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

最近，在最新的火箭喷管中观察到大的侧向载荷在启动和关闭瞬态期间。本研究的目的是阐明产生侧向载荷的机制。在这项研究中，实验和数值研究进行。在数值研究中，进行了三维和二维模拟。三维模拟结果表明，自由激波分离（FSS）和限制激波分离（RSS）的同时发生产生了较大的侧向载荷。在二维模拟中，流场被替换为二维平面场，以便可以观察到不对称的流动模式。结果表明，气膜冷却的小台阶对侧向载荷的影响很大。在一定的压比范围内，分离点被捕获，并在一定的压比下迅速向喷嘴出口移动。这种移位不对称地发生，并且产生大的侧载荷。利用二维超声速喷管进行了实验研究。结果表明，非对称流型是由激波下游剪切层的不稳定性引起的。但在二元喷管中，流动是从试验段的侧面分离的，这影响了喷管壁面上的分离模式。

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.