射流间的声屏蔽对啸叫的作用

用纹影流动显示、声学特性测量和理论分析相结合方法，研究欠膨胀超声速双射流布局对声学特性的影响。欠膨胀超声速双射流的啸叫基频模式与单自由射流相比，在模式切换对应压比上不同，但基本规律相同。但双射流的三维空间流动特性，使不同空间方位上测得的声学特性不同，射流间对彼此处于螺旋啸叫C模式的声辐射有显著的屏蔽作用，在上、下游靠近主轴的方位角处屏蔽效果最大。利用双射流的声屏蔽特性，可达到降噪目的。

Effect of twin jets shielding on screech tones

The effects of arrangements of twin jets on the acoustical characteristics were investigated by the schlieren visualization, noise measurement and theoretical analysis. For under-expanded supersonic twin jets, the fundamental frequencies and modes were similar to those for a single jet; The pressure ratios corresponding to switching from one mode to another mode were different compared with the single jet. Due to three-dimensional flow characteristics, acoustical properties were different in different azimuthal measurement planes. Shielding occurred for under-expanded supersonic twin jets, especially for the helical screech mode C. The shielding reduced the screech intensities most effectively in the upstream and downstream directions near the jet axis. The noise attenuation can be achieved by acoustical shielding.