Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session ZC31: Shock Boundary Layer Interactions |
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Chair: Jeonglae Kim, Arizona State University Room: 255 C |
Tuesday, November 26, 2024 12:50PM - 1:03PM |
ZC31.00001: Mach Number and Separation-Scale Effects on the Unsteady Dynamics of Shock/Boundary-Layer Interaction Using Fast-Response PSP and Time-Resolved PIV Yoo Jin Ahn, Mustafa Musta, Jayant Sirohi, Noel T Clemens The dynamics of shock/boundary layer interactions are experimentally investigated at two different Mach numbers and with different separated flow length-scales. The primary diagnostics include fast-response pressure-sensitive paint (PSP) and time-resolved particle image velocimetry (PIV). Three different cases of SBLI are studied: (i) Mach 2 with 20 degree compression ramp (weak interaction), (ii) Mach 5 with 26.5 degree ramp (weak interaction), and (iii) Mach 5 with 28 degree ramp (strong interaction). By analyzing surface pressure fields, the spatio-temporal organization of flow structures was examined, revealing streamwise-elongated structures, likely Gӧrtler vortices, which are present in the Mach 2 SBLI but are much more prominent in the Mach 5 case. The pressure data also show the SBLI dynamics are significantly more influenced by fluctuations in the upstream boundary layer at Mach 2 than Mach 5. Both the weak and strong Mach 5 interactions exhibit similar dynamics. Time-resolved PIV (x-y plane) was taken at 50 kHz for Mach 2 and 100 kHz for Mach 5. From the velocity-field movies, we are able to analyze turbulent structures in the incoming boundary layer as well as those in the shear layer and recovering boundary layer. Statistical analyses, including coherence, cross-correlation and conditional analysis, are used to understand and compare the physical mechanisms underlying the unsteady dynamics of ramp-induced SBLI in each case. |
Tuesday, November 26, 2024 1:03PM - 1:16PM |
ZC31.00002: Insights from Time-Resolved Pressure Sensitive Paint Data using Momentum Potential Theory Datta V Gaitonde, Anshul Suri Momentum potential theory (MPT) has yielded invaluable insights from scale-resolved simulations because of its ability to exactly separate acoustic, hydrodynamic and thermal content of arbitrarily large turbulent fluctuations without the need for linearization. Recently, sub-elements of MPT have been employed to analyze schlieren data by using the rate of change of directional density gradients as source terms to the Poisson equation that filters the irrotational (acoustic plus thermal) component. When combined with data-driven methods, the results have aided in assessing the dynamics of jet noise and hypersonic transition from schlieren data alone. In this work, we process pressure fluctuations, as obtained from pressure-sensitive paints (PSP) in an analogous fashion. Focusing on 2D, simple-swept and compound shock/boundary layer interactions, we show that MPT extracts acoustic components of pressure fluctuations near the surface. These are then interpreted either in terms of local information propagation pathways (feedback) or as imprints of structures from the outer parts of the separated flows that are not directly accessible to time-resolved diagnostics. A parallel assessment of simulated pressure fluctuation data from large-eddy simulations provides further insights into the interpretation of MPT-filtered PSP data. |
Tuesday, November 26, 2024 1:16PM - 1:29PM |
ZC31.00003: Spectral Proper Orthogonal Decomposition of Unsteady High Speed Flows over Compression Expansion Corners IRMAK TAYLAN KARPUZCU, Deborah A. Levin High speed flows over several compression-expansion ramp configurations with high angles that create large separation regions have been studied with direct simulation Monte Carlo (DSMC). These large separation regions enable the detailed investigation of mean flow parameters such as scaled angle of the triple deck theory or recirculation strength when the flow reached the maximum separation size, i.e. when the whole flow region is separated up until the expansion corner. It is shown that the stability of the single recirculation in the separation region, that is characterized by the appearance of the secondary recirculation and unsteadiness in two dimensional simulations, is more sensitive to the wall temperature and the free stream velocity than the physical ramp angle. In addition, the flows are observed to be unsteady for the configurations when the secondary recirculation regions are present in the flow. Spectral proper orthogonal decomposition analysis reveals that low frequency unsteadiness is present in these configurations and confirms the power spectral density analysis from the DSMC probe data. Mode shapes of the discrete frequencies with highest mode energies shows that unsteadiness originates mainly from the reattachment shock and reattachment location, with some contribution from secondary separation for configurations with low wall temperature. Travelling waves resembling Kelvin-Helmholtz instabilities are also observed in the mode shapes within the shear layer. |
Tuesday, November 26, 2024 1:29PM - 1:42PM |
ZC31.00004: Unsteady shock-driven separation simulations with application to unstart Casey Lauer, Jonathan Ben Freund Scramjets can famously fail by unstart, which involves the upstream travel of a compression structure in the isolator. A notable feature of this is that the speed by which this occurs is significantly slower than obvious flow time scales: for example, it is typically well less than 10 percent of the flow speed. It can also be nearly steady in a long channel, suggesting that it does not significantly depend on downstream conditions, despite becoming subsonic. Compressible Navier-Stokes simulation models are used to study the shock-driven unsteady separation propagation in a model flow, particularly dependence on shock and boundary layer characteristics, seeking to identify their role in the slow time scales associated with motion. Adaptive mesh refinement affords excellent resolution of boundary and separated shear layers and localizes the shocks, which in turn allows broad parametric evaluation of slow-time-scale mechanisms. A central result concerns the accelerating influence of a thicker boundary layer on upstream propagation speed. It is not a simple scaling (and might not be expected to be simple). For the configuration simulated, it delays the formation of a steady upstream separation zone. Implications for unstart speed will be discussed. The slower the propagation, the more time to avoid unstart. |
Tuesday, November 26, 2024 1:42PM - 1:55PM |
ZC31.00005: Hypersonic Sharp Fin Shock/Boundary-Layer Interaction Predictions Over a Thermomechanically-Compliant Panel Joseph Michael Signorelli, Ian R Higgins, Samuel A Maszkiewicz, Stuart J Laurence, Daniel J Bodony Reducing design conservatism for high-speed flight systems requires accurately modeling shock/boundary-layer interactions (SBLI) and any aerothermoelastic phenomena resulting from them. The three-dimensional sharp fin SBLI introduces quasi-conical symmetry with significant thermal and mechanical load enhancements in an otherwise undisturbed flat-plate system. While studied extensively at lower supersonic Mach numbers, there is limited data on these interactions at hypersonic-relevant Mach numbers, and efforts have only recently begun towards understanding fluid-thermal-structural interaction (FTSI) associated with them. This work investigates the sharp fin interaction for three different flow conditions in conjunction with experiments at the NASA Langley Research Center: two Mach 6 (low and high Reynolds number) cases and a Mach 10 case. Results from steady and unsteady aerothermal simulations are discussed. SBLI footprints are quantified with virtual conical origin and inceptive origin predictions. Comparisons of pressure and wall heat flux against empirical models are discussed, and flowfield regimes are determined. Unsteady FTSI computations from a thin, compliant panel underneath the interaction are also analyzed. |
Tuesday, November 26, 2024 1:55PM - 2:08PM |
ZC31.00006: Investigating Shock-Boundary layer Interaction via Direct Numerical Simulations Jagmohan Singh, Shivank Sharma, Venkatramanan Raman Shock-boundary layer interaction (SBLI) in the isolator of scramjet engines is a critical phenomenon that significantly affects the performance and stability of hypersonic air-breathing propulsion systems. This study investigates this complex interaction through direct numerical simulations (DNS) coupled with adaptive mesh refinement (AMR) and the Embedded Boundary (EB) method, enabling the resolution of shocks at the finest scales while maintaining computational efficiency. Initially, the effect of inflow turbulence on the near-wall region is explored by maintaining a sufficiently low back pressure to avoid the formation of shock-trains. Subsequently, the back pressure is increased which leads to the formation of shock-trains, and the effect of inflow turbulent conditions on shock-train dynamics is investigated. The results show a prominent effect of the inflow turbulence on the shock-train dynamics and in turn the shock-trains lead to flow separation near the wall and enhance the near-wall turbulence which have direct implications on the air-fuel mixing downstream of the isolator. |
Tuesday, November 26, 2024 2:08PM - 2:21PM |
ZC31.00007: ABSTRACT WITHDRAWN
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Tuesday, November 26, 2024 2:21PM - 2:34PM |
ZC31.00008: Abstract Withdrawn
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Tuesday, November 26, 2024 2:34PM - 2:47PM |
ZC31.00009: Shock-wave/turbulent boundary layer interaction over curved compression ramp Yujoo Kang, Sang Lee In this study, the shock-wave/turbulent boundary layer interaction over concave surfaces with two different radii of curvature is compared to a compression ramp for a free stream Mach number M∞ = 2.9 and Reynolds number Reθ = 2400 using direct numerical simulation. Both the compression ramp (R24) and the curved compression ramps have a total turning angle of 24°, with the radii of curvature of the curved ramps being 7 (C7) and 14 (C14) times the thickness of the incoming turbulent boundary layer. The rounding of the corner mitigates the relaxation effect of the adverse pressure gradient, thereby influencing the formation of the separation bubble. Both R24 and C7 exhibit transitory detachment, with R24 displaying a rear-strong separation bubble and C7 showing a frontal-strong separation bubble. In contrast, C14 experiences incipient detachment, which does not lead to the formation of a mean separation bubble. The turbulent kinetic energy (TKE) is amplified across the ramps. While R24 shows both first and second TKE amplification points, C7 lacks the second amplification. Overall, TKE amplification is lower over C14, but the second amplification is distinctly prominent. The power spectrum density of wall pressure fluctuations reveals low-frequency instability in both R24 and C7 cases, while mid-frequency instability is suppressed due to the corner rounding on C7. Notably, the C14 case does not exhibit evident low-frequency instability. |
Tuesday, November 26, 2024 2:47PM - 3:00PM |
ZC31.00010: ABSTRACT WITHDRAWN
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