Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session T27: Flow Instability: Richtmyer-Meshkov and Shock Instabilities |
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Chair: Alexander Ames, Los Alamos National Laboratory (LANL) Room: 251 E |
Monday, November 25, 2024 4:45PM - 4:58PM |
T27.00001: Richtmyer-Meshkov-induced turbulence in shock-tube experiments Sam L Pellone, Tiffany R Desjardins, Filipe Pereira, Alexander M Ames, Adam A Martinez, John J Charonko Experiments of the Richtmyer-Meshkov instability are carried out in a vertical shock tube to investigate the effect of initial conditions on the late-time turbulence and mixing. An initially 2D perturbed interface separating a light fluid from a heavy fluid (air from SF6, Atwood number A ≈ 0.6) is first accelerated by the passage of an incident shock (of Mach number Ms ≈ 1.15 and Ms ≈ 1.25), followed by reshock. State-of-the-art diagnostics are used to measure the density and velocity fields simultaneously at four different downstream visualization windows past the initial shock (3 before reshock, 1 after reshock). Typical quantities characterizing the time evolution of the instability are measured, such as the perturbation amplitude, x-t diagrams, and vorticity fields. At each window, the shots are repeated multiple times at a high-repetition rate (∽ 100 shots per window), providing a unique ensemble data set used to obtain turbulence statistics. |
Monday, November 25, 2024 4:58PM - 5:11PM |
T27.00002: Shock Interaction with Variable Density Grid Turbulence Tiffany R Desjardins, Alexander M Ames, Adam A Martinez Shock tube experiments have studied the effects of initial conditions on Richtmyer-Meskov instability for several decades. Improvements in diagnostics continue to lead to further understanding of the physics of RMI. However, experiments fail to obtain turbulence in a single shock. Reshock experiments aim to reach this turbulent state, but often fall short. This leaves a regime not well studied: turbulent variable density mixing and reshock of turbulent variable-density mixing. This regime may be of importance to mixing in inertial confinement fusion capsules, which have high Atwood numbers and multiple shocks driving the mixing. To study this regime, Los Alamos National Laboratory has implemented a series of experiments in a vertical shock tube. These experiments insert a grid across the shock tube; as the shock accelerated air-SF6 interface is accelerated, passing through the grid at velocities > 80 m/s, grid turbulence is generated. The reflected shock off the bottom of the shock tube is then used to study shock interaction with a variable density turbulent layer. Updates on the experiments will be presented. |
Monday, November 25, 2024 5:11PM - 5:24PM |
T27.00003: Richtmyer-Meshkov instability coupled with a chemical reaction Riccardo Bonazza, Tanner J Diring, Eri R Amezcua, Jason Oakley, David Rothamer The Richtmyer-Meshkov Instability (RMI) and the resulting mixing at the impulsively-accelerated interface between two fluids is of great importance in astrophysics, proposed high-speed combustion systems, and pursuits towards inertial confinement fusion. Past experimental studies of the RMI have typically used inert gases, whereas in the applications of interest involving the RMI, the instability occurs concurrently with either chemical or nuclear reactions. Here we present the first experiments investigating the RMI coupled with a chemical reaction. The experiments are performed in a vertical, downward-firing shock tube. The initial interface consists of a shear layer between a 94% He/6% acetone mixture and Ar, above and below the interface, respectively (the acetone is added to perform planar laser-induced fluorescence). To create the shear layer, in past experiments Ar and the He/acetone mixture were flowed horizontally (immediately above and below the interface, respectively). In the present experiments, an 85% O2/15% Kr mixture replaces the Ar in the horizontal injection. A M=1.9 planar shock wave accelerates the interface, and upon reshock the acetone/O2 mixture ignites. Initial visualization experiments are presented here. |
Monday, November 25, 2024 5:24PM - 5:37PM |
T27.00004: Shock acceleration of a vortex-perturbed interface Alexander M Ames, Tiffany R Desjardins, Adam A Martinez, Antonio B Martinez Periodic surface roughness has been extensively studied as a source of material mixing at interfaces subject to shock acceleration as found in inertial confinement fusion capsules. However, non-periodic defects like pits, voids, and engineering features like the capsule fill tube have been identified as a significant contributor to mixing. Because of their anisotropic, inhomogeneous, aperiodic nature, these features break many of the assumptions that underpin models of variable-density turbulent mixing driven by the Richtmyer-Meshkov and Rayleigh-Taylor instabilities. |
Monday, November 25, 2024 5:37PM - 5:50PM |
T27.00005: Characterizing the dynamic strength of a polymer epoxy using the Richtmyer-Meshkov Instability Athena Padgiotis, Travis J Voorhees, Tracy J Vogler, Scott I Jackson Solid materials can exhibit fluid mechanical instabilities, such as the Richtmyer-Meshkov instability (RMI), when subjected to shock compression loading. Dynamic strength acts as a dissipating force to arrest RMI growth, similar to viscosity in fluids. In this study, we use RMI to characterize the dynamic strength and equation of state of the epoxy created by curing Epon 828 resin with diethanolamine (DEA). At the Dynamic Compression Sector of the Advanced Photon Source, plate impact experiments were performed to drive a steady shock compression wave through a sinusoidally corrugated copper-Epon 828/DEA interface, generating RMI at stresses ranging 4-12 GPa and strain rates near 106 /s. X-ray phase contrast imaging recorded shock propagation and interface evolution. Analysis of these images calibrated the equation of state of Epon 828/DEA and, in conjunction with numerical modeling, its dynamic strength. The equation of state was validated against plate impact experiments. The dynamic strength was compared to prior data for Epon-based epoxies at lower strain rates and found to exhibit significant strain rate and pressure-hardening effects. These findings suggest that Epon 828/DEA exhibits dynamic strengths comparable to high strength metals at these dynamic conditions. |
Monday, November 25, 2024 5:50PM - 6:03PM |
T27.00006: Measurements on the Richtmyer-Meshkov Instability using time-resolved PLIF in a dual-driver vertical shock tube Avery Sanford, Jeffrey W Jacobs Experiments on the Richtmyer-Meshkov Instability (RMI) using time-resolved Planar Laser Induced Fluorescence (PLIF) are presented. Experiments utilize a dual-driver vertical shock tube in which controlled-strength shock waves are generated from opposite directions to impact a perturbed interface between air and Sulfur Hexafluoride (SF6). The order of shock arrival and time between shock impacts on the interface can be controlled, and shock strengths are chosen such that the bulk flow is halted after the arrival of the second shock wave. This allows the instability to develop within the frame of a single high-speed video camera which records the experiment. The interface contains multi-modal, random perturbations generated by Faraday resonance using a pair of speakers. The experimental setup has been modified for PLIF, which utilizes the fluorescence of acetone seeded in one of the two gases and excited by a high-speed pulse-burst laser to visualize the flow and obtain concentration measurements. These measurements are then used to obtain the mixing layer growth rate and to quantify molecular mixing. |
Monday, November 25, 2024 6:03PM - 6:16PM |
T27.00007: Richtmyer-Meshkov Flow Simulation: Ensemble-Averaged or Instantaneous Interfaces? Filipe Pereira, Sam L Pellone, Alexander M Ames, John J Charonko, Tiffany R Desjardins, Forest Doss This work investigates the impact of the interface characterization in the simulation of an Air-SF6 Richtmyer-Meshkov (RM) flow. Toward this end, two-dimensional instantaneous and ensemble-averaged density fields defining diffusive interfaces measured experimentally are used as initial condition of high-fidelity RM computations. Three-dimensionality is added through density perturbations of distinct amplitudes and modes. Among others, quantities of interest comprise the density field, mixing layer width and mixedness, kinetic energy, and vorticity production mechanisms. The study demonstrates the critical role of mimicking the initial material interface, especially its instantaneous features. Their replication enables a deeper understanding of the RM flow physics and higher-fidelity simulations. Compared to the case based on the instantaneous initial condition, it is shown that the mixing layer height and mixedness can vary 50% when the initial density field of the interface is ensemble averaged (with or without added perturbations). Such variations are more pronounced for higher-order quantities of interest. In summary, this study clearly highlights the role of the diffusive interface characterization level in predicting and understanding RM material mixing flows. |
Monday, November 25, 2024 6:16PM - 6:29PM |
T27.00008: Abstract Withdrawn
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Monday, November 25, 2024 6:29PM - 6:42PM |
T27.00009: Non-Linear Instabilities of Two Supersonic Wall Bounded Jets Impinging at an Angle Zac Q Pyle, Gustaaf B Jacobs The impingement of two planar, wall-bounded jets angled towards each other leads to several non-linear instabilities. |
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