Controlling the large-scale motions in a turbulent boundary layer

Abstract

In this paper we consider a strategy to manipulate the large-scale structures in wall-bounded turbulent flows, which have recently been shown to be a key mechanism for modulating levels of the skin-friction drag. For this, we use a rectangular wall-normal jet to target the large-scale structures as detected by an upstream spanwise array of skin-friction sensors. A second spanwise array of sensors, located downstream of the jet, records any modifications to the large-scale structure. In addition, a traversing hotwire probe is mounted above the second spanwise array of sensors to study the effects across the depth of boundary layer. It is found that the jet is able to create a low-speed region and when targeted on a high-speed structure changes the associated footprint at the wall.