Numerical investigation of the effect of rim seal on turbine aerodynamic design parameters and end wall flows in low-aspect ratio turbine

Turbomachinery design is associated with a comprehensive understanding of the end wall loss mechanism which is more complicated when the rim seal purge flow is taken into consideration. Ensuring an adequate life of high pressure turbine requires efficient cooling method to keep the disk temperature at an acceptable level. Hence, purge flow is injected through the rim seal in axial turbine in order to prevent hot gas ingestion into the rotor disk. This paper focused on the effect of upstream rim seal purge flow on turbine aerodynamic design parameters in a low aspect ratio axial turbine. Besides, end wall secondary flows and interaction between the rim seal purge flow and mainstream were also highlighted. Two different rim seal configurations were taken into account, i.e., inclined axial rim seal configuration and radial rim seal configuration. The purge flow rate approximately equaled to 1% of main flow which is the typical value in modern aero-engine secondary air system. Results show that inclined axial rim seal configuration is obviously superior to the radial one in terms of aerodynamic and sealing performance. The turbine aerodynamic design parameters and end wall flows are significantly modified by the purge flow. The change of pressure field and vortex structure near the hub region directly leads to the variation of turbine aerodynamic design parameters. In addition, the pressure leg of horse shoe vortex nearly disappears and cavity induced vortex appear when the flow is injected from rim seal. Moreover, the two legs of cavity induced vortex have the same rotating direction which form the passage vortex and propagate downstream in the main passage. Current research demonstrates that it is important to consider the effect of rim seal purge flow in turbine aerodynamic design and end wall profile optimization.

► We study the effect of rim seal purge flow on aerodynamic design parameters and related physical mechanisms in axial turbine numerically.
► The influence of rim seal purge flow on axial turbine is not clear especially for axial turbine routine design.
► Purge flow can significantly modify the end wall flows and change turbine aerodynamic design parameters.
► The results in this research will provide a design guideline on how to take rim seal purge flow into consideration.