Suppression of Cavitation and Unstable Flow in Throttled Turbopumps

This paper describes a system in which high-energy fluid is tapped from the discharge of a turbopump and injected tangentially upstream of its inducer to improve flow distribution and suppress cavitation and instabilities that occur when the turbopump is throttled. In various tests of inducers in a water tunnel and of a complete experimental pump, the critical suction specific speed was increased by 20 to 50%. Here the critical 5S is defined as the value at which there is a 2% loss in pump head due to cavitation. The critical Ss is related to (NPSHCJ)~314: and, accordingly, the net positive suction head was reduced by 15 to 40% for a given throttled pump output. Unstable flow in the pump was reduced over the cavitating and noncavitating flow range. Typically, good results were obtained with approximately 10% bleed flow injected tangentially from a nozzle ring 1 diam upstream of the inducer and with injection angles relative to the wall of Oj = 0° (tangential) and 7/ = 45° to 60° (axial, downstream). The system, although tested only with water to date, shows promise for application to throttlcable liquid rocket engines.