Measurement and Visualization of Three-Dimensional Flows in a Linear Turbine Cascade

To know the internal flows and the loss generation mechanisms in turbine blade passages, three–dimensional flows in a linear turbine cascade were measured in detail using a five–hole Pitot tube. Flow visualization tests were also carried out with oil smoke to see the unsteady behavior of the internal flows. The flow visualization tests show generation of various vortices occurring inside the cascade passage, which were hardly detectable with steady flow measurement. Many of the vortices behave unsteadily. The evolution of two legs of the leading edge horseshoe vortex was clearly visualized as a combined vortex system. Low energy fluids inside the boundary layer on the blade suction surface were seen to circulate very slowly and were fairly unstable. Rotational directions of the low energy fluids depend on the interaction with the surrounding vortex system. Many separated and strong reverse flows were also seen near the blade trailing edge.