Numerical investigations on the sealing performance and ingestion mechanism of rim seals for a 1+1/2 counter-rotating turbine

Abstract

Rim seals at the periphery of cavities can prevent high-temperature gas from ingesting into the disk cavity. The sealing performance of rim seals and ingestion mechanism for the counter-rotating cavity of a 1 + 1/2 counter-rotating turbine are studied by solving the three-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) equations via shear stress transfer (SST) turbulence model. The accuracy of the numerical method is verified by comparing with the experimental data. The sealing effectiveness in cavities and flow field in rim seal clearance of three rim seals are analyzed, and the impact factor of unsteady flow pattern is explored. The results show that, the sealing effectiveness ${\epsilon }_c$ of the disk cavity of LPR lipped rim seal is the highest within the full sealant flow rate ${\mathrm{\Phi }}_0$ range. When the non-dimensional sealant flow rate ${\mathrm{\Phi }}_0$ is 0.034, the sealing effectiveness ${\epsilon }_c$ at the high-pressure rotor (HPR) disk at r/b = 0.96 for LPR lipped rim seal is 10.96% higher than that of the axial seal which is the smallest; the sealing effectiveness ${\epsilon }_c$ on the low-pressure rotor (LPR) disk at r/b = 0.96 is 18.99% higher than that of HPR lipped rim seal. A clockwise Kelvin-Helmholtz (K-H) unstable vortex within the rim seal clearance is formed due to the large radial gradient of circumferential velocity. The existence of unstable vortices significantly changes the flow pattern of ingress and egress, which can block the axial clearance and reduce the amount of gas ingestion by reducing discharge coefficients. Affected by the supersonic flow inside HPR blades, shock waves occurred near the trailing edge of the HPR blades, including inner-extending shock (IES) and outer-extending shock (OES) and the non-axisymmetry of circumferential pressure coefficient $C_p$ at the trailing edge significantly increases. The K-H unstable vortex and non-axisymmetric circumferential distribution of the pressure coefficient $C_p$ jointly affect on the ingress and egress process. When the radial inward flow of the vortex is downstream of the high and low circumferential pressure, gas ingestion is enhanced and weakened, respectively.