小口径轴对称收缩喷嘴射流冲击大平板噪声指向特性研究

实验研究了3毫米口径轴对称收缩喷嘴在各种压比下射流垂直冲击和倾斜冲击坚固大平板产生的噪声的指向特性。发现噪声在过平板法线和喷嘴轴线的平面内呈近似四瓣分布，当喷嘴与平板距离减小时，指向壁射流下游的瓣得到增强，反之，指向喷嘴上游的瓣得到增强。喷嘴压比增加时，指向壁射流下游的瓣得到增强，反之，指向喷嘴上游的瓣得到增强。根据自由射流噪声的基本指向特性、射流冲击噪声基本指向特性、声波在平板处发生镜面反射和声波能量叠加的设定，建立了一个冲击射流总体噪声指向特性的模型，成功解释了实验结果，并揭示了形成冲击射流总体噪声指向特性的内在机理。

Noise Directivity of Impinging Jet From a Small Diameter Axis Ymmetric Convergent Nozzle on a Large Flat Plate

The noise directivity pattern of the impinging jet from a 3 millimeters diameter axisymmetric convergent nozzle normally and obliquely impacting the large rigid flat plate was studied experimentally with different pressure rates and different nozzle-to-plate distances. It is found that the directivity results demonstrate four-leafed clover pattern on the plane containing jet axis and plate normal. A model of the directivity pattern of the total noise of impinging jet was established according to the basic directivity pattern of free jet noise and jet impinging noise, the mirror reflection of the sound wave on the large flat plate and the assumption of the superposed noise energy in the overlapped region. The mechanism of the directivity pattern and the variation of the directivity pattern with pressure ratio and nozzle-to-plate distance was interpreted by the model.