An Investigation Into a Novel Turbine Rotor Winglet: Part I — Design and Model Rig Test Results

Abstract

In modern gas turbines hot section components, the over tip leakage (OTL) flow that occurs between the stationary casing and rotating tip of a shroudless HP turbine is still a considerable source of loss of performance. The principal means of reducing this loss have been to minimise the tip gap and/or to apply a rotating shroud to the rotor. Tip clearance control systems continue to improve, but a practical limit on tip gap remains. Winglets have been identified by a number of researchers as having potential, but none have yet to enter commercial service. Harvey & Ramsden [1] analysed a novel design of one, which indicated that it could significantly reduce OTL loss. This paper presents the design of such a winglet as applied to the rotor blade of a research high pressure turbine carried out as part of the ANTLE (Advanced Near Term Low Emissions) technology demonstrator programme. The use of Computational Fluid Dynamics (CFD) calculations in the design process is discussed. In particular, the use of coarse meshes and idealised geometries, for computational speed, did involve some compromise with accuracy. Results from high speed model rig testing of this research turbine are presented. The turbine efficiency was measured for three different tip gaps over a range of conditions. In addition detailed measurements of the flow field were taken, principally exit area traverses and rotor surface static pressures. These experimental results are very encouraging and show a high potential for further development. Part II of this paper presents a post-test re-analysis of the rig results using the state of the art Rolls-Royce in-house CFD code HYDRA, good agreement being found between the two.