矩形喷口欠膨胀超声速射流对撞的实验研究

An experimental study of rectangular under-expanded supersonic jets collision

在不同喷口间距和射流压力下开展了矩形喷口欠膨胀超声速射流对撞实验并与自由射流进行了对比.实验表明:超声速射流对撞的辐射噪声中存在四种不同的啸音模式,且随喷口距离和射流压力的变化在不同模式间切换.在射流压力大于0.5MPa且喷口间距小于50mm时,射流对撞面在两个喷口外形成两道正激波之间,啸音基频维持在3kHz左右.随喷口间距的增大或射流压力的降低,射流对撞面在一侧喷口外的弓形激波与另一侧喷口外的正激波之间.对撞面也有可能出现在两个弓形激波之间,对应的啸音基频约为9kHz,但容易受扰动而回到喷口一侧或是在喷口之间大幅度振荡.当射流压力小于0.36MPa且喷口间距大于70mm后,对撞面在两个喷口之间大幅度振荡,产生基频在1kHz左右并随射流压力的降低和喷口间距的增大而降低的啸音.

Rectangular under-expanded supersonic jet collision experiment is carried out under different nozzle distances and jet pressures and compared with that in the case of free jet. Experiments indicate that there are four screech tone modes of supersonic jet collision, switched from one mode to another depending on the nozzle distance and jet pressure. Two normal shock waves are present between nozzles as jet pressure is more than 0.5 MPa and nozzle distance is less than 50 mm, radiating a stable screech tone with a frequency of about 3 kHz. With nozzle distance increasing or jet pressure decreasing, a bow shock is present at one nozzle exit and a normal shock wave appears at the other exit with the collision surface oscillating between them. Collision surface might be kept balanced in the centre of two nozzles with a 9 kHz frequency screech tone, however, it is vulnerable to disturbance and would return to the equilibrium position near nozzle exit or oscillate between nozzles with large amplitude. When jet pressure is less than 0.36 MPa and nozzle distance greater than 70 mm, the collision surface substantially oscillates between the nozzles, radiating a screech tone with a frequency of about 1 kHz which decreases with jet pressure decreasing and nozzle distance increasing.