Influence of a Non-Axisymmetric Endwall on the Flow Field in a Turbine Passage: High-Resolution LDV

Abstract

The present paper focuses on the influence of a non-axisymmetric endwall on the flow field in a turbine passage. Therefore, laser Doppler velocimetry (LDV) is applied to both a non-axisymmetric endwall and a flat endwall as reference. Time mean values and fluctuating components of the velocity field are evaluated. Three-component LDV with up to 38000 valid coincident events per second is carried out up- and downstream of a linear cascade with high resolution, especially in the near-wall region of the suction surface, where secondary vortices are expected. The three velocity components recorded by the LDV are transformed into the orthogonal coordinate system of the turbine cascade, and several flow quantities, like turbulence parameters and parameters describing the secondary regime, are assessed. By comparing the data for the non-axisymmetric endwall and the flat endwall, the influence of the contouring on the secondary flow field is shown. To substantiate the measurements and gain a deeper insight, the data are compared to previous surface oil flow visualizations and specific results of former thermal studies.