Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session Q05: Compressible Flows: Supersonic and Hypersonic Flows |
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Chair: Thomas Corke, University of Notre Dame Room: 204 |
Tuesday, November 26, 2019 7:45AM - 7:58AM |
Q05.00001: Reducing shock related unsteadiness of supersonic flow over spiked bodies Jacob Cohen, Devabrata Sahoo, S. K. Karthick, Sudip Das Spikes, mounted at the stagnation point of a blunt body moving at supersonic speed, are utilized to reduce the forebody drag at the expense of increase in flow unsteadiness. We examine three configurations: flat, hemispherical and elliptical blunt bodies. Our goal is to distinguish between the unsteadiness mechanisms associated which each configuration, using experiments and CFD conducted at M$=$2. Drag is measured by in-house built balance, whereas unsteady pressure transducers and high-rate Shadowgraph snapshots, subjected to POD and DMD analysis, are utilized to quantify the flow unsteadiness. The flat blunt case has been investigated in the past and two modes of unsteadiness have been reported: a mild flapping oscillation and a violent axial pulsation. The latter mode is used to validate our results. When a spike is attached to hemisphere/ellipse body, the upstream strong detached bow shock wave is replaced by a system of weaker oblique shocks. The flow then separates over the spike body forming of a separated flow region bounded by an axisymmetric shear layer. Within the shear layer KH vortices are formed and shocklets are attached to these vortices and all move together downstream. We find the separation angle, separation shock and the separated volume to govern the flow unsteadiness. These are further demonstrated by using the hemispherical forebody with hemispherical spike tip. [Preview Abstract] |
Tuesday, November 26, 2019 7:58AM - 8:11AM |
Q05.00002: Instantaneous velocity fields in a hypersonic wake Yibin Zhang, Daniel Richardson, Steven Beresh, Katya Casper, Melissa Soehnel, Russell Spillers The cold wake behind a slender object in hypersonic flow offers a challenging environment for off-body measurements. Femtosecond Laser Electronic Excitation Tagging (FLEET) is a simple (single-laser, single imaging system) diagnostic that permits flowfield visualization without seeding or physical probes. FLEET optical and imaging parameters are tailored for measurements in the wake of a sharp cone in Mach 8 nitrogen flow, over freestream Reynolds numbers from 4*10$^{\mathrm{6}}$/m to 14*10$^{\mathrm{6}}$/m. Fluorescing FLEET lines for 1D velocity measurements and crosses for 2D measurements are written into the flow. The signal-to-noise ratio and tagging efficiency are maximized by using third harmonic FLEET at 267 nm, which has never before been implemented in a hypersonic test case. Flow tagging captures prominent wake features such as the separation shear layer, wake turbulence and two-dimensional velocity components. [Preview Abstract] |
Tuesday, November 26, 2019 8:11AM - 8:24AM |
Q05.00003: Stability and dynamics of supersonic axisymmetric bluff-body wake flows Simon GALIVEL, Samir BENEDDINE, Denis SIPP, Sebastien ESQUIEU The dynamics of separated wake flows behind an axisymmetric bluff body, where complex aerodynamic phenomena occur, is of primary importance for a correct estimation of its drag and trajectory. Those phenomena have been widely studied in incompressible flows, showing the existence of two bifurcations in the laminar regime which first steadily breaks the axisymmetry of the baseflow and then generates vortex shedding. The corresponding laminar large scale structures persist in turbulent regime. Unfortunately, an equivalent study for supersonic conditions is absent from the literature. Thus this work focuses on a supersonic wake of such bluff body ($\mathit{M} = 4$) in the laminar regime. A detailed study of unsteady simulations shows several instabilities: the breaking of the axisymmetry, complex flapping and rotation of the backflow region and an oscillating expanded region. Global stability analyses are then carried out to identify and study the flow mechanism of these instabilities. It highlights the driving role of the shear layer, of the backflow region, and of the expansion fan, and shows that the dynamics is significantly different from its incompressible counterpart. [Preview Abstract] |
Tuesday, November 26, 2019 8:24AM - 8:37AM |
Q05.00004: DNS of transitional hypersonic boundary layers at high enthalpies Mario Di Renzo, Parviz Moin, Javier Urzay Aerospace vehicles flying at hypersonic speeds are subject to boundary-layer transition, which causes a strong localized increase in wall heat transfer and friction. The influences of air dissociation at high-Mach numbers on the full process, including the non-linear early stages of turbulence, remain mostly unknown, and cannot be easily accessed by linear stability analyses or parabolized stability equations. In this presentation, DNS results of a hypersonic transitional boundary layer of dissociating air at high-enthalpy conditions are discussed, with particular focus on thermochemical effects on peak values of heat and shear stress. These simulations employ a novel task-based high-order solver written in the programming language Regent that is designed for exploiting GPU-based supercomputers. [Preview Abstract] |
Tuesday, November 26, 2019 8:37AM - 8:50AM |
Q05.00005: Frequency-Wavenumber Spectrum of Surface Pressure Fluctuations Induced by High-Speed Turbulent Boundary Layers Junji Huang, Yuchen Liu, Lian Duan Spatio-temporal structure of the fluctuating pressure field induced from high-speed turbulent boundary layers is analyzed by using a database of direct numerical simulations (DNS). Specifically, DNS are used to examine and compare the frequency-wavenumber spectrum of wall pressure generated by Mach 8 turbulent boundary layers developing spatially over several canonical geometries including a 2-D flat wall, the inner wall of an axisymmetric nozzle, and a sharp slender circular cone. The study provides insights into the scaling of pressure disturbance spectrum with respect to the boundary-layer parameters and the flow configuration. Such information is important to developing physics-based models that could adequately predict the magnitude, frequency content, location, and spatial extent of boundary-layer-induced pressure fluctuations at high speeds for the structural design of high-speed vehicles. [Preview Abstract] |
Tuesday, November 26, 2019 8:50AM - 9:03AM |
Q05.00006: Particle Relaxation Time for Titanium Dioxide in Hypersonic Flow Jose Rodriguez, Brian Rice, Christopher McKenna A critical component of the experimental technique Particle Image Velocimetry (PIV) is the response time of the seeding particles. Shock waves are commonly found in high-speed flow regimes, resulting in velocity discontinuities between pre- and post-shock regions. Seeding particles experience a time delay in the normal component of velocity as they transit the shock wave, known as particle relaxation time (PRT) Ragni et. al (J Exp. Fluids, 2011). This delay is a function of the diameter and density of the particle and the surrounding fluid's viscosity. These properties influence the particles' light-scattering ability and Stokes number (a ratio between the particle and fluid time scales) Melling et. al (J Meas. Sci. Tech, 1997). These properties contribute to imaging quality and how accurately the particles trace the flow. The PRT for TiO2 across an oblique shock was characterized via 2D PIV conducted in the von Karman Gas Dynamics Facility Tunnel D at Arnold Air Force Base. A 6.5 degree wedge was used to generate the oblique shock wave in a Mach 5 freestream. The PIV data was fit to exponential Stokes drag decay to obtain the PRT. These findings will be compared with results for other particles that are currently being used throughout the community. [Preview Abstract] |
Tuesday, November 26, 2019 9:03AM - 9:16AM |
Q05.00007: Dependence of penetration and entrainment on injectant properties for a jet in supersonic crossflow Dan Fries, Devesh Ranjan, Suresh Menon Four gases with different molecular weights and specific heat ratios are injected as circular, sonic jets into a supersonic crossflow (Mach 1.72). The jet fluid concentration distribution is quantified using a solid particle Mie-scattering technique. To account for the freestream Mach number, the bow shock in front of the jet and boundary layer thickness, an effective momentum flux ratio and a penetration relation based on momentum balance between jet and crossflow are used to improve the collapse of jet trajectories. The trajectory results also suggest a systematic influence of injectant properties on penetration that goes beyond what has been considered in the past. Trends are presented and analyzed further by association with Particle Image Velocimetry velocity data. The development of the velocity field especially in the windward shear layer of the jet elucidates changing compressibility effects on jet spreading and crossflow fluid mass entrainment. [Preview Abstract] |
Tuesday, November 26, 2019 9:16AM - 9:29AM |
Q05.00008: Stationary-Traveling Cross-Flow Transition Study on a Sharp Cone at Mach 6 Eric Matlis, Alexander Arndt, Thomas Corke, Michael Semper Experiments at Mach 6 in the 3-D boundary layer on a right-circular cone at an angle of attack have revealed evidence of a nonlinear (quadratic) interaction between stationary and traveling cross-flow modes that affect the boundary layer transition Reynolds number. The wavenumber of the stationary modes was controlled by passive patterned roughness located at Branch I. A glow-discharge electrode surface actuator was sputter-deposited just upstream of the patterned roughness to excite the traveling modes at a particular frequency. The observed stationary-traveling interaction was documented with miniature Kulite probes and appeared as an azimuthal variation in the amplitude of the traveling cross-flow mode with azimuthal wavenumbers that corresponded to the sum and difference of the azimuthal wavenumbers of the primary stationary and traveling modes. Cross-bicoherence verified a triple phase locking between the two primary modes and the summed mode for both the ``critical" and ``subcritical" roughness cases. [Preview Abstract] |
Tuesday, November 26, 2019 9:29AM - 9:42AM |
Q05.00009: Sensitivity of hypersonic boundary layers to $n$-periodic surface roughness-element arrays and finite-rate chemistry Athanasios Margaritis, Taraneh Sayadi, Olaf Marxen, Peter Schmid Finite-rate thermochemical effects have an order-one influence on the macroscopic behavior of hypersonic boundary layers, hence they have to be accounted for in numerical simulations. Flow stability and heat loads are significantly affected by the modelling approaches in such simulations. Highly-parametrized thermochemical models are commonly used, introducing large amount of uncertainty. Furthermore, the effect of surface roughness and its potential interaction with finite-rate chemistry effects remains unexplored. A mathematical framework for linearized analysis of $n$-periodic systems of roughness elements is developed, allowing us to extract information about wake synchronization from reduced-cost simulations of a single unit or a triplet of units; this modifies the restrictive assumption of single-unit periodicity. An efficient adjoint-based sensitivity analysis is used to identify critical roughness or chemical model parameters, with respect to their effect on output flow quantities. This framework is applied to generic flat-plate boundary layer configurations for validation; extensions to more complex flow configurations are readily feasible. Preliminary results of an $n$-periodic system analysis for reacting and non-reacting flows will be presented. [Preview Abstract] |
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