A Numerical Study of the Influence of Grid Refinement and Turbulence Modeling on the Flow Inside a Highly Loaded Turbine Cascade

Abstract

A thorough numerical study was conducted to simulate the flow field inside a highly loaded linear turbine cascade. The numerical investigation was focused on the secondary flow field as well as on the prediction of the overall design goals within reasonable accuracy limits. The influence of grid resolution was investigated in order to obtain detailed information about the requirements of a grid-independent solution. Three different two-equation turbulence models were applied to two numerical grids of different resolution. Emphasis was laid on separating the influences of grid resolution and turbulence models. The Mach and Reynolds numbers as well as the level of free-stream turbulence were set to values typical of turbomachinery conditions. The computational study was carried out using a three-dimensional state-of-the-art block structured Navier–Stokes solver. The comparison of the numerical results with experiments clearly revealed the different degree of agreement between simulation and measurement. This paper describes the application of a modern flow solver to a test case that is relevant for practical turbomachinery design purposes. The agreement between the experiments and the results of the numerical study is good and in most cases well within the accuracy limits proposed by Strazisar and Denton (1995). It was found out that the main effect on the quality of the computations is the resolution of the numerical grid. The finest grid used reached over one million points halfspan, showing clearly superior results compared with a coarser, though still fine grid. The influence of different turbulence models on the numerically obtained flow field was relatively small in comparison with the grid influence.