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 S33: Flow Instability: Richtmyer-Meshkov, Computational |
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Chair: Peter Vorobieff, University of Minnesota Room: 615 |
Tuesday, November 26, 2019 10:31AM - 10:44AM |
S33.00001: Direct numerical simulation of Richtmyer-Meshkov instability with broadband initial perturbations Michael Groom, Ben Thornber The effects of Reynolds number on the early to intermediate time behaviour of a mixing layer induced by Richtmyer-Meshkov instability (RMI) are investigated through a series of direct numerical simulations (DNS) using the finite-volume code FLAMENCO. This study presents, for the first time, results from direct numerical simulations of RMI evolving from amplitude perturbations containing a broad bandwidth of initial modes. In particular, two different broadband perturbations are analysed, defined by their initial radial power spectra $P(k)=Ck^m$ where $m=-1,-2$. The amplitudes of individual modes are defined such that the total standard deviation of the two perturbations are the same and all modes are initially linear. The DNS results are compared with implicit large eddy simulations (ILES) of the same initial conditions in the high Reynolds number limit, showing that although there is significant suppression of turbulence in the low Reynolds number DNS, the growth in integral width $W$ is higher. This increased growth in $W$ is found to be due to high levels of molecular diffusion, indicating that there are substantial Schmidt number effects present at low Reynolds numbers in RMI mixing layers. [Preview Abstract] |
Tuesday, November 26, 2019 10:44AM - 10:57AM |
S33.00002: Additive Manufacturing and Richtmyer-Meshkov Initial Condition Studies Tiffany Desjardins, Adam Martinez, John Charonko, Kathy Prestridge With the advances in materials and additive manufacturing we have begun to re-explore the application of membranes in RMI experiments. At the Vertical Shock Tube facility, we are using AM techniques to develop shaped membranes for studies of different types of initial interfaces, motivated by the need to explore non-diffuse initial conditions with specific geometrical configurations. The need for understanding of features in applications such as inertial confinement fusion (ICF) drives this work. The goal is the development of a barrier at the initial interface that repeatably breaks, minimally influences the growth of the instability, and can be shaped to look at desired interface configurations. We have found a material fragile enough that when hit with an M $=$ 1.2 shock, it is returned to a near complete dust state. The particles are heavy enough to lag behind the interface region and preliminary experiments studying single modes will be presented. [Preview Abstract] |
Tuesday, November 26, 2019 10:57AM - 11:10AM |
S33.00003: Validation of a Simplified WENO Scheme with Artificial Viscosity for a Shock Interface Interactions Brian Romero, Svetlana Poroseva, Peter Vorobieff The goal of this work is to validate numerical simulation of the shock-driven evolution of an initially axisymmetric cylindrical particle cloud (or a heavy gas column) against laboratory experiments. In the initial conditions in the experiment, there is a density gradient in gas, an average density gradient due to the particle seeding, or both. The cylindrical column is comprised of a mixture of sulfur hexafluoride, acetone, and air, and surrounded by air, leading to the representative Atwood number of 0.61. The Mach number in experiments varied from 1.2 to 2.0. Simulations were conducted at Mach numbers matching the experiment using a simplified WENO scheme incorporating a new C-method for artificial viscosity. The initial modeling/validation exercises featured a two-dimensional simulation of shock interaction with the gas column, with variations in the level of initial diffusion on the density interface – from a sharp interface to a diffuse boundary matching the conditions measured in experiment. Further studies include 3D problems with multiple gas species and immersed boundary conditions, and shock wave refraction for various values of the gas constant $\gamma$. The limit case for comparisons is shock interaction with a solid cylinder. [Preview Abstract] |
Tuesday, November 26, 2019 11:10AM - 11:23AM |
S33.00004: Numerical Simulation of Richtmyer-Meshkov Instability in Converging Geometries Zuoli Xiao, Jinxin Wu A high-order turbulence solver in curvilinear coordinates is developed for numerical simulation of multi-species compressible flows with discontinuities, in which high-order compact finite difference schemes and localized artificial diffusivities are employed to satisfy the need for high accuracy and discontinuity capturing. The Richtmyer-Meshkov instability (RMI) induced mixing flows driven by imploding shock in both cylindrical and spherical geometries are numerically investigated using direct numerical simulation method. The detailed evolutions of RMI are compared with experimental data and theoretical results, and reasonably good consistency is observed both qualitatively and quantitatively before reshock. The vortex dynamics of RMI after shock impingement is also discussed, and the initially deposited circulation on the interface during shock-interface interaction is calculated from the simulation, which is in accordance with the results of theoretical prediction. Moreover, effects of the modes and amplitude of initial perturbations, as well as the incident shock Mach number on the interfacial growth rate are evaluated during the shock implosion and reflection from the center. [Preview Abstract] |
Tuesday, November 26, 2019 11:23AM - 11:36AM |
S33.00005: A Comparison of Two- and Three-Dimensional Single-Mode Reshocked Richtmyer--Meshkov Instability Growth Marco Latini, Oleg Schilling The growth dynamics of two- and three-dimensional single-mode reshocked Richtmyer--Meshkov instability are compared using data from high-resolution implicit LES of a model of the Mach 1.3 air(acetone) and sulfur hexafluoride Jacobs and Krivets shock tube experiment. The numerical amplitude growth is compared to the predictions of several nonlinear instability growth models. The dynamics of reshock are described, and the post-reshock mixing layer amplitude growth rate is compared to the predictions of several reshock models. It is shown that using two-dimensional simulations to understand three-dimensional dynamics is valid only at early-to-intermediate times before reshock. At intermediate-to-late times the three-dimensional growth is larger than the two-dimensional growth. The reshock dynamics are also different between two and three dimensions. [Preview Abstract] |
Tuesday, November 26, 2019 11:36AM - 11:49AM |
S33.00006: Effects of the secondary baroclinic vorticity on turbulent energy cascade in the Ritchmyer--Meshkov instability Naifu Peng, Yue Yang We study turbulent mixing in the Richtmyer--Meshkov instability (RMI) induced by a planar shock wave at Mach $1.5$ with multimode interfacial perturbations between air and SF$_6$. By separating different types of the perturbations, we develop a double-density model for simplifying the RMI, and find that the effects of the secondary baroclinic vorticity (SBV) play an important role during the flow evolution. The SBV, caused by the misalignment of the pressure gradient produced by the velocity perturbation and the density gradient near the interface, leads to the nonlinear evolution of the interface with the generation of spike- and bubble-like structures. Moreover, the SBV produces small-scale vortical structures and affects the turbulent energy cascade in the mixing zone. The kinetic energy spectrum affected by the SBV is closer to the $-3/2$ scaling law than the classical $-5/3$ law for constant-density homogeneous isotropic turbulence. [Preview Abstract] |
Tuesday, November 26, 2019 11:49AM - 12:02PM |
S33.00007: Computational study of the interactions of two bubbles along an interface undergoing the Richtmyer-Meshkov instability Michael Wadas, Eric Johnsen In addition to its prevalence in astrophysics, the shock-driven growth of~interfacial perturbations (the Richtmyer-Meshkov instability, or RMI) has~important practical consequences in applications of fusion research. Our~objective is to numerically investigate the generation of vortex dipoles~that escape the confines of the mixing region, as well as the~reacceleration of bubbles, by focusing on the interaction of two adjacent~bubbles of different sizes subjected to the RMI. Our hypothesis is that~the escape of a vortex dipole can be predicted from the initial conditions~based on the vorticity associated with the bubbles. Simulations are~performed using an in-house, high-order accurate Discontinuous-Galerkin~code. We demonstrate deviations from existing bubble merging models in the~non-linear regime caused by the interaction of adjacent pairs of spikes,~which had not previously been considered. We further develop a criterion~that predicts the regime that will emerge for a given interface. [Preview Abstract] |
Tuesday, November 26, 2019 12:02PM - 12:15PM |
S33.00008: Impulse-driven Richtmyer-Meshkov instability in Hall-magnetohydrodynamics Naijian Shen, Dale Pullin, Vincent Wheatley, Ravi Samtaney We utilize the incompressible, Hall-MHD model for conducting fluids to investigate the effect of Hall current on the stability of an impulsively-accelerated, perturbed density interface, or contact discontinuity (CD) separating two fluids in the presence of a background magnetic field. This is used as a simple model, in a conducting fluid, of a Richtmyer-Meshkov (RM) flow that is characterized in a neutral-fluid by a shock-wave-density-interface interaction. The linearized equations of motion are formulated for a sinusoidal interface perturbation, and then solved as an initial-value problem using a Laplace transform method. The presence of the magnetic field is found to suppress the incipient interfacial growth associated with neutral-gas, RM instability (RMI). When the ion skin depth is finite, the vorticity dynamics that drive the suppression of the RMI differs markedly from the ideal MHD, RM flow. Hall MHD allows the presence of a tangential slip velocity leading to finite circulation deposition at the CD. Vorticity is produced by the perturbed magnetic fields and transported to infinity by a dispersive wave system leading to decay of the velocity slip at the interface with the effect that that interface growth remains bounded but distorted by damped oscillations. [Preview Abstract] |
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