Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session R5: Compressible Flow: Shock-boundary Layer Interaction (computational) |
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Chair: Javier Urzay, Stanford University Room: B113 |
Tuesday, November 22, 2016 1:30PM - 1:43PM |
R5.00001: Upstream and Downstream Influence in STBLI Instability Pino Martin, Stephan Priebe, Clara Helm Priebe and Mart\'{i}n (JFM, 2012) show that the low-frequency unsteadiness in shockwave and turbulent boundary layer interactions (STBLI) is governed by an inviscid instability. Priebe, Tu, Mart\'{i}n and Rowley (JFM, 2016) show that the instability is an inviscid centrifugal one, i.e G\"{o}rtlerlike vortices. Previous works had given differing conclusions as to whether the low-frequency unsteadiness in STBLI is caused by an upstream or downstream mechanism. In this paper, we reconcile these opposite views and show that upstream and downstream correlations co-exist in the context of the nature of G\"{o}rtler vortices. We find that the instability is similar to that in separated subsonic and laminar flows. Since the turbulence is modulated but passive to the global mode, the turbulent separated flows are amenable to linear global analysis. As such, the characteristic length and time scales, and the receptivity of the global mode might be determined, and low-order models that represent the low-frequency dynamics in STBLI might be developed. The centrifugal instability persists even under hypersonic conditions. This work is funded by the AFOSR Grant Number AF9550-15-1-0284 with Dr. Ivett Leyva. [Preview Abstract] |
Tuesday, November 22, 2016 1:43PM - 1:56PM |
R5.00002: Transition in oblique shock/boundary layer interactions at Mach 5.92 Anubhav Dwivedi, Prakash Shrestha, Nathaniel Hildebrand, J.W. Nichols, M.R. Jovanovic, G.V. Candler We use the compressible flow solver US3D to perform DNS of an oblique shock wave interacting with a laminar boundary layer over an adiabatic flat plate at Mach $5.92$. Simulations are repeated with different spanwise extents. The adverse pressure gradient created by the shock causes the boundary layer to separate, leading to the formation of a recirculation bubble downstream. We consider interactions of various strengths by varying the shock angle. A sufficiently strong interaction causes the flow to become $3-D$, unsteady and eventually transition to turbulence. We observe long streamwise streaks downstream of the reattachment point which eventually break into turbulence. In the present work, we characterize the spatio-temporal dynamics of the unsteady separation bubble and these streaks using Fourier analysis and Sparsity Promoting Dynamic Mode Decomposition. To investigate the origin of these streaks we also analyze the role of linear G\"{o}rtler instability resulting from the curvature of the streamlines induced by the separation bubble. [Preview Abstract] |
Tuesday, November 22, 2016 1:56PM - 2:09PM |
R5.00003: Global stability analysis of oblique shock/boundary layer interactions at Mach 5.92 Nathaniel Hildebrand, Anubhav Dwivedi, Prakash Shrestha, Joseph W. Nichols, Mihailo R. Jovanovic, Graham V. Candler We investigate the mechanisms by which an oblique shock impinging on a hypersonic, laminar boundary layer can transition to turbulence. As the shock angle increases, the initially stable flow undergoes a three-dimensional bifurcation to instability. We apply Direct Numerical Simulation (DNS) and global stability analysis to characterize the frequency and spanwise wavenumber selected by this bifurcation. The compressible flow solver US3D was used to perform DNS as well as to construct steady, two-dimensional base flows. Direct and adjoint global modes were extracted about each base flow with the shift-and-invert Arnoldi method. Linear stability analysis was repeated for various shock angles to identify when the bifurcation occurs. An angle of 14 degrees resulted in unstable eigenvalues for spanwise wavenumbers around 0.32. The most unstable mode resides in the shear layer and creates streaks downstream. Multiplying this direct mode by its corresponding adjoint, we find the wave maker for this instability and show it's sensitive to changes near the reattachment point. We also use the adjoint modes to project DNS data on the direct modes to see their physical relevance. [Preview Abstract] |
Tuesday, November 22, 2016 2:09PM - 2:22PM |
R5.00004: Confinement effects in shock/turbulent-boundary-layer interaction through wall-modeled LES Ivan Bermejo-Moreno, Laura Campo, Johan Larsson, Julien Bodart, David Helmer, John Eaton Wall-modeled large-eddy simulations (WMLES) are used to investigate three-dimensional effects imposed by lateral confinement on the interaction of oblique shock waves impinging on turbulent boundary layers (TBLs) developed along the walls of a nearly-square duct. A constant Mach number, $M=2.05$, of the incoming air stream is considered, with a Reynolds number based on the incoming turbulent boundary layer momentum thickness $Re_{\theta}\approx14,000$. The strength of the impinging shock is varied by increasing the height of a compression wedge located at a constant streamwise location that spans the top wall of the duct at a 20° angle. Simulation results are first validated with particle image velocimetry (PIV) experimental data obtained at several vertical planes. Emphasis is placed on the study of the instantaneous and time-averaged structure of the flow for the stronger-interaction case, which shows mean flow reversal. By performing additional spanwise-periodic simulations, it is found that the structure and location of the shock system and separation bubble are significantly modified by the lateral confinement. Low-frequency unsteadiness and downstream evolution of corner flows are also investigated. [Preview Abstract] |
Tuesday, November 22, 2016 2:22PM - 2:35PM |
R5.00005: Separation control in a hypersonic shock wave / turbulent boundary-layer interaction Anne-Marie Schreyer, Ivan Bermejo-Moreno, Jeonglae Kim, Javier Urzay Hypersonic vehicles play a key role for affordable access to space. The associated flow fields are strongly affected by shock wave/turbulent boundary-layer interactions, and the inherent separation causes flow distortion and low-frequency unsteadiness. Microramp sub-boundary layer vortex generators are a promising means to control separation and diminish associated detrimental effects. We investigate the effect of a microramp on the low-frequency unsteadiness in a fully separated interaction. A large eddy simulation of a $33{\circ}$-compression-ramp interaction was performed for an inflow Mach number of 7.2 and a Reynolds number based on momentum thickness of $Re_{\theta}=3500$, matching the experiment of Schreyer et al.(2011). For the control case, we introduced a counter-rotating vortex pair, as induced by a single microramp, into the boundary layer through the inflow conditions. We applied a dynamic mode decomposition (DMD) on both cases to identify coherent structures that are responsible for the dynamic behavior. Based on the DMD, we discuss the reduction of the separation zone and the stabilization of the shock motion achieved by the microramp, and contribute to the description of the governing mechanisms. [Preview Abstract] |
Tuesday, November 22, 2016 2:35PM - 2:48PM |
R5.00006: LES of shock wave/turbulent boundary layer interaction affected by microramp vortex generators Laurent Joly, Arnaud Grebert, Stéphane Jamme, Julien Bodart At large Mach numbers, the interaction of an oblique shock wave with a turbulent boundary layer (SWTBLI) developing over a flat plate gives rise to a separation bubble known to exhibit low-frequency streamwise oscillations around $St_{L}= 0.03$ (a Strouhal number based on the separated region length). Because these oscillations yield wall pressure or load fluctuations, efforts are made to reduce their amplitude. We perform large eddy simulations to reproduce the experiments by Wang etal (2012) where a rake of microramp vortex generators (MVGs) were inserted upstream the SWTBLI with consequences yet to be fully understood. There is no consensus on the flow structure downstream MVGs and this is first clarified in the case of MVGs protruding by $0.47\delta$ in a TBL at Mach number $M=2.7$ and Reynolds number $Re_\theta = 3600$. Large-scale vortices intermittently shed downstream the MVGs are characterized by a streamwise period close to twice the TBL thickness and a frequency $f \approx 0.5 U_e/\delta$, two orders of magnitude higher than the one of the uncontrolled SWTBLI. We then characterize the interaction between the unsteady wake of the MVGs with the SWTBLI resulting in the reduction of the interaction length and the high-frequency modulation of the shock feet motions. [Preview Abstract] |
Tuesday, November 22, 2016 2:48PM - 3:01PM |
R5.00007: Characterization of the low-frequency unsteadines in LES data of supersonic and hypersonic STBLI Clara Helm, Pino Martin In a recent study, Priebe \textit{et al.} (JFM 2016) used Dynamic Mode Decomposition (DMD) to analyze DNS data of a Mach 3 ramp-generated shock and turbulent boundary layer interaction (STBLI). The authors found that the reconstructed low-frequency DMD modes took on the form of G\"{o}rtler-like vortices downstream of separation. The five reconstructed modes reproduced the low-frequency dynamics of the separation bubble accurately. Mart\'{i}n \textit{et al.} (AIAA2016-3341) and Mart\'{i}n \textit{et al.} (APS, DFD 2016) show that the low-frequency unsteadiness in STBLI results from an inviscid centrifugal instability similar to that found in separated subsonic and laminar flows, and that the turbulence is modulated but passive to the global mode. In this work we further characterize the G\"{o}rtler-like vortices using LES data of Mach 3 and Mach 7 separated STBLIs. We find that the G\"{o}rtler-like vortices are unsteady, and we quantify the wavelength, amplitude and the aperiodic development of these structures. This work is supported by the Air Force Office of Scientific Research under grant AF9550-15-1-0284. [Preview Abstract] |
Tuesday, November 22, 2016 3:01PM - 3:14PM |
R5.00008: An explicit filtering framework based on Perona-Malik anisotropic diffusion for shock capturing and subgrid scale modeling of Burgers' turbulence Romit Maulik, Omer San In this work, we introduce a relaxation filtering closure approach to account for subgrid scale effects in explicitly filtered large eddy simulations using the concept of anisotropic diffusion. We utilize the Perona-Malik diffusion model and demonstrate its shock capturing ability and spectral performance for solving the Burgers turbulence problem, which is a simplified prototype for more realistic turbulent flows showing the same quadratic nonlinearity. Our numerical assessments present the behavior of various diffusivity functions in conjunction with a detailed sensitivity analysis with respect to the free modeling parameters. In comparison to direct numerical simulation (DNS) and under-resolved DNS results, we find that the proposed closure model is efficient in the prevention of energy accumulation at grid cut-off and is also adept at preventing any possible spurious numerical oscillations due to shock formation under the optimal parameter choices. In contrast to other relaxation filtering approaches, it is also shown that a larger inertial range can be obtained by the proposed anisotropic diffusion model using a compact stencil scheme in an efficient way. [Preview Abstract] |
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