Research on Flow Characteristics of Rim Seal and Aerodynamic Performance of Gas Turbine Stage

As an important component of the secondary air system in gas turbines, rim seal can effectively prevent the gas ingestion. However, the excessive cooling air significantly affects the aerodynamic performance of turbine stage due to the coolant egress and mixing with the mainstream through rim seal. The flow characteristics of rim seal and aerodynamic performance of turbine stage was numerically investigated using three-dimensional unsteady Reynolds averaged Navier-Stokcs (URANS) and shear stress transfer (SST)&-a> turbulence model. The numerical scaling effectiveness of rim seal is consistent with the experimental data. The accuracy of the employed numerical method is validated. The flow characteristics of the rim seal and aerodynamic performance of turbine stage is studied at three different coolant flow rates. The flow pattern in the stator-rotor cavity, gas ingestion and coolant egress characteristics are analyzed. The obtained results show that the inner cavity of the rim seal is completely scaled at three coolant flow rates. A lower coolant flow rate for the last stage can achieve a higher sealing effectiveness of rim seal. The average sealing effectiveness of the outer cavity rotor disk is 4. 4% higher than that of the stator disk at the lowest coolant flow rate. For the last stage of turbine, externally-induced ingress caused by the uneven distribution of mainstream circumferential pressure is dominant and the pressure field near the leading edge of blades has a greater impact on gas ingestion than the pressure field at the wake of vanes. For every 1.0% increase in coolant mass flow ratio, the total-to-total efficiency of the turbine stage decreases by around 1.0%. The impact of cooling air outflow from the rim seal on the aerodynamic performance of downstream blades is greater. The flow direction of the egress lags behind the mainstream in the tangential direction, causing the mixed airflow to strike the leading edge of the suction surface of blades at a negative angle of attack, and increasing the pressure on the leading edge of the suction surface. This research can provide a reference for studying the flow characteristics of rim seal and its impact on the aerodynamic performance of turbine stage. © 2024 Xi'an Jiaotong University. All rights reserved.