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

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 1 ' 5 with speci c 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 signi cantly smaller than the viscous length scale.

Second-mode attenuation and cancellation by porous coatings in a high-speed boundary layer

“…For various acoustic Reynolds numbers Re relevant to hypersonic flight, the reflection coefficient was computed as a function of the incident acoustic wave frequency and angle of incidence θ , for coatings of different porosities φ and constant length-to-depth ratio AR = 0.12, matching the aspect ratio of the cylindrical cavities used in the experiment by Rasheed et al (2002). To further investigate the effect of the cavity depth and porosity, additional simulations and comparisons are performed in the present work.…”

“…State-of-the-art active and reactive laminar flow control techniques seem to be impractical under the severe conditions of hypersonic flight (e.g. Kimmel 2003), but passive techniques that can be integrated with a thermal protection system, such as porous coatings, have been shown to significantly increase laminar run in wind-tunnel experiments (Rasheed et al 2002). Fedorov (2011) provides a review of stability and laminar-turbulent transition in highspeed boundary-layer flows.…”

Effect of Concave Wall Geometry on Heat Transfer in Hypersonic Boundary Layers

“…This type of thermocouple gauge is used extensively in the T5 reflected shock tunnel at GALCIT. [16][17][18] The high enthalpy test conditions result in adequate signal levels and the robust design of the gages make them highly resistant to damage caused by particulates in the test gas as well as the large heat fluxes. 16 The output signal is processed by a differential amplifier circuit mounted exterior to the test section.…”

Free transition on a slender cone in a quiet and a conventional wind tunnel and the effect of ultrasonically absorptive materials

“…Rasheed et al [1] demonstrated a damping of the second (Mack) modes and a delay of the transition on a 5 degree half cone with a regular porous surface at Mach 5. Fedorov et al [2] and Wagner et al [3] veri¦ed the damping of these acoustic waves with a 7 degree half cone and a porous coating of random microstructures at Mach 6.…”