Rotordynamic Forces from Discharge-to-Suction Leakage Flows in Centrifugal Pumps: Effects of Geometry.

The rotordynamic forces generated by the fluid flow through the impeller leakage path of a centrifugal pump are now well established. The present paper examines the effects of modifying the leakage path geometry by changing the front shroud, from a conical shape to a more typical curved design, and the effects of low pressure seal design on these forces. It is found that only the cross-coupled stiffness is affected by the change of path geometry. Changing the low pressure seal from an axial to a radial clearance does, however, significantly affect the rotordynamic forces. A bulk flow numerical model is found to predict the same general result for the low pressure seal tests. The model agrees with the general trends with increasing leakage flow coefficient exhibited by the data, but appears to underpredict the magnitude of the normal force.