Recent Progress In A Hybrid-Grid CFD Solver For Turbomachinery Flows

Abstract

In recent years, further developments in the computer technology have led to advanced CFD codes being able to analyze complex three-dimensional flow behavior of turbo-machines. At present, most components in regular shape can be meshed with high-quality structured grids. However, the generation of structured grids is very difficult for some parts or areas, such as casing treatments or coolant channels, even if multi-block topologies are applied. In these cases, unstructured grids have to be introduced. Therefore, a hybrid structured/unstructured solver should be favored supporting both grid topologies in the same modeling. This paper presents recent progress in the development of the hybrid CFD solver with regard to the transition modeling. In low pressure turbines, laminar boundary layers are usually encountered due to the prevalent low Reynolds numbers. On the one hand, they produce fewer losses in comparison with turbulent boundary layers. On the other hand, they are more sensitive to flow separation leading to higher overall losses. Therefore, appropriate transition models have to be included in the CFD solver to be able to predict the overall losses quantitatively. The CFD code is now able to reproduce transport phenomena and the transitional effects regardless of the used grid topology. To validate and demonstrate the efficiency of the advancements, two test cases are introduced, a three-dimensional planar turbine cascade and two-dimensional turbine profile for unsteady analysis.