Heated Helium to Simulate Surface Pressure Fluctuations Created by Rocket Motor Plumes

The solid-rocket plumes from the abort motor of the multipurpose crew vehicle were simulated using hot, high-pressure, helium gas to determine pressure fluctuations on the vehicle surface in the event of an abort. About 80 different abort situations over a Mach number range of 0.3 to 1.2, and vehicle attitudes of ±14  deg, were simulated using a 6% scaled model inside the NASA Ames Transonic Wind Tunnel. The test showed very high level of surface pressure fluctuations caused by the hydrodynamic near-field of the plume shear layer. The plumes grew in size with increasing flight Mach number, which was associated with a lowering of the ambient pressure. This caused an increase of plume impingement on the vehicle. Interestingly, the trend was a decrease in the level of pressure fluctuations with increasing impingement. The wind-tunnel data were compared against flight data from the Pad Abort 1 flight test. Despite various differences between the transient-flight situation and the steady-state wind-tunnel simu...