Dynamic Roughness for Manipulation and Control of Turbulent Boundary Layers: An Overview

The use of dynamic roughness or small, oscillating, wall roughness elements to manipulate the structure of turbulent boundary layers is reviewed with a view to imposing true active control techniques. Linear and nonlinear responses to simple oscillations are detailed, such that the modifications of the overall structure of the turbulence and interactions between scales can be inferred. Although the work considered here uses mechanical actuation, the approach is considered sufficiently general to be implemented by a range of techniques, including engineered microelectromechanical system devices and metamaterial actuators.