A Study of Side Loads in Rocket Nozzles during Startup and Shutdown Transients

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Recently, the large side loads is observed in the latest rocket nozzles during start-up and shutdown transient. The objective of this study is to clarify the mechanisms of producing the side loads. In this study, both experimental and numerical studies are performed. In the numerical studies, both the three-dimensional and two-dimensional simulations are performed. The results of three-dimensional simulations show that the simultaneous occurrence of the Free Shock Separation (FSS) and the Restricted Shock Separation (RSS) produces the large side load. In the two-dimensional simulations, the flow field is replaced with a two-dimensional planer field so that it is possible to observe the asymmetric flow patterns. The results show that the small step for film cooling gives great effect on the side load. At the steps, the separation points are trapped in the certain range of pressure ratio, and rapidly shifts to the nozzle exit at the certa(in press)ure ratio. This shift occurs asymmetrically and it produces the large side load. The experimental studies are performed by using the two-dimensional supersonic nozzles. The results show that the asymmetric flow patterns are produced by the instability of shear layer in the downstream of shock wave. But in two-dimensional nozzles, the flow is separated from sides of the test section, and the affects the separation pattern on the nozzle wall.