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Monday, February 23, 2015
09:30 AM - 10:30 AM
CNLS Conference Room (TA-3, Bldg 1690)


Linear Stability of High Enthalpy Boundary Layers

Neal P. Bitter
California Institute of Technology

Laminar-turbulent transition of hypervelocity boundary layers is analyzed using linear stability analysis. The analysis targets flows having large stagnation enthalpy, such as those found in shock tunnels, expansion tubes, and atmospheric flight at high Mach numbers. Two transition mechanisms are considered: exponential growth of unstable boundary layer modes and transient growth of stable disturbances. For both mechanisms, the growth of disturbances is mapped out over a wide range of Mach number and wall temperature conditions, and regions of the parameter space are identified where each mechanism is dominant. The influence of vibrational nonequilibrium on the stability characteristics is also discussed. Finally, linear stability analysis is used to assess the effects of gas injection into a boundary layer, which has been proposed as a means of controlling boundary layer transition, achieving film cooling, and simulating ablation. Body shaping is used to alleviate the adverse pressure gradient associated with injection. Both first mode and second mode instabilities are analyzed, which is the first time that the effects of injection on oblique waves have been studied. Both first and second mode disturbances are found to be strongly destabilized by injection.

Host: Scott Jackson and Mark Short, WX-9