Demonstration of an Actuator Array to Generate Wave-Like Perturbations through Surface Deformations*

An actuator mechanism was demonstrated to generate traveling wave-like perturbations at the wall using surface deformations. The mechanism consisted of individually controllable solenoid actuators that introduced active surface deformations. Each solenoid actuator was designed to generate a positive (into the flow), controllable surface deformation that resembled a "Gaussian-bump" on a smooth, flexible surface. These surface deformations were designed with a maximum amplitude of less than or about 30 wall units. The actuators were arranged in a two-dimensional array to actuate in the streamwise and spanwise directions. As the actuators were individually controllable, various formations of surface perturbations could be introduced. These include traveling streamwise (with and against the flow), spanwise, and combined streamwise-spanwise surface perturbations. Further, these surface deformations can be produced in continuous or burst (or impulsive) mode. Preliminary, demonstrative measurements in a zero-pressure gradient turbulent boundary layer with a nominal friction Reynolds number of 2400 were presented.