Session G13: Shock-Boundary Layer Interactions I

Aerothermoelastic Simulation of a Sharp-Fin Induced Shock Wave/Boundary-Layer Interaction in a Mach 6 Flow

The thermo-mechanical response caused by shock/boundary-layer interactions is an important phenomenon to consider in the design of hypersonic vehicles, yet only recently has been studied. A common configuration considered is a sharp fin mounted on a flat plate, which induces a three-dimensional shock/boundary-layer interaction. In this study, the effects of this swept-shock/boundary-layer interaction grazing over a thin, thermally- and mechanically-compliant panel are investigated for a Mach 6 flow. Unsteady RANS-based simulations using SU2 are completed for simulating the fluid domain. The thermal- and mechanical-response of the thin panel is calculated using a finite element approximation built upon the MFEM library. The solvers are fully-coupled in time using preCICE. Effects of the fluid-thermal-structural interaction on the flowfield and the panel are characterized.   

SPOD Analysis of the Transonic Buffet-Induced Unsteady Flow Field over a Supercritical Airfoil.

Transonic buffet refers to the shock oscillations on an airfoil surface that coincide with strong variations in the flow field. This interaction causes fluctuations in lift and pressure on an airframe, which may reduce aircraft performance and can potentially lead to critical structural damage. A thorough understanding of this phenomenon is integral in ensuring the structural integrity, stability, and control of aircraft throughout the entire flight regime. To better understand the temporal and spectral behavior of transonic buffet, we carried out an experimental wind tunnel investigation of an OAT15A model at a Reynolds number of 2 x 106 and Mach numbers of 0.68 < M < 0.80. High-speed focusing schlieren images acquired across different buffet regimes, including buffet onset, developed buffet, and offset, are used to resolve the dynamic interaction in time. We use a spectral proper orthogonal decomposition (SPOD) approach to discern the spatially coherent structures attributed to the shock-induced separation. These results are compared to a power spectral density (PSD) analysis to describe both the dominant spatial structures of buffet and the associated spectral footprint across the captured flow domain and throughout the buffet regimes.   

Control of shock-induced dynamic response of compliant surfaces using air-jet vortex generators

Shock-wave/turbulent boundary-layer interactions (STBLI) are unsteady and detrimental flow phenomena ubiquitous to aerospace applications. As many surfaces in aerospace systems are not rigid, the strong aerodynamic loads imposed by STBLIs result in coupled dynamics with compliant surfaces, which can harm system integrity. An established technique to alleviate the adverse effects of STBLIs is by using air-jet vortex generators (AJVGs). AJVGs induce streamwise vortices by injecting steady air-jets into the crossflow, redistributing the boundary-layer momentum and mitigating flow separation. In this study, we place an array of AJVGs upstream of a flexible panel and 24º compression ramp at Mach 2.52 to investigate the potential to modify the coupled dynamics of compliant surfaces and SWBLI.

The shock motion and panel deformation were simultaneously captured using highspeed focusing-schlieren and digital image correlation, respectively. Spectral proper orthogonal decomposition was used to resolve the unsteady dynamics of the interaction and quantify the ability of AJVGs to modify the compliant surface dynamic response. We observe that while the panel bending modes are dependent on aspect ratio, AJVG control decreases the dominant frequency of the panel vibrations and reduces the energy associated with the low frequency shock motion.   

Data assimilation in high-speed flow over a cone-flare at Mach 6

Incident disturbances in high-speed boundary layers are often probed by a limited number of wall-pressure sensors. Flow separation has a dramatic impact on the sensitivity of these sensors to the disturbance field, especially when sensors are placed within separation. This sensitivity ultimately determines the capacity to estimate the flow from measurements. We perform data assimilation in a cone-flare configuration at free-stream Mach number M=6, using an ensemble-variational (EnVar) approach (Buchta et al, J. Fluid Mech., 947, R2, 2022). Starting from a few, isolated pressure probes, we determine the upstream disturbance that reproduced the measurements. We discuss the impact of separation on the forward evolution of the instability waves and the dual problem of state estimation. As expected, sensors within separation, downstream of the compression wave, have degraded sensitivity to second-mode waves. However, they remain essential for accurate prediction of the trans-separation region, and for reproducing the experimental measurements. The results provide a first-of-its-kind interpretation of wall-pressure measurements on a cone-flare at high Mach number.