Passage shaping in Axial Flow Turbines

Abstract

This thesis describes the novel combination of reverse compound lean, leading edge extension and non-axisymmetric endwall profiling in a highly loaded turbine geometry, for the reduction of secondary flow and loss. The thesis describes each geometrical modification in turn (in addition to their combination) and details their development from concept to experimentally measured performance. The designs are assessed using 3D Navier Stokes modelling. The best performing designs were manufactured and tested experimentally using pneumatic probes, flow visualisation and static pressure tappings. The key sections of the thesis include: • A review of previous non-axisymmetric profiled endwalls, with a view to understanding their performance in a full 3D passage design • The assessment of reverse compound lean in a highly loaded turbine cascade • The design development and subsequent testing of a 3D turbine passage design for minimising pressure loss associated with and kinetic energy in secondary flows. In summary, Passage Shaping works by using reverse compound lean to draw the secondary flows in to the endwall, where a combination of leading edge extension and non-axisymmetric endwall profiling work on the secondary flows to reduce their intensity. The key changes in the downstream flowfield, as a result of the passage shaping designs, are a reduction in loss (both profile and secondary) and a reduction in secondary flow, resulting in a more uniform exit yaw angle