Aerodynamic and Heat Transfer Effects of an Endwall Boundary Layer Fence in a 90 Degree Turning Square Duct.

摘要

This experimental study investigates the utility of boundary layer fences in turbine passage flow. Boundary layer fences have recently been reintroduced as a possible method to achieve favorable effects in turbines. Previous studies have used linear cascades which necessarily introduce a horseshoe vortex resulting from the endwall boundary layer impinging on the blade leading edge. The present study uses a curved square duct that exhibits no horseshoe vortex, but does have the characteristic passage vortices of a turning flow. The turbine passage is simulated to study the interaction effects of the boundary layer fence and the passage flow dominated by the passage vortices. Specifically, a single boundary layer fence of varying dimensions is attached to a heated endwall of the duct. The flow is fully turbulent at the inlet of the duct. Five-hole probe and liquid crystal thermography experimental techniques are used to determine the changes in the aerodynamic flowfield and the heat transfer coefficient of the heated endwall as compared to the same duct with no fence. Hotwire measurements are also presented for the description of the inlet flow field turbulence. This study adds to the currently small volume of information on fences in passage flow in several important aspects. The effect of the fence on the passage vortex is studied in a known flow configuration. Extensive flowfield mapping was completed in the same duct and presented in Wiedner and Camci (1993b). The increased pressure losses of thicker (wider) fences are investigated and results show a significant dependence on fence dimensions. Liquid crystal thermography is used to obtain a high-resolution map of the endwall heat transfer coefficient for two fence configurations.