Abstract
Results of a theoretical and an experimental research investigation of the various noise sources encountered by a high-speed rocket sled are presented. The objective was to isolate and determine quantitatively the contribution of each noise source to the over-all noise level inside the rocket sled. The noise sources investigated were those due to turbulent boundary layer, base pressure fluctuation, wake noise, and the propulsive jet motors. A wedge-shaped Mach 3.0 rocket sled was heavily instrumented to obtain the interior and pseudoboundary noise levels. At higher Mach numbers, the turbulent boundary-layer noise represents the greatest single noise source with a broad frequency spectrum. Noise due to base-pressure fluctuations was also high, but was confined to a narrower frequency band that can be related to a modified Strouhal relationship. The contribution from the wake noise and the rocket-jet noise diminished with increasing vehicle speed and became insignificant beyond Mach 1.0. Although the instrument compartment was constructed of aluminum honeycomb material and fiberglass lining with a total density of 1.7 lb/sq ft, its acoustic qualities were insufficient to prevent damaging noise levels to electronic and test components within the sled at Mach number approaching 1.0.
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