Spatiotemporal Perturbations of a Turbulent Boundary Layer Using Discrete Surface Actuation

An actuator mechanism was developed to generate large-scale, space-time perturbations in the form of traveling waves. These perturbations were introduced using a two-dimensional array of actuators that produced discrete surface deformations, each creating a localized, Gaussian-like bump at the wall. Both one-dimensional and two-dimensional actuator configurations were designed to generate traveling waves in the streamwise (upstream and downstream) and spanwise directions. The flow had a smooth-wall friction Reynolds number of approximately 2400. In the case of the one-dimensional array, the actuator forcing produced a periodic low-speed region at the wall that propagated downstream. As this region moved downstream, an initial increase in near-wall turbulence intensity was observed, followed by a decrease as the low-speed region moved away from the wall. The magnitude and extent of these changes depended on the type of imposed forcing. Ongoing work to implement fully two-dimensional traveling waves at the wall will also be presented.