Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session U22: Turbulence: Compressible Flows |
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Chair: Peter Hamlington, University of Colorado Boulder Room: 208 |
Tuesday, November 22, 2022 8:00AM - 8:13AM |
U22.00001: A compressibility correction to k-ω models for hypersonic wall-bounded flows Mustafa Engin Danis, Paul A Durbin In this talk, we introduce a compressibility correction for k-ω models such that the effects of high Mach numbers and wall-cooling are explicitly taken into account. The compressibility correction is validated by a Direct Numerical Simulation database with and without pressure gradient for a range of Mach numbers between 2.5 and 14, and wall-to-recovery temperature ratios between 0.18 and 1. In the present approach, assuming a correspondence between compressible and incompressible eddy viscosity in the near-wall region, we demonstrate that the standard models fail to calculate accurate eddy viscosity profiles for hypersonic turbulent boundary layers with a cold wall. By only modifying the production and destruction terms of the ω-equation, the proposed correction collapses the eddy viscosity profiles on the incompressible eddy viscosity data. This results in significant improvements in velocity, temperature, skin friction, and wall heat transfer coefficient profiles. The present formulation is local and can easily be implemented for any k-ω models in existing codes. |
Tuesday, November 22, 2022 8:13AM - 8:26AM |
U22.00002: Energy spectra in compressible turbulence: regimes and scaling Diego A Donzis, John Panickacheril John, K.R. Sreenivasan The energy spectrum in compressible turbulence is studied systematically using a large direct numerical simulation (DNS) database of forced isotropic compressible turbulence with solenoidal and dilatational forcing. The database comprises a wide range of compressibility conditions. We demonstrate that traditional parameters (Reynolds and turbulent Mach numbers) fail to characterize the complex behavior manifested by the dilatational part of the energy spectrum. We develop a new asymptotic analysis based on two compressibility parameters, Mt and δ the ratio of dilatational to solenoidal root-mean-square velocity. The scaling laws predicted by the asymptotic analysis agree well with the DNS data. Analysis of dominant terms stemming from the asymptotic expansion show a number of different regimes (based on Mt and δ) of compressible turbulence. They include cascade and non-cascade regimes, pseudo-sound, as well as different equipartition regimes. Our analysis further allows us to identify specific spectral behavior in each of these regimes, which are compared to DNS data. All the results are discussed in the context of the δ-Mt plane to reconcile disagreements in the literature. |
Tuesday, November 22, 2022 8:26AM - 8:39AM |
U22.00003: Transition and Multiphysics in 3D ICF Capsule Implosions Fernando F Grinstein, Vincent Chiravalle, Brian M Haines ICF capsules are unique with regards to hydrodynamic instabilities: time-scales are short relative to turbulence development, so understanding the 3D transition is particularly important; 2) as the core heats, viscosity becomes important so that there is not much scale separation between the outer length scale and the viscous dissipation length scale; 3) jetting is a unique and critical phenomenon to ICF applications that arises due to Rayleigh-Taylor instability growth in a thin shell. Experiments at NIF create a new urgency for assessing the new computational paradigms and the verification and validation of their 3D modeling aspects in the research codes. We build on prior ICF simulations work, using a Navier-Stokes based plasma viscosity model in conjunction with LANL’s new xRAGE HLLC hydrodynamics with directionally unsplit algorithms and low-Mach-number correction enabling higher fidelity on coarser grids [1]. We simulate an indirect-drive NIF cryogenic capsule experiment, N170601 [2] requiring multi-group radiation diffusion to transport x-ray energy from the cylindrical Hohlraum to the target capsule. The 3D simulation model involves miscible (gas / plasma Schmidt number ~ 1) material interfaces and 3T plasma physics treatments. We use relatively coarse 2D runs through onset of turbulence, followed by mapping to highly resolved 3D mesh with suitable 3D seed-perturbations. We assess ICF predictions with the new xRAGE numerical hydrodynamics. Challenges coupling 3D hydrodynamics and multiphysics are discussed in this context. [1] Grinstein and Pereira, PoF, 33, 035126, 2021. [2] Haines et al., PoP, 27, 082703, 2020. |
Tuesday, November 22, 2022 8:39AM - 8:52AM |
U22.00004: DNS of compressible turbulent plane Couette flows Jie Yao, Fazle Hussain Direct numerical simulations of compressible turbulent plane Couette flows are performed at two different wall Mach numbers Mw = 0.8 and 1.5 for wall Reynolds numbers up to Rew = 10000. Various turbulence statistics are examined and compared with their incompressible counterparts at comparable semilocal Reynolds numbers. With proper scaling transformations, both the mean velocity and turbulent Reynolds stresses profiles collapse well between the compressible and incompressible cases, with the only exception for the inner peak of the streamwise Reynolds stress – found to increase with increasing Mw. The streamwise and spanwise energy spectra reveal that the size of near-wall structures does not vary with the Mw. Consistent with the observations in incompressible flows, the superstructures (i.e., the large-scale streamwise rollers) with a typical spanwise scale of λz/h ≈ 1.5π become stronger with increasing Rew and contribute about 40% of the Reynolds shear stress at the center of the domain for the highest Rew studied. Interestingly, flow visualization and correlation analysis reveal that the streamwise organization of these structures degrades with increasing Mw. |
Tuesday, November 22, 2022 8:52AM - 9:05AM |
U22.00005: Lagrangian Analysis of the Entrainment Process in a High-speed Turbulent Boundary Layer Reza Jahanbakhshi Direct numerical simulations of zero-pressure-gradient Mach-4.5 turbulent boundary layer (TBL) is preformed to examine the mechanisms of the entrainment process. The two mechanisms by which the outer irrotational flow can be entrained into the turbulent region and their relative contribution to the growth of the spatially developing boundary layer are evaluated: (i) nibbling is the vorticity transport across the turbulent/non-turbulent interface (TNTI), and (ii) engulfment is the entrapment of pockets of irrotational flow inside the TBL prior to finally breaking apart. The analysis involves the temporal advancement (time tracking) of a certain number of fluid particles. At each time step, particle velocity and position vectors are obtained from the three-dimensional DNS data using an interpolating scheme. This approach is more suited to study the entrainment since the turbulence statistics are calculated for the particle trajectories and reflect the actual distance of the fluid particles to the TNTI during the entrainment process. The results highlight the engulfment mechanism as the dominant form of entrainment in a high-speed TBL. |
Tuesday, November 22, 2022 9:05AM - 9:18AM |
U22.00006: Effective Drift Velocity from Turbulent Transport by Vorticity in Compressible Turbulence Shikhar Rai, Hao Yin, Hussein Aluie, Aarne Lees, Dongxiao Zhao, Stephen Griffies, Jessica Shang We analyze turbulence transport generated by strong shocks. Using a systematic non-perturbative expansion due to Eyink [1], we show that unlike strain, which acts as an anisotropic diffusion/anti-diffusion tensor, vorticity's contribution is solely a conservative advection by an eddy-induced non-divergent velocity, v*, that is proportional to the curl of vorticity. Therefore, material (Lagrangian) advection of coarse-grained (in a simulation) or under-resolved (in a lab measurement) quantities is accomplished not by the coarse-grained flow velocity, û, but by the effective velocity, û+v*. The physics of this effective transport is missing from current turbulence models and may aid in the interpretation of data from experiments. |
Tuesday, November 22, 2022 9:18AM - 9:31AM |
U22.00007: Statistics of density gradients in compressible turbulence using quantitative schlieren imaging Hazel T Rivera-Rosario, Naoki N Manzano-Miura, Shikha Shikha, Gregory P Bewley Direct numerical simulations show shock-like structures at turbulent Mach numbers as low as 0.1. Quantifying the conditions that generate these structures is key to understanding their role in natural and engineered settings. In a pressurized vessel, we adjust the speed of sound using different gases including SF6 in order to increase the turbulent Mach number up to 0.15 while holding the Taylor-Reynolds number constant, up to 1000. In this way, we can distinguish between the role of the Reynolds number and Mach number in the development of extreme events. Schlieren imaging reveals density gradients in a turbulent jet, which we quantify by implementing a weak calibration lens. Analyzing the time-varying signals from single pixels of a high-speed camera, we compare the temporal energy spectra and distributions with simulation results from literature. We then present the first visualizations of the turbulent flow and statistics of the density gradient fluctuations at various Mach and Reynolds numbers. |
Tuesday, November 22, 2022 9:31AM - 9:44AM |
U22.00008: Multi-fidelity validation of variable-density turbulent mixing models Britton J Olson, Benjamin Musci, Devesh Ranjan In this study, ensembles of experimental data are presented and utilized to compare and validate two models |
Tuesday, November 22, 2022 9:44AM - 9:57AM |
U22.00009: Modeling and simulation in supersonic carbon dioxide turbulent channel flows Guiyu Cao, Yipeng Shi, Kun Xu, Shiyi Chen The present work focuses on bulk viscosity and multi-temperature effect of carbon dioxide carbon dioxide in supersonic wall-bounded turbulent flows. Mars's atmosphere consists of 95.32% carbon dioxide, for accurate predictions of surface drag and heat flux on Martian vehicles, which is necessary to take the peculiarities of carbon dioxide into account. Different with the dominant diatomic gases nitrogen and oxygen on earth, carbon dioxide is a linear and symmetric triatomic molecular. Two essential ingredients should be addressed for compressible turbulent carbon dioxide flows, the inherit large bulk viscosity (i.e., 1000 times larger than shear viscosity) and the multi-temperature effect arising from the interactions among translational, rotational, and vibrational modes. On above two concerns of carbon dioxide, current research pioneers detailed physical models and simulate supersonic wall-bounded turbulent carbon dioxide flows. Bulk viscosity and multi-temperature effect of carbon dioxide have been modeled in an extended triple-temperature BGK-type equation within the well-established kinetic framework. Numerical simulations show the bulk viscosity and multi-temperature effect of carbon dioxide enlarge the heat transfer and decrease the frictional force. Current research envisions long-term applicability for further Mars exploration. |
Tuesday, November 22, 2022 9:57AM - 10:10AM |
U22.00010: Dynamic multiscaling in stochastically forced Burgers turbulence Sadhitro De, Dhrubaditya Mitra, Rahul Pandit We carry out a detailed study of dynamic multiscaling in the turbulent nonequilibrium, but statistically steady, state of the stochastically forced one-dimensional Burgers equation. We introduce the concept of interval collapse times τcol, the time taken for an interval of length l, demarcated by a pair of Lagrangian tracers, to collapse at a shock. By calculating the dynamic scaling exponent of the order-p moment of τcol, we show that (a) there is not one but an infinity of characteristic time scales and (b) the probability distribution function of τcol is non-Gaussian and has a power-law tail. Our study is based on (a) a theoretical framework that allows us to obtain dynamic-multiscaling exponents analytically, (b) extensive direct numerical simulations, and (c) a careful comparison of the results of (a) and (b). We discuss possible generalizations of our work to dimensions d>1, for the stochastically forced Burgers equation, and to other compressible flows that exhibit turbulence with shocks. |
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