Improving 3D Flow Characteristics in a Multistage LP Turbine by Means of Endwall Contouring and Airfoil Design Modification: Part 2 — Numerical Simulation and Analysis

Abstract

Endwall losses contribute significantly to the overall losses in modern turbomachinery, especially when aerodynamic airfoil load and pressure ratios are increased. Hence, reducing the extend and intensity of the secondary flow structures helps to enhance overall efficiency. This work will focus on secondary flow reduction in typical aero engine low pressure turbines. From the large range of viable approaches, a promising combination of axis symmetric endwall contouring and 3D airfoil thickening was chosen. Aerodynamic design, experimental verification and further analysis based on numerical simulation are described in a two part paper. In the second part the implications of the 3D modifications on the flow structure are analyzed by employing a 3D Navier-Stokes simulation based on the experimental data reported in part one. For obtaining reliable flow simulations at typical LP turbine conditions, it is important to apply a 3D Navier-Stokes solver with proven turbulence and transition modeling to the three-stage LP turbine of the Institute of Aeronautical Propulsion at Stuttgart University. Numerical and experimental results exhibit regions, where the modified design leads to a change in flow pattern in accordance with the design intent, as well as regions with an actual increase in loss production. The flow changes in both regions are evaluated and discussed. It is found that a certain local loss increase phenomenon can also be found in other LP turbine rigs. The reasons for this behavior are analyzed by a comparison with data from other turbine rigs and by an additional variation of the 3D design of the first stage of the investigated turbine.