Visualization of Rotor Endwall, Tip Gap, and Outer Casing Surface Flows in a Rotating Axial Turbine Rig

Abstract

Visualization of surface flows in a large-scale, low speed, axial turbine rig was conducted using a visualization mixture of oil and pigment. Rotor endwall flows were visualized by applying a film of visualization material on the endwall. Tip surface flows were visualized by applying paint dots and oil film to the blade pressure surface. The visualization material is carried up on the blade surface due to rotation and some of the material seeps into the tip gap. The paint dot technique was used on blades with gap heights of 1.40% blade height and 0.72% blade height. Oil film visualization was used on blades with gap heights, as percent blade height, of 0.72%, 0.81%, 1.2%, and 1.40%. Outer casing boundary layer characteristics were also visualized by the oil film technique. Surface streamlines on the rotor endwall identify features such as saddle point, horseshoe vortex system, and skewed passage boundary layer. Tip surface streamlines indicate the presence of chord-wise flow on the tip surface, along with a distinct reattachment region. Variation of surface streamlines characteristics is correlated to the gap height. Outer casing surface streamlines show the variation in wall shear stress vector orientation through the rotor.