Improvement of Inlet Flow Characteristics of LE-7A Liquid Hydrogen Pump

Abstract

LE-7A engine inducers require high head rise and high suction performance in spite of cavitating conditions because a low-speed, low-pressure pump is not used in front of the main pump in the LE-7A engine. During the development phase, use of the LE-7A fuel turbopump with an original inducer resulted in a noticeable deterioration of suction performance near the required net positive suction head. When the pump inlet pressure was gradually reduced, the inducer caused sudden remarkable head degradation, and the rotor vibration was greatly amplified because the frequency of the vibration almost coincided with that of the second critical speed of the turbopump. This vibration was caused by a rotating-stall-type phenomenon, which is considered to be closely related to backflow cavitation at the inducer inlet. Improvement of the inducer was indispensable for enhancement of the reliability of the hydrogen turbopump. Thus, an inlet flow coefficient larger than that of the original inducer was selected to reduce the inlet backflow. A redesign of the original inducer and test results of the hydrogen turbopump with the newly developed inducer are reported.