In liquid propellant rocket engines, turbopumps are used with cryogenic fluids such as liquid oxygen, etc. These pumps are run at a very high rotational speed to achieve compactness. This makes these pumps more prone to cavitation. Hence, axial inducers are used ahead of impellers to prevent cavitation inside the impellers. Experiments with water cannot be extrapolated to cryogenic fluids as thermal effects caused by the evaporation of cryogenic fluids is absent in water experiments. Hence, numerical work is carried out for flow inside the cryo-pump consisting of inducer-impeller-casing and the same will be presented in this seminar.

Fully three-dimensional multiphase simulations are carried out using the commercial CFD package Ansys Fluent. The Schnerr-Sauer cavitation model, which is a mass transfer model, is chosen for the current study. Pumps are designed with secondary passages such as sidewall, wear ring clearances and shaft lubricating circuit through which leakage loss may take place. Simulations are carried out to show the effect of secondary flow on the pump performance, including cavitation behaviour. It is observed that the presence of secondary passages in the model significantly influences the cavitation and rotodynamic behaviour of the pump. Unlike the cavitation in water, the presence of thermal cavitation inhibits the extent of the cavity developed in cryogenic liquids. Pump performances are compared for two working fluids, water and liquid oxygen, and it is observed that the turbopump with liquid oxygen as the working fluid has a lower breakdown NPSH value.