Restricted Shock Separation Research Articles

B3 ロケットノズルに生じる横推力に関する3次元非定常CFD

Recently, a large side load is observed during start-up and shutdown sequences of Japanese LE-7A rocket engine nozzle. The objective of the present paper is to clarify the mechanism producing the large side loads during start-up process. The unsteady 3-D Navier-Stokes equations are solved for start-up process of three types of nozzle contours. That is, truncated perfect (TP) nozzle, 86% compressed truncated perfect (CTP) nozzle and CTP50-R5-L nozzle. The contour of TP nozzle and the contour of 86% CTP nozzle are LE-7 nozzle and the original LE-7A nozzle respectively. Asymmetric flow fields and large side loads are observed for LE-7A and CTP50-R5-L nozzles. There are two flow patterns which cause the large side loads. The first is the simultaneous occurrence of the Free Shock Separation (FSS) and the Restricted Shock Separation (RSS). The second is the oscillation of Mach disk under the RSS condition.

Restricted Shock Separation in Rocket Nozzles

In overexpanded rocket nozzles the e ow separates from the nozzle wall at a certain pressure ratio of wall pressure to ambient pressure. Flow separation and its theoretical prediction have been the subject of several experimental and theoretical studies in the past decades. Two distinctive e ow separation phenomena, the freeshock and restricted-shock separation, were observed in experiments with nozzles. Both phenomena are discussed in detail, and the system of recompression shocks and expansion waves is described. For the free-shock case three different shock structures in theplume can occur, namely the regular shock ree ection, the Mach disk, or a cap-like shock pattern. Theappearanceofthesedifferentplumepatternsis discussed. Theseshock structuresareconserved for the full-e owing, but overexpanded, nozzle. Numerical results obtained for existing rocket nozzles, e.g., Space ShuttleMain EngineorVulcain, show a qualitativegood agreement with experimental photographs.Furthermore, an explanation for the appearance of restricted shock separation, which has been widely unknown up to now, is given, analyzing why and under what conditions it occurs. The type of nozzle contour strongly ine uences this form of e ow separation, and restricted shock separation also occursin full-scale, thrust-optimized rocket nozzles. Based on the results established for e ow separation, an outlook on the generation of side loads is given.