Numerical investigations of different tip designs for shroudless turbine blades

Abstract

Copyright © 2015 by Rolls-Royce plc. The over-tip leakage represents a third of the loss encountered in a typical high-pressure turbine stage. In this paper numerical investigations are carried out to study the effects of different tip designs on the aerodynamic performance and cooling requirements. A parametric design tool is used to conduct an automatic optimisation of the blade tip. The parameterisation allows overhangs to be added to the tip of the aerofoil to form a winglet and in addition a recessed cavity can be applied to produce a squealer tip. The squealer rim may also be opened near the Leading-Edge and the Trailing-Edge of the aerofoil. Flow computations are performed by an in house 3D high fidelity CFD solver for predicting the performance of the component. The solver has been validated with experimental data. Following a preliminary design of experiment, a meta-model is built and an automatic, multi-objective optimisation is carried out to reduce the loss introduced by the over-tip leakage and minimise the heat load on the blade. Three novel designs from the Pareto front have been further analysed. They show a significant improvement over a reference closed squealer in terms of the aerodynamic performance and the heat load. The flow mechanisms providing these benefits are explained in detail