isosurfaces with well-defined initial shapes and turbulence structures based on the Q criterion are tracked across the shock, analyzing relations between local geometry and physical quantities mapped on the surfaces. [Preview Abstract] |
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