Flow Physics and Vortex Evolution in Annular Turbine Cascades
The evolution of flow vortices downstream of annular cascades with a specific focus upon the association between vorticity and the mechanisms of aerodynamic loss generation has been experimentally investigated. Spatially-resolved experimental results on an unstructured measurement pattern is used to identify small scale flow structures on the surface of the investigated blades and downstream of two different cascades. The test case comparison is based upon two moderately loaded turbine blade profiles, one stacked prismatically and the other on a bowed stacking line. The design operating conditions for both cascade is at a nominal exit Mach number of 0.5. The measurements were made using an ultra miniature (0.9 mm Dia) 5-hole probe. The measurement were made on 4 planes behind and one plane in front of the trailing and leading edge of the cascade respectively. The experimental results clearly show the influence of the flow structure on the evolution of the stream wise vorticities behind the blading. Detailed measurements are used to compare and evaluate the mixing processes downstream of these two cascades. It is shown that the interaction of the different vortices with the endwall boundary layer has a substantial impact on the overall total pressure loss generation.