Study of Compound Choking Phenomena and Compound Shock Waves in Compressible Internal Flows

1.在不同上游滞止压力与背压比的条件下，对亚音速平行两股流经收敛喷管汇流时的复合堵塞进行了实验研究。得到了不同喷嘴在喷管出口发生复合堵塞时，收敛喷管两端的临界压比。在考虑两股气流混合的情况下，计算了复合堵塞的临界压力比。计算结果与实验结果吻合较好。从复合喷管流动堵塞的角度，对两个亚音速气流通过单个收敛喷管的行为进行了数值分析。考虑了横跨整个出口通道的声速线的增长，提出了一种新的复合堵塞判据。将该判据与以前的流动模型判据进行了比较和讨论。即使在两股亚音速平行流通过收敛喷管的复合流动被堵塞时，随着背压的降低，喷管出口附近的流动状况也会发生变化。这意味着复合堵塞并不像一维等熵理论所假设的那样在喷管出口处建立，而是发生在出口附近的有限区域附近。用一维分析和实验相结合的方法研究了压力波在等面积直管道中与两个平行的亚音速气流的传播。通过这些研究，明确了复合声波的特性。压力波在水流中的传播是分叉的，其形状是三维的，但传播速度与以前的一维流动模型近似相等。

1. The compound choking by confluence of two subsonic and parallel streams through a converging nozzle was experimentally investigated for various ratios of the upstream stagnation pressure to the back pressure. The critical pressure ratio across the converging nozzle when the compound choking occurs at the nozzle exit was obtained for various nozzles. Also, the critical pressure ratio of the compound choking was calculated where the mixing of the two streams is taken into consideration. The calculated results agree well with the present experimental results.2. The behavior of two subsonic streams through a single converging nozzle was numerically analyzed from the viewpoint of the choking of the compound nozzle flow. A new criterion of the compound choking was presented taking the growth of the sonic line extending across the entire exit passage into consideration. The present criterion was compared and discussed with the criterion of the previous flow model.3. Even when the compound flow of two subsonic and parallel streams through a converging nozzle is choked, the flow condition near the exit of the nozzle changes if the back pressure is reduced. This means that the compound choking is not established at the nozzle exit just as the one-dimensional isentropic theory assumes, but the compound choking occurs near a finite region near the exit.4. The pressure wave propagating against two parallel subsonic streams in a constant area straight duct was investigated by both one-dimensional analysis and experiment. From these studies, the characteristics of compound sound waves were made clear. The pressure wave propagating against the streams is bifurcated and the shape is three dimensional, but the propagation velocity is nearly equal to the value by the previous one dimensional flow model.