Swirl Brake Effect on the Rotordynamic Stability of a Shrouded Impeller

The swirling motion of the shroud-to-housing leakage flow in pumps is known to have an adverse impact on the impeller rotordynamic stability. Swirl brakes, under such circumstances, would enhance the stability margin by reducing or, ideally, eliminating, the prerotation at the leakage passage inlet station. The numerical analysis outlined in this paper provides a quantitative means of predicting the effectiveness of such devices. The computed results also illustrate the mechanism with which the fluid/rotor interaction, with the aid of a typical brake, is altered towards relative overall rotordynamic stability. This is done through a comparative examination of the pressure perturbation distribution over the shroud surface for a wide range of backward and forward impeller-whirl frequencies. The conclusions in this study are consistent with recent experimental findings and have important design implications.