Yasuhide Watanabe

LE-7A Engine Nozzle Problems during Transient Operations

Under development the LE-7A engine encountered two major troubles of nozzle extension. These two problems are the large side loads and the damage of some regenerative cooling tubes during start up and shut down processes. In the investigation results, it was clear that there are two kinds of large side loads and their origins are different. One kind of side load origin is the transition between Free Shock Separation (FSS) and Restricted Shock Separation (RSS) during start up and shut down processes. This RSS occurrence is also the reason of the damage of some regenerative cooling tubes. The second large side load origin is the stagnation and sudden movement (‘jump’) phenomena of the separation point. This paper presents a focus on the LE-7A engine separation phenomenon caused by the two kinds of the large side loads and the damage of some regenerative cooling tubes of the upper nozzle extension during the startup and shutdown transients. Nomenclature Symbols Pa ambient pressure Pc main combustion chamber pressure e nozzle expansion ratio Abbreviations FSS Free Shock Separation RSS Restricted Shock Separation CTP Compressed Truncated Perfect TP Truncated Perfect NPR Nozzle Pressure Ratio (=Pc/Pa)

Three Dimensional Unsteady Flow Simulation of Compressed Truncated Perfect Nozzles

Recently, a large side load was observed during the startup and shutdown transients of the Japanese LE-7A rocket engine nozzle. The objective of the present paper is to clarify the mechanism producing the large side loads during the startup transient. The unsteady three-dimensional Navier-Stokes equations are solved for the startup transients of the three types of nozzle contours – the Truncated Perfect (TP) nozzle, the 86% Compressed Truncated Perfect (CTP) nozzle and the CTP50-R5-L nozzle. The contour of the TP nozzle is the LE-7 nozzle and the contour of the 86% CTP nozzle is the LE-7A nozzle. The CTP50-R5-L nozzle was tested by Tomita et al and Takahashi et al . The asymmetric flow patterns and the large side loads are observed in LE-7A and CTP50-R5-L nozzle. There are two types of flow patterns that 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 shock wave under RSS condition . The interaction between the internal shock and the Mach disk causes the cap shock and the trapped vortex. For both flow patterns, the trapped vortex oscillates with the cap shock. The trapped vortex is developed with oscillation as the Nozzle Pressure Ratio (NPR) increases. At a certain range of the NPR, oscillations of the cap shock and the trapped vortex become larger, and then the supersonic jet on the both sides of the cap shock reattaches to the nozzle wall partially –the FSS and the RSS occur simultaneously. The second flow pattern is observed in CTP50-R5-L nozzle. With the RSS, the cap shock oscillates with the trapped vortex. These flow patterns produce the asymmetric wall pressure distribution and the large side load. Nomenclature p : Pressure R : Gas constant γ : Specific heat ratio M : Mach number NPR : Nozzle Pressure Ratio, a c p p / Subscript c : combustion chamber a : ambient Introduction Several new rocket engines in the world have the new-shaped nozzle instead of the conventional Truncated Perfect (TP) nozzle. For example, the thrust-optimized nozzles are applied for the American Space Shuttle Main Engine (SSME) and the European Vulcain. On the other hand, the Japanese LE-7A nozzle is designed as the Compressed Truncated Perfect (CTP) nozzle. In these nozzles, the large side loads are observed during the startup and shutdown transients at the sea level firing test. The side loads are undesirable since it may damage the engine support system. The side loads in rocket nozzles have been the subjects of various studies, but the detailed flow structures and the mechanisms of the side loads have not been understood completely. The flow separates from the nozzle wall under the low chamber pressure condition during the startup and shutdown transients. It is considered that the behavior of the separated flow influences on the side load. *Graduate Student, Graduate School of Engineering Science, Osaka University †Associate Professor, Department of Mechanical Engineering, Nagoya Institute of Technology, Member AIAA ‡Professor, Graduate School of Engineering Science, Osaka University, Member AIAA §Senior Engineer, NASDA, Member, AIAA ¶Associate Senior Engineer, NASDA, Member AIAA 38th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit 7-10 July 2002, Indianapolis, Indiana AIAA 2002-3991 Copyright

LE-7A Engine Nozzle Flow Separation Phenomenon and the Possibility of RSS Suppression by the Step inside the Nozzle

LE-7A engine was encountered two nozzle extension troubles under the early development. These troubles are the two kinds of large side loads and the some nozzle tubes damage during the start up and shut down transients. The Restricted Shock Separation caused a kind of large side loads and regenerative cooling tube damage. The largest side loads was caused by the separation point stagnation and jump on the film cooling step inside the nozzle. The LE-7A original nozzle phenomenon such as ‘the separation stagnation and jump’ and ‘the RSS annihilation and occurrence’ indicates a significant suggestion to suppress the RSS flow by the small step inside the nozzle. This paper presents a focus on the LE-7A engine specific separation phenomenon during the startup and shutdown transients and the possibility of RSS suppression by the step inside the nozzle.