He F, Zhang X W
Department of Engineering Mechanics, Tsinghua University, Beijin, People's Republic of China.
J Acoust Soc Am. 2002 Sep;112(3 Pt 1):966-71. doi: 10.1121/1.1492818.
Experiments were conducted to investigate the acoustic characteristics of underexpanded supersonic twin jets in different azimuthal measurement planes. Compared with two independent jets, the twin jets produced additional noise due to the enhanced mixing and entrainment. The larger pressure ratio for switching from the axisymmetric mode to the helical mode led to lower noise levels at 90 degrees than for two independent jets. For pressure ratios greater than 5.00, the noise reduction was due to cessation of screeching of the twin jets while screeching of a single jet was still detected. The apparent shielding phenomenon was measured for the screech helical mode. The screech tone intensities were attenuated largely due to the shielding effects. The noise reductions due to shielding were obtained over a wide range of pressure ratios relative to the sum of two independent jets.
进行了实验以研究不同方位测量平面内欠膨胀超声速双喷流的声学特性。与两个独立喷流相比，双喷流由于增强的混合和卷吸作用产生了额外的噪声。从轴对称模式切换到螺旋模式的压力比越大，90度处的噪声水平比两个独立喷流时更低。对于大于5.00的压力比，降噪是由于双喷流的啸叫停止，而仍能检测到单个喷流的啸叫。对啸叫螺旋模式测量到了明显的屏蔽现象。由于屏蔽效应，啸叫音调强度大幅衰减。相对于两个独立喷流的总和，在很宽的压力比范围内都获得了屏蔽导致的降噪效果。
