Three-Dimensional Blade Boundary Layer and Endwall Flow Development in the Nozzle Passage of a Single Stage Turbine

Abstract

The three-dimensional viscous flow field development in the nozzle passage of an axial flow turbine stage was measured using a “x” hot-wire probe. The measurements were carried out at one axial station on the endwall and blade surfaces and at several spanwise and pitchwise locations. Static pressure measurements and flow visualization, using a fluorescent oil technique, were also performed to obtain the location of transition and the endwall limiting streamlines. The boundary layers on the blade surface were found to be very thin and laminar, except on the suction surface downstream of 70% axial chord. Strong radial pressure gradient, especially close to the suction surface, induces strong radial flow velocities in the trailing edge regions of the blade. On the endwalls, the boundary layers were turbulent and much thicker, especially near the suction corner of the casing surface, caused by the secondary flow. The secondary flow region near the suction casing surface corner indicated the presence of the passage vortex detached from the blade surface. The boundary layer code accurately predicts the three-dimensional boundary layers on both vane surfaces in regions where the influence of secondary flow is small.