Optimisation of Purge Seal for Turbopump

Abstract

Seals are very essential elements of a r ocket propulsion system. These are used to avoid inappropriate mixing, loss of propellant, contamination of system and also to meet lubrication challenges in some cases. Purge seals are used to separate the mixing fluids with the h elp of a pressurised, non-reactive purge flu id such as helium. In rocket propulsion, they are used to prevent the mixing of LOX with the hydrogen rich turbine hot gases. LPSC utilises these seals for the same purpose. However, problems such are the wear of the seal,damage of the seal due to shaft impact are being faced.Thus, causing the seal ring to perform a floating action with the help of the hydrodynamic force generated due to shaft rotation is advisable. This project aims at optimising the purge seal so as to inc rease the net hydrodynamic force and also to reduce the friction between the side sliding sur face and the seal housing.This optimisation is done with regards to the clearance, taper angle and the seal cross sectional geometry. It has been observed that the lifting force first increases with the clearance, and then decreases. An optimum value of clearance is sought. Additionally, the force increases with the taper.These parameters have been optimised using CFD. Nature of the flow at small clearances has been taken into account for this analysis.The balance ratio is also improved by introducing asymmetry in the seal geometry.