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.

A second-mode stability analysis has been performed for a hypersonic boundary layer on a wall covered by a porous coating with equally spaced cylindrical blind microholes. Massive reduction of the second mode amplication is found to be due to the disturbance energy absorption by the porous layer. This

A second-mode stability analysis has been performed for a hypersonic boundary layer on a wall covered by a porous coating with equally spaced cylindrical blind microholes. Massive reduction of the second mode amplication is found to be due to the disturbance energy absorption by the porous layer. This

Measurements have been made of the growth by the Richtmyer-Meshkov instability of nominally single-scale perturbations on an air/sulfur hexafluoride ͑SF 6 ) interface in a large shock tube. An approximately sinusoidal shape is given to the interface by a wire mesh which supports a polymeric membrane separating the air from the SF 6 . A single shock wave incident on the interface induces motion by the baroclinic mechanism of vorticity generation. The visual thickness ␦ of the interface is measured from schlieren photographs obtained singly in each run and in high-speed motion pictures. Data are presented for ␦ at times considerably larger than previously reported, and they are tested for self-similarity including independence of initial conditions. Four different initial amplitude/wavelength combinations at one incident shock strength are used to determine the scaling of the data. It is found that the growth rate decreases rapidly with time, d␦/dtϰt Ϫp ͑i.e., ␦ ϰt 1Ϫp ), where 0.67ՇpՇ0.74 and that a small dependence on the initial wavelength 0 persists to large time. The larger value of the power law exponent agrees with the result of the late-time-decay similarity law of Huang and Leonard ͓Phys. Fluids 6, 3765-3775 ͑1994͔͒. The influence of the wire mesh and membrane on the mixing process is assessed.

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A second-mode stability analysis has been performed for a hypersonic boundary layer on a wall covered by a porous coating with equally spaced cylindrical blind microholes. Massive reduction of the second mode amplication is found to be due to the disturbance energy absorption by the porous layer. This

No abstract

NASA proposals for future planetary spacecraft involve the use of aerocapture to save propellant mass needed to enter planetary orbit. One concept that is being studied uses inflatable structures (ballutes) towed behind the spacecraft to provide the necessary drag while minimizing vehicle heating and flow unsteadiness. Experiments of the tandem body configuration of a toroidal ballute towed behind a spacecraft were performed in the T5 Hypervelocity Shock Tunnel. The test gases studied were carbon dioxide, nitrogen and hydrogen to simulate actual future missions to Mars, Titan and Neptune, respectively. Stagnation point heat transfer measurements were made and were found to compare well with theoretical estimates. In addition, flow visualization shadowgraphs were used to confirm that the flow was steady. The carbon dioxide and nitrogen tests successfully matched both the Reynolds number and enthalpy similarity criteria for the specific NASA missions. The hydrogen shots, however, failed to match the enthalpy criteria for the intended mission and care must be taken when using those results.