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

本文介绍了降低工业上常用的拉瓦尔喷管超音速喷流噪声的试验研究和高效喷管的研制。喷管的设计马赫数为2.0，喉部直径为20mm，出口直径为26mm。实验在喷管压力比从2.0到18.0的范围内进行，包括过膨胀和欠膨胀射流。测量在提供自由场环境的消声室中进行。纹影技术被用来作为工具，定性研究的冲击波图案，这是主要负责尖叫音。实验研究了锯齿唇厚度对尖鸣音的影响。结果表明，当喷嘴唇缘厚度小于一个出口直径时，过膨胀工况下的尖叫音幅值随唇缘厚度的增加而增大，射流振荡模式从轴对称向轴对称转变， ...更多信息 对称到螺旋或扑动，而对于超过两个喷嘴出口直径的前缘厚度，尖叫音幅度随着前缘厚度的增加而减小。本文提出了两种新的超音速喷流降噪技术，一种是由直径很小的长圆柱体组成的十字丝，其位置沿喷流轴线方向变化;另一种是由直径很小的不锈钢长丝组成的网筛。十字丝对射流结构有显著影响。纹影照片表明，横丝破坏了激波室结构，削弱了强度。因此，钢丝可降低尖叫音的振幅。网筛垂直地放置在喷嘴出口平面处，并且在筛的中心部分穿孔以扰动初始射流剪切层。网筛导致喷射尖叫音和所有声压级的实质性抑制。小孔尺寸是影响超声速喷流噪声的重要因素。少

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