Thomas/Alford Force on a Partial-Admission Turbine for the Rocket Engine Turbopump

Abstract

This paper describes an imbalanced torque force, called the Thomas/Alford force, of a partial-admission turbine for the rocket engine turbopump. The Thomas/Alford force is a destabilizing force imposed on the rotor that could cause rotor dynamic instability. This, in turn, may impair stable operation of the rocket engine and trigger mission failure. Such destabilizing force should be avoided as its characteristics have not been discussed in detail. In this study, Thomas/Alford forces for typical symmetric partially open/closed nozzle patterns with an open/closed ratio are analyzed. For such an open/closed ratio, it was determined that the Thomas/Alford force varied with the whirling angle, and whether the open/closed ratio may impair stable operation and reliability of the rocket engine turbopump is contingent on avoiding such fluctuation. The reason for such fluctuation was investigated by mathematical methodology, which was then extended to determine a general rule of patterns for rocket engine designers. This rule would, thus, prove useful in the future development of a partial-admission turbine for a rocket engine turbopump.