| Previous experimental and analytical results have shown that discharge-to-suction leakage flows in the annulus of a shrouded centrifugal pump contribute substantially to the fluid induced rotordynamic forces (Adkins, 1988). Experiments conducted in the Rotor Force Test Facility (RFTF) at Caltech on an impeller undergoing a prescribed circular whirl have indicated that the leakage flow contribution to the normal and tangential forces can be as much as 70% and 30% of the total, respectively (Jery, 1986). Recent experiments at Caltech have examined the rotordynamic consequences of leakage flows and have shown that the rotordynamic forces are functions not only of the whirl ratio but also of the leakage flow rate and the impeller shroud to pump housing clearance. The forces were found to be inversely proportional to the clearance and a region of forward subsynchronous whirl was found for which the average tangential force was destabilizing. This region decreased with flow coefficient (Guinzburg, 1992).; The present research is a continuation of the previous experimental work and has been motivated by the rotordynamic stability problems with the recently developed Alternate Turbopump Design (ATD) of the Space Shuttle High Pressure Oxygen Turbopump. The present study investigates the influence of swirl brakes, installed in the annular leakage path, as a means of reducing the undesirable rotordynamic forces over a range of flow rates. Also, the present study evaluates the effect of the rotordynamic forces of tip leakage restrictions at discharge used by the ATD for establishing axial thrust balance. As a first step to understanding the flow field in the leakage annulus, the region is probed with a laser velocimeter to provide basic information on these unsteady turbulent three-dimensional leakage flows and to serve as a standard of comparison for approximate theoretical models as well as applications of computational fluid dynamics. |
