Spatial-temporal turbulent flow-field and heat transfer behavior in end-wall junctions

The spatial-temporal velocity and surface heat transfer behavior in a rectangular end-wall junction are examined experimentally for an impinging turbulent boundary layer. The study is done in a water channel on a fast response, constant heat-flux surface using flow visualization, scanned-laser particle image velociemtry (PIV), and thermochromic liquid crystals (LC). Particle image visualizations and PIV-derived vorticity isocontours in the junction region of a rectangular block illustrate that a dominant unsteady horseshoe vortex resides in the junction region, as suggested by previous studies(2) (Devenport and Simpson 1990; Pierce and Shin 1992). The horseshoe vortex moves sporadically within a spatial envelope, due to the interaction with both (1) vortices from the impinging turbulent boundary layer; and (2) intermittent, opposite rotation vortices spawned by eruptive vortex-surface interactions (Walker 1978; Peridier et al. 1991). Companion surface heat transfer studies using thermochromic liquid crystals of both a canonical turbulent boundary layer and the rectangular block junction illustrate the presence of initially discrete spanwise variations in heat transfer on the approach surface caused by the presence of the streamwise, near-wall ''streaks'' in the impinging turbulent boundary layer; in the junction region, these streaks undergo a rapid metamorphosis into discrete, transverse regions of high heat transfer. These localized regions display significant transient, three-dimensional (3-D) behavior, appearing to be directly associated with vortex-surface interactions by the resident horseshoe vortex. This milieu of turbulent vortex development/interaction results in increases of 62% in spatially averaged Stanton number and increases of over 200% in local Stanton number compared to the canonical turbulent boundary layer. (C) 1997 by Elsevier Science Inc.