A Computational Study of a Novel Turbine Rotor Partial Shroud

Abstract

The over tip leakage (OTL) flow that exists between the stationary casing and the rotor tip of a shroudless HP turbine remains a major source of loss of performance for modern aero gas turbines. To-date the principal approaches to reducing OTL loss have been to minimise the clearance gap and/ or apply a rotating shroud to the rotor. Tip clearance control systems continue to improve, but a practical limit on tip gap remains. A rotating shroud is highly effective but increases the rotor weight forcing it to run more slowly, thus increasing other aerodynamic losses. Additional means of reducing OTL loss are still needed. Partial shrouds (winglets) have been tried but none have entered commercial service to-date. This paper presents a novel design of partial shroud derived from a review of past research. The (arbitrary) objectives were to halve the OTL loss of a shroudless rotor, at less than half the size of a full shroud. This design has been analysed using a steady flow RANS CFD code to qualitatively determine its benefits. Attention has been paid to its validation and a realistic determination of its capabilities. The winglet is predicted to significantly improve the efficiency of a highly loaded HP turbine, by 1.2–1.8% at 2% tip gap/ span. A detailed understanding of the flow field shows this to be credible.