Evaluation of Axial Fluid Force Acting on a Centrifugal Impeller with and without Balance Holes

In this research, we investigated the effect of balance holes in centrifugal impellers on axial dynamic characteristics. To measure the unsteady fluid force applied to the impeller, we performed the axial oscillation test for a model impeller for rocket turbopumps with and without balance holes. Additionally, we carried out CFD-based investigations and compared the results between experiments and computations. The axial dynamic characteristics predicted by the unsteady simulations generally agree with that of the experiments. The axial thrust amplitude under oscillation becomes greater with balance holes than without balance holes because of the additional supply of leakage flow from balance holes. We also found the phase difference between axial displacement and thrust varies depending on the presence or absence of balance holes. From these results, we confirmed the change of leakage flow due to balance holes resulted in the change of pressure distribution at the back of the impeller and dynamic characteristics for centrifugal pumps.