Effects of Blade Boundary Layer Fences on Secondary Flow and Losses in a Turbine Cascade

Abstract

An investigation was performed to reduce secondary flow and losses in a linear turbine rotor cascade by attaching boundary layer fences to the blade suction surfaces. Kiel and X-wire hot-wire probes, used to measure total pressure and flow velocity, were traversed downstream of the cascade with varying endwall distance of fences. Surface oil flow visualization were carried out. Losses, thickness of secondary flow region, secondary vorticities, outlet flow angle changes, and secondary kinetic energy were obtained with two distinct optimum endwall distances. Losses were minimized at the distance equal to the inlet boundary layer thickness, other secondary flow properties showing minima at a shorter distance. Limits of endwall distance within which fences trap passage and trailing vortices were shown. Fences were found to reduce pitch-averaged underturning between the position of maximum underturning and midspan, but hardly to change the maximum underturning itself.