Secondary flow effects and mixing of the wake behind a turbine stator

Abstract

In highly loaded turbines with large hub/tip ratios there is a marked increase in secondary flow effects. The optimization of the turbine flow requires detailed knowledge both of three-dimensional cascade flow and of the wake impinging on the downstream rows of airfoils. Therefore, in the DFVLR, thorough investigations of a single-stage turbine with cold air flow were performed. The stator of this turbine was designed for transonic flow and has a hub/tip ratio of 0.756 and an aspect ratio of 0.56. First, measurements were taken without the rotor in several sections behind the turbine stator with special regard to the mixing of the wakes and secondary vortices. Distributions of total pressure loss coefficient and flow direction give the order of magnitude of the mixing losses. Also, position, intensity, structure, and development of secondary vortices are shown. Some complementary measurements were carried out using five-hole probes. They confirm the above described results from two-dimensional measurements.