Reduction in Supersonic Jet Noise from a Laval Nozzle available in Various Industry and Development of a High Efficiency Nozzle

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The present paper describes the experimental investigations on reduction in supersonic jet noise from a Laval nozzle available in various industry and development of a high efficiency nozzle. A design Mach number of the nozzle is 2.0 with the throat diameter of 20mm and the nozzle exit diameter of 26mm. The experiments have been conducted over a range of nozzle pressure ratios from 2.0 to 18.0 including the overexpanded and the underexpanded jets. The measurements were conducted in an anechoic room providing a free-field environment. Schlieren technique was used as the tool to study qualitatively the shock wave patterns which are primarily responsible for screech tones. The effect of the nozzle-lip thickness on screech tones has been investigated experimentally. As a result, for the nozzle-lip thickness below one nozzle exit diameter, the screech tone amplitude at the overexpanded condition increases with increasing the nozzle-lip thickness, and the jet oscillation mode changes from ax … More isymmetric to spiral or flapping, while for the nozzle-lip thickness beyond the two nozzle exit diameter, the screech tone amplitude decreases with increasing the nozzle-lip thickness. Two new techniques on supersonic jet noise reduction are proposed, one is the method by a cross-wire which is composed of long cylinders with a very small diameter and its location is varied in the jet axis direction in the supersonic jet stream, the other a mesh screen which is long stainless wires with a very small diameter. The cross-wire is significantly affects the jet structure. Schlieren photographs show that the cross-wire destroys the shock cell structure and weakens the strength. Therefore, the wire reduces the amplitude of screech tones. The mesh screen is perpendicularly placed at the nozzle exit plane and the hole is perforated in the central part of the screen to perturb the initial jet shear layer. The mesh screen leads to a substantial suppression of jet screech tones and the over all sound pressure level. The hole size is an important factor in reducing the supersonic jet noise. Less