Unsteady numerical investigation on viscous shear loss caused by rim seal purge flow

One of the most important loss sources is viscous shear caused by interaction between the turbine stator-rotor cavity rim seal purge flow and main flow and has not yet been studied systematically. To assess viscous shear loss, numerical simulations under different purge flow rate are presented. Results show that interaction between the purge flow and main flow causes three high viscous dissipation regions: two regions are located in the main passage resulting from interaction between egress flow and main flow and a third region is situated inside the cavity, mainly induced by the mixing between ingress main flow and purge flow. For both ingress and egress, the circumferential velocity difference between the purge flow and main flow is responsible for most of the viscous dissipation. Furthermore, the velocity difference and viscous shear loss increase as purge flow rate is increased. On average, relative to the design condition, viscous shear loss increases by approximately 127% per 1% increase in purge flow rate. Viscous dissipation continues to decrease as the swirl ratio is increased. Moreover, the influence on viscous shear loss of cavity angle of inclination, cavity location, and cavity exit width are negligible because these three parameters do not significantly affect the circumferential velocity difference.