Detailed flow structures in turbulent flow through a rectangular channel containing built-in winglet type vortex generators have been analyzed by means of solutions of the full Navier-Stokes equations using a Large-Eddy Simulation (LES) technique. The Reynolds numbers of investigation is 6000. The geometry of interest consists of a rectangular channel with a built-in winglet pair on the bottom wall with common-flow-down arrangement. The winglet pair induces streamwise longitudinal vortices behind it. The vortices swirl the flow around the axis parallel to the mainstream direction and disrupt the growth of thermal boundary layer entailing enhancement of heat transfer. The influence of the longitudinal vortices persists far downstream of the location of the winglet-pair. Since the structure of the turbulence is strongly affected by the streamline curvature, the flow of interest, despite the simplicity of its geometry, turns out to be extremely complex. Therefore it calls for more accurate calculation of the turbulence quantities. In the present study, flow structures are studied by using time-averaged quantities, such as the iso-contours of velocity components, vortices and turbulent stresses. The simulation shows that the secondary flow is stronger in the regions where the longitudinal vortices are more active. The wake like structures of streamwise velocity occurs due to strong distortion of the boundary layer by vortices. The spanwise distributions of turbulent kinetic energy and Reynolds stresses show the evidence of strong secondary flow. The computational results compare well with the experimental data qualitatively.

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