Experiments on Passive Hypervelocity Boundary-Layer Control Using an Ultrasonically Absorptive Surface

TLDR

Linear stability analyses predict that hypersonic boundary‑layer transition can be delayed by an ultrasonically absorptive surface that dampens the second (Mack) mode. The authors conducted boundary‑layer transition experiments on a 5.06° half‑angle round cone in the T5 Hypervelocity Shock Tunnel, using a half‑smooth control surface and a half‑porous ultrasonically absorptive surface, testing nitrogen and carbon dioxide at Mach ≈ 5 with reservoir enthalpy 1.3–13 MJ/kg and pressure 9–50 MPa, and comparing results to prior smooth‑surface data. The porous absorptive surface effectively delayed transition only when its pore size was much smaller than the viscous length scale.

Abstract

Recently performed linear stability analyses suggested that transition could be delayed in hypersonic boundary layers by using an ultrasonically absorptive surface to damp the second mode (Mack mode). Boundary-layer transition experiments were performed on a sharp 5.06-deg half-angle round cone at zero angle of attack in the T5 Hypervelocity Shock Tunnel to test this concept. The cone was constructed with a smooth surface around half the cone circumference (to serve as a control) and an acoustically absorptive porous surface on the other half. Test gases investigated included nitrogen and carbon dioxide at M∞ ≃ 5 with specific reservoir enthalpy ranging from 1.3 to 13.0 MJ/kg and reservoir pressure ranging from 9.0 to 50.0 MPa. Comparisons were performed to ensure that previous results obtained in similar experiments (on a regular smooth surface) were reproduced, and the results were extended to examine the effects of the porous surface. These experiments indicated that the porous surface was highly effective in delaying transition provided that the pore size was significantly smaller than the viscous length scale.