Turbulence control with wall-adjacent thin layer damping spanwise velocity fluctuations

Direct numerical simulations (DNSs) have been carried out for fully developed turbulent channel flow and heat transfer with an assumption of a thin layer adjacent to the wall, in which a virtual body force acts to damp the spanwise velocity fluctuations. Fourth-order finite difference computations were made over a relatively small computational volume to repeat simulations under various damping force conditions. It is found that both turbulent friction and heat transfer coefficients are substantially reduced in such manipulated flows. Compared with the pumping power saved, the extra dissipation due to the damping is sufficiently small as long as the damping layer exists close to the wall. In addition, the present control method is most efficient if the damping is imposed on the layer in contact with the wall rather than away from the wall. It is observed that the streamwise elongated streaky structures meander less in the spanwise direction and the coherent vortical structures are attenuated in scale and intensity. Thus, the vortex regeneration as well as the primary turbulence mechanisms, such as the production redistribution of Reynolds stresses played by the vortical structures, should be considerably suppressed by the selective damping of the near-wall spanwise velocity fluctuations.