Rotordynamic forces acting on a centrifugal open impeller in whirling motion by using active magnetic bearing

¹ Japan Aerospace Exploration Agency 1 Takakuzo, Jinjiro, Kakuda, Miyagi 981-1526, Japan
² EBARA Corporation 78-1 Shintomi, Huttsu, Chiba 293-0011, Japan

Abstract

Rotordynamic forces acting on a centrifugal open impeller of a rocket engine turbopump were measured using a rotordynamic test stand controlled by active magnetic bearings. The tangential rotordynamic force f_t had a small constantly negative value in the measured range. The direct stiffness K had a positive value under various test conditions. In general, direct stiffness K of a closed impeller had a negative value because of the Bernoulli effect. In the case of open impellers, the Bernoulli effect is speculated to be smaller because the absence of a front shroud makes K positive.