Steady computations of ingress through gas turbine rim seals

In gas turbines, rim seals are fitted at the periphery of the wheel-space between the turbine disc and its adjacent casing; their purpose is to reduce the ingress of hot mainstream gases. This paper describes the use of a three-dimensional, steady-state model to investigate ingress through engine-representative single and double radial-clearance seals. The three-dimensional Reynolds-averaged Navier–Stokes computations of a simplified turbine stage are carried out using the commercial computational fluid dynamics code ANSYS CFX v13, and the model is based on the geometry of an experimental test rig at the University of Bath. The measured variation of the peak-to-trough pressure difference in the annulus, which is the main driving mechanism for ingress, is reproduced well qualitatively by the computations; quantitatively, the maximum local differences between computation and experiment are less than 20% of the measured peak-to-trough circumferential variation. The radial variation of swirl ratio in the rotor–stator wheel-space is well predicted over the range of flow rates and rim seal geometries studied. The radial distribution of sealing effectiveness determined from experiments is reproduced inward of the mixing region near the seal clearance over a range of sealing flow rates; some over-prediction of the effectiveness was found for both seals at high radius, probably due to limitations in the turbulent mixing modelling. The three-dimensional steady-state approach may be a practical tool for the engine designer where there is a lack of experimental data, providing quantitative predictions of the flow structure within the rotor–stator wheel-space and qualitative predictions of the sealing effectiveness for a given rim seal geometry.