Document Type : Original Article


1 Researcher, Space Thrusters Research Institute, Tabriz, Iran

2 Researcher / Space Thrusters Research Institute, Iranian Space Research Center, Tabriz, Iran

3 Professor assistant,, Iranian Space Research Center, Space Thrusters Institute

4 Iranian Space Research Center


Backflow is a phenomenon that occurs due to the increase of upstream pressure compared to downstream pressure. In converging-diverging nozzles, by increasing the outlet pressure compared to the design pressure, the phenomenon of backflow is observed in the divergent part, which causes a decrease in the output velocity and thrust. In this paper, a converging- diverging nozzle with suitable expansion ratio for vacuum condition is selected and the propellant flow, which is considered as butane in this research, is simulated by finite volume method for output pressure equal to vacuum pressure and atmospheric pressure conditions. It has seen that in the atmospheric pressure, backflow occurs in the nozzle in order to determine the appropriate expansion ratio for the nozzle operating in atmospheric pressure, the flow inside the nozzle is simulated for the different expansion ratios and the average outlet axial velocity at the output of theses nozzles is obtained. According to the results, the most suitable expansion ratio of the surface has the highest average axial velocity. Also, to verify the obtained results from finite element simulation, four nozzles with different surface expansion ratios were manufactured and the thrust force obtained from experimental test on the measuring stand with equivalent results obtained from the simulations were compared


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