Secondary Flow Control and Loss Reduction in a Turbine Cascade Using Endwall Fences

Abstract

An attempt to control secondary flow was made in order to improve turbine aerodynamic performance. Boundary layer fences were attached to endwalls of a linear turbine rotor cascade. Measurements of total pressure losses and three-dimensional flow velocities were taken for 5 different heights and 7 different pitchwise locations of the fences. It was found that the fences were most effective when they were 1/3 of the inlet boundary layer thickness high and located half a pitch away from the blades. These optimum fences reduced streamwise vorticities, the thickness of the endwall loss region, secondary kinetic energy, and the maximum underturning by half. Moreover they diminished the secondary loss by 22 percent, and the gross loss, including kinetic energy dissipation, by 25 percent. A critical fence height above which the fences trap the pressure side legs of horseshoe vortices was found, and the optimum fences proved to be fences of the minimum critical height.