Bulletin of the American Physical Society
74th Annual Meeting of the APS Division of Fluid Dynamics
Volume 66, Number 17
Sunday–Tuesday, November 21–23, 2021; Phoenix Convention Center, Phoenix, Arizona
Session H29: Compressible Flows I |
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Chair: Tim Colonius, Caltech Room: North 229 A |
Monday, November 22, 2021 8:00AM - 8:13AM |
H29.00001: Theory of turbulence augmentation across hypersonic shock waves Alberto Cuadra Lara, Cesar Huete, Marcos Vera, Javier Urzay The interaction between a weakly turbulent free stream and a hypersonic shock wave is investigated theoretically by using linear interaction analysis (LIA). Modified Rankine-Hugoniot jump conditions that account for dissociation and vibrational excitation are derived and employed in a Fourier analysis of a hypersonic shock interacting with three-dimensional isotropic vortical disturbances. Besides confirming known endothermic effects of hypersonic thermochemistry in decreasing the mean post-shock temperature and velocity, these LIA results indicate that the enstrophy, anisotropy, intensity, and turbulent kinetic energy of the fluctuations are much more amplified through the shock than in the calorically perfect case. Additionally, the turbulent Reynolds number is amplified across the shock at hypersonic Mach numbers in the presence of dissociation and vibrational excitation, as opposed to the attenuation observed in the calorically perfect case. These results suggest that turbulence may persist and get augmented across hypersonic shock waves despite the high post-shock temperatures. |
Monday, November 22, 2021 8:13AM - 8:26AM |
H29.00002: Laminar hypersonic flow over compression ramp with sharp leading edge: separation and upstream influence Sampson K Davis, Thomas Ward, Eli Shellabarger, James Miller The present work aims to study the effects of shock wave - boundary layer interaction in 2D hypersonic flow at the sharp leading edge of a flat plate. A key parameter in this work is the hypersonic interaction parameter Χ, defined as Χ ≡ C M_{∞}^{3} / Re_{∞,L}^{1/2}. This flow is modeled as a perfect gas and it's behavior is studied over various compression ramp configurations, ranging from 0° - 20°, using a semi-analytical reduced-order model. To study these resulting effects we focus on characterizing the viscous boundary layer for an adiabatic flow over an insulated wall, improving on existing semi-analytic methods in terms of obtaining a non-singular solution, and using the tangent wedge approximation to match the pressure on the boundary layer. Flow separation, which occurs at the compression ramp corner, is studied as a function of the ramp angle. Locations of flow separation and reattachment along the plate are predicted and compared with results obtained from a commercial flow solver. Upstream influence resulting from the compression ramp is also investigated and compared with previously developed correlations. |
Monday, November 22, 2021 8:26AM - 8:39AM |
H29.00003: Measurement of the density field around supersonic conical projectiles using quantitative schlieren photography Jason Falls, Michael J Hargather, Alejandro Campos The density variation around supersonic projectiles is characterized through quantitative high-speed schlieren photography. The projectiles were 10° half-angle sharp cones fired from a 0.50"-caliber (12.7mm-diameter) gun barrel. The projectiles were imaged while traveling at approximately 700 m/s, or approximately Mach 2. A lens-based schlieren system with a high-speed digital camera recorded images which were used to obtain density fields via quantitative schlieren. An inversion algorithm is used to obtain three-dimensional results for density variation from the two-dimensional schlieren projection assuming an axi-symmetric flow. Classical compressible aerodynamics solutions for conical projectiles is presented and used for comparison as a theoretical density profile. Agreement with theory is presented via a line profiles taken from the experimental density reconstruction. The experimentally measured density fields are within a 5% error of the theoretical density variation around the conical projectiles. |
Monday, November 22, 2021 8:39AM - 8:52AM |
H29.00004: Low-Frequency, Spanwise Oscillation in a Finite-Width Cavity Aaron M Turpin, Rachelle Speth, Scott Sherer, Kenneth Granlund A joint experimental–computational program examined low-frequency, spanwise oscillations in supersonic flow over a finite-width cavity. Lowpass-filtered rear wall surface pressure revealed that shear layer impingement was most often biased to one side of the wall, switching sides at a frequency two orders of magnitude below resonance. Therefore, a bifurcation into two spanwise-asymmetric, mirrored, quasi-steady states could be defined. The states were described by biased impingement/ejection near the rear wall, asymmetry of the shear layer, and centrifugal inner-cavity flow. Resonance amplitudes were also found to be spatially modulated by the low-frequency flow switching. A yawed inflow was found to force one of the asymmetric states. |
Monday, November 22, 2021 8:52AM - 9:05AM |
H29.00005: Forward and inverse problems in high-speed boundary layers using DeepONets Yue Hao, Patricio Clark Di Leoni, Lu Lu, Charles Meneveau, George E Karniadakis, Tamer A Zaki Fast prediction of instability waves in high-speed boundary layers is numerically challenging. We show how DeepONets, deep neural network architectures designed to approximate operators, can be used to (1) map an incoming perturbation to its corresponding downstream field accurately and (2) determine the original perturbation out of downstream measurements. Moreover, we show that informing the training of the DeepONet with the continuity equation improves the accuracy of the results. We trained the DeepONets using data generated from solutions of the linear parabolized stability equations and from direct numerical simulations of the compressible Navier-Stokes equations. These results are a necessary step towards to application of neural-network technology to more complex high-speed flow configurations and to data assimilation problems. |
Monday, November 22, 2021 9:05AM - 9:18AM |
H29.00006: Turbulent/Non-Turbulent Interface in a High-Mach Number Boundary-layer Flow Reza Jahanbakhshi The results of the direct numerical simulation (DNS) of a Mach-4.5 spatially developing boundary layer are used to study the flow characteristics across the turbulent/non-turbulent interface (TNTI). The DNS data is obtained by solving the compressible form of the conservation equations for mass, momentum and energy, and by assuming a calorically perfect gas which is a reasonable assumption at the current Mach number and free-stream conditions. In order to generate realistic turbulent boundary layer, the simulation was performed of an initially laminar, Blasius boundary layer that undergoes transition to turbulence. The Blasius boundary layer is forced at the inflow plane by broadband disturbances obtained from Orr-Sommerfeld and Squire eigenvalue problem, which are introduced inside the region of mean shear only and hence the free stream is irrotational. The transition process is similar to bypass breakdown, where streaks are formed, amplify, and ultimately lead to the formation of turbulent spots that spread and merge together to form the fully turbulent boundary layer. The main objective of this work is to study kinematics and dynamics of the TNTI in a high-speed boundary layer. |
Monday, November 22, 2021 9:18AM - 9:31AM |
H29.00007: Optimal disturbances in a cooled-wall hypersonic boundary layer using the One-Way Navier-Stokes (OWNS) Equations Omar Kamal, Georgios Rigas, Matthew T Lakebrink, Tim Colonius The dominant instability observed in adiabatic-wall flat-plate hypersonic boundary layers is the second Mack mode, which manifests itself as trapped acoustic waves between the wall and the relative sonic line. If the wall is highly cooled, not only is this mode destabilized, but an additional mode may emerge – the supersonic mode, which is characterized by an acoustic emission from the boundary layer. Accurate prediction of this mode via LST or PSE is challenging due to their underlying assumptions whereas DNS and global methods are computationally expensive. To overcome this, we instead use the One-Way Navier-Stokes (OWNS) Equations, which efficiently approximates a rigorous parabolization of the equations of motion by removing disturbances with upstream group velocity using a higher-order recursive filter. By using this method in an input/output optimization framework, we will investigate the mechanistic shift from subsonic to supersonic second mode of a Mach-6 flat-plate boundary layer by parametrically varying the wall temperature and frequency. We aim to characterize optimal disturbances under different cost functions, spatial support, and physical nature of the external disturbances. |
Monday, November 22, 2021 9:31AM - 9:44AM |
H29.00008: Flow Field Estimation of Supersonic Open Cavity Flows Conditioned on Time-Resolved Pressure Measurements Surabhi Singh, Lawrence Ukeiley Open cavity flows are dynamically complex flows which are further complicated by aero-acoustic resonance phenomena. The complex phenomena in the flow are driven by the dynamics of the shear layer at the cavity opening and how it interacts with the downstream wall. To better understand the complex nature of the flow, it is essential to comprehend the flow in a simplified and reduced manner. To this end, experiments were conducted in a supersonic wind tunnel flow facility operating at Mach 1.4 for an open cavity of L/D = 6. The measurements comprised of particle image velocimetry with synchronous time-resolved pressure measurements at multiple points on the cavity floor and aft wall. Stochastic estimation and other flow estimation techniques in conjunction with proper orthogonal decomposition were applied to the measurements to estimate the spatio-temporal modes of the velocity field conditioned on the pressure measurements. Decomposition in this manner helped better analyze Rossiter modes that dominate the scales and dynamics of the flow at specific frequencies. Furthermore, the temporal estimation of the cavity shear layer demonstrates the complex fluid interactions with the cavity aft wall. |
Monday, November 22, 2021 9:44AM - 9:57AM |
H29.00009: Domain of dependence of wall-pressure measurements in transitional high-speed boundary layers David Buchta, Qi Wang, Tamer A Zaki Measurements in high-speed flows are extremely difficult to make. To maximize their utility, it is important to understand what influences an instantaneous measurement. Flow events, or perturbations, that are invisible to a sensor may prevent detection of key physics. Conversely, perturbations away from a sensor prior to the measurement may impact its signal at the measurement time. The collection of these latter perturbations defines the domain of dependence (DOD) which can be evaluated efficiently using adjoint methods. For Mach 4.5 transitional flat-plate boundary layers, we consider the DOD of an instantaneous and localized wall-pressure observation, akin to a PCB probe that is common for flight and wind-tunnel experiments. In the time preceding the pressure measurement, the DOD retreats upstream from the probe, and the sensitivity to flow perturbations amplifies. The sensitivity forms a wavepacket structure, concentrates near the boundary-layer edge, and radiates a portion above the boundary layer indicating a receptivity to freestream disturbances. We contrast the measurement sensitivity to different components of the perturbation field, e.g., temperature and velocity perturbations, and the impact of sensor placement in the pre-transitional and turbulent regions. |
Monday, November 22, 2021 9:57AM - 10:10AM |
H29.00010: Effect of dissociation/vibrational-relaxation coupling on laminar hypersonic boundary layers Christopher T Williams, Mario Di Renzo, Javier Urzay, Parviz Moin High-enthalpy hypersonic boundary layers are subject to a number of finite-rate thermochemical processes, including dissociation, recombination, vibrational relaxation, and ionization. A locally self-similar formulation for laminar hypersonic boundary layers with multicomponent diffusion, finite-rate chemistry, and vibrational nonequilibrium is derived, and numerical solutions are presented in order to evaluate the relative performance of the Park (Park 1989) and CVDV (Marrone and Treanor 1963) two-temperature models. The effects of chemical and thermodynamic nonequilibrium on laminar hypersonic boundary layers are discussed together with the sensitivity of the similarity solutions to the choice of thermochemical model. The similarity solutions are compared with direct numerical simulations (DNS) in order to evaluate the scope of applicability for the self-similar formulation. |
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