Heat transfer and flow structure in end-wall boundary layers

Research progress is described for a combined analytical/experimental program examining the flow structure and resultant surface heat transfer in end-wall boundary layers (e.g. wing-body. type junctures). Emphasis is placed on flow structure development and correlation of vortex-induced surface interactions with transient, local surface heat transfer. Analytically, numerical studies using an impulsively-started approach flow have documented the flow development and surface heat transfer on the symmetry plane for several end-wall flows; highly unsteady vortex formation and ejection are observed, with concomitant sharp, transient variations in surface heat transfer. Analysis of the complete three-dimensional behavior indicates the presence of strong interactions between the end-wall (surface) and the side-wall (bluff-body) boundary layers. Experimentally, a constant heat flux test system has been developed and instrumented for surface temperature detection using temperature-sensitive liquid crystals and color computer-image analysis; tests indicate dramatic effects of transient end-wall vortices on surface heat transfer, confirming the analytical results. A systematic visualization study indicates a very strong influence of the junction-induced pressure gradient on the approach boundary layer in promoting the unsteady vortex formation processes in the end-wall region.