Three-dimensional flow characteristics downstream of a blade endwall corner.

摘要

The flow downstream of the corner formed by an airfoil and a flat plate was investigated experimentally. The region for this study was simulated by attaching two uncambered, unswept NACA 65-015 airfoils on either side of a flat plate. The airfoils had a semicircular leading edge. The initial 7 cm of the leading edge of flat plate was artificially roughened by gluing a strip of sand paper to promote a thicker turbulent boundary layer. Free stream turbulence of the order of 1.5% was introduced, by inserting a combination of two grids, to avoid a separation bubble on the airfoil.;Measurement techniques employed in this investigation were; surface flow visualization, conventional pitot-static probe, the Preston tube, and the five hole probe. Surface flow visualization defined the boundaries of the vortex system and provided information on the direction and the magnitude of the wall shear stress. Local wall shear stress was measured using specially constructed Preston tubes. The characteristics of the Preston tube were also investigated. Total and static pressure distribution, including the flat plate surface, were made using a pitot-static probe. The five hole probe was used, in the semi-nulling mode, to collect data on the three components of mean velocity. The measurements were carried out at eight axial stations downstream the trailing edge of the airfoil.;At every axial location downstream the trailing edge of the airfoil forming the corner with a flat plate, a single dominant horseshoe vortex was identified which persisted more than one chord length downstream. A smaller and weaker corner vortex was also identified. It dissipated and ceased to exist by a downstream axial location of approximately 0.2C. There was no evidence of stress induced vortices in the region of this investigation. The secondary flow system redistributes the mean flow momentum and distorts total pressure profiles and contours. In planes parallel to the flat plate, total pressure profiles were found to be higher than the undisturbed two-dimensional boundary layer at that height. Surface static pressure was found to be at its maximum at the airfoil trailing edge location and it decreased in both the downstream and transverse directions. There was no significant static pressure variation in the spanwise direction.