Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session D35: Compressible Flow II: Stability and Boundary Layers |
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Chair: James Hermanson, University of Washington Room: 2001A |
Sunday, November 23, 2014 2:15PM - 2:28PM |
D35.00001: A Navier-Stokes-Based Approach for Mean Flow Perturbation Analysis Swagata Bhaumik, Datta Gaitonde, Mbu Waindim The manner in which a basic state, obtained from a time-averaged unsteady flowfield, processes perturbations can provide significant insight into the cause and evolution of instabilities. A widely used approach is based on Parabolized Stability Equations (PSE), which limits streamwise mean flow variation and is often applied to 2-D base flows. To avoid some of these issues, we advance a Navier-Stokes-based method, which can address non-trivial three-dimensional fields. The method stems from that employed by Touber and Sandham (Theor. Comput. Fluid. Dyn., 23, 79-107, 2009) to analyze global modes in nominally 2-D shock-wave turbulent-boundary layer interactions (STBLI). We first develop its theoretical underpinnings by examining conditions under which it degenerates to traditional methods. We then illustrate the application by considering perturbations to an entropy layer at Mach 6, a turbulent supersonic jet at Mach 1.3 and STBLI at Mach 2.3. For the entropy layer and jet cases, known linear stability and PSE results are successfully reproduced, while global modes are obtained for STBLI. The results not only validate the proposed technique, but also demonstrate its suitability in analyzing instabilities for any general 3D basic state, including impulse response. [Preview Abstract] |
(Author Not Attending)
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D35.00002: Parametric sensitivity for frequency response analysis of large-scale flows Miguel Fosas de Pando, Peter Schmid When studying the frequency response of globally stable flows, direct and adjoint information from a resolvent analysis has to be computed. These computations involve a sizeable amount of effort, which suggests their reuse to identify sensitivity measures to changes in the governing parameters, base/mean flow fields, boundary conditions or other changes to the underlying linearized operator. We introduce and demonstrate a general technique to determine first-order changes in the frequency response induced by general changes to the governing equations. Examples will include changes to the Reynolds and Mach number for a tonal-noise airfoil problem, sensitivity to heating of a mixing layer past a splitter plate and closeness to global instability for a simplified model equation. [Preview Abstract] |
Sunday, November 23, 2014 2:41PM - 2:54PM |
D35.00003: An h/p adaptive Discontinuous Galerkin method for Three-Dimensional Compressible Flows John Ekaterinaris, Konstantinos Panourgias High order discontinuous Galerkin (DG) discretizations possess features making them attractive for computations of three-dimensional complex, compressible flows with discontinuities. Development of unified limiting procedures for the DG method that ensure accurate capturing of discontinuities for unstructured meshes, required for simulations in domains with nontrivial geometry, is needed. A TVB limiter is used and applied in the canonical computational space. It results into a unified limiting procedure for DG discretizations with any type of elements. The performance of the unified limiting approach is shown for different types of elements employed in mixed-type meshes and for a number of standard test problems including strong shocks to demonstrate the potential of the method. Furthermore, hierarchical higher-order limiting with the proposed approach is demonstrated. Increased order of expansion and adaptive mesh refinement is introduced in the context of h/p- adaptivity in order to locally enhance resolution of three-dimensional flow simulations that include discontinuities and complex flow features. [Preview Abstract] |
Sunday, November 23, 2014 2:54PM - 3:07PM |
D35.00004: Meshless Compressible Flow Simulations on Graphical Processor Units (GPUs) John Thomas, Jacob Alldredge A computationally efficient framework for performing compressible flow simulations over rigid solids is presented. This framework, which is based on a lattice-Boltzmann model, incorporates a volume fraction-based voxelation algorithm to eliminate the explicit meshing process. Moreover, as a framework tuned to run on graphical processers units (GPUs), simulations involving tens-of-billions of grid points can be run on hobby-sized computers in about one day. We validate predictions from this framework using experimental data for flow past wedges, spheres, and airfoils at a variety of Mach numbers. [Preview Abstract] |
Sunday, November 23, 2014 3:07PM - 3:20PM |
D35.00005: Compression wave structure on droplets under supersonic conditions Eric Lin, James Hermanson The compression wave structure in the vicinity of droplets deforming in a continuously accelerating, supersonic flow was examined in a draw-down supersonic wind tunnel. This flow configuration allowed droplets to achieve a Mach number of up to 1.7 relative to the surrounding air stream. Neat 2-propanol droplets 100 microns in diameter were generated upstream of the tunnel entrance using a Droplet-On-Demand generator. Schlieren imaging was performed to visualize the deforming droplets and to image the shock wave structure. Theoretical predictions provided a first estimate for bow shock parameters under these flow conditions such as shock thickness, standoff distance, and shock reaction time, suggesting that detached shock waves can be expected to be present for droplets experiencing the locally supersonic conditions in this investigation. The observed shock waves have characteristics broadly consistent with those expected for detached bow shock waves in front of a bluff body. The relative droplet Mach numbers, inferred from the Mach angle suggested by the schlieren images, are consistent with droplet Mach numbers determined previously in this flow configuration by direct imaging. [Preview Abstract] |
Sunday, November 23, 2014 3:20PM - 3:33PM |
D35.00006: Measurements of Vibrational Non-equilibrium in Supersonic Jet Mixing and Combustion Heath Reising, Timothy Haller, Noel Clemens, Philip Varghese A new experimental facility has been constructed to study the effects of thermal non-equilibrium on supersonic mixing and combustion. The facility consists of a Mach 1.5 turbulent jet issuing into an electrically heated coflow. The degree of non-equilibrium in the jet shear layer is quantified using high spectral resolution time-averaged spontaneous Raman scattering. Since the Raman spectra are time-averaged, they are susceptible to non-linear weighting effects induced by temperature fluctuations. The effect of local turbulent temperature fluctuations on the Raman fitting procedure is quantified by using spectral simulations that use the actual temperature fluctuations present in the flow measured by instantaneous Rayleigh scattering thermometry. It is shown that the temperature fluctuations are not large enough to induce significant errors in the vibrational temperature fitting results. Vibrational non-equilibrium is shown to occur in the jet shear layer, and its magnitude and trend are shown to be similar to recent large-eddy-simulation results. Since CO$_{\mathrm{2}}$ is known to cause faster vibrational relaxation of N$_{\mathrm{2}}$, a series of experiments were conducted to verify that the non-equilibrium effects could be controlled by CO$_{\mathrm{2}}$ addition. This work is being extended to reacting flows, to assess the impact of non-equilibrium on supersonic shear-layer combustion. [Preview Abstract] |
Sunday, November 23, 2014 3:33PM - 3:46PM |
D35.00007: Space-time measurements in a shock wave/turbulent boundary layer interaction Anne-Marie Schreyer, Pierre Dupont We study a reflected shock interaction with separation at Mach 2, contributing to a better understanding of rocket engine nozzle flows. The flow field contains a wide range of characteristic frequencies between $O(100)$Hz for the oscillation of the reflected shock and $O(100)$kHz for the turbulent microscales. To explain the origin and interdependence of the physical phenomena in the interaction, we need access to the spatio-temporal links. We thus require a measurement technique allowing the resolution of the entire frequency range while also providing sufficient spatial resolution and a large field of view. Our newly developed Dual-PIV system satisfies these requirements. First measurements with this system in an interaction flow field were performed in the continuous hypo-turbulent wind-tunnel at IUSTI at a momentum thickness Reynolds number of $Re_{\theta}=5024$ and a deflection angle of $\theta=8.75^{\circ}$. We present a detailed characterization of the flow field including turbulence measurements. From measurements at a range of temporal delays, we determined autocorrelations at crucial points in the flow field (incoming boundary layer, mixing layer, relaxation zone). From these, spatio-temporal information like the integral scales and the convection velocity are deduced. [Preview Abstract] |
Sunday, November 23, 2014 3:46PM - 3:59PM |
D35.00008: ABSTRACT WITHDRAWN |
Sunday, November 23, 2014 3:59PM - 4:12PM |
D35.00009: Shock wave Boundary layer interaction in supersonic flow over a forward-facing step Jayaprakash Narayan M., Raghuraman Govardhan Shock wave boundary layer interactions (SWBLI) are known to result in low-frequency large-scale shock oscillations, the origin of which has been a subject of debate. Motivated by this debate, we study in the present work, the SWBLI in supersonic flow over a Forward-Facing Step (FFS) at a Mach number of 2.5. The FFS configuration, which consists of a 90 degree step of height $h$, may be thought of as an extreme case of the compression ramp geometry, with the main geometrical parameter here being ($h/\delta$) ($\delta$ is the boundary layer thickness). This configuration is less studied and has some inherent advantages for experimentally studying SWBLI as the size of the separation bubble is large. In the present experimental study, we use high-speed schlieren and PIV measurements to help understand the features of SWBLI in the forward-facing step case. PIV measurements show a clear time-averaged separation bubble ahead of the step, with very large variations of the separation bubble in time. From instantaneous PIV velocity fields, a number of features are extracted including size of the separation bubble and the shock location, to comment on their variations in time, and to determine correlation coefficients. [Preview Abstract] |
Sunday, November 23, 2014 4:12PM - 4:25PM |
D35.00010: Preliminary LES of Hypersonic Shock/Turbulent Boundary Layer Interaction Clara Helm, Pino Martin Preliminary results from the Large Eddy Simulation (LES) of two hypersonic Shock/Turbulent Boundary Layer Interactions (STBLIs) are presented. First it is demonstrated with the simulation of a Mach 3 interaction over a $24^{\rm{o}}$ compression ramp that the LES method used is capable of resolving the relevant features of the complex dynamics present in separated STBLIs. Features such as the separation low-frequency dynamics, turbulence magnification, shear layer dynamics, and wall and skin friction distributions are validated against the Direct Numerical Simulation (DNS) data of the same Mach 3 flow. The LES is then validated for the computation of hypersonic conditions by simulating an attached Mach 7 STBLI generated by an $8^{\rm{o}}$ compression ramp and comparing results to DNS data of the same flow conditions. Lastly, initial results from the LES of a Mach 7 separated interaction over a $33^{\rm{o}}$ compression ramp at experimentally achievable conditions will be presented and discussed. This work is supported by the Air Force Office of Scientific Research under grant AF/9550-10-1-0164. [Preview Abstract] |
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