Drag reduction and transient growth of a streak in a spanwise wall-oscillatory turbulent channel flow

The drag-reduction mechanism of spanwise wall oscillation in a turbulent channel was investigated as an extension the work Yakeno et al. [“Modification quasi-streamwise vortical structure drag-reduced flow with oscillation,” Phys. Fluids 26, 085109 (2014)] at low Reynolds number. Flow instability evaluated by computing transient energy growth under oscillating base which governed generation near-wall streak structure. Oscillation affected optimal mode, whose characteristics were reasonably consistent those direct numerical simulation. tilted-streak mode enhanced thicker Stokes layer longer periods, while that original weakened. transition perturbation showed shear contributed considerably more to modification than velocity did. A new performance estimation model suggested using acceleration based on formation oscillation, restrains transfer streamwise vortices via tilting delay due oscillation. This simple worked well even long periods and theoretically change stress vortex