Hypersonic Stability and Transition Experiments on Blunt Cones and a Generic Scramjet Forebody

Purdue University continues to develop a 9.5-inch Mach-6 Ludwieg tube, which presently operates with quiet flow only at low Reynolds number. Efforts towards achieving high quiet Reynolds numbers are reported. Measurements of stability and transition are also being carried out, using the existing conventional-noise Mach-6 flow. Model geometries include blunt round cones at zero and non-zero angle of attack, and the Hyper2000 forebody, which is generic for the Hyper-X class of airbreathing cruise vehicles. The transition literature for these cases is reviewed. Stationary streamwise-vortex instabilities are induced on the Hyper2000 using small roughness elements. Their growth is measured with temperature-sensitive paints. Temperature-paints measurements on a sharp cone at angle of attack show preliminary indications of the stationary crossflow vortices. Finally, a preliminary hot-wire profile was obtained on a blunt cone in a single tunnel run using a newly automated traverse. Hypersonic Transition and Quiet Tunnels Laminar-turbulent transition in hypersonic boundary layers is important for prediction and control of heat transfer, skin friction, and other boundary layer properties. However, the mechanisms leading to transition are still poorly understood, even in lownoise environments. Applications hindered by this ∗Associate Professor. Associate Fellow, AIAA. †Research Assistant. Student Member, AIAA. ‡Research Assistant. Student Member, AIAA. §Research Assistant. Student Member, AIAA. ¶Research Assistant. Student Member, AIAA. Copyright c ©2003 by Steven P. Schneider. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. lack of understanding include reusable launch vehicles [1], high-speed interceptor missiles [2], hypersonic cruise vehicles [3], and ballistic reentry vehicles [4]. Many transition experiments have been carried out in conventional ground-testing facilities over the past 50 years. However, these experiments are contaminated by the high levels of noise that radiate from the turbulent boundary layers normally present on the wind tunnel walls [5]. These noise levels, typically 0.5-1% of the mean, are an order of magnitude larger than those observed in flight [6, 7]. These high noise levels can cause transition to occur an order of magnitude earlier than in flight [5, 7]. In addition, the mechanisms of transition operational in small-disturbance environments can be changed or bypassed altogether in high-noise environments; these changes in the mechanisms change the parametric trends in transition [6]. Only in the last two decades have low-noise supersonic wind tunnels been developed [5, 8]. This development has been difficult, since the test-sectionwall boundary layers must be kept laminar in order to avoid high levels of eddy-Mach-wave acoustic radiation from the normally-present turbulent boundary layers. A Mach 3.5 tunnel was the first to be successfully developed at NASA Langley [9]. Langley then developed a Mach 6 quiet nozzle [10]. Unfortunately, this nozzle was removed from service due to a space conflict. No hypersonic quiet tunnels are presently operational anywhere in the world. The general prediction of transition based on simulations of the transition mechanisms is a very complex and difficult problem. There are several known receptivity mechanisms, several different known forms of instability waves, many different parameters that affect the mean flow and therefore modify the stability properties, and many known nonlinear breakdown mechanisms. The parameter space is large. The scramjet-vehicle forebody and