Steady-state analysis of purge flow passage on the performance of the high-pressure transonic axial turbine at different mass flow ratios

The bleed air from the compressor, in the form of purge flow, is injected into the mainstream to prevent hot air ingestion into the axial turbine’s wheel space. This purge flow increases aerodynamic losses by altering the flow characteristics of the mainstream flow. Therefore, there is a need to optimise the purge flow to achieve a trade-off between efficiency and hot air ingestion. The present study is devoted to the performance analysis of the single radial rim seal of the first-stage generic high-pressure transonic axial turbine with and without the purge flow passage. Turbine characteristics are studied numerically at different mass flow ratios. The simulations bring out the interaction of purge with the mainstream flows in terms of streamlines, density gradient, temperature, and pressure contours. As the mass flow ratio increases, the total-to-total isentropic efficiency decreases due to changes in the vortex structure of the flow produced by the blades. The cooling effectiveness on the endwall and the sealing effectiveness in the purge domain increases with increased mass flow ratios. Hence, an optimum purge mass flow rate should be chosen to control the secondary flow losses and thus minimise the aerodynamic loss of the turbine. The optimum mass flow ratio is identified as 0.7%, which reduces the hot air ingestion and secondary flow losses.