Gas ingestion mechanism and unsteady flow characteristics of fish-mouth rim seals in an axial gas turbine

Rim seals fitted between the turbine stator and adjacent rotor disc, together with sealing air bled from compressor to pressurize the wheel-space, serve to suppress hot gas ingestion from mainstream in axial gas turbines. This paper investigates the distributions of pressure, swirl ratio, and sealing efficiency in two fish-mouth rim seal configurations using a 1.5-stage turbine rig, under engine-relevant flow coefficients and turbulent flow parameters. In parallel, unsteady numerical simulations are performed to determine the gas ingestion mechanism. Various sealing air supply cases are compared over a range of sealing flow rates, with the sealing efficiency deduced from tracer-gas CO 2 concentration measurements. The effect of rotational Reynolds number ( Re ϕ ) on sealing and flow characteristics of baseline configuration is analyzed, and numerical results agree well with the test measurements. The effect of auxiliary sealing flow on gas ingestion is clarified at both low and high rotational Reynolds numbers. The vertically injected auxiliary sealing flow intensifies Kelvin-Helmholtz (K-H) instability and simultaneously enhances both egress and ingress effects at Re ϕ = 2.53 × 10 6 . Furthermore, the effect of the intake angle of auxiliary sealing flow is elucidated. The auxiliary sealing flow with positive pre-swirl suppressed K-H instability at Re ϕ = 2.53 × 10 6 , improving sealing efficiency by up to 17.33% compared with baseline configuration under the studied cases. The findings may deepen the understanding of complex flow behavior near rim seals at varying rotational Reynolds numbers.