Wall Shear Stress Measurement in Blade End-Wall Corner Region

Abstract

Experimental results on the local wall shear stress vector and surface pressure measurements upstream and in the blade end-wall corner region are presented in this paper. The measurements were obtained at a free stream velocity of 27.3 m/s with the Reynolds number based on Preston tube outer diameter and friction velocity varying from 30 to 100. A specially constructed Preston tube, the tip of which can be concentrically rotated about its axis of rotation at the measurement location, was employed for the measurement of wall shear stress vector. The magnitude of the wall shear stress in the vicinity of the corner was observed to increase significantly (≈170 % max.) compared to its far upstream value. This increase was consistently found to be higher on the blade surface compared to its value on the plate surface of the blade end-wall corner. On both the surfaces in the blade end-wall corner, the variation of the wall shear stress direction was found to be more predominant in the vicinity of the blade leading edge location. The trend of the measured wall shear stress direction showed good agreement with the limiting streamline directions obtained from the flow visualization studies. The surface pressure variation, at any axial station in the corner region, on the flat plate part of the blade end-wall corner was found to be relatively larger than on the blade surface. Some plausible explanation for the observed variation in the local wall shear stress and surface pressure in the blade end-wall corner are described here.