Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session B29: Interfaces and MixingInvited Live Streamed

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Sponsoring Units: DFD Chair: Nikolaus Adams, Tech Univ Muenchen Room: McCormick Place W190B 
Monday, March 14, 2022 11:30AM  12:06PM 
B29.00001: Interface dynamics in ideal and realistic fluids Invited Speaker: Snezhana I Abarzhi Interface and mixing and their nonequilibrium kinetics and dynamics couple micro to macro scales. They are ubiquitous to occur in fluids, plasmas and materials, over scales of celestial to atoms. The understanding of interfaces and mixing has crucial importance for science, mathematics and technology. Stellar evolution, plasma fusion, reactive fluids, purification of water, and nanofabrication are a few examples of many processes to which dynamics of interfaces is directly relevant. This talk yields the theory of interface stability to rigorously solve a singular boundary value problem at a freely evolving unstable discontinuity – a task even more challenging than the Millennium problem on the NavierStokes equation. We directly link the structure of macroscopic flow fields with microscopic interfacial transport, quantify the contributions of macro and micro stabilization mechanisms to interface stability, and discover fluid instabilities never previously discussed. In ideal and realistic fluids, the interface stability is set primarily by the interplay of the macroscopic inertial mechanism balancing the destabilizing acceleration, whereas microscopic thermodynamics create vortical fields in the bulk. By linking micro to macro scales, the interface is the place where balances are achieved. Scaleinvariant dynamics of unstable interfacial mixing belongs to a special selfsimilar class. 
Monday, March 14, 2022 12:06PM  12:42PM 
B29.00002: Kadanoff Prize (2022): TBD Invited Speaker: K. R Sreenivasan TBD 
Monday, March 14, 2022 12:42PM  1:18PM 
B29.00003: Impact of Numerical Hydrodynamics in Coarse Grained Simulations of Turbulent Material Mixing Invited Speaker: Fernando F Grinstein Underresolved simulations are typically unavoidable in high Reynolds (Re) and Mach (Ma) number turbulent flow applications at scale. Implicit LargeEddy Simulation (ILES) often becomes the effective strategy to capture the dominating effects of convectively driven flow instabilities. ILES modeling can be based on effectively codesigned physics and numerics solving the compressible conservation equations with nonoscillatory finitevolume algorithms. We evaluate distinct numerical strategies for ILES and assess their impact simulating onset, development, and decay of turbulence: i) the HartenLaxvan Leer (HLL) Riemann solver applying Strang splitting and a LagrangeplusRemap formalism to solve the directional sweep; ii) the HartenLaxVan LeerContact (HLLC) Riemann solver using a directionally unsplit strategy and parabolic reconstruction; and iii) the said unsplit scheme with added LowMa Correction (LMC) – denoted unsplit*. The LMC addresses the problem of excessive leading numerical dissipation ~1/Ma associated with upwinding critical in many applications of interest where most of the mixing actually occurs where the flow is weakly compressible. Modified equation analysis, a technique for generating approximate equations for the computed solutions, is used to elucidate the subgrid models associated with the algorithms underlying ILES. Fundamental case studies considered in this presentation include, homogeneous isotropic turbulence, the TaylorGreen Vortex, RayleighTaylor flow, and shocktube studies. For given spatiotemporal grid resolution, significantly more accurate predictions (reduced numerical uncertainties) are provided by the unsplit discretizations, specially when augmented with the LMC. Relevant comparisons of ILES based on Euler and NavierStokes equations are presented. Overall, the unsplit* reveals instrumental in capturing the spatiotemporal development and their validation on coarser grids. 
Monday, March 14, 2022 1:18PM  1:54PM 
B29.00004: A dual scale LES model for interface dynamics Invited Speaker: Marcus Herrmann While significant progress has been made in the past decade to predict atomization using detailed numerical simulations, these come at significant computational cost since the range of scales that must be resolved exceeds those of a single phase turbulent flow significantly. A switch to a Large Eddy Simulation (LES) approach would be desirable, however, the underlying assumption of LES methods that the dynamics of the unresolved subfilter scale can be inferred from the resolved scales is questionable when atomization occurs. Similar to viscosity in singlephase flows, surface tension scales with the inverse of a lengthscale, but unlike viscosity, it can act to either dissipate surface corrugations preventing breakup, giving rise to the Hinze scale, or enhance surface corrugations due to the RayleighPlateau instability, resulting in breakup. Which process is dominant on the subfilter scale seems to depend entirely on the subfilter interfacial geometry, i.e., if the interface is in the shape of ligaments, the surface tension can lead to breakup, whereas in other cases, surfacetension forces can inhibit breakup. Unfortunately, the subfilter geometry cannot be inferred from the filtered interfacial geometry alone. LES approaches going beyond the traditional singlephase cascade hypothesis may be required for twophase flows with atomization. 
Monday, March 14, 2022 1:54PM  2:30PM 
B29.00005: Beyond RichtmyerMeshkov Instability Invited Speaker: Peter Vorobieff RichtmyerMeshkov instability (RMI) develops on an impulsively accelerated, initially perturbed density interface in fluid. The stability problem for such an interface can be initially considered using the same simplifications as KelvinHelmholtz and RayleighTaylor instabilities: ideal fluid, two dimensions, small perturbations. This work was carried out by R.D. Richtmyer in the late 1950s, and the first experimental observations of RMI were published by E.E. Meshkov in the 1960s. Since then, major progress was made in understanding RMI, which is relevant to a large number of problems, from astronomy to engineering. The focus of this talk is on many of these problems where the classical formulation fails to describe either the complexity of the situation or the dominant instability mechanism. An important case of the former is shock interaction with a multiphase medium, where a macroscopic density interface may not exist, but volumeaveraged density is nonuniform. Such an interaction can lead to vortex formation due to shockdriven multiphase instability (SDMI). An example of the latter (dominant instability) is shock interaction with a planar density interface at an angle to the plane of the shock. Vorticity deposition mechanism in this case is the same as for RMI, but it results in formation of a vortex sheet developing into shockdriven KelvinHelmholtz instability. We discuss the possibility of formulating a generalized framework for these problems, including introduction of dimensionless parameters and scale selection mechanisms. 
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