Fluid-dynamics of Turbine Rim Seal Structures: A physical Interpretation Using URANS

Unsteady Reynolds-Averaged Navier-Stokes modelling (URANS) is a valuable and cost-effective tool for Computational Fluid Dynamics (CFD), including the investigation of mainstream-cavity interaction in turbines. Despite the gap in accuracy with higher order CFD methodologies, URANS is among the few simulation strategies of industrial interest suitable for predicting ingress/egress over a wide range of conditions.
This paper presents a numerical study of the flow-field in the upstream double-radial seal of a 1.5 stage turbine. Various configurations are tested, including non-purged and purged conditions. Rigour of the approach is ensured by a set of sensitivity analyses, allowing the delineation of a best practice on the use of
URANS in rim seal simulations: this includes an assessment of the effects of sector size, cavity domain size and blade count.
Time-averaged and time-resolved flow predictions capture coherent structures in the rim gap. An association between the 3D morphology of these structures and different ingress/egress mechanisms is proposed. Regions of enhanced radial activity are identified to correspond with the blade leading edges. A frequency analysis of unsteady pressure signals probed in the rim gap leads to a calculation of the structure number and speed.