The Influence of Swirl Brakes on the Rotordynamic Forces Generated by Discharge-to-Suction Leakage Flows in Centrifugal Pumps

Abstract

Increasing interest has been given to swirl brakes as a means of reducing destabilizing rotordynarnic forces due to leakage flows in new high speed rocket turbopumps. Although swirl brakes have been used successfully in practice (such as with the Space Shuttle HPOTP), no experimental tests until now have been performed to demonstrate their beneficial effect over a range of leakage flow rates. The present study investigates the effect of swirl brakes on rotordynarnic forces generated by discharge-to-suction leakage flows in the annulus of shrouded centrifugal pumps over a range of subsynchronous whirl ratios and various leakage flow rates. In addition, the effectiveness of swirl brakes in the presence of leakage inlet (pump discharge) swirl is also demonstrated. The experimental data demonstrates that with the addition of swirl brakes a significant reduction in the destabilizing tangential force for lower flow rates is achieved. At higher flow rates, the brakes are detrimental. In the presence of leakage inlet swirl, brakes were effective over all leakage flow rates tested in reducing the range of whirl frequency ratio for which the tangential force is destabilizing.

Flow Inside the Sidewall Gaps of Hydraulic Machines: A Review

“…It results in tangential forces with destabilizing effects and a potential increase in the magnitude of the rotordynamic forces. It is in agreement with Sivo et al [144], where authors demonstrated that reduction of the leakage flow swirl using ribs or swirl brakes on the housing can effectively reduce the destabilizing tangential force. On the contrary, Hsu and Brennen [145] showed that the reduction of the swirl within the leakage path using ribs and grooves as swirl brakes brings benefits only at low leakage flow rates, since, at higher flow rates, the anti swirl devices increase the destabilizing tangential forces.…”

Fluid-induced rotordynamic forces and instabilities

“…Though some early data on the rotordynamic forces in a centrifugal pump were obtained by Shoji and Ohashi [8], the Caltech program added greatly to the data base. Data were obtained for many different types of impellers (centrifugal and axial, shrouded and unshrouded, with and without cavitation), for many different types of volutes and for parametric variations of the forces with pump operating point, pump cavitation and various clearances and other factors [6,7,[9][10][11][12][13][14][15][16][17][18][19]. Typical data for the dimensionless normal and tangential forces, F n and F t ; as a function of the frequency ratio, o=O; are presented in Figure 3 for a conventional centrifugal pump impeller operating in a single vaneless volute.…”

“…We now shift attention from inlet swirl to swirl reduction by vanes installed within the leakage passage. An important finding by Sivo et al [15] was that anti-swirl vanes installed on the stator within the leakage flow path could be very effective in reducing the destabilizing region of forward whirl. This is important from a practical point of view because it suggests that anti-swirl vanes in the leakage path could be used to tailor the rotordynamic behaviour of high-speed pumps.…”