Internal Flow and Axial Thrust Balancing of a Rocket Pump

Abstract

Large axial thrust is produced on the rotor assembly of high-pressure rocket pumps. Thus, to ensure the reliability of bearings supporting the high rotational speed rotor, precise axial thrust balancing is essential. To realize complete axial thrust balancing, the back shroud of the main impeller is employed as the balance piston of a self-balancing type axial thrust balancing system in which the rotor assembly moves axially to compensate unbalance axial force. In this balancing system, which is often applied, complicated internal flow characteristics and pressure distributions are very important for predicting the precise characteristics of the axial thrust produced by the system. In the present study, a calculation method for analyzing the internal flow system taking into account effects of boundary layer conditions and angular momentum change in the impeller side-chambers is applied to the system combining the balance piston and grooves on the casing wall of the balance piston chamber. The analysis program is able to detect phenomena which could not be captured in past calculations and is effective for calculating internal flow characteristics much faster than possible with CFD analysis. A combination of balance piston and grooves on the casing wall of the balance piston chamber was confirmed to be suitable for extending the dynamic range of axial thrust balancing although installation of the grooves increased the leakage flow rate and friction torque at the same time.