Controlled Experiments on Instabilities and Transition to Turbulence on Elliptic Cones at Hypersonic Mach Numbers

摘要

This work involved the study of instabilities and transition to turbulence in boundary layers on cones at different angles of attacks at high supersonic and hypersonic Mach numbers. It utilized facilities at NASA Langley Research Center, which makes use of 'quiet' design nozzles to minimize the level of acoustic disturbances. The experiments involved two models. The first was a 7 half-angle circular cross-section cone designed by Cavalier. It was used in experiments at zero angle of attack, where the principle instability is pairs of traveling oblique wave pairs; and at angles of attack where the principle instability is cross-flow modes. The circular cone at an angle of attack has a 3-D boundary layer, which is similar to that on elliptic cone, which was the second model built. This consisted of a 10 half-angle cone with a 4:1 elliptic cross-section. The elliptic cone was designed to operate in a new Mach 8 tunnel at NASA Langley. It mounts on a sting, which placed it inside the worst-case estimate on the location of the nozzle quiet zone. The model is annealed and hardened to withstand the 900 deg F free-stream temperature, and maintain a polished finish. A 3-D traversing mechanism capable of following the tapered elliptic surface, and operating at high temperatures in the hypersonic flow was also designed. Unfortunately, the elliptic cone was never used because of technical problems with the Mach 8 tunnel, which prevented it from ever operating. However, the elliptic cone was also designed to operate in the Mach 3.5 tunnel used for the circular cone experiments. A pending AFOSR proposal describes an experimental program for its use at the lower Mach number.