Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session KS: Compressible Turbulence |
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Chair: Dale Pullin, California Institute of Technology Room: Hilton Chicago Stevens 4 |
Monday, November 21, 2005 4:10PM - 4:23PM |
KS.00001: Examination of the dominant azimuthal structures in the near-field pressure region of a high-speed turbulent jet Andr\'{e} Hall, Mark Glauser Numerous experiments have been conducted on characterizing the near-field region of the turbulent axisymmetric jet. The modal distribution of the velocity field has been shown to be characterized by a substantial amount of energy, both in the lower Fourier-azimuthal modes (0,1,{\&} 2), as well as the higher modes (4,5,{\&} 6). The near-field pressure region has demonstrated energy in the lower azimuthal modes (0,1,{\&} 2) only. Capturing the signature of higher modes known to be present in the velocity field, in the pressure field, would be valuable in a controls application. In particular if sensed at the jet lip. Experiments are conducted using a jet nozzle 50.8mm in diameter at exit, with a flow temperature of 25$^{\circ}$C, balanced with ambient conditions. Fluctuating pressure measurements are captured by an azimuthal array of 15 \textit{Kulite }transducers, at an exit velocity of \textit{Mach }0.85 (\textit{Re}=9.8E5). The array is repositioned downstream at several streamwise locations in the fully turbulent, high Reynolds number compressible flow field in an attempt to capture the higher modes found in the velocity field. If no signature of higher modes is found in the fluctuating pressure field at locations where the higher modes are present in the velocity field, these experiments will confirm that pressure cannot resolve these higher modal events. A transfer function between the two distributions can also be evaluated. [Preview Abstract] |
Monday, November 21, 2005 4:23PM - 4:36PM |
KS.00002: Predictions of Transverse Injection of Air or Helium into Supersonic Crossflow. C. Randall Truman, Amol Palekar, Peter Vorobieff Predictions of a sonic jet of air or helium injected into a Mach 2 crossflow are presented. The injection is transverse, characterized as a jet in crossflow (JICF). The Wilcox two-equation model was used to model turbulence. The predictions are steady and symmetric about the center of the circular injection hole. Results from the two cases are compared with ensemble-averaged experimental results by Gruber et al. (1996). Predictions of shock structures, including the barrel shock and Mach disk, and the counter-rotating vortex pair that dominates mixing are in good agreement with the experiment [Preview Abstract] |
Monday, November 21, 2005 4:36PM - 4:49PM |
KS.00003: Aerodynamic Control and Mixing with Ramp Injection Paul Dimotakis, Michael Johnson, Michael Slessor, Jeffrey Bergthorson Experiments were conducted to investigate the behavior of a flow and geometry with many features that are potentially useful for a Supersonic Combustion Ramjet (SCRAMJET) engine: a recirculation zone for flameholding, enhanced mixing between fuel and air, and low total-pressure losses. In subsonic flow with no mass injection, the exit velocity and guidewall static- pressure profiles are found to collapse over a large range of inlet Reynolds numbers. Significant control of exit velocity and guidewall pressure profiles is possible via injection through a perforated ramp into the freestream. The control authority on the overall pressure coefficient increases with increasing inlet Reynolds number. Simple control volume analysis bounds the expected overall pressure coefficient for the device. In transonic/low-supersonic flow, the area ratio calculated from measured pressures agrees well with the visual shear-layer thickness, confirming low total-pressure losses. Further flow control is possible through variable heat release from a fast- chemical reaction between reactants carried in the two streams. At the highest heat release studied, mass injection requirements are lowered by, roughly, a factor of two. Measurements of mixing inferred from the temperature rise in reacting flow indicate higher mixing levels vs. classical free shear layers. As in free shear layers, however, mixing levels decrease with increasing heat release. [Preview Abstract] |
Monday, November 21, 2005 4:49PM - 5:02PM |
KS.00004: Turbulent subsonic particle-laden flow over an open backward-facing step with and without countercurrent shear at {R}e=3000 Gustaaf Jacobs, David Kopriva, Farzad Mashayek We present a numerical study of the subsonic particle-laden flow over an open backward-facing step at a Reynolds number of $Re$=3000. The compressible Navier-Stokes equations are simulated without turbulence models using a multidomain spectral method. Point particles are tracked assuming a Stokes flow model. We focus on the compressibility effects and the effect of countercurrent shear on the zero and first order turbulence statistics and flow topology for low to moderate Mach numbers. At $Mach$=0.1 our results compare well with published incompressible numerical simulations and experiments. At $Mach$=0.4 we show that the shear layer reattaches 10\% closer the step than at the nearly incompressible $Mach$=0.1 as a result of transient compressibility effects related to pressure-dilatational dissipation. The application of a moderate level of countercurrent shear destabilizes the shear layer immediately increasing turbulence intensity and particle deposition behind the step, and decreasing the reattachment length with 12\%. Countercurrent shear also creates large structures that shed with a distinct period frequency. [Preview Abstract] |
Monday, November 21, 2005 5:02PM - 5:15PM |
KS.00005: Large-scale coherence in a supersonic turbulent boundary layer Bharathram Ganapathisubramani, Noel. T Clemens, David S. Dolling Wide-field particle image velocimetry measurements were performed in a Mach 2 turbulent boundary layer to study the characteristics of large scale coherence at two wall-normal locations ($y/\delta = 0.16$ and $0.45$). Instantaneous velocity fields at both locations indicate the presence of elongated streamwise strips of uniform low- and high-speed fluid (length $>8\delta$). These long coherent structures exhibit strong similarities to those that have been found in subsonic boundary layers, which suggests an underlying similarity between the subsonic and supersonic regimes. Two-point correlations of streamwise velocity fluctuations show coherence over a longer streamwise distance at $y/\delta = 0.45$ than at $y/\delta = 0.16$, which indicates an increasing trend in the streamwise length scale with wall-normal location. The spanwise scale of these uniform velocity strips increases with increasing wall-normal distance as found in subsonic boundary layers. The large scale coherence is consistent with the presence of ``hairpin packets'' (a model previously proposed for subsonic boundary layers). [Preview Abstract] |
Monday, November 21, 2005 5:15PM - 5:28PM |
KS.00006: Unsteady Effects in Shock/Turbulent Boundary Layer Interaction at M=2.25 Sergio Pirozzoli, Francesco Grasso The interaction of a supersonic flat plate boundary layer flow at $Re_{\theta} \approx 4000$ with an impinging oblique shock wave ($M_{\infty}=2.25$, $\beta=32.7^{\circ}$) is analyzed by means of direct numerical simulation of the Navier-Stokes equations. Under the selected conditions the incoming boundary layer undergoes a mild unsteady separation and the incident shock undergoes a severe flapping motion due to the interaction with the large scale structures embedded in the boundary layer. The analysis of the unsteady flow properties indicates that such quantities as pressure are characterized by a broadband spectrum extending to high frequencies, superposed with low frequency oscillations associated with the large scale motion of the separation shock. The main contribution of the present work is to provide a link between the unsteady motion of the shock wave and the unsteady shedding of the large vortical structures generated next to the separation point; such structures are also shown to be responsible for the amplification of turbulence kinetic energy and shear stress across the interaction zone and for the slow relaxation of the boundary layer to an equilibrium state. [Preview Abstract] |
Monday, November 21, 2005 5:28PM - 5:41PM |
KS.00007: Large Eddy simulation of compressible flows with a low-numerical dissipation patch-based adaptive mesh refinement method Carlos Pantano, Ralf Deiterding, David Hill, Dale Pullin We describe a hybrid finite difference method for large-eddy simulation (LES) of compressible flows with a low-numerical dissipation scheme and structured adaptive mesh refinement (SAMR). Numerical experiments and validation calculations are presented including a turbulent jet and the strongly shock-driven mixing of a Richtmyer-Meshkov instability. The approach is a conservative flux-based SAMR formulation and as such, it utilizes refinement to computational advantage. The numerical method for the resolved scale terms encompasses the cases of scheme alternation and internal mesh interfaces resulting from SAMR. An explicit centered scheme that is consistent with a skew-symmetric finite difference formulation is used in turbulent flow regions while a weighted essentially non-oscillatory (WENO) scheme is employed to capture shocks. The subgrid stresses and transports are calculated by means of the streched-vortex model, Misra \& Pullin (1997) [Preview Abstract] |
Monday, November 21, 2005 5:41PM - 5:54PM |
KS.00008: Comparison of Modern Methods for Shock Hydrodynamics Andrew Cook The accuracy and efficiency of several methods are compared for simulating multi-fluid compressible flows. The methods include a Godunov scheme, a Weighted Essentially Non-Oscillatory (WENO) method, an Arbitrary Lagrangian Eulerian (ALE) algorithm and a Spectral/Compact (S/C) scheme. Test problems include a compressible breaking wave, Shu's problem, Noh's problem, the Taylor-Green vortex, decaying turbulence, Rayleigh-Taylor instability and Richtmyer-Meshkov instability. The S/C method employs an artificial bulk viscosity for treating shocks and an artificial shear viscosity for modeling turbulence. A polyharmonic operator, applied to the strain rate, imparts spectral-like behavior to the viscosities, thus eliminating the need for ad hoc limiters and/or switches to turn them off in smooth regions, e.g., expansion, uniform compression, solid-body rotation etc. A low-pass filter is applied to the flow variables to reduce aliasing errors. The S/C method is demonstrated to capture shocks as well as the other schemes, while providing superior resolution of small features. [Preview Abstract] |
Monday, November 21, 2005 5:54PM - 6:07PM |
KS.00009: Local Stencil Adaption Properties of a WENO Scheme in Direct Numerical Simulations of Compressible Turbulence Ellen M. Taylor, M. Pino Martin Weighted essentially non-oscillatory (WENO) methods can simultaneously provide the high order of accuracy, high bandwidth-resolving efficiency, and shock-capturing capability required for the detailed simulation of compressible turbulence. However, rigorous analysis of the local error properties of these nonlinear numerical methods is difficult. We use a bandwidth-optimized WENO scheme to conduct direct numerical simulations (DNS) of two- and three-dimensional decaying isotropic turbulence, and we evaluate the performance of quantitative indicators of local WENO adaption behavior within the resulting flow fields. One aspect of this assessment is the demarcation of shock-containing and smooth regions where the WENO method should respectively engage its adaption mechanism and revert to its linear optimal stencil. Our results show that these indicators, when synthesized properly, can provide reliable and valuable quantitative information suitable for statistical characterization. [Preview Abstract] |
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