Analytical Investigation of a Low Pressure Turbine With and Without Flowpath Endwall Gaps, Seals and Clearance Features

Abstract

Numerical simulations for low pressure turbine (LPT) stages of a high bypass turbofan engine are presented and discussed in this study. A smooth flowpath configuration and a flowpath configuration with endwall features consistent with the actual engine geometry were considered for the numerical analysis to demonstrate the significance of including hub and tip flowpath details for proper performance prediction and design improvement studies. Fully three-dimensional, multistage, mutiblock, viscous flow analysis methodology was applied for first three stages of a moderately loaded LPT to predict aerodynamic performance of individual components, stage and for the overall turbine. Numerical results were obtained first for the smooth endwall configuration that ignores flowpath cavities, gaps and leaks in the numerical model. Following the smooth endwall calculations, a second set of calculations was performed with hub and tip flowpath details to closely represent actual engine geometry and experimental rig hardware. The approach of using smooth endwall contours for multi stage, multi blade row computational analysis is quite common for modeling simplicity. However, as the flow features are expected to be more complex in high pressure ratio, highly loaded turbine stages of next generation aircraft engines, it is imperative that flowpath and endwall geometry details such as gaps, seals, leakage and clearance effects are included in the numerical simulation for improved component design and stage performance prediction. This study addresses this particular issue by including endwall details and quantifies performance differences between the two modeling approaches. An O-H mesh topology was utilized for the blades, wheel space cavities, labyrinth seals and clearances for better flowfield resolution and numerical accuracy. Component performance, secondary flow details of endwall cavities, seal leakage and loss features of each blade row, for individual stage and for the overall turbine stage is presented and discussed for the two sets of calculations. Computed results are compared with experimental data obtained with high speed rig testing for verification and for understanding of the flow physics.