Investigations of energy savings in a turbulent channel flow by combining wall transpiration and spanwise wall oscillation

There are numerous wall-based control strategies in turbulent wall-bounded flows that can lead to net energy savings. Two well-known methods are wall-normal transpiration and spanwise wall oscillation. Their individual potential for drag and power reduction has been thoroughly investigated, but their combined effect remains unexplored. This study investigates their simultaneous application to one wall of a channel flow at a nominal friction Reynolds number of 180, focusing on the resulting impact on drag and energy savings. Direct numerical simulations to solve the incompressible Navier–Stokes equations were performed using an in-house code, which employs a Fourier basis in the streamwise and spanwise directions, and 7th-order B-splines in the wall-normal direction. The results are compared against an uncontrolled reference case, as well as cases with only transpiration and only spanwise oscillation, to isolate and analyze their combined influence.