An Euler-Based Throughflow Approach for an Axial Turbine at Supersonic Flow Regimes

Flexible, fast and reliable design tools are essential in turbomachinery design process. Especially off-design performance characteristics of stationary gas turbines have become more important due to the increase of renewable powers in the last two decades. Additionally, the design process of fully new turbine designs without the existence of complete airfoil geometries is being pushed to its limits to have the potential for optimization of off-design performance for the final versions.Within preliminary design phase throughflow methods are still a core component of turbine design process. These methods deliver span-wise distributions of flow quantities and enable turbine performance prediction. Besides being fast, these methods have the advantage that solutions can be calibrated to match fleet measurements. In this paper the results of a throughflow method using a finite-volume solver based on the Euler-equations are presented. The method incorporates a deviation model as well as a blockage model. A distributed-loss model is implemented to account for losses at design and off-design conditions. Applying a time-marching Euler approach allows considering shock patterns and improves the numerical stability compared to traditional 2D-throughflow approaches.The high power output per stage of modern gas turbine designs may lead to supersonic flow conditions at full-load operating points. In order to understand the axisymmetric effects of three-dimensional shock patterns a comparative study between the circumferentially averaged Navier-Stokes solutions of a 1.5 stage axial turbine and the results of the throughflow approach is carried out. The influence of deviation angle prediction and loss prediction for transonic flow regimes are investigated qualitatively. Suggestions are made to improve the quality of preliminary design calculations for high Mach-number flow regimes.Keywords: Meridional, Throughflow, Distributed Loss Model