The effect of secondary passages on cavitation and radial forces in a liquid propellant turbopump

Numerical studies on rocket pumps are computationally expensive and hence the secondary passages such as sidewall clearance gaps, wear ring gaps, axial balancing mechanism, coolant/lubricant paths, etc. in the pump are usually not considered. In this study, a liquid propellant pump with and without secondary passages are modelled and flow simulation results are compared to analyse the differences in cavitation, vortices and radial force predictions arising due to the presence/absence of the secondary flow passages. Single-phase and multiphase simulations are conducted for the design and two off-design points. It is predicted that the presence of secondary passages has a significant effect on the type of cavitation instability predicted and on the volume of cavity generated in the inducer due to which the radial forces generated also differ significantly. The presence of secondary passages predicted large fluctuations from the average radial forces generated by the inducer. These are not obtained if the leakages are not considered. This type of underprediction during the design phase might cause severe wear and tear in the bearings during actual operation. Thus, this study stresses the need for incorporating the secondary passages even at the design stages. This study also highlights the possibility of cavitation instability type manipulation using some means in the inducer which would be significant for cavitation control research in rocket pumps.