Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session D27: Supersonic Flows I |
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Chair: Xiaolin Zhong, University of California, Los Angeles Room: 31C |
Sunday, November 18, 2012 2:15PM - 2:28PM |
D27.00001: Characterization of the Shear Layer in a Mach 3 Shock/Turbulent Boundary Layer Interaction Clara Helm, Stephan Priebe, Pierre Dupont, Pino Martin A detailed characterization of the shear layer in a direct numerical simulation of a Mach 3 shock/turbulent boundary layer interaction for a $24\rm{^o}$ ramp is presented. The behaviour of the shear layer as a plane mixing layer will be demonstrated through similarity profiles of the mean velocity and Reynolds stresses. The existence of large scale coherent eddies associated with the Kelvin-Helmholtz structures characteristic of plane mixing layers is investigated. An estimation of the time and length scales associated with these eddies is conducted. Also presented is evidence of the modulation of the fluctuating intensities in the shear layer by the low-frequency motion of the shock. This work is supported by the Air Force Office of Scientific Research under grant AF/9550-10-1-0164. [Preview Abstract] |
Sunday, November 18, 2012 2:28PM - 2:41PM |
D27.00002: Shock Boundary Layer Interaction Sensitivity to Upstream Geometric Perturbations Laura Campo, David Helmer, John Eaton Shock boundary layer interactions (SBLIs) can have drastic effects on the performance of external aerodynamics and propulsion systems in high speed flight vehicles. In such systems, the upstream and boundary conditions of the flow are uncertain, and the sensitivity of SBLIs to perturbations in these conditions is unknown. The sensitivity of two SBLIs -- a compression corner interaction and an incident shock interaction -- to small geometric perturbations was investigated using particle image velocity measurements. Tests were performed in a continuously operated, low aspect ratio, Mach 2.1 wind tunnel. The shock was generated by a 1.1mm high $20^{\circ}$ wall-mounted compression wedge, and various configurations of small ($h<0.2\delta$) steady bumps were introduced upstream on the opposite wall. 100 perturbed cases were tested in order to generate a dataset which is well suited for validation of CFD codes. Both SBLIs were very sensitive to perturbations in a given region and insensitive to perturbations outside of it. Depending on the location of the perturbations, the compression corner interaction could be significantly strengthened or weakened. The position of the incident SBLI was also a strong function of both the location and size of the upstream perturbations. [Preview Abstract] |
Sunday, November 18, 2012 2:41PM - 2:54PM |
D27.00003: LES Study of Shock Wave and Turbulent Boundary Layer Interaction Justine Li, Stephan Priebe, Pino Martin The large eddy simulation (LES) of a 24$^{\circ}$ compression ramp shock wave and turbulent boundary layer interaction (STBLI) is presented. This work builds on previous work on the direct numerical simulation (DNS) of STBLI with similar incoming boundary layer flow conditions (Priebe and Mart\'{i}n, JFM 2012). The fully-turbulent inflow boundary layer is at Mach 2.9 and the Reynolds number based on momentum thickness is Re$_{\theta}$ = 2900. The LES data cover a sufficiently long time to statistically resolve the low-frequency aperiodic cycle characteristic of supersonic STBLI. We present the characterization of the dynamics in the downstream separated flow. [Preview Abstract] |
Sunday, November 18, 2012 2:54PM - 3:07PM |
D27.00004: Large-Eddy Simulation of a Shock Train in a Duct with Side Walls Brandon Morgan, Karthik Duraisamy, Sanjiva Lele Large-eddy simulation (LES) is utilized to investigate the three-dimensionality of a shock train in a constant-area isolator model with fully resolved side walls ($M_{\infty }$ = 1.61, Re$_{\theta} \approx $ 1660). Flow conditions and geometry are selected to match experimental conditions investigated by Carroll (1988); although Reynolds number is reduced to ensure adequate mesh resolution. Simulations with spanwise periodic boundary conditions are first performed, the results of which are compared to experiment and validated with a three-level grid refinement study. The same shock train interaction is then simulated in a three-dimensional, low-aspect ratio rectangular duct geometry with particular emphasis placed on characterizing secondary corner flows and the effects of these corner flows on the location and structure of the shock train. It is found, for instance, that location of the initial shock is particularly sensitive to the effects of spanwise confinement. Most significantly, it is observed that the same pressure ratio which results in a stable shock train with periodic boundary conditions may result in isolator unstart when side-wall effects are fully resolved. [Preview Abstract] |
Sunday, November 18, 2012 3:07PM - 3:20PM |
D27.00005: Toluene PLIF temperature and pressure imaging in supersonic flows Victor Miller, Mirko Gamba, M. Godfrey Mungal, Ronald K. Hanson Planar laser-induced fluorescence (PLIF) of toluene is used to image temperature, T, and pressure, P, in supersonic flows. Toluene fluorescence is broadband and exhibits a red-shift at elevated temperatures, enabling two-camera, dual-band imaging of temperature. With the temperature field known, the original LIF signal from a single camera is converted to pressure. This technique is demonstrated by imaging Mach 2.3 flow of nitrogen seeded with 0.5\% toluene (by volume) over a wedge and a cylinder; PLIF-imaged T and P fields are compared to computed solutions of these flowfields, and preliminary comparisons show promise. [Preview Abstract] |
Sunday, November 18, 2012 3:20PM - 3:33PM |
D27.00006: A Multi-Zone and Cut-Cell Method for High-Order Numerical Simulations of Compressible Flow Over Arbitrary Geometries Patrick Greene, Jeff Eldredge, Xiaolin Zhong, John Kim The primary goal of our work is to study the effects of isolated roughness elements on the stability of hypersonic flow. To achieve this goal, we have been developing a high-order finite-difference compressible Navier-Stokes solver with the ability to simulate high-speed flow over arbitrary roughness geometries. A high-order cut-cell method is used to impose the roughness geometry on a simple Cartesian grid. The main idea behind the cut-cell method is to switch to a high-order non-uniform one-sided finite-difference stencil whenever the normally used stencil will cross a fluid-solid interface. In addition, a multi-zone method is implemented to provide more precise control over the placement of grid points compared to a single grid with clustering. The method allows a coarse grid to be placed over the entire domain with smaller high-resolution grids placed in regions where complex flow physics are expected. Results are presented for hypersonic flow over a cylindrical roughness on a flat plate. The roughness height is on the same order of magnitude as the boundary layer thickness. The results will be compared to recent experiments. [Preview Abstract] |
Sunday, November 18, 2012 3:33PM - 3:46PM |
D27.00007: Rainbow Schlieren Deflectometry Measurements With a Pulse Detonation Engine Charles DeSio, Christopher Stevens, Rudy Johnson, Semih Olcmen Unsteady, under-expanded, Mach five flow is observed and measured with the use of a rainbow schlieren deflectometry technique. Measurements are taken on a pulse detonation engine system at the exit of a 0.5 inch diameter pre-detonation tube and at the exit of a two inch diameter thrust tube. The predetonator is fueled with propane/nitrous oxide, and the thrust tube is fueled with hydrogen/air. Collimated light illuminates the flow field after passing a 100 micron slit in a conventional schlieren setup. The collected light is focused on a color filter, and light ray deflections fall on different color bands. The defections can be calculated using a simple calibration. Angular deflections due to density changes in the flow are recorded by a high-speed, color camera. Density gradients are calculated along the flow axis as well as perpendicular to the flow axis. Structures observed without post-processing include: Shock waves, flame fronts, Mach disk, and shock diamonds. The color schlieren system is simple to set up and use, relatively inexpensive to purchase, and produces accurate, nonintrusive flow data. [Preview Abstract] |
Sunday, November 18, 2012 3:46PM - 3:59PM |
D27.00008: Planar Imaging of Mach 3 Hypermixer Flowfields with Varying Geometry Ross Burns, Noel Clemens At the high Mach number associated with hypersonic flight, potentially excessive pressure loads and changes in air chemistry necessitate supersonic flow within a scramjet combustor. A form of mixing enhancement is therefore required to enable proper mixing of the fuel and air streams and maintain efficient combustion. Hypermixers have shown promise as an effective mixing enhancement strategy, utilizing streamwise vorticity to enhance large scale transport and micromixing rather than relying solely on turbulence. An experimental investigation of several strut-based Mach 3 hypermixing flowfields is being conducted, concentrating on the effect of geometric variations (ramp angle and spacing) on the flowfield mixing characteristics. Global flow features are examined through the use of planar laser scattering (PLS) and two-component particle image velocimetry (PIV). The evolution of streamwise vortical structures is observed at different streamwise locations using stereoscopic PIV. Finally, the interaction of these vorticies with an injected scalar is studied by combining the use of two- and three-component PIV with planar laser-induced fluorescence (PLIF). [Preview Abstract] |
Sunday, November 18, 2012 3:59PM - 4:12PM |
D27.00009: Numerical investigation of non-equilibrium effects in hypersonic turbulent boundary layers Pilbum Kim, John Kim, Xiaolin Zhong, Jeff Eldredge Direct numerical simulations of a spatially developing non-equilibrium hypersonic turbulent boundary layer have been conducted. A pure oxygen flow over a non-catalytic flat plate at the wall temperature, $T_w = 1,000\;K$, is considered. The boundary edge conditions are given as $M_e = 9.1$, $T_e = 792\;K$, and $P_e = 6,565\;Pa$, which are corresponding to flow conditions around a blunt wedge with a $3.174\;mm$ radius and $7^{\circ}$ half angle at $M_\infty = 15.3$, $T_\infty = 285\;K$, and $P_\infty = 664\;Pa$. The initial conditions are obtained from a turbulent boundary layer simulation of a perfect gas. In addition, the species concentrations and vibrational temperature at the inlet are prescribed as equilibrium concentrations and the translational/rotational temperature, respectively. The data samples are collected at a downstream location at which a statistically stationary state has been achieved. From the collected data set, turbulence quantities are computed and compared with those from a perfect gas simulation in order to investigate the effects of thermal and chemical non-equilibrium on turbulent boundary layers. Those comparisons will be reported. [Preview Abstract] |
Sunday, November 18, 2012 4:12PM - 4:25PM |
D27.00010: Transition within a hypervelocity boundary layer on a 5-degree half-angle cone in freestream air/CO$_{2}$ mixtures Joseph Jewell, Ross Wagnild, Ivett Leyva, Graham Candler, Joseph Shepherd The effect of freestream CO$_{2}$ content on transition in hypervelocity flow over a slender cone was investigated in experiments and computations. Experimental data were obtained in Caltech's T5 reflected shock tunnel. The model was a 5 degree half-angle sharp cone instrumented with thermocouples, providing heat transfer measurements from which transition locations were determined by comparison with laminar and turbulent heat flux correlations. Four carbon dioxide/air gas mixtures were tested at reservoir enthalpies from 7--10 MJ/kg and reservoir pressures from 55--60 MPa to attempt to reproduce the largest shift in transition location implied by computations using the semi-empirical e$^{N}$ approach. By mass fraction of carbon dioxide these mixtures were 0.0 (e.g. all air), 0.5, 0.75, and 1.0. For tests at an enthalpy of $\sim $9.2 MJ/kg, transition delays of up to 30{\%} in terms of x-location, 38{\%} in terms of edge Reynolds number, and 140{\%} in terms of the Reynolds number evaluated at reference conditions were documented for increasing CO$_{2}$ mass fractions compared with similar experiments in air. [Preview Abstract] |
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