Numerical Characterization of Hot Gas Ingestion through Turbine Rim Seals

This paper deals with a numerical study aimed at the characterization
of hot gas ingestion through turbine rim seals. The
numerical campaign focused on an experimental facility which
models ingress through the rim seal into the upstream wheel-space
of an axial-turbine stage. Single-clearance arrangements
were 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 reasonably
well. The greater insight of flow field provided by the computations
illustrates the thermal buffering effect when ingress occurs:
for a given sealing flow rate, the effectiveness on the rotor
was significantly higher than that on the stator due to the axial
flow of hot gases from stator to rotor caused by pumping effects.
The predicted effectiveness on the rotor was compared with a
theoretical 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 of
the 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.