Development of CFD-Based Tip Clearance Loss and Deviation Models for Axial-Flow Turbines

Abstract

Accurate Loss correlations are crucial for reliable low-fidelity turbine performance predictions, but conventional tip clearance models disregard important 3D loss effects. The objective of this thesis is the development of more realistic tip clearance models by means of high-fidelity CFD simulations. Therefore, a numerical model of a single-stage, high-pressure turbine was used in a numerical parameter study, in which all significant tip clearance parameters were varied individually. The mixed-out tip clearance losses and outflow angle deviations were evaluated to formulate a set of CFD-based tip clearance correlations. Furthermore, Kriging surrogate models were developed to account for interrelations between the effects. Both tip clearance models were implemented into a 2D through-flow program and validated by performance calculations of a four-stage air turbine. In comparison to conventional correlations, the new models yield more accurate tip clearance losses and deviations and increase the agreement with the efficiency and pressure ratio data of the turbine experiments. In particular the performance results obtained with the Kriging surrogate model at part load operation improved.