Laminar-Turbulent Transition in High-Speed Compressible Boundary Layers withCurvature: Controlled Receptivity and Extent-of-Transition Measurements

摘要

This grant supported experimental research into two aspects of the transitionmechanisms on an elliptic cross section cone, at zero angle of attack. The Purdue Mach-4 Quiet Flow Ludwieg Tube was completed, allowing measurements under low noise conditions comparable to flight. The boundary layer on the elliptic cone was laminar to the maximum quiet flow length Reynolds number of 400,000, despite preliminary e**N transition estimates suggesting transition at 100,000. Apparatus was developed for generating repeatable perturbations, so that unambiguous and repeatable results can be obtained; this development continues. Repeatable localized perturbations were successfully generated abead of the cone, using a pulsed laser. The receptivity and instabilities of a hemispherical nose and a forward facing cavity were studied by measuring the development of the perturbations as they convected through the shock wave into the body. Measurements of the laser spot convecting into the elliptic cone boundary layer are continuing, although preliminary measurements indicate that the growth of the disturbance is small. Controlled localized perturbations are also being generated at the surface of the cone, using a glow discharge perturber. Finally, progress was made toward the design and fabrication of a larger Ludwieg tube with a higher quiet flow Reynolds number.