A computational study of a novel turbine rotor partial shroud

The over tip leakage (OTL) flow that exists between the stationary casing a nd 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 approach es to reducing OTL loss have been to minimize the clearance gap and/or appl y 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 hi ghly effective but increases the rotor weight, forcing it to run more slowl y and thus increasing other aerodynamic losses. Additional means reducing O TL loss are still needed. Partial shrouds (winglets) have been tried but no ne have entered commercial service to date. This paper presents a novel des ign of partial shroud derived from a review of past research. The (arbitrar y) objectives were to halve the OTL loss of a shroudless rotor, at less tha n half the size of a full shroud. This design has been analyzed using a ste ady flow RANS CFD code to qualitatively. determine its benefits. Attention has been paid to its validation and a realistic determination of its capabi lities. The winglet is predicted to significantly improve the efficiency of a highly loaded HP turbine, by 1.2 percent-1.8 percent at 2 percent tip ga p/span. A detailed understanding of the flow field shows this to be credibl e.