Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session L4: Turbulence and Mixing IV |
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Chair: Daniel Livescu, Los Alamos National Laboratory, Sivaramakrishnan Balachandar, University of Florida Room: Grand H |
Tuesday, June 16, 2015 3:45PM - 4:00PM |
L4.00001: Subgrid-scale backscatter after the shock-turbulence interaction Daniel Livescu, Zhaorui Li The interaction of a shock wave with isotropic turbulence (IT) represents a unit problem for studying some of the phenomena associated with high speed flows, such as hypersonic flight, supersonic combustion and Inertial Confinement Fusion (ICF). In general, in practical applications, the shock width is much smaller than the turbulence scales and the upstream turbulent Mach number is modest. In this case, recent high resolution shock-resolved Direct Numerical Simulations (DNS) (Ryu and Livescu, J. Fluid Mech., 756, R1, 2014) show that the interaction can be described by the Linear Interaction Approximation (LIA). By using LIA to alleviate the need to solve the shock, DNS post-shock data can be generated at much higher Reynolds numbers than previously possible. Here, such results are used to investigate the properties of the subgrid scales (SGS). In particular, it is shown that the shock interaction decreases the asymmetry of the SGS dissipation PDF as the shock Mach number increases, with a significant enhancement in size of the regions and magnitude of backscatter. The LIA results are compared to the DNS database of Ryu and Livescu and then used to examine the backscatter properties at shock Mach numbers much larger than those feasible in DNS. [Preview Abstract] |
Tuesday, June 16, 2015 4:00PM - 4:15PM |
L4.00002: Observations of Variable-Density Turbulence From a Complex Fluid Interface David Reilly, John Carter, Mohammad Mohaghar, Dorrin Jarrahbashi, Jacob McFarland, Devesh Ranjan The inclined shock tube facility in the Georgia Tech Shock Tube and Advanced Mixing Laboratory was used to study a complex inclined interface initial condition for the Richtmyer-Meshkov instability. The inclined interface is essentially a long wavelength, extremely large amplitude perturbation between two gases. In this case, the light gas was chosen to be nitrogen and the heavy gas carbon dioxide, giving an Atwood number of 0.23. The complex interface is formed by perturbing the inclined interface with counter-flowing jets, which create shear and buoyancy effects. The modal content of the initial conditions was determined by taking the Proper Orthogonal Decomposition of a large set of realizations. PLIF images of the shocked flow-field (\textit{M}$\sim$1.5) were captured with the angle of the shock tube with respect to the horizontal at 80$^\circ$. Enhanced mixing in the complex interface was quantified through p.d.f.s, mixed mass, and the density self-correlation. Work that is currently underway will investigate the effect of these initial conditions on intermediate and late-time mixing as well as the transition to turbulence before reshock by implementing simultaneous PLIF and PIV measurements. [Preview Abstract] |
Tuesday, June 16, 2015 4:15PM - 4:30PM |
L4.00003: Shock-driven variable density mixing experiments at the Vertical Shock Tube Katherine Prestridge, Brandon Wilson, Ricardo Mejia-Alvarez The Vertical Shock Tube (VST) facility at Los Alamos National Laboratory is studying shock driven mixing of a perturbed air-SF6 interface using simultaneous Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF). We are examining the effects of incident Mach number in the range 1.2 to 2, and the effects of changing the amplitude and wavelength of 3D perturbations on the air-SF6 interface. Through measurements of density fields, velocity fields, vorticity, strain rate, and Reynolds stress, we are examining differences in the largest and smallest scales of turbulent mixing. Results of Mach number and initial condition effects will be presented, including characterization of the initial conditions using spectra and proper orthogonal decomposition, and understanding the dynamic behavior of the evolving flow in an instantaneous as well as a statistical sense. Our observations indicate differences in both the large-scale mixing features as well as earlier development of smaller scales of mixing that are impacted by both initial Mach number and the modal nature of the initial conditions. Calculations of Taylor microscales based upon both density and velocity fields will also be presented in the context of understanding the development of the mixing. [Preview Abstract] |
Tuesday, June 16, 2015 4:30PM - 4:45PM |
L4.00004: An Extended Pressure Equilibrium Model for Multiphase Flows - Application to Shock-Induced Particle Dispersion Thomas McGrath, Jeffrey St. Clair, Sivaramakrishnan Balachandar Multiphase flows containing a dispersed particle phase interacting with a background continuous phase are important in applications ranging from volcanic eruptions to advanced energetics. Modern multiphase models offer well-posed governing equations that treat each phase as compressible and allow each to retain separate velocities, temperatures, and pressures. Such models have been widely used in the investigation shock propagation over energetic material or porous media. In cases where one phase is much stiffer than the others, such as metal particles immersed in a background fluid, it is common to assume that the stiffer phase is completely incompressible. In this work, we seek a set of model equations that naturally transitions between the limits of fully-compressibility of all phases and near-incompressibility of one phase. An extended pressure equilibrium model that progresses toward this goal is presented. Using a simple assumption of the pressure relaxation path, a modified set of governing equations with the desired transitional properties is attained. The governing equations and mathematical characteristics of the model are discussed and analyzed, and preliminary numerical results are presented. [Preview Abstract] |
Tuesday, June 16, 2015 4:45PM - 5:00PM |
L4.00005: High Fidelity Modeling of Turbulent Mixing and Chemical Kinetics Interactions in a Post-Detonation Flow Field Neeraj Sinha, Andrea Zambon, James Ott, Michael DeMagistris Driven by the continuing rapid advances in high-performance computing, multi-dimensional high-fidelity modeling is an increasingly reliable predictive tool capable of providing valuable physical insight into complex post-detonation reacting flow fields. Utilizing a series of test cases featuring blast waves interacting with combustible dispersed clouds in a small-scale test setup under well-controlled conditions, the predictive capabilities of a state-of-the-art code are demonstrated and validated. Leveraging physics-based, first principle models and solving large system of equations on highly-resolved grids, the combined effects of finite-rate/multi-phase chemical processes (including thermal ignition), turbulent mixing and shock interactions are captured across the spectrum of relevant time-scales and length scales. Since many scales of motion are generated in a post-detonation environment, even if the initial ambient conditions are quiescent, turbulent mixing plays a major role in the fireball afterburning as well as in dispersion, mixing, ignition and burn-out of combustible clouds in its vicinity. Validating these capabilities at the small scale is critical to establish a reliable predictive tool applicable to more complex and large-scale geometries of practical interest. [Preview Abstract] |
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