The Influence of Artificially Induced Turbulence Upon Boundary Layer Transition in Supersonic Flows.

Acoustic disturbances and high frequency-low amplitude vibrations have been studied as a means to promote early boundary layer transition in a supersonic stream. A theoretical analysis of the stability characteristics of the leading edge of a blunted delta-wing was used to guide the choice of acoustic and vibration frequencies employed in this experimental study. Air driven acoustic generators, located in the stagnation chamber of the wind tunnel, produced a strong resonant tone at 4.6 KHz, with a sound level above 148 dB. Comparison of the Reynolds number dependent flow field on a delta model at angle of attack, using an oil streak technique for flow visualization, provided an index of the effectiveness of the acoustic disturbances. Operation of the tunnel with the tunnel air supplied through the acoustic generators and with the normal air supply indicated the effective Reynolds number of the wind tunnel was increased by a factor near 1.4 by the acoustic generators. Extensive test section total pressure and flow angularity surveys and force and moment measurements on a winged body showed this increase in effective Reynolds number was produced with no degradation of flow quality. Piezoelectric vibration transducers were mounted in the supporting sting of the delta models, vibrating the models at frequencies ranging from 2.9 KHz to 82 KHz with peak-to-peak amplitudes from 49 microinches to 0.0015 inches. These vibrations were not as efficient as surface roughness of a height comparable to the peak-to-peak vibration amplitude in stimulating boundary layer transition. Author