Numerical investigation of the purge flow mechanisms and heat-transfer characteristics of turbine rim seals

Abstract

In gas turbine and aeroengine, the rim seal is set between the turbine stator and rotor to prevent ingestion of the high-temperature mainstream into the rotating cavity. This study examined the sealing efficiency, flow mechanisms, and heat-transfer characteristics of three types of radial rim seal structures, which seriously affect the turbine aerodynamic efficiency and thermal safety. The flows and thermal fields were simulated using steady and unsteady numerical simulations, and dynamic modal decomposition was carried out to extract the unsteady characteristics. The results show that the seal cavity shape affects the seal efficiency. It was found that dolphin-nose with a hook and large cavity results in a higher sealing efficiency. The nose configuration of the cavity upper part also affects the outflow form of the purge flow. The purge flow from a shark-nose seal will inhibit the strength of the mainstream passage vortex, while that from a dolphin-nose seal will result in Kelvin-Helmholtz instability under certain flow rates and induce unsteady vortices. The purge flow will increase the thermal load of the blade and the hub at low flow rates. In particular, the overall thermal load with a dolphin-nose seal is 50% higher than that with a shark-nose structure. It is necessary to balance the sealing efficiency, flow instability characteristics, and heat-transfer characteristics to select an appropriate rim seal configuration.

Keywords

• Turbine
• Rim seal
• Sealing effectiveness
• Flow instability
• Heat transfer
• Dynamic modal decomposition