Numerical Analysis of Turbulent Flow and Heat Transfer in a Channel With Longitudinal Vortex Generators Using LES
P. Sahaa and G. Biswasb
Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208 016, India.
arpankaj@iitk.ac.in
bgtm@iitk.ac.in
ABSTRACT
A method of enhancing heat transfer in industrial heat exchangers is the generation of longitudinal vortices embedded in the flow close to the wall. One of the means of generating such vortices is an array of winglets on the heat exchanger walls. In the present investigation, the flow structure in turbulent flows 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, at Reynolds number 6000. 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 boundary layer entailing enhancement of mixing. In the present computation, an incompressible finite difference code, based on MAC method with a staggered grid arrangement is adopted and a locally dynamic-subgrid-stress model has been used as closure. The flow structure is studied by using instantaneous and time-averaged quantities, such as the iso-contours of velocity components, vortical structures and the skin friction. Large spanwise variations of the skin friction result due to strong distortion of the boundary layer by vortices.
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