Publications

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This experimental work investigates the flow field associated with a tandem expansion-compression geometry in the Sandia Trisonic Wind Tunnel. PIV measurements of the boundary layer before the expansion characterized properties of the incoming boundary layer. Schlieren and oil-flow experiments were conducted at Mach 1.5 and 2 for a range of stagnation pressures. Further PIV experiments were conducted across the expansion and compression corners to observe the post-expansion changes in the boundary layer and its influence on the shock/boundary-layer interaction at the compression corner. Velocity profiles qualitatively matched well with RANS simulations and showed rapid growth of the boundary layer following the expansion, tapering off to a slower rate of growth with distance. Turbulence intensity, exemplified by the streamwise component of turbulent normal stress, diminished substantially after the expansion corner leading to the belief that relaminarization processes were occurring. Comparison with analysis from the literature suggests that the distortion of the boundary layer due to expansion leads to a separation length 30% larger than for an equilibrium turbulent boundary layer.

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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.

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