Design and analysis of secondary flow ejector in a high altitude test facility

Usually, ground testing of space engines is performed in high altitude test facility. The facility is equipped with a supersonic diffuser that expels automatically engine gases to the atmospheric pressure and maintains a vacuum pressure around its nozzle and motor. If the motor pressure is lower than a certain amount, the supersonic flow in the diffuser will not be established. In this situation, it is necessary to use auxiliary ejector at the end of the diffuser. In the present study, a new algorithm has been developed in the design of supersonic ejector. Unlike conventional methods, this algorithm can be used for different primary (input from the ejector nozzle) and secondary fluids (outlet from the diffuser end). In the design of the ejector, the main parameters are determined by the algorithm, while the secondary parameters are selected from the empirical test results of the proved references. In this algorithm, a safe margin is considered for the safe operation of the ejector and this margin is predicted by numerical simulation. Also, numerical simulation is used to validate the design method. Finally, using the proposed algorithm, an ejector is designed to reduce the start-up pressure of an engine-diffuser assembly. An integrated simulation of the diffuser-ejector was performed for both cases that rocket motor is off and on, and the appropriateness of the designed ejector was confirmed in both modes of operation