DRAG REDUCTION BY INTRODUCTION OF SHEAR-FREE SURFACES IN A TURBULENT CHANNEL FLOW
Drag reduction in internal turbulent flows is feasible by altering the large-scale flow structures by making use of shear-free surfaces (SFSes) (Sood, Cholemari and Srinivasan ). Kinematic wall blocking by these surfaces attenuates the wall normal transport of momentum and hence reduces the drag. In this paper the optimization of the process is done with the size, placement and number of the shear-free surfaces as parameters. 3-D RANS simulations using ANSYS CFX 15.0 have been done with Stress Transport (SST) RANS model. It is seen that the location of SFSes in the cross-section is critical; placement in regions where turbulent shear-production is large, greatly reduces the transport. The shear-free surfaces need not be solid; even for a solidity ratio of 0.2 significant drag reduction occurs. The effect of the Reynolds number is also investigated.