Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session A19: Richtmeyer-Meshkov Instability I |
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Chair: Katherine Prestridge, Los Alamos National Laboratory Room: 322 |
Sunday, November 20, 2011 8:00AM - 8:13AM |
A19.00001: A pneumatic driver for shock wave production Megan Leftwich, R. Mejila-Alvarez, K. Prestridge We are presenting a novel technique to generate shock waves in shock tube experiments. Typically this is done with a high pressure driver section that is separated from the low pressure driven section by a physical membrane. The membrane is burst at a specific pressure and a shock wave is formed. This process limits the repetition of experiments, and membrane particles must be removed from the shock tube after each experiment. The driver presented here does not contain a membrane. Instead, it uses a series of high pressure chambers and fast-acting pistons to create the pressure jump between the high pressure driver section and low pressure driven section. The entire system is controlled remotely and requires no insertion or cleanup of membranes between experiments. The system is designed to achieve shock waves exceeding Mach 3 with air as the working fluid (higher Mach numbers can be generated with other working fluids). It will allow high repetition rates, even in challenging experimental environments (such as a vertical shock tube configuration). We present results from the initial characterization of this driver system. [Preview Abstract] |
Sunday, November 20, 2011 8:13AM - 8:26AM |
A19.00002: Vertical Shock Tube for simultaneous velocity and concentration measurements of Richtmyer-Meshkov Instabilities R. Mejia-Alvarez, K. Prestridge, M.C. Leftwich Most experimental studies on Richtmyer-Meshkov Instabilities (RMI) have been restricted to mixing layer growth and pointwise turbulence characterization. To date, the only exception to this trend encompasses simultaneous measurements of velocity and concentration via combined PIV and PLIF over a curtain of heavy gas with initial varicose perturbations.\footnote{Phys. Fluids 20, 124103 (2008)} Since no parallel of this work has been conducted on single interface configurations, the Extreme Fluids Team at Los Alamos National Laboratory has developed a new Vertical Shock Tube (VST) to carry out such measurements. When fully operational, this facility will allow simultaneous characterization of velocity and concentration fields at different stages of development of single-interface RMI flows. The extraction of turbulence statistics from velocity measurements will not only be instrumental in understanding the basic physics behind the single-interface RMI, but also the benchmark for RANS models and ILES. We present a description of the breath of functionality and diagnostic capabilities of LANL's new Vertical Shock Tube facility. [Preview Abstract] |
Sunday, November 20, 2011 8:26AM - 8:39AM |
A19.00003: Mach number dependence of the Richtmyer-Meshkov instability with simultaneous density and velocity measurements Gregory Orlicz, Sridhar Balasubramanian, Kathy Prestridge Experiments are performed to study the effect of incident shock Mach number (M) on the development of the Richtmyer-Meshkov instability after a shock wave impulsively accelerates a varicose-perturbed, heavy-gas curtain (air-SF$_{6}$-air). Incident shock strength is varied within the weak shock regime (M $\le $ 1.5), and the resulting instability and subsequent fluid mixing is measured using simultaneous Planar Laser-Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV). We investigate the mechanisms that drive the instability, at both large and small scales, by examining the time evolution of simultaneous, 2-D density and vorticity fields for each Mach number. Mixing layer width, vorticity, circulation, velocity fluctuations, turbulent kinetic energy, and the density self-correlation parameter are examined as a function of time. These quantities are also examined versus time scaled with the convection velocity of the mixing layer, showing that the rate of change of several of these quantities is independent of Mach number. [Preview Abstract] |
Sunday, November 20, 2011 8:39AM - 8:52AM |
A19.00004: Single and multi-mode initial condition influence on turbulent mixing in Richtmyer-Meshkov flows Sridhar Balasubramanian, Greg Orlicz, Kathy Prestridge Experimental evidence is needed to verify and validate the numerical hypothesis that shock-driven flows retain the memory of initial conditions. We present the results of an experimental study to understand the influence of initial condition parameters, namely amplitude and wavelength of perturbations, on mixing and transition in Richtmyer Meshkov flows. Single and multi-mode membrane-free initial conditions in form of a gas curtain (\textit{air-SF}$_{6}$\textit{-air}) at Mach number $M = 1.2$ and Atwood number, $A$=0.67 was used. The evolution of instability is captured using high resolution simultaneous PLIF and PIV. Statistics such as mixing widths, density self-correlation parameter, turbulent kinetic energy, turbulent Reynolds number, and variances of velocity fluctuations were measured to quantify the amount of mixing. Some of these statistics were found to be in disagreement with the linear theory. Based on the results, a correlation between mixing at late times and initial condition parameters is found. [Preview Abstract] |
Sunday, November 20, 2011 8:52AM - 9:05AM |
A19.00005: The Richtmyer-Meshkov Instability of a New Type of Broadband Initial Condition Christopher Weber, Nicholas Haehn, Jason Oakley, David Rothamer, Riccardo Bonazza The Richtmyer-Meshkov instability is experimentally investigated using a broadband initial condition imposed on an interface of helium+acetone over argon. The initial condition is created, first by setting up a gravitationally stable stagnation plane, and then injecting the gases horizontally at the interface to create a shear layer. The perturbations along the shear layer create a statistically repeatable broadband initial condition. The interface is accelerated by a $M$ = 1.6 and $M$ = 2.1 planar shock wave, inducing a growth of the interface perturbations. The development of this turbulent mixing layer is investigated using PLIF. [Preview Abstract] |
Sunday, November 20, 2011 9:05AM - 9:18AM |
A19.00006: Planar Shock Acceleration of a Droplet-Seeded Gas Jet: Three-Dimensional Features Peter Vorobieff, Joseph Conroy, Michael Anderson, Ross White, C. Randall Truman, Sanjay Kumar When a planar shock wave generated in a shock tube accelerates a nominally two-dimensional density interface, the large-scale flow structure is usually regarded as quasi-two-dimensional. We examine the limitations of this assumption due to interaction with wall boundary layers, growth of three-dimensional instabilities, and other factors. The initial conditions are produced by a laminar cylindrical jet of gas vertically injected into the test section of the shock tube. Flow visualization images in several planes intersecting the flow reveal a non-trivial three-dimensional structure. Experiments are conducted both for ``classical'' Richtmyer-Meshkov instability and for its multiphase analog induced by particle seeding. [Preview Abstract] |
Sunday, November 20, 2011 9:18AM - 9:31AM |
A19.00007: Modeling a Shock-Accelerated Fluid - Multiphase Fluid Interface Michael Anderson, Peter Vorobieff, Ross White, Joseph Conroy, C. Randall Truman, Sanjay Kumar The hydrocode SHAMRC has been used in the past to study the formation and growth of the Richtmyer-Meshkov Instability (RMI). While RMI involves impulsively accelerating two continuous fluids of differing densities, a similar class of instabilities has recently been described for multiphase flow. In this scenario, a shock wave passes through a region containing ambient air seeded with particles which have a non-trivial mass and density much greater than that of the surrounding and embedding fluid. In this scenario, no baroclinic vorticity is generated due to the lack of a fluid-fluid density interface. After the shock passage, the particles or droplets lag behind the surrounding gas. Momentum exchange between the embedded phase and the embedding phase leads to non-uniform local equilibrium velocity distribution, and thus to shear and vortex formation. As the primary mechanism for this instability formation is momentum transfer via drag, the morphology of the instability is strongly dependent of the sizes of the particles in the initial conditions. The simulations described here attempt to model the effects of changing the particle size on the morphology and growth rate of this instability. [Preview Abstract] |
Sunday, November 20, 2011 9:31AM - 9:44AM |
A19.00008: Shock-initiated Combustion with New Insights into the Nature of the Shock-focusing Phenomenon Nicholas Haehn, Christopher Weber, Jason Oakley, David Rothamer, Devesh Ranjan, Riccardo Bonazza Shock-focusing that results from the interaction of a planar shock wave with a spherical density inhomogeneity is used to ignite a reactive mixture of gases. Due to the singular nature of this process, the task of quantifying the effect of the shock-focusing is challenging from a numerical and analytical point of view. As such, there is a lack of understanding regarding the thermodynamic conditions that are achieved during the shock-focusing process. These conditions, and this process in general, are important to a wide range of disciplines, including inertial confinement fusion, astrophysics, and supersonic combustion. A bubble is prepared using a stoichiometric mixture of fuel and oxidizer and diluted with Xe, which increases the overall density of the mixture. The experiments are performed in the Wisconsin Shock Tube Laboratory (WiSTL) in a 9.2 m vertical shock tube with a 25.4 cm $\times {\rm g}$5.4 cm square cross-section. The bubble is accelerated by a planar shock wave (2.0 $< \quad M \quad <$ 2.8). Planar Mie scattering and chemiluminescence are used simultaneously to visualize the bubble morphology and combustion characteristics. In turn, the combustion can be used as a diagnostic to assess the conditions that exist near the shock-focusing region. [Preview Abstract] |
Sunday, November 20, 2011 9:44AM - 9:57AM |
A19.00009: Oblique Shock Interaction with a Gas Cylinder Ross White, Joseph Conroy, Michael Anderson, Peter Vorobieff, C. Randall Truman, Sanjay Kumar In the majority of shock-tube studies of Richtmyer-Meshkov instability, when a planar shock interacts with a perturbed density interface, the orientation of the interface plane or the largest interface feature (e.g., axis of a gaseous column) is parallel to the plane of the shock. Here we experimentally study the flow developing after an interaction of an \emph{oblique} shock wave with a gravity-stabilized cylindrical heavy gas (SF$_6$) column surrounded by less dense gas (air). To introduce an oblique angle into the initial conditions, we tilt the shock tube to an angle of 15$^\circ$ with respect to the horizontal. Flow visualization in several planes is conducted to highlight the differences between the features characterizing planar and oblique shock-cylinder interaction. Several flow structures peculiar to oblique interaction appear to exist over a range of Mach numbers from 1.2 to 2.1. [Preview Abstract] |
Sunday, November 20, 2011 9:57AM - 10:10AM |
A19.00010: The Oscillation and Rupture of a Water-filled Balloon Hugh Lund, Stuart Dalziel Experimental observations of the impact of a water-filled balloon on a rigid surface have shown that capillary-like waves form on the membrane, with the tension in the membrane as the restoring force. If the membrane ruptures during the impact, two forms of instability occur on the air/water interface. First, the rapid retraction of the membrane creates a small-scale shear instability. Second, larger scale growth of the interfacial amplitude occurs, as the restoring force for the capillary-like waves is lost while the kinetic energy within the water remains. A water-filled balloon that is held and forcibly oscillated then ruptured with a sharp object displays the same three phenomena: capillary-like waves, shear instability and larger-scale interfacial growth. In air, the large-scale growth of the interfacial amplitude becomes asymmetric, leading to the formation of so-called bubbles of the air phase and spikes of the water phase. For such a balloon held underwater, the interfacial growth is symmetric. In this paper, we present examples of the phenomena described above. Further, we explain why the late-time growth of the interfacial amplitude is a manifestation of the Richtmyer-Meshkov instability. Unlike the classical instability, growth may occur when there is no density difference across the interface. At late-time, measurements of the displacement of the maximum amplitude of the interface suggest a power law of the form $t^{\theta}$, where $t$ is time and $\theta$ is around $2/3$. [Preview Abstract] |
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