This paper presents a computational study, with some experimental validation, of a low-turning transonic turbine cascade. A comparison is presented between the time-consuming and difficult to generate hexa-structured meshing approach, and the mostly automated tetra-unstructured meshing approach. The paper compares the predicted flow physics and losses, with discussion of the challenges in griding and convergence between both approaches.
Computations were carried out using a commercial RANS solver (ANSYS CFX 12) using the Shear Stress Transport turbulence model, and the Gamma-Theta transition model. The computational domain encompassed a half blade span, and one blade pitch with periodic boundary conditions; griding for both approaches was done using ANSYS ICEM CFD. Computational results from both griding approaches were compared to corresponding experimental data. The outlet Mach number was 0.90. The experiment was carried out using a linear cascade in a blow-down type wind tunnel. Downstream seven-hole pressure probe measurements at 1.8 axial chord lengths from the leading edge provided loss, streamwise vorticity, and secondary kinetic energy distributions and integrated coefficient values.
It was found that both griding approaches predicted similar downstream endwall flow structures to those observed in the experiment. The tetra-unstructured mesh solution predicted higher losses, but both predicted lower losses than the experiment. Overall results suggest that for capturing of the basic flow physics, both approaches suffice, with the tetra-unstructured being the much easier approach, but with limitations on the level of grid refinement. For more accurate capturing of the flow physics, the time-consuming and difficult to generate hexa-structured meshing approach can be justified.