Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session F28: Flow Instability: Rayleigh-Taylor/Richtmyer-Meshkov I |
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Chair: Oleg Schilling, LLNL Room: Georgia World Congress Center B316 |
Monday, November 19, 2018 8:00AM - 8:13AM |
F28.00001: The effect of initial conditions on the growth of Richtmyer–Meshkov instability Mohammad M Mansoor, Adam A Martinez, Sean Dalton, Tiffany Desjardins, Katherine P Prestridge The baroclinic generation of vorticity at a stratified interface when subjected to a shock-wave occurs in a process known as the Richtmyer–Meshkov instability. This study investigates the growth of single-mode sinusoidal perturbations on an air/sulfur hexafluoride (SF6) interface by this process using a 7m tall vertical shock tube (1.2 Ma). The perturbations are induced by subjecting the interface to an undulating cross-flow structure produced by steady-state oscillations of a symmetrical motorized airfoil flapper in the cross-stream. For various flapper frequencies and sweeping angles employed, both the initial perturbation wavelength (λ0) and amplitude (η0) produced are noted to affect the late-time growth rates, significantly. The perturbation amplitude (η) follows a power-law dependence with downstream distance and can be collapsed for all flapper conditions by a dimensional-scaling k(η/ η0) = 0.21(kx)0.44 . Turbulent statistics of the mixing region in addition to vortex identification and swirl strength within are also investigated for obtaining correlations with the flapper oscillation characteristics. |
Monday, November 19, 2018 8:13AM - 8:26AM |
F28.00002: Experimental Investigation of the effects of Mach number and initial condition on mixing transition in shock-driven flow Mohammad Mohaghar, John D Carter, Juan Sebastian Rubio, Gokul Pathikonda, Devesh Ranjan Effects of initial condition and incident shock strength (Mach number) on the Richtmyer-Meshkov instability (RMI) evolution are presented here. The interface between light (N2) and heavy (CO2) gases is inclined with respect to shock propagation by 10 degrees (amplitude to wavelength ratio of 0.088), which forms the predominantly single-mode perturbation. A perturbed, multi-mode inclined interface is also created via shear-buoyancy induced roll-ups between the two gases superposed on the dominant inclined mode. These two interface conditions are accelerated by planar shock waves of M≈1.55 and M≈1.9 to investigate the RMI development and mixing transition in this flow. Ensemble-averaged turbulence statistics are computed using simultaneous planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) measurements at two times after incident shock and two times after reshock. The observations from turbulent kinetic energy spectra and mixing Reynolds number indicate that the criteria for mixing transition can be satisfied at late time after the incident shock for the multi-mode case at higher Mach number, and after reshock for both Mach numbers and both initial conditions. |
Monday, November 19, 2018 8:26AM - 8:39AM |
F28.00003: Simultaneous Velocity and Concentration Measurements of a Twice-Shocked Mixing Layer Christopher Noble, Alexander M Ames, Jason G Oakley, David Rothamer, Riccardo Bonazza The twice-shocked Richtmyer-Meshkov instability is investigated in the vertical shock tube of the Wisconsin Shock Tube Laboratory at the University of Wisconsin–Madison. The initial condition is a shear layer, containing broadband perturbations, formed at the interface between a Helium-Acetone mixture and Argon. The interface is accelerated with a shock of nominal strength M=1.9 with an initial Atwood number of A=0.43. The evolution of the interface is investigated at 4 distinct post-reshock times. Acetone is used as a molecular tracer for PLIF, allowing the extraction of concentration data, while the interface and the regions above and below it are seeded with titanium dioxide particles, to allow the use of PIV to measure 2-D velocity fields. Turbulence is investigated using the measured velocity and concentration fields which are analyzed via energy spectra, structure functions, and PDFs. Integral parameters such as interface thickness and degree of mixedness are evaluated as well as the Reynolds stresses, the Taylor microscale, and the internal and external Reynolds numbers. |
Monday, November 19, 2018 8:39AM - 8:52AM |
F28.00004: Experiments on the Richtmyer-Meshkov Instability in a dual-shock vertical shock tube Kevin Ferguson, Everest Sewell, Jeffrey Jacobs Experiments on the Richtmyer-Meshkov Instability (RMI) using Particle Image Velocimetry (PIV) in a dual-shock vertical shock tube are presented. Two shock waves travel in opposing directions impact an initially stably stratified, perturbed interface formed between Air and Sulfur Hexaflouride (SF6). Perturbations are formed using a pair of voice coil driven pistons that generate Faraday waves on the interface. The incident shock wave arrives from air side of the interface which initiates the RMI. Shortly afterward a second shock wave arrives from the SF6 side which generates reshock. The temporal separation between the arrival of the two shock waves is controlled so that the effect of varying the shock-to-reshock time period may be studied. Shock strengths are chosen to result in halted interface motion after passage of the second shock wave, permitting a long observational window in which the instability can evolve and yielding a simplified optical and recording setup as compared to typical single-driver experiments. Information on the growth of the RMI, including measurements of the growth exponent, θ, as measured both from the decay of turbulent kinetic energy and the growth of the mixing layer enstrophy width, is presented. |
Monday, November 19, 2018 8:52AM - 9:05AM |
F28.00005: Spatio-temporal investigation of Richtmyer-Meshkov instability by simultaneous velocity-density measurements at high frame rates John D Carter, Gokul Pathikonda, Naibo Jiang, Sukesh Roy, Devesh Ranjan The inclined shock tube at the Shock Tube and Advanced Mixing (STAM) laboratory was used to investigate the spatio-temporal evolution of Richtmyer-Meshkov instability (RMI). A light-to-heavy gas interface that is inclined with respect to the incident shock formed the dominant mode of the initial condition before shock interaction. Experiments were conducted with and without small scales superposed on this dominant mode, and at various Mach (1.55 and 1.9) and Atwood (0.22 and 0.67) numbers. An ensemble of simultaneous velocity-density (PIV—Acetone-PLIF) measurements were made at a frame rate of 60 kHz using high speed CMOS cameras and a pulse burst laser (capable of 532 nm and 266 nm). Preliminary comparisons with our previous high resolution data, literature and theoretical comparisons show high fidelity of measurements. The dataset enables a description of velocity and mixing characteristics of RMI in a temporal framework. |
Monday, November 19, 2018 9:05AM - 9:18AM |
F28.00006: Experimental Study of the Incompressible Richtmyer-Meshkov Instability Matthew Mokler, Jeffrey Jacobs Incompressible Richtmyer-Meshkov instability (RMI) experiments are conducted using miscible and immiscible fluid pairs with matched viscosity and Atwood number (A = 0.22). Dioctyl sulfosuccinate sodium salt (AOT) surfactant is added to the immiscible pair. Forced and unforced initial perturbations are examined. Initially stably stratified fluid pairs are accelerated in the destabilizing direction using an 8 meter linear induction motor drop tower for a duration of 100 ms. RMI occurs when the fluid pairs enter free fall following this initial acceleration. Mixing between the two fluids is visualized using planar laser induced fluorescence (PLIF) with images captured by a high speed camera. Time dependent mixing region widths for both miscible and immiscible fluid pairs are obtained from the PLIF image sequences. Mixing region behaviors for both fluid combinations are compared. Time-dependent interfacial tension measurements are also conducted in order to examine the effects of AOT surfactant on the immiscible fluid pair. Interfacial tension measurements are obtained from pendant drop tensiometry. Measurements of varying drop sizes and durations are compared to structure sizes and times observed in the RMI experiments. |
Monday, November 19, 2018 9:18AM - 9:31AM |
F28.00007: Experimental Technique for the Measurement of Velocity and Droplet Lag Distance in a Shock Accelerated Multiphase System John Middlebrooks, Wolfgang Black, Roy Allen, Jacob A McFarland A shock tube study has been conducted to investigate hydrodynamic instabilities that arise from the impulsive acceleration of a heterogeneously seeded multiphase field. In the experiment, a cylindrical interface comprised of micron sized acetone droplets seeded in nitrogen was created in a test section and accelerated by a planar shock wave. Nitrogen saturated with acetone vapor was mixed into the interface as a tracer and to prevent early evaporation of droplets. The development of both the dispersed and carrier phases was captured through a series of Planar Laser Mie Scattering (PLMS) and Planar Laser Induced Fluorescence (PLIF) images respectively. Lag effects between the phases were visualized and quantified. Velocity fields from images were constructed, and the results were compared to simulations for validation. This study has applications in many scientific and engineering systems, but has particular relevance to systems that involve high speed or shock induced multiphase combustion. |
Monday, November 19, 2018 9:31AM - 9:44AM |
F28.00008: A Richtmyer-Meshkov Experiment at the NIF Tiffany Desjardins, Carlos Di Stefano, Kirk Flippo, Elizabeth Merritt, Derek Schmidt, Thomas Day, Barbara DeVolder, Forrest Doss The Richtmyer-Meshkov instability (RMI) arises when a shock crosses the boundary between materials of disparate densities. In an ICF capsule, the boundary between the thin ablator layer and cold fuel can give rise to the RMI, causing mixing between the ablator and fuel, reducing performance. Secondary shocks from the source, as well as rarefactions and reflections within the capsule can drive the RMI into a turbulent state, further degrading the performance. The Mshock platform is a miniature shock tube designed to be fired at the National Ignition Facility (NIF) studying the RMI in a thin layer similar to an ICF capsule, but in a planar geometry. The goals are to understand how the instability is affected by initial conditions and multiple shocks. Recent experiments at NIF have tested the feedthrough of two initial conditions with a similar single mode perturbation, but a different broadband (noisy) profile with a simple shock and re-shock setup. The results indicate that the mixing is dependent initial conditions. Detailed analysis and comparison with LANL’s BHR mix model are currently underway. This talk will discuss the platform, experimental results, and give a preliminary comparison with the BHR mix model. |
Monday, November 19, 2018 9:44AM - 9:57AM |
F28.00009: Examination of Metal Strength at High Strain Rates Using Richtmyer-Meshkov Instability Experiments at the Advanced Photon Source Joseph D. Olles, Christopher F. Tilger, Nathaniel J. Sanchez, Brian J. Jensen Recent advances in ultra-high-speed x-ray diagnostics allow high-fidelity, in-situ investigation of material properties under extreme conditions. Richtmyer-Meshkov instability (RMI) experiments were performed with a gas gun in the Advanced Photon Source (APS) located at Argonne National Laboratory. Shock compressed metal targets (copper and aluminum) with a prescribed sinusoidal interface, were studied using photonic Doppler velocimetry and x-ray phase contrast imaging (PCI). These initial perturbations on the shocked metal interface evolve into jets and bubbles. The instability was recorded using x-ray PCI having a spatial resolution of 2-3 microns with sub-nanosecond exposures. Due to challenges with artifacts associated with PCI, a phase congruency feature detection was used to output quantitative descriptors of edges for the metal jet size and shape. This data is reduced systematically and reliably identifies points with impedance gradients. The jet shape and velocity provide details necessary for high-strain rate dependent strength models for shock compressed metals. While other experiments and models have been shown in literature, the added spatial and temporal resolution of our measurements allow validation and expansion of these works. |
Monday, November 19, 2018 9:57AM - 10:10AM |
F28.00010: Development of an Experiment for Investigating the Magnetohydrodynamic Richtmyer-Meshkov Instability Roy C. Allen, Wolfgang Black, William C Maxon, Jacob A McFarland The magnetohydrodynamic Richtmyer-Meshkov instability (MHD RMI) is being investigated by the Fluid Mixing Shock Tube Laboratory (FMSTL) at the University of Missouri through implementation of experimental methods and simulation techniques. Hydrodynamic instabilities (HI) such as the RMI are prevalent in high energy density systems where fluid mixing, driven by HIs, ultimately results in energy yield reduction and equilibrium consequences. The implementation of magnetic fields is being explored as an option to suppress the development of HIs thus preventing undesirable effects from arising. To do so, a conducting fluid (e.g. plasma) is generated by an atmospheric pressure plasma torch and resulting effects are studied whilst an external magnetic field is imposed onto the plasma flow field. The work presented here will outline the efforts made at the FMSTL to experimentally study the RMI in MHD as well as predictive ideal MHD simulation results. Preliminary experimental results as well as those achieved by simulations show that suppression of the MHD RMI is achievable. |
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