Hypervelocity skin-friction reduction by boundary-layer combustion of hydrogen

Shock-tunnel measurements of Stanton number and skin-friction coefficient a re reported for the injection of hydrogen through a 1.6-mm slot into a turb ulent boundary layer in a l-m-long duct. The mainstream Mach number of 4.5, stagnation enthalpy of 7.8 MJ/kg, pressure of 50 kPa, and temperature of 1 500 K provided a combination of flow variables that was sufficient to ensur e boundary-layer combustion of the hydrogen. The experiments were also simu lated by a numerical mode). The experiments and the numerical model indicat ed that the Stanton number was only slightly affected by boundary-layer com bustion. However, the numerical simulation indicated that injection with co mbustion caused a reduction of approximately 50% in the skin friction coeff icient, whereas the experiments yielded an even greater effect, with the re duction in skin-friction coefficient reaching 70-80% of the values of skin friction with no injection. Numerical simulation of a constant pressure flo w indicated that boundary-layer combustion caused the skin-friction reducti on to persist for at least 5 m downstream.