Endwall Cavity Flow Effects on Gaspath Aerodynamics in an Axial Flow Turbine: Part II — Source Term Model Development

Abstract

Axial flow turbine designers are currently using Navier-Stokes flow solvers to reveal the details of the three dimensional flowfield inside individual bladerow passages. This new capability has allowed designers to focus on secondary flow reduction to improve turbine efficiency. These steady bladerow solvers include viscous and film cooling effects and show good agreement with test measurements in the midspan region. However, the difference between computational results and experimental data at the endwalls is significant due to the exclusion of endwall cavity effects. A clear understanding of how the cavity flow interacts with the gaspath aerodynamics, in conjunction with an accurate computational model, is needed to predict accurately the secondary flow patterns and endwall losses. In Part I, the experimental and computational results from an investigation of the endwall cavity and gaspath flow interaction in a low pressure turbine were presented. Steady and unsteady computational analyses were utilized to model different combinations of the cavity and bladerow geometries. The data and computations confirmed that endwall cavity flows have a significant influence on gaspath aerodynamics and that these flows need to be included in bladerow computations for accurate results. However, the level of effort required to construct the computational grid and obtain a flow solution renders these computational models prohibitive. In Part II, the development of a source term model for a steady bladerow solver that simulates endwall cavity flows in a low pressure turbine is reviewed. Different levels of model complexity were evaluated to determine the impact of endwall geometry and source term distributions on analysis accuracy. The source term model adequately captured endwall cavity effects and accurately predicted secondary flow in the adjacent bladerow. This source term model gives designers the capability to investigate new ideas of reducing secondary flow in a timely manner, leading to improvements in overall turbine efficiency.