The Effect of an Active Travelling Wave Wall Motion on the Structure of a Turbulent Boundary Layer

The topic of drag reduction (DR) in wall-bounded turbulent flows has received great attention over the past thirty years. This effort is motivated by the notion that the internal near wall structure of a turbulent flow can be substantially affected if a force is exerted on the fluid by a traveling wave propagating transversely on an active compliant surface. The work presented here supports this notion by demonstrating that the active skin results in organizing the structures that populate the near wall flow. For the first time, this mechanism is shown to significantly reduce the contribution of the Reynolds stresses to the viscous drag. The modification of the turbulent near wall flow as a function of actuation frequency is investigated and the persistence of the flow control is explored. In addition, the performance of the mechanical active skin actuator is characterized and a first order estimate of its energetics is achieved.