Publications

Fluid–structure interactions were measured between a representative control surface and the hypersonic flow deflected by it. The control surface is simplified as a spanwise finite ramp placed on a longitudinal slice of a cone. The front surface of the ramp contains a thin panel designed to respond to the unsteady fluid loading arising from the shock-wave/boundary-layer interactions. Experiments were conducted at Mach 5 and Mach 8 with ramps of different angles. High-speed schlieren captured the unsteady flow dynamics and accelerometers behind the thin panel measured its structural response. Panel vibrations were dominated by natural modes that were excited by the broadband aerodynamic fluctuations arising in the flowfield. However, increased structural response was observed in two distinct flow regimes: 1) attached or small separation interactions, where the transitional regime induced the strongest panel fluctuations. This was in agreement with the observation of increased convective undulations or bulges in the separation shock generated by the passage of turbulent spots, and 2) large separated interactions, where shear layer flapping in the laminar regime produced strong panel response at the flapping frequency. In addition, panel heating during the experiment caused a downward shift in its natural mode frequencies.

This work applies Filtered Rayleigh Scattering (FRS) for the study of shock wave/boundary layer interactions on a cone-slice-ramp geometry. As FRS measures a planar slice of the flow, the three-dimensionality of this geometry can be captured, rather than in path-integrated imaging such as schlieren. A carbon dioxide seeding system designed for the Sandia Hypersonic Wind Tunnel provides sufficient light scattering for FRS measurements. Strong background rejection in the images was achieved using a molecular gas filter, resulting in detailed visualization of flow structures within the boundary and shear layers. Images show separation and reattachment shock, as well as structures related to flow instability and transition to turbulence. A highly unsteady separation region was investigated, showing instantaneous shaping of the shock structure with turbulence.

This study explores the evolution of a turbulent hypersonic boundary layer over a spanwise-finite expansion-compression geometry. The geometry is based on a slender cone with an axial slice that subjects the cone boundary layer to a favorable pressure gradient. The mean flow field was obtained from a hybrid RANS-LES computation that showed the thickening of the boundary layer, a decrease in the mean pressure and the development of incipient streamwise vortical structures on the slice. The experiments use fluctuating surface pressure and shear-stress sensors along the centerline of the slice which demonstrate significant reduction in turbulence activity on the slice indicating relaminarization of the boundary-layer. These observations were corroborated by high framerate schlieren, filtered Rayleigh scattering and scanning focused laser differential interferometry. When a 10◦ ramp is introduced at the aft end of the slice, the effectively relaminarized boundary-layer separates upstream of the slice-ramp corner due to its increased susceptibility to separation in comparison to a turbulent boundary layer.

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This experimental study explores the fluid-structure interactions occurring between a control surface and the hypersonic flow deflected by it. The control surface is simplified for this work as a spanwise finite wedge placed on a longitudinally sliced part of the cone. The front surface of the wedge is a thin panel which is designed to respond to the unsteady fluid loading arising from the shock-wave/boundary layer interactions. Experiments have been conducted in the Sandia Hypersonic Wind Tunnel at Mach 5 and Mach 8 at wedge angles of 10◦, 20◦ and 30◦ . High-speed schlieren and backside panel accelerometer measurements capture the unsteady flow dynamics and structural response of the thin panel, respectively. For attached or small separation interactions, the transitional regime has the strongest panel fluctuations with convective shock undulations induced by the boundary layer disturbance shown to be associated with dominant panel vibrations. For large separated interactions, shear layer flapping can excite select panel modes. Heating of the panel causes a downward shift in natural mode frequencies.

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