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

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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.