Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session MF: Shock and Blast Waves |
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Chair: Mark Short, Los Alamos National Laboratory Room: 003B |
Tuesday, November 25, 2008 8:00AM - 8:13AM |
MF.00001: Direct numerical simulation of canonical shock/turbulence interaction Johan Larsson, Sanjiva Lele, Parviz Moin The problem of isotropic turbulence passing through a nominally normal shock wave is studied by direct numerical simulation. Special attention is paid to the nonlinear regime of strong turbulence interacting with a relatively weak shock, in which the turbulence-induced shock movement is considerable. Instantaneous profiles through the shock show a wide variation, including single strong compressions, double compressions, and essentially smooth and continuous compressions. The second- order statistics are compared to linear analysis, and the effect of interaction- nonlinearity is discussed. [Preview Abstract] |
Tuesday, November 25, 2008 8:13AM - 8:26AM |
MF.00002: Different sorts of unsteadiness in shock induced separation Jean-Paul Dussauge, Sebastien Piponniau, Louis-Jacques Souverein, Pierre Dupont, Jean-Francois Debi\`eve The unsteadiness observed in shock induced separation may be produced by different mechanisms which lead in all cases to low frequency motions. This is discussed in some cases: impinging oblique shocks (with well developed and incipient separation), compression ramp flows. A scenario based on mass conservation in the separated zone is proposed to explain the low frequency unsteadiness in separated impinging shock cases, when separation is followed by reattachment. This seems also to give a right evaluation of the unsteadiness frequency in different cases of compression ramp flows, although in many cases, the perturbations of the incoming boundary layer still play a role. In the case of incipient separation produced by an oblique shock reflection, intermittent separation is put in evidence. In such conditions the relevance of the previous analysis is examined and discussed for the separated and non separated events. [Preview Abstract] |
Tuesday, November 25, 2008 8:26AM - 8:39AM |
MF.00003: Toward Uncertainty Quantification in Turbulent Boundary Layer Shock Interactions Gianluca Iaccarino The prediction of the interaction between shocks and turbulent boundary layers remains a challenge in computational fluid dynamics. The overall wall pressure and skin friction are typically misrepresented by conventional Reynolds-averaged approaches. Many modifications have been introduced to overcome model limitations: near wall behavior, turbulence anisotropy, response to compression, unsteadiness have been all identified as fundamental motivations for the incorrect predictions. This work attempts to clarify the relative importance of the various sources of errors in conventional two-equation turbulence models by introducing the concept of physics sensors. The first step is to determine the limitations of the various assumptions used in the model formulation. As an example the turbulence production across a shock is initially considered. It is well known that conventional models over predict the kinetic energy amplification. A sensor identifies the shock location and the turbulence production is locally modified by introducing a random variable representing the uncertainty is the precise amplification rate. Similarly the effect of turbulence anisotropy and near-wall treatment is considered. The corresponding stochastic problem is solved using a Monte Carlo technique and the solution envelope is compared to experimental data for the transonic flow over a bump. [Preview Abstract] |
Tuesday, November 25, 2008 8:39AM - 8:52AM |
MF.00004: Direct Numerical Simulations of Shock-Turbulence Interactions Mark Petersen, Daniel Livescu, Jamaludin Mohd-Yusof, Sumner Dean We explore the nature of shock-turbulence interaction in three configurations: forced compressible isotropic turbulence, isotropic and anisotropic turbulence passing through a planar shock. The last problem is relevant to the turbulence changes during the re-shock in a classical Richtmyer-Meshkov problem. Results from direct numerical simulations are used to examine the modifications in the turbulence properties due to compressibility and as it interacts with the shock, including spectral laws and the kinetic energy, mass flux, and density-specific volume correlation transport equations budgets. The simulations are performed at resolutions up to $1024^3$, over a large range of turbulent Mach numbers ($M_t=0.02\ldots 0.4$), and for Taylor Reynolds numbers, $Re_{\lambda}$, up to 300. [Preview Abstract] |
Tuesday, November 25, 2008 8:52AM - 9:05AM |
MF.00005: Accurate simulations of slowly moving shocks with applications to shock-turbulence interaction. Eric Johnsen, Johan Larsson, Sanjiva K. Lele Shock-capturing schemes typically exhibit unsteady behavior in problems in which a shock moves slowly with respect to the grid. Though the nature of the problem is not fully understood, prior work (Jin {\&} Liu, JCP 1996) has shown that numerical diffusion in the density leads to a spike in the momentum for the Euler equations. Furthermore, downstream-propagating oscillations are generated when using approximate Riemann solvers such as Roe or HLL; the magnitude of these oscillations in the momentum can be significant and thus can contaminate the flow downstream of the shock. In the present work, we consider the unsteady nature of this spike in a variety of solvers. In particular, we show that these oscillations are related to the upwinding and that they can be suppressed by specifying appropriate bounds on the wave speeds used in the solver. Present one-dimensional results for the Euler equations show an improved behavior. Extension to multi-dimensional problems including shock-turbulence interaction will be discussed. [Preview Abstract] |
Tuesday, November 25, 2008 9:05AM - 9:18AM |
MF.00006: Experimental Studies of Unstart Dynamics in an Inlet/Isolator Model Justin Wagner, Kemal Yuceil, Noel Clemens, David Dolling The dynamics of the unstart process in an inlet/isolator model mounted to the floor of a Mach 5 wind tunnel are investigated using PIV, high-speed (8 kHz) schlieren imaging and fast-response surface pressure measurements. The inlet section contains a 6-degree compression ramp and the isolator is a rectangular straight duct that is 25.4 mm high by 50.8 mm wide by 242.3 mm long. For the fully-supersonic flow, three ramp shock reflections are contained within the isolator. Unstart is initiated by a motorized flap that is located at the downstream end of the isolator section. Unstart proceeds with the formation of an unstart shock system that propagates upstream at an average velocity of about 37 m/s. The unstart process is seen to be associated with strong shock-induced separation that leads to large reverse flow velocities up to about 275 m/s. Both the schlieren imaging and PIV data suggest the dynamics of the unstart process are dependent on the initial reflected oblique shock system. Specifically, during unstart, boundary layer separation occurs near the impingement points of these initial reflected shocks. The separation of the isolator ceiling boundary layer appears to result in a decrease in propagation velocity of the unstart shock system. Since the initial oblique shock system appears to affect unstart dynamics, additional experiments will be conducted with different inlet geometries. [Preview Abstract] |
Tuesday, November 25, 2008 9:18AM - 9:31AM |
MF.00007: Simulation of the shock-induced dynamics of bubble arrays Ratnesh Shukla, Hong Zhao, Carlos Pantano, Joanna Austin, Jonathan Freund Simulation of shock-induced collapse of air bubbles in a stiff medium, such as water, poses a significant challenge to conventional shock-capturing schemes. Previous studies have often been limited to relatively low density and pressure ratios along with simplified equations of state, due to the spurious oscillations which develop at the bubble medium interface. We present results utilizing a high-fidelity shock capturing multi-material compressible-flow solver, which combines the features of a level-set method and a moving mesh technique. We demonstrate application of our numerical methodology to the collapse of arrays of bubbles after they are impulsively accelerated by a planar shock. The role of the strength of the incident shock and initial bubble configuration in the subsequent motion and merger of the bubbles is investigated. Comparison of the full compressible solutions with a vortex-sheet model initialized with the baroclinic vorticity deposited during the interface-shock interaction show good agreement with respect to the motion of the bubbles. [Preview Abstract] |
Tuesday, November 25, 2008 9:31AM - 9:44AM |
MF.00008: Blast-Induced Pressure Fields Beneath a Military Helmet for Non-Lethal Threats David Mott, Douglas Schwer, Theodore Young, Jeffrey Levine, Jean-Philippe Dionne, Aris Makris, Graham Hubler Coordinated experiments and numerical simulations investigated the pressure field surrounding a head with a helmet subjected to a blast wave typical of injurious but non-lethal threats. Experiments were conducted with C4 explosive charges ranging from 0.75 kg to 5 kg, and two anthropomorphic test mannequins (Hybrid III) located 3 m from the explosive. Experimental diagnostics included pressure sensors mounted at selected locations around each mannequin's head and in the free-field. Numerical modeling was done using a two-step approach. First, the blast and ground reflection were computed using a multi-component, reacting flow model. Second, the results were used to specify the boundary conditions for a three-dimensional unsteady simulation of the head-helmet complex subjected to a blast wave. The helmet was shown to provide protection against primary blast injury both in computations and experiments. The simulations indicate that pressure waves entering the gap between the helmet and head focus on the side of the head away from the blast and produce pressures comparable to that experienced on unprotected surfaces subjected to the blast. [Preview Abstract] |
Tuesday, November 25, 2008 9:44AM - 9:57AM |
MF.00009: Nonlinear propagation of acoustic-gravity waves from explosive sources in the atmosphere Christophe Millet, Virginie Daru The linear euler equations are widely used by the geophysical community to compute low frequency acoustic waves in the atmosphere. Although this model permits to explain basic properties of signals associated with large-intensity events, it fails to predict both waveforms and amplitudes. Due to the exponential decrease of air density with altitude, the acoustic waves give rise to shock waves, especially in the stratosphere. In this study, we compute both acoustic waves and gravity waves generated by the high explosive ``Misty Picture'' test, on May 14, 1987. In order to represent, in the same computation, different-scale wave motions without generating spurious numerical oscillations, we use a recent class of shock-capturing schemes, the so-called OSMP schemes. The wavefront arrival times of acoustic waves are in good agreement with computations based on Dispersion-Relation-Preserving (DRP) schemes used in our former studies. Comparisons of calculations and experimental data permit to discuss the role of atmospheric absorption and nonlinear propagation on amplitudes of signals. [Preview Abstract] |
Tuesday, November 25, 2008 9:57AM - 10:10AM |
MF.00010: Development of high energy molecular beam source using ultra small shock tube Nobuya Miyoshi, Yuta Yoshimoto, Ikuya Kinefuchi, Kazuya Shimizu, Shu Takagi, Yoichiro Matsumoto The molecular beam technique is one of the powerful methods to investigate the gas-surface interactions in rarefied gas flows. The scattering experiment particularly with the beam translational energy over a wide range including the activation energies of surface reactions enables us to understand the phenomena in great detail. In order to generate the high energy beam in a range of 1 - 5 eV without any undesirable impurities, we have been developing a molecular beam source with a non- diaphragm type shock tube which can operate at a repetition rate high enough for efficient data acquisition. The volume of our shock tube is much smaller than that of conventional ones so that the evacuation time between each shot can be made as short as possible. The inner diameter of the shock tube is only 2 mm and thereby leads to the strong effect of the boundary layer on the acceleration and attenuation processes of shock waves. Hence we measured the shock Mach number as a function of the position along the tube to optimize the tube length. Finally we installed the shock tube in our molecular beam setup and measured the time- of-flight distributions of the shock-heated beams. These results suggest the design criteria for optimizing the molecular beam source with the adequate performance. [Preview Abstract] |
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