Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session U10: Compressible Flows: Supersonic and Hypersonic |
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Chair: Perry Johnson, University of California, Irvine Room: 137 |
Tuesday, November 22, 2022 8:00AM - 8:13AM Author not Attending |
U10.00001: Vibrational-excitation effects on a hypersonic turbulent boundary layer over a compression ramp Mario Di Renzo, Christopher T Williams, Javier Urzay, Sergio Pirozzoli The effects of vibrational excitation of gas molecules on shock-wave/turbulent-boundary-layer interactions are investigated in this fundamental study via direct numerical simulations (DNS) of a canonical Mach-5 turbulent boundary layer over a cold isothermal compression ramp. The DNSs are performed using an enhanced version of the Hypersonic Task-based Research (HTR) solver (Di Renzo et al., Comp. Phys. Comm. 255, 2020) that is now capable of integrating the conservation equations on curvilinear grids while retaining low numerical-dissipation properties. The numerical results encompass cases obtained using both calorically perfect and imperfect gases, including air, in order to isolate the effects induced by vibrational excitation. The analysis focuses on the peak temperature, skin friction coefficient, wall heat flux, Reynolds analogy factor, and wall pressure spectra that underscore the need for considering high-temperature gasdynamic effects in designing wall models for hypersonic turbulent boundary layers at relevant stagnation enthalpies. |
Tuesday, November 22, 2022 8:13AM - 8:26AM |
U10.00002: Computational Approach for Direct Simulation of High-Enthalpy Turbulent Hypersonic Flows in Thermochemical Nonequilibrium Christopher T Williams, Mario Di Renzo, Javier Urzay, Parviz Moin Aerodynamic heating in hypersonic turbulent boundary layers at high enthalpies induces finite-rate thermochemical processes, including dissociation and vibrational-electronic relaxation. A novel computational framework is presented to enable fundamental studies of these phenomena via direct numerical simulation of canonical hypersonic turbulent flows at high enthalpies. The framework is based on a two-temperature description of the conservation equations discretized with finite differences. A high-order Euler flux reconstruction procedure is utilized in conjunction with second-order treatment of diffusive terms, while explicit time marching is performed using a strong-stability-preserving Runge Kutta method. Boundary conditions are enforced via the extended Navier-Stokes characteristic boundary conditions to account for dissociation and vibrational-electronic relaxation. This framework is implemented in the Hypersonics Task-based Research solver (Di Renzo et al., Comp. Phys. Comm. 255, 2020) and its performance is evaluated in thermochemical regimes ranging from near-equilibrium to strong nonequilibrium in canonical hypersonic flows. |
Tuesday, November 22, 2022 8:26AM - 8:39AM |
U10.00003: Adaptive Resolvent Analysis: Application to High Enthalpy Boundary Layers Salvador R Gomez, Christopher T Williams, Mario Di Renzo, Peter J Schmid, Beverley J McKeon A method is presented to adaptively and efficiently sample the regions in spectral and physical space where the resolvent operator produces the highest gain. At each iteration, Gaussian Process Regression exploits previously acquired gains and their sensitivities to produce a prior and related uncertainties. The next point to sample is chosen by maximizing an acquisition function that balances increasing the value of the prior while decreasing the uncertainty in the prediction, as in Bayesian Optimization. Compared to a fixed grid resolution, which can be expensive for complicated geometries and base flows, this method utilizes fewer query points clustered in the most energetic regions in the spectral space. The method is then applied to a high-enthalpy boundary-layer flow along with masking of the resolvent to isolate the input-output relationships between variables and phenomena, identifying key length and time scales for each relationship. |
Tuesday, November 22, 2022 8:39AM - 8:52AM |
U10.00004: Global receptivity analysis: physically realizable input-output analysis of hypersonic boundary layers Omar Kamal, Matthew T Lakebrink, Tim Colonius In the context of transition analysis, linear global resolvent, or input-output analysis, determines worst-case disturbances to a laminar base flow based on a generic right-hand-side volumetric/boundary forcing term. The worst-case forcing is not physically realizable, and, to our knowledge, a generic framework for posing physically realizable worst-case disturbance problems is lacking. In natural receptivity analysis, disturbances are forced by matching (typically local) solutions within the boundary layer to outer solutions consisting of free-stream vortical, entropic, and acoustic disturbances. We pose a scattering formalism to restrict the input forcing to a set of realizable disturbances associated with plane-wave solutions of the outer problem. We validate the formulation by comparing with direct numerical simulations (DNS) for a Mach 4.5 flat-plate boundary layer. We show that the method provides insight into transition mechanisms by identifying those linear combinations of plane-wave disturbances that maximize energy amplification in flat-plate boundary layers over a range of Mach numbers and frequencies. |
Tuesday, November 22, 2022 8:52AM - 9:05AM |
U10.00005: Resolvent analysis of spatially developing hypersonic boundary layers: A study of freestream acoustic waves Gregory Stroot, Beverley J McKeon The Resolvent analysis is applied to a hypersonic streamwise developing zero pressure gradient boundary layer (ZPGBL), where-in we focus on the study of freestream propagating pressure waves. The Resolvent analysis is a reformulation of the Navier-Stokes (NS) where we linearise around a 2-D mean state (function of streamwise and wall-normal direction) and consider the non-linear terms to be an unknown forcing to the linear terms, thus obtaining a linear model. We compare the freestream propagating waves obtained as responses from the resolvent to those that were obtained as an optimal linear response from the resolvent analysis around the 1-D mean flow (function of wall-normal direction alone) by Bae et al. (J. Fluid Mech., vol. 883, 2020, pp. 336-382, pp. A29). These freestream propagating acoustic waves were derived as solutions to the 1-D Linearized NS equations for a ZPGBL by Mack (California Inst of Tech Pasadena Jet Propulsion Lab, 1984.). Further, the findings of Mack have been found to be consistent with experimental and subsequent numerical observations. In the present study, we analyze the effects of the streamwise development of the hypersonic boundary layer on the freestream propagating waves and study how spatial dependence affects the generation of these waves. |
Tuesday, November 22, 2022 9:05AM - 9:18AM |
U10.00006: Global linear analysis of Stetson's Mach 8 blunt cone experiment Tim J Flint, M. J. Philipp Hack, Parviz Moin Experiments by Stetson et al. 1984 recorded in detail the disturbances present in the laminar boundary layer on a blunt cone at Mach 8 with two nose-radii. The authors observed, for large nose bluntness, large fluctuation amplitude in the entropy layer, above the boundary layer, near the blunt nose which moved down into the boundary layer as they traveled downstream. Understanding the development of the entropy layer instability will be important for transition prediction on similar geometries with various nose radii. In this work we study the perturbation behavior and receptivity through global linear analysis of the blunt cone flow. We compute and analyze direct and adjoint modes which reveal the spatially unstable modes within the boundary layer and their receptivity to free-stream disturbances, which travel through the bow shock, while comparing their structure to that seen in the experiments by Stetson et al. |
Tuesday, November 22, 2022 9:18AM - 9:31AM |
U10.00007: Direct Numerical Simulations of the Mach 6 Flow Past a Control Fin Chinmay S Upadhye, Daniel J Bodony Control fins that enable maneuvers of high-speed flight vehicles experience pressure and thermal loads that cause them to deform. To understand these loads, we use direct numerical simulation (DNS) to simulate the Mach 6 flow past a representative fin geometry at zero and four degrees angles of attack. The fins are swept with a constant-thickness diamond airfoil cross section and have blunted leading and trailing edges. The DNS boundary conditions are informed by corresponding Reynolds-averaged Navier-Stokes (RANS) simulations of the fins mounted to a blunted conical centerbody. We focus our discussion on the boundary layer transition that occurs on the fin surface and on its sensitivity to freestream disturbances that pass through the shock. |
Tuesday, November 22, 2022 9:31AM - 9:44AM |
U10.00008: Angular Momentum and Moment of Enthalpy Integral Equations for Compressible Boundary Layers Armin Kianfar, Mario Di Renzo, Christopher T Williams, Ahmed Elnahhas, Perry L Johnson It is a matter of basic observation and high engineering importance that boundary layer (BL) skin friction and surface heat flux are strongly augmented by turbulence. To enhance our understanding of this phenomenon in high-speed flows, the angular momentum integral (AMI) [Elnahhas & Johnson, 2022, J. Fluid Mech., 940, A36] and moment of temperature integral (MTI) [Kianfar et al., AIAA 2022-0944] equations are here extended to compressible BLs. The compressible AMI equation quantifies the skin friction coefficient (Cf) as the sum of a laminar Cf and augmentations due to the Reynolds stress, as well as other flow features such as mean wall-normal fluxes and freestream pressure gradients. A similar approach to the wall heat flux leads to the moment of enthalpy integral (MEI) equation, a quantitative relationship for how turbulence and other BL flow features influence the Stanton number of compressible BL flows. In this talk, the AMI and MEI equations will be applied to generate observations and insight from flat plate BL DNS having a range of edge Mach numbers and wall temperatures, using the Hypersonic Task-based Research (HTR) solver [Di Renzo et al., Comp. Phys. Comm. 255, 2020]. |
Tuesday, November 22, 2022 9:44AM - 9:57AM |
U10.00009: Optimal placement of wall-pressure sensors for data assimilation in high-speed boundary layers Melissa Kozul, David A Buchta, Tamer A Zaki Measurements in hypersonic flows, in particular during flight, are often limited, for example to wall-pressure data at discrete locations. Rather than regard these measurement data as mere records of the wall pressure at the measurement times, data assimilation can predict the entire flow field that satisfies the governing equations and optimally reproduces the measurements (Buchta & Zaki, J. Fluid Mech., 916, A44, 2021). The convergence and accuracy of the assimilation procedure depends on characteristics of the measurements, including the flow quantity being measured, the number of sensors and their placement. In this work, we focus on the impact of sensor position on the accuracy of the data assimilation procedure, and the capacity to accurately estimate high-speed transitional boundary layers. We introduce an algorithm for optimizing the positions of a network of sensors. We then compare the convergence and accuracy of assimilating wall-pressure measurements from the best and worst sensor networks, for an independent flow condition. |
Tuesday, November 22, 2022 9:57AM - 10:10AM |
U10.00010: Compressible Boundary Layer Velocity Transformation Based on a Generalized Form of the Total Stress Han Lee, Owen Williams, Pino Martin We demonstrate that density and viscosity fluctuations have a significant impact on the near-wall stress balance of compressible boundary layers. Utilizing a DNS simulation dataset of wall-bounded hypersonic flow cases with wall-cooling, semi-local Reynolds numbering ranging from 800 to 34000 and Mach number up to 12, fluctuating viscosity and density-related terms were seen to consistently exceed 5% of the wall shear stress for all cases. In some cases, these terms exceeded 30% of the wall shear stress. The growth in the Morkovin-scaled turbulent stress peak is seen to increase with the semi-local Reynolds number, Re*. By retaining terms to account for density and viscosity fluctuations, the near wall momentum balance expected from the incompressible wall bounded turbulence is restored in a generalized form and used to identify two key properties: (1) the near-wall momentum balance for the generalized total stress and (2) the relative contributions from the viscous and turbulent stresses to the total stress, which are found to be approximately Mach-invariant. Utilizing these properties, we propose a mean velocity transformation for compressible wall bounded hypersonic flows that builds upon the recent transform proposed by Griffin, Fu and Moin (2021) to produce a tighter collapse of log-layer intercept and slope and that closely matches that observed for incompressible flows. |
Tuesday, November 22, 2022 10:10AM - 10:23AM |
U10.00011: Transition between unsteady flow states over a high-speed spike-cylinder body Vaisakh Sasidharan, Subrahmanyam Duvvuri The spike-cylinder, which consists of a spike as the fore-body and a right-circular cylinder as the aft-body, is a canonical geometry used in high-speed flow studies. This flow exhibits two distinct states of unsteadiness, termed "pulsation" and "oscillation." Pulsations are characterized by large-amplitude shock wave motion, whereas oscillations are characterized by small-amplitude unsteady distortions in shock wave structure. The flow state is determined by the single governing geometric parameter -- ratio of the spike length L to the cylinder diameter D. The present effort is aimed at obtaining a detailed understanding of the mechanics of transition between flow states. Wind tunnel experiments at Mach 6 were performed with spike-cylinder models of various L/D values in the range 0.2 to 4. Particular attention was given to L/D values around 1.5, since transition between flow states nominally occurs at L/D = 1.5. High-speed schlieren recorded in these experiments allows for careful visualization of changes in the flow structure during the transition process. The full set of experimental results and a discussion will be presented at the meeting. |
Tuesday, November 22, 2022 10:23AM - 10:36AM |
U10.00012: Laminar hypersonic boundary layer flow over compression ramp with sharp leading edge and upstream influence Sampson K Davis, Eli Shellabarger, James Miller, Thomas Ward 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° - 6°, 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. Upstream influence is studied as a function of the ramp angle and compared with new and previously developed correlations. |
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