Study of Bow-Shock Wave Unsteadiness in Hypervelocity Flow from Reservoir Fluctuations

The unsteadiness of the bow-shock wave in front of a 7-inch diameter Apollo-shaped capsule was measured in the T5 hypervelocity shock tunnel at GALCIT. The pressure fluctuations in the reservoir generate expansion and compression waves traveling down the nozzle which interact with the bow-shock in front of the model. The resulting bow-shock displacement is measured using a high-speed Schlieren system where the shock position is extracted using a sub-pixel tracking algorithm. Oscillations of the shock position with amplitudes between ±1% to ±5% of the standoff distance are measured. The power spectrum of the bow-shock motion displays frequencies in the 10 kHZ range corresponding to the frequency content of the pressure fluctuations measured in the reservoir. The RMS free stream pressure disturbances in that frequency range are estimated to be between 3.5% and 7%. Simulations of the effect of acoustic waves on spheres were used to give a crude estimate of the facility noise level in the 10 kHz range