Numerical characterization of hot gas ingestion through turbine rim seals

This paper deals with a numerical study aimed at the characterizationof hot gas ingestion through turbine rim seals. Thenumerical campaign focused on an experimental facility which models ingress through the rim seal into the upstream wheel-spaceof an axial-turbine stage. Single-clearance arrangementswere considered in the form of axial- and radial-seal gap configurations.With the radial-seal clearance configuration, CFD steady state solutions were able to predict the system sealing effectiveness over a wide range of coolant mass flow rates reasonablywell. The greater insight of flow field provided by the computationsillustrates the thermal buffering effect when ingress occurs:for a given sealing flow rate, the effectiveness on the rotorwas significantly higher than that on the stator due to the axialflow of hot gases from stator to rotor caused by pumping effects.The predicted effectiveness on the rotor was compared with atheoretical model for the thermal buffering effect showing good agreement.When the axial-seal clearance arrangement is considered,the agreement between CFD and experiments worsens; the variation of sealing effectiveness with coolant flow rate calculated by means of the simulations display a distinct kink. It was found that the ”kink phenomenon” can be ascribed to an over-estimation ofthe egress spoiling effects due to turbulence modelling limitations.Despite some weaknesses in the numerical predictions, the paper shows that CFD can be used to characterize the sealing performance of axial- and radial-clearance turbine rim seals.