Document Type : Original Article


1 Space Transportation Research Institute, Iranian Space Research Center

2 Ferdowsi University of Mashhad


In the present study, the effect of pre- evacuation on starting process of a second throat exhaust diffuser has been investigated experimentally by examining a thrust optimized parabolic nozzle. An experimental setup called high- altitude test facility has been used with compressed air as operating fluid. According to the importance of area ratio parameter (Ad/Ast) of a second throat diffuser, the effect of this parameter variation has been examined on the start- up performance of the nozzle and diffuser. In each of the diffuser geometries, in order to evaluate the instantaneous performances, the pressure in the nozzle chamber has charged instantly in two modes; with and without pre- evacuation. Then, the vacuum chamber pressure and static pressure distribution along the diffuser were measured by a data acquisition system. The results show that pre- evacuation in the test chamber reduces the start- up time of the diffuser by 50 to 60%. In addition, pre- evacuating the test chamber eliminates the destructive transition phenomenon from the flow separation pattern during start- up of the nozzle and diffuser. Also, It has been observed that with the narrowing of the diffuser’s second throat duct, the minimum starting pressure of the diffuser increases and eventually flow chocks at the second throat in a certain area ratio.


Main Subjects

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