Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session BM: Compressible Flows |
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Chair: Godfrey Mungal, Stanford University Room: 200B |
Sunday, November 22, 2009 10:30AM - 10:43AM |
BM.00001: Boundary Layer Entrainment and Combustion in a Transverse Jet in Supersonic Crossflow Will Heltsley, Mirko Gamba, Godfrey Mungal, Ronald Hanson Recent experiments have reconstructed the 3D structure of the combustion regions around burning jets-in-supersonic-crossflow using OH-PLIF in multiple orthogonal planes. A sonic hydrogen jet with a momentum-flux ratio of $J$ = 4 was injected normally into high temperature air crossflows at two freestream conditions: (a) $T $= 1250 K, $M $= 2.7, $P $= 25 kPa, and (b) $T $= 1500 K, $M $= 2.4, $P $= 25 kPa. These freestream conditions produce stable combustion in the shear layer of the jet at $J$ = 4. The $T$ = 1500 K case also produces an intermittently reacting recirculation region in the shock foot region at the front of the jet, and a highly reactive boundary layer. The boundary layer ignites in the recirculation region, wraps around the jet at the base of the jet's bow shock cell and develops downstream where it is entrained into the jet wake. This previously unreported fuel entrainment and ignition in the near field boundary layer may be a significant mechanism for ignition and flame stabilization in the far field of such transverse jets. [Preview Abstract] |
Sunday, November 22, 2009 10:43AM - 10:56AM |
BM.00002: Simulation of Scramjet Fuel Injection Using a Hybrid RANS/LES Approach David Peterson, Graham Candler A methodology is presented for the simulation of realistic scramjet combustor sections at actual operating conditions. A flow solver with an unstructured grid framework is used such that grids can be constructed for complex geometries. Numerics are chosen for robustness and reliability, while not being overly dissipative as to overwhelm the actual flow physics. The flow around a scramjet fuel injector is highly unsteady and dominated by coherent, large-scale structures. The goal is to be able to capture the key physics of the flow field, without resolving all of the detail of the flow. In regions of the flow where unsteady phenomenon are important, such as where mixing occurs or in massively separated regions, LES is used. RANS is used in regions of attached flow, such as boundary layers, where RANS performs well. In addition, RANS is also used as a wall model for the LES regions of the flow. This allows for realistic Reynolds number to be simulated at reasonable cost. Comparisons are made between simulations and available experimental data. [Preview Abstract] |
Sunday, November 22, 2009 10:56AM - 11:09AM |
BM.00003: A Computational Study of Hypervelocity Boundary Layer Stability by Means of Carbon Dioxide Injection Ross Wagnild, Graham Candler An experimental method for introducing carbon dioxide as a means of stabilizing a hypervelocity boundary layer over a slender bodied vehicle is investigated through the use of numerical simulations. The motivation for this concept is derived from the results of previous experiments and calculations which demonstrated the ability of fluid flows in chemical and thermal non-equilibrium to absorb energy from acoustic disturbances, particularly flows involving carbon dioxide. In the current study, the computational model is a five-degree half-angle cone with a single row of injector ports. The effect of the injection and the transition location are determined by solving the parabolized stability equations and using the semi-empirical eN method. The preliminary results show a delay in the transition location as compared to a cone without injection under the same flight conditions. [Preview Abstract] |
Sunday, November 22, 2009 11:09AM - 11:22AM |
BM.00004: Boundary Layer Transition on Elliptic Cones in Hypersonic Flow Matthew Bartkowicz, Pramod Subbareddy, Graham Candler We are studying transition to turbulence at hypersonic conditions using a combination of parabolized stability equations and direct numerical simulations. In this work we perform DNS of acoustic disturbances interacting with the Mach 8 flow over a 4:1 elliptic cross-section cone to model the experiments of Huntley and Smits (2000). A fourth-order accurate low-dissipation numerical method is used, with large-scale body-fitted grids to obtain accurate results. A spectrum of planar random phase acoustic disturbances are introduced in the free-stream with amplitudes consistent with experiment. We observe instability growth and non-linear behavior similar to that observed in the filter Rayleigh scattering flow visualization taken at Princeton. [Preview Abstract] |
Sunday, November 22, 2009 11:22AM - 11:35AM |
BM.00005: Unsteadiness of low-Reynolds-number shock / boundary layer interactions Venkateswaran Narayanaswamy, Noel Clemens Low Re shock wave / boundary layer interactions (SWBLI) generated by compression ramps in a Mach 3 flow are studied experimentally. Ramp angles ranging from 16\r{ } to 24\r{ } are used to produce separated flows of varying strength (or length-scale). The upstream boundary layers are turbulent with Re$_{\theta } \quad \approx $ 3000 - 5500. This study aims to understand the dominant mechanisms that drive the low-frequency oscillations of the separation bubble as a function of separated flow scale. The organization of the separation bubble is studied using simultaneous wall pressure measurements underneath the separation bubble. Coherence and magnitude of cross correlation between pressure fluctuations in the intermittent region and inside separation bubble is found to be between those of low Re impinging SWBLI and high Re SWBLI. Simultaneous PIV in the upstream boundary layer and wall pressure measurements are used to characterize the influence of the incoming boundary layer fluctuations on the separation bubble dynamics. Furthermore, correlations between the velocity within the separated flow and wall pressure fluctuations are used to study instabilities intrinsic to the separated flow. [Preview Abstract] |
Sunday, November 22, 2009 11:35AM - 11:48AM |
BM.00006: Helium injection in a turbulent boundary layer at hypersonic speeds Parthav Desai, Dipankar Sahoo, Alexander Smits Low level of helium injection into a transitional or turbulent boundary layer can have substantial effect on the boundary layer structure, as shown by Auvity, Etz, Smits (Physics of Fluids, Vol 13 no 10, 2001) for the flow over a flat plate at Mach 8. Here, we report the results of additional experiments to study the effects of helium injection on the turbulence statistics and the wall heat flux. We use PIV to obtain the velocity fields, and infrared thermography to derive the wall heat transfer distribution. The helium is injected through a slot just downstream of the trip wire, and the ratio of the momentum flux of the helium to that of the freestream flow is varied from 0 to about 0.16, as in the case of Auvity et al. Supported under NASA Grant NNX08AB46A, Program Manager Catherine McGinley. [Preview Abstract] |
Sunday, November 22, 2009 11:48AM - 12:01PM |
BM.00007: Measurement of Fluctuating Wall Pressures Beneath a Supersonic Turbulent Boundary Layer Steven Beresh, John Henfling, Russell Spillers, Brian Pruett Accurate measurement of fluctuating wall pressure spectra beneath a supersonic turbulent boundary layer has proven elusive, such that a compilation of past efforts exhibits an alarming degree of scatter and hinders the development of engineering models. Recent experiments conducted in Sandia's Trisonic Wind Tunnel up to Mach 3 have provided wall pressure data to frequencies exceeding 100 kHz to help reconcile conflicts in the historical data. Data were acquired using piezoresistive silicon pressure transducers effective at low- and mid-range frequencies, then supplemented by piezoelectric quartz sensors capable of detecting very high frequency events. The two sensor types were dynamically calibrated against a condenser microphone reference standard, then combined into a single curve describing the wall pressure spectra. Such spectra show that an increase in Mach number produces a reduction in the normalized magnitude, though the shape of the spectra remain similar; Reynolds number effects were detectable but considerably smaller for the range of test conditions. Results are compared with historical data and consequences of the measurement limitations are discussed. [Preview Abstract] |
Sunday, November 22, 2009 12:01PM - 12:14PM |
BM.00008: LES and DNS of Shock-Boundary Layer Interactions. Avinash Jammalamadaka, Zhaorui Li, Farhad Jaberi Large-eddy simulations (LES) of an incident oblique shock wave interacting with a flat-plate supersonic turbulent boundary layer at various flow/shock conditions are performed and the results are compared with the direct numerical simulation (DNS) data. The objectives are to evaluate the performance of compressible subgrid-scale (SGS) models in shock-turbulence flow regions and to study the effects of shock angle, Mach number and other parameters on the shock-boundary layer interactions. The filtered compressible Navier-Stokes equations are solved with a seventh-order Monotonicity-Preserving scheme for the Euler fluxes and a sixth-order compact scheme for the viscous terms. Comparison of DNS and LES results reveal the significance of the SGS model in supersonic boundary layer flow, particularly in the shock-turbulence regions. Due to its excessive dissipative nature, the standard Smagorinsky and gradient type models are found to predict a significantly larger mean separation bubble size when compared to the DNS data. In contrast, the predicted results by the scale-similarity, mixed or dynamic Smagorinsky models are found to be in reasonably good agreement with the DNS. Similar trends are observed for all the major flow variables. In general, the dynamic models, though computationally expensive, are found to generate better results when compared to other models. [Preview Abstract] |
Sunday, November 22, 2009 12:14PM - 12:27PM |
BM.00009: Upstream Boundary Condition Sensitivity of the Shock-Boundary Layer Interaction David Helmer, Tonkid Chantrasmi, Chris Elkins, Gianluca Iaccarino, John Eaton A low aspect ratio Mach 2.1 wind tunnel with a 20 $^{\circ}$ compression wedge is being used to validate uncertainty quantification techniques for CFD. The tunnel is operated continuously, with a mass flow rate of $\sim $0.7kg/s. The incoming pressure, temperature, and mass flow rate are monitored, and the variation in these boundary conditions is documented to provide bounds for the fluctuation applied in the CFD. The compression wedge causes an oblique shock to form, resulting in flow separation at the base of the wedge. Pressure data are measured using a closely-spaced array of taps near the base of the wedge to map the 2D footprint of the shock. These data show that the flow is only weakly three dimensional. PIV measurements are taken throughout the field, with a focus on the shock-boundary layer interaction at the base of the compression wedge. The field of measurement also includes the location where the shock impinges on the opposite wall, where another separation occurs. Measurements are compared to various CFD simulations to see how different modeling assumptions affect the result and to evaluate the validity of CFD uncertainty quantification techniques. [Preview Abstract] |
Sunday, November 22, 2009 12:27PM - 12:40PM |
BM.00010: MHD Flow Control of Oblique Shock Induced Separation John Ekaterinaris The effect of magnetic fields on the flow of conducting fluids is well known. There is current interest to exploit the body forces induced by they magnetic field for the control of separation, transition, and turbulence. The wave structure of ionized gas high speed flows under the influence of magnetic fields, which contains slow, Alfv$\iota $n, and fast waves, is more involved than the waves of ordinary gas dynamics. High resolution is required to accurately compute interactions of complex wave discontinuities and smooth flow features. Numerical solutions of the ideal and viscous magnetohydrodynamic (MHD) equations are obtained with a high order accurate shock capturing scheme. The numerical method was validated to ensure that it provides crisp resolution of discontinuities, it maintains high-order accuracy for the smooth parts of the flow, it preserves numerical stability, and eliminates nonphysical features that result from the violation of the divergence-free condition for the magnetic field. The numerical method was then applied to simulate separation control at the interaction region of an oblique shock with a laminar boundary layer under the influence of magnetic fields. It was found that magnetic fields can significantly reduce shock induced separation that appears upstream of the interaction region and can cause rapid transition to turbulence. [Preview Abstract] |
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