Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session A4: Boundary Layers I: Shock Wave Boundary Layer Interaction |
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Chair: Farrukh Alvi, Florida State University Room: 326 |
Sunday, November 24, 2013 8:00AM - 8:13AM |
A4.00001: The Anatomy of a Shock-Boundary Layer Interaction in Hypervelocity Flow Andrew Knisely, Andrew Swantek, Joanna Austin We examine laminar shock-boundary layer interaction over a double wedge geometry in hypervelocity flow. The macroscopic features of this configuration have been shown to be sensitive to the thermochemical energy exchange occurring on a molecular scale. In the current work, an expansion tube is used to accelerate air and nitrogen gas to hypervelocity flow conditions (3.8 km/s, 8.0 MJ/kg) over a 30-55 degree double wedge model. To examine the response of the gas dynamic flow features to real gas effects, we ``tune'' the chemical composition (O2 content) of the freestream by varying the relative ratio of nitrogen gas and air in the initial test gas. High speed schlieren and chemiluminescence (100k fps) are used to produce overlaid images that visualize the flow structures and identify regions of increased thermochemical activity. These qualitative data are combined with quantitative, pointwise NO vibrational temperature measurements made in the A-X transition band (220--255 nm) to investigate regions of interest such as behind the bow shock and in the shear layer. A transition in bow shock standoff distance and post-shock temperature profiles is identified at 50\% O2 content. [Preview Abstract] |
Sunday, November 24, 2013 8:13AM - 8:26AM |
A4.00002: Response of Hypervelocity Boundary Layers to Global and Local Distortion William Flaherty, Joanna Austin Concave surface curvature can impose significant distortion to compressible boundary layer flows due to multiple, potentially coupled, effects including an adverse pressure gradient, bulk flow compression, and possible centrifugal instabilities. Approximate methods provide insight into dominant mechanisms, however few strategies are capable of treating heat transfer effects and predictions diverge significantly from the available experimental data at larger pressure gradient. In this work, we examine the response of boundary layers to global and local distortions in hypervelocity flows where thermochemical energy exchange has significant impact on boundary layer structure and stability. Experiments are carried out in a novel expansion tube facility built at Illinois. We demonstrate that reasonable estimates of the laminar heat flux augmentation may be obtained as a function of the local turning angle, even at the conditions of greatest distortion. As a model problem to study the evolution of large-scale structures under strained conditions, streamwise vortices are imposed into the boundary layer. The impact of the additional local distortion is investigated. The heat transfer scaling is found to be robust even in the presence of the imposed structures. [Preview Abstract] |
Sunday, November 24, 2013 8:26AM - 8:39AM |
A4.00003: \textit{A priori} estimates of subgrid-scale terms for LES of shock-boundary layer interactions Avinash Jammalamadaka, Farhad Jaberi The shock wave interaction with a turbulent boundary layer in high speed flows is very complex and requires high-fidelity numerical methods like direct numerical simulation (DNS) and large-eddy simulation (LES) to capture the flow physics. With the obvious limitations of DNS, we look upon LES as a viable alternative to provide us with an accurate description of shock-boundary layer interaction (SBLI) in high Reynolds number flows. Although there have been some promising results for SBLI, and compressible flows, in general, using LES, there still exists a potential to further improve the accuracy of the numerical model. In this study, \textit{a priori} estimates of various subgrid-scale (SGS) terms in the compressible filtered Navier-Stokes equations are made using highly accurate DNS data for SBLI. The SGS stresses and their components, namely, Leonard, Cross and Reynolds, are examined in various regions of the flow for different shock strengths and filter widths. The backscatter in various regions of the flow was computed and was found to be significant only instantaneously. A term-by-term analysis of the SGS terms in the filtered total energy equations indicated that while each term was significant by itself, the net contribution by all the terms was relatively small and this was indicated in the \textit{a posteriori} analysis as well. [Preview Abstract] |
Sunday, November 24, 2013 8:39AM - 8:52AM |
A4.00004: Multi-fidelity numerical simulations of shock/turbulent-boundary layer interaction with uncertainty quantification Ivan Bermejo-Moreno, Laura Campo, Johan Larsson, Mike Emory, Julien Bodart, Francisco Palacios, Gianluca Iaccarino, John Eaton We study the interaction between an oblique shock wave and the turbulent boundary layers inside a nearly-square duct by combining wall-modeled LES, 2D and 3D RANS simulations, targeting the experiment of Campo, Helmer \& Eaton, 2012 (nominal conditions: $M=2.05$, $Re_{\theta}=6,500$). A primary objective is to quantify the effect of aleatory and epistemic uncertainties on the STBLI. Aleatory uncertainties considered include the inflow conditions (Mach number of the incoming air stream and thickness of the boundary layers) and perturbations of the duct geometry upstream of the interaction. The epistemic uncertainty under consideration focuses on the RANS turbulence model form by injecting perturbations in the Reynolds stress anisotropy in regions of the flow where the model assumptions (in particular, the Boussinesq eddy-viscosity hypothesis) may be invalid. These perturbations are then propagated through the flow solver into the solution. The uncertainty quantification (UQ) analysis is done through 2D and 3D RANS simulations, assessing the importance of the three-dimensional effects imposed by the nearly-square duct geometry. Wall-modeled LES are used to verify elements of the UQ methodology and to explore the flow features and physics of the STBLI for multiple shock strengths. [Preview Abstract] |
Sunday, November 24, 2013 8:52AM - 9:05AM |
A4.00005: Conditional Analysis of a Shock Wave and Turbulent Boundary Layer Interaction Justine Li, Stephan Priebe, M. Pino Martin The characterization of the aperiodic cycle of unsteadiness in shock wave and turbulent boundary layer interaction (STBLI) is presented for a 24$^{\circ}$ compression ramp configuration with a fully turbulent incoming boundary layer at Mach 2.9. In previous work on the direct numerical simulation (DNS) at similar conditions, Priebe and MartÃn (JFM 2012) found that the aperiodic low-frequency unsteady shock motion is related to the phase of separation bubble growth and collapse. At a reduced computational cost as compared to the DNS, the large eddy simulation (LES) enables the generation of data covering a sufficiently long sampling time to converge the conditional statistics on the phases of the cycle. [Preview Abstract] |
Sunday, November 24, 2013 9:05AM - 9:18AM |
A4.00006: Characterization of the Shear Layer in a Mach 3 Shock/Turbulent Boundary Layer Interaction Clara Helm, Stephan Priebe, Justine Li, Pierre Dupont, Pino Martin The unsteady motion of fully separated shock and turbulent boundary layers interactions (STBLIs) is characterized by an energized low-frequency motion that is two orders of magnitude lower than that of the incoming turbulence. In addition, the spectra shows significant energy content at frequency that is between the characteristic low frequency and the higher frequency motions of the incoming turbulence. The intermediate frequency content is hypothesized to be associated with the existence of Kelvin-Helmholtz type structures, which form in the shear layer downstream of the separation shock and are shed near the reattachment point downstream of the interaction. The current research is concerned with investigating the origins of the intermediate frequencies, and how they may be related to or possibly influence the low-frequency unsteadiness. Specifically, LES data of a Mach 3 STBLI over a 24o ramp are used to estimate convection velocities within the shear layer downstream of the shock. In addition, Brown and Thomas type correlations are used to estimate time and length scales of the eddies in the shear layer. This work is supported by the Air Force Office of Scientific Research under grant AF/9550-10-1-0164. [Preview Abstract] |
Sunday, November 24, 2013 9:18AM - 9:31AM |
A4.00007: Transient unsteadiness of SWBLI in an axisymmetric geometry Woutijn J. Baars, Charles E. Tinney Shock wave boundary layer interactions (SWBLIs) inside an axisymmetric large area ratio nozzle ($M_e = 5.58$) are studied by way of unsteady wall pressure measurements. First, a case of non-transient SWBLI is considered by operating at a nozzle pressure ratio of 28.7, at which a RSS structure forms with trapped annular separation bubbles [Baars et al. AIAA J. 50:1, 2012]. Conditional selection of the data [Erengil and Dolling, AIAA J. 29:5, 1991] resemble similar unsteady features as encountered in nominally 2D interactions. That is, 1) pressures increase in the separated regions as the incipient separation shock translates downstream, and vice versa, which indicates a breathing behavior, and 2) the PDF of the time between shock crossings in the intermittent region is highly skewed, e.g. the shock zero frequency is 33\% of the most probable frequency. Secondly, ramping the pressure ratio sweeps the shock system over the transducers and allows the study of transient SWBLI. Time-frequency analyses reveal global features of the unsteady wall signatures, such as low-frequency oscillations in separated regions, and it is identified that nozzle shut-downs are more energetic than start-ups. [Preview Abstract] |
Sunday, November 24, 2013 9:31AM - 9:44AM |
A4.00008: Constrained Large-eddy Simulation of Supersonic Turbulent Boundary Layer over a Compression Ramp Liang Chen, Zuoli Xiao, Yipeng Shi, Shiyi Chen The mean and statistical quantities as well as the flow patterns of a supersonic turbulent boundary layer over a compression ramp are numerically investigated using the constrained large-eddy simulation (CLES) method. The compression ramp is characterized by a deflection angle of 24. The free-stream Mach number is Ma$=$2.9, and the Reynolds number based on the inlet boundary layer thickness is Re$\theta =$2300, in accordance with the reference experiment. A rescaling recycling technique is utilized for imposing the inflow boundary. Both the spatial average and the time average methods are employed in the constraint conditions for the Reynolds stresses and heat flux in the near-wall region. The results from CLES are well compared with those from detached-eddy simulation (DES), Reynolds-averaged Navier-Stokes (RANS) simulation, traditional large-eddy simulation (TLES), the experimental and DNS data. It is found that the wall-friction distribution, the wall-pressure distribution, the size of separation bubble, etc., predicted by CLES are in good agreement with the experimental and/or DNS data. Meanwhile, CLES proves to be able to predict the locations of separation and reattachment more accurately than DES, RANS and TLES. [Preview Abstract] |
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