激光多普勒测速方法研究超声速冲击射流

在超声速射流噪声的产生中 ,喷嘴出口的激波栅格结构有关键的作用 ,激波栅格的间距是推测激波噪声基频的基本参数。应用激光多普勒测速方法对收缩喷嘴欠膨胀射流垂直冲击平板的流场进行了测量 ,获取了射流轴线上的速度分布。从该轴线速度的起伏推算出自由射流段的激波栅格间距与前人用接触测量方法得到的经验公式基本一致 ,但是比该经验公式值低 5 %以上 ,表明由该接触测量所得的经验公式描述的激波栅格间距可能大于实际的激波间距。

On the supersonic impinging jet by Laser Doppler Velocimetry

Shock cell structure plays a crucial role in the generation of jet screech and broadband shock noise in supersonic jet. The shock cell spacing is a fundamental parameter for predicting the jet screech frequency. Laser Doppler Velocimetry is applied to measure the flow velocity along the axis of supersonic impinging jet, which is from a convergent nozzle and normal to a large flat plate. The variation of velocity along the jet axis is found to be consistent with the schlieren picture. The shock cell spacing derived from the velocity variation is in good agreement with the former experimental formula derived from the variation of mean static pressure along the jet axis. It is found that the shock cell spacing from LDV is less than that from the experimental formula by more than 5%. It indicates that the value from the mean static pressure may be greater than the actual shock cell spacing.