Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session H22: Instability: Richtmyer-Meshkov I |
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Chair: Praveen Ramaprabhu, University of North Carolina at Charlotte Room: 2012 |
Monday, November 24, 2014 10:30AM - 10:43AM |
H22.00001: Numerical simulations of the Single-mode, Doubly-shocked Richtmyer-Meshkov (RM) Instability Varad Karkhanis, Praveen Ramaprabhu We describe results from numerical simulations of a single-mode, doubly-shocked material interface between gases of different densities. The time interval between the shocks was varied to observe interfacial growth due to Richtmyer-Meshkov Instability initialized with different amplitudes. The simulations were performed with low and high density ratio fluids (A $=$ 0.15 and A $=$ -0.99), where the latter case is relevant to ejecta formation. We compare the growth rates from our simulations after the first and second shocks with linear, nonlinear [1] and ejecta models [2,3]. In the heavy to light configuration (A $=$ -0.99), we observe two consecutive phase inversions following each shock. We have also investigated the effect of variations in the initial interface perturbation to include sine, chevron, sawtooth, and square-wave form, and find our results to be of relevance to machined target experiments. \\[4pt] [1] Guy Dimonte and P. Ramaprabhu, Phys. Fluids 22, 014104 (2010).\\[0pt] [2] W. T. Buttler et al., J. Fluid Mech., 703 (2012).\\[0pt] [3] Guy Dimonte et al., J. Appl. Phys. \textbf{113}, 024905 (2013). [Preview Abstract] |
Monday, November 24, 2014 10:43AM - 10:56AM |
H22.00002: ABSTRACT WITHDRAWN |
Monday, November 24, 2014 10:56AM - 11:09AM |
H22.00003: Numerical simulations of a chemically reacting Richtmyer-Meshkov turbulent mixing layer Hilda Varshochi, Nitesh Attal, Praveen Ramaprabhu We report on results from detailed numerical simulations that capture the evolution through the Richtmyer-Meshkov instability of a multi-mode interface that initially separates a fuel (H$_{2})$ and a corresponding oxidizer (O$_{2})$. The three-dimensional simulations were carried out at a resolution of 512 x 512 x 3072 using a modified version of the FLASH code, capable of handling detailed H$_{2}$-O$_{2}$ combustion chemistry [1], temperature-dependent equation of state, and temperature-dependent molecular transport properties. The perturbation interface was initialized with ``alpha-group'' [2] type perturbations, and impacted by a Mach 1.2 incident shock travelling from the light (H$_{2})$ to heavy (O$_{2})$ fluid. We track several quantities through the linear, non-linear and turbulent stages of evolution, and make comparisons with the corresponding non-reacting flowfield from a separate set of simulations. The turbulent mixing layer is also subjected to reshock, which dramatically increases the combustion efficiency at the interface. \\[4pt] [1] Attal, N. et al., submitted to Computers and Fluids for review.\\[0pt] [2] Dimonte, G. et al., Phys. Fluids, 16, p. 1668, 2004. [Preview Abstract] |
Monday, November 24, 2014 11:09AM - 11:22AM |
H22.00004: Energy dynamics in the Richtmyer-Meshkov instability induced turbulent mixing flow Zuoli Xiao, Han Liu The Richtmyer-Meshkov instability (RMI) induced turbulent mixing flow in a shock tube is numerically investigated by using direct numerical simulation based on an effective in-house high-order turbulence solver (HOTS). The energy transfer and transport characteristics are studied both before and after re-shock. The celebrated Kolmogorov -5/3 spectrum can be observed in a long inertial subrange during the development of the turbulent mixing zone (TMZ). Insight is taken into the underlying mechanism by evaluating the energy-budget equations. A posteriori analysis of the influence of subgrid scales on resolved motions also gives a consistent picture of energy transfer in the RMI-induced turbulent mixing. Moreover, the kinetic energy cascade in the TMZ is discussed by using Favre filtering approach in physical space. A nonlinear vortex-stretching model for the subgrid-scale stress serves to explain the underlying mechanism of the energy cascade in the RMI-induced turbulence. [Preview Abstract] |
Monday, November 24, 2014 11:22AM - 11:35AM |
H22.00005: Linear Simulations of the MHD Richtmyer-Meshkov Instability in Cylindrical Geometry Abeer Baksh, Ravi Samtaney, Vincent Wheatley Numerical simulations and analysis indicate that the Richtmyer-Meshkov instability (RMI) is suppressed in ideal magnetohydrodynamics (MHD) in Cartesian slab geometry. Motivated by the presence of hydrodynamic intstabilities in inertial confinement fusion and suppression by means of a magnetic field, we investigate the RMI via linear MHD simulations in cylindrical geometry. The physical setup is that of a Chisnell-type converging shock interacting with a density interface with either axial or azimuthal (2D) or a combination of both (3D) perturbations. The linear stability is examined in the context of an initial value problem (with a time-varying base state) wherein the linearized ideal MHD equations are solved by an extension of the numerical method proposed by Samtaney (J. Comput. Phys. 2009). Linear simulations in the absence of a magnetic field, indicate that RMI growth rate during the early time period similar to that observed in Cartesian geometry. However, this RMI phase is short-lived and followed by a Rayleigh-Taylor growth phase with an accompanied exponential increase in the perturbation amplitude. We examine several strengths of the magnetic field (characterized by $\beta=\frac{2p}{B^2}$) and observe a significant suppression of the instability for $\beta\approx 2$. [Preview Abstract] |
Monday, November 24, 2014 11:35AM - 11:48AM |
H22.00006: The magnetohydrodynamic Richtmyer-Meshkov instability in two-dimensional implosions Wouter Mostert, Vincent Wheatley, Dale Pullin, Ravi Samtaney We present numerical results showing the behaviour of the magnetohydrodynamic Richtmyer-Meshkov instability in two-dimensional implosions in the presence of an externally applied seed magnetic field. An initially perturbed cylindrical density interface is accelerated from the outside by a set of imploding magnetohydrodynamic shocks, themselves generated by a cylindrical Riemann problem. We characterize the process of shock refraction with the density interface and examine the subsequent growth of the interface perturbations, comparing with the zero-field case. We test two candidate seed magnetic field configurations: a uniform-strength, unidirectional field; and a field with a saddle point at the domain origin. Both field configurations show suppression of interface perturbation growth, with the latter exhibiting the least asymmetry in the implosion. [Preview Abstract] |
Monday, November 24, 2014 11:48AM - 12:01PM |
H22.00007: Instability evolution in shock-accelerated inclined heavy gas cylinder Dell Olmstead, Patrick Wayne, Peter Vorobieff, Daniel Davis, C. Randall Truman A heavy gas cylinder interacts with a normal or oblique shockwave at Mach numbers $M$ ranging from 1.13 to 2.0. The angle between the shock front and cylinder axis is varied between 0 and 30$^\circ$, while the Atwood numbers $A$ range from 0.25 (SF$_6$-N$_2$ mix) to 0.67 (pure SF$_6$). The evolution of the column is imaged in two perpendicular planes with Planar Laser Induced Fluorescence (PLIF). For oblique shock interactions, the nature of the flow is fully three-dimensional, with several instabilities developing in separate directions. In the plane that captures a cross-section of the column, Richtmyer-Meshkov instability (RMI) leads to formation of a pair of counter-rotating vortex columns. A uniform scaling appears to govern the primary instability growth in this plane across the $M$ and $A$ ranges, when the length scale is normalized by a product of the minimum streamwise scale after shock compression and M$^{0.5}$. In the vertical plane through the column, Kelvin-Helmholtz vortices form with regular spacing along the column. The dominant wavelength of the structures in the vertical plane also appears to scale with the minimum compressed streamwise length. [Preview Abstract] |
Monday, November 24, 2014 12:01PM - 12:14PM |
H22.00008: Droplet tracer characterization in shock-driven multiphase flow Francisco Vigil, Miquela Trujillo, Peter Vorobieff, C. Randall Truman Small glycol droplets have long been introduced into shock-accelerated gas as a tracer, to track the evolution of Richtmyer-Meshkov instability (RMI). However, it was observed that droplets are not passive tracers when shock-accelerated - to the extent that their introduction itself can lead to vortex formation. Because of the complex interplay between the droplets and surrounding gas, it is imperative to know the droplet size and population density. The absence of this knowledge has led to differences between results from numerical models, Planar Laser-Induced Fluorescence (PLIF) measurements, and Mie scattering observations. To gain a better understanding of the droplet velocity and inertial flow fields, a more involved study of droplet sizing is required. A Malvern laser diagnostic system is used to determine the sizes of the glycol droplets seeded into the flow. A series of tests are performed to analyze differences in glycol droplet size and population distribution that result from changing gaseous mediums in the test section. These measurements facilitate better quantification of the velocity fields in shock accelerated flow and improve interpretation of results from Mie scattering. [Preview Abstract] |
Monday, November 24, 2014 12:14PM - 12:27PM |
H22.00009: Vortex formation in oblique shock interaction with a heavy gas column Patrick Wayne, Dell Olmstead, C. Randall Truman, Peter Vorobieff, Sanjay Kumar In an oblique shockwave interaction with a column of heavy gas, we observe both the expected counter-rotating vortex pairs (same as caused by normal shockwaves) and periodic co-rotating vortices that vary with Mach number. We study the effects of oblique shock interaction with a column of acetone-infused sulfur-hexafluoride (SF$_6$) gas. Visualization of the shock-accelerated gas column is accomplished via Planar Laser-Induced Fluorescence (PLIF) imaging. The shock tube itself is inclined at a 30$^\circ$ angle, while the initial conditions (ICs) are introduced into the test section vertically. Because of the inclined angle, the normal shock propagates down the shock tube and impacts the ICs at a 30$^\circ$ down-angle, producing an oblique shock. Vertical plane PLIF images reveal vorticity deposition between the SF$_6$ column and the surrounding air leading to Kelvin-Helmholtz instability. The evolving vortices cascade down the entire vertical length of the gas column, and interact with the counter-rotating vortex structures along the column. The most interesting aspect of this discovery is that these small-scale instabilities exhibit periodic behavior and, according to preliminary data, this behavior is Mach number dependent. [Preview Abstract] |
Monday, November 24, 2014 12:27PM - 12:40PM |
H22.00010: Transition in Hypersonic Boundary Layers: Role of Dilatational Waves Chuanhong Zhang, Yiding Zhu, Qing Tang, Huijing Yuan, Jiezhi Wu, Shiyi Chen, Cunbiao Lee, Mohamed Gad-el-Hak Transition and turbulence production in a hypersonic boundary layer is investigated in a Mach 6 quiet wind tunnel using Rayleigh-scattering visualization, fast-response pressure measurements, and particle image velocimetry. A previously undiscovered unusual behavior of the second instability mode is noticed. Very high frequency dilatational waves are observed to grow rapidly followed by very fast annihilation. The second instability mode is a key modulator of the hypersonic laminar-to-turbulence transition, and the bulk viscosity plays an important role in that dynamical process. At its peak, the second mode strongly interacts with the first instability mode to directly promote a rapid growth of the latter and immediate transition to turbulence. This interaction can be explained by a nonlinear coupling of vorticity and dilatation in the interior of the boundary layer, combined with a viscous linear coupling at the wall. Our study of transition in hypersonic flows suggests that more attention should be given to the inviscid dilatational waves and their coupling with transverse vortical structures. [Preview Abstract] |
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