Active Flow Control of Turbulent Refractive Interfaces in Separated Shear Layers for Laser Beam Propagation

The behavior of turbulent refractive interfaces, and means for the optimization of these interfaces, is essential in various basic and applied studies concerning the propagation of optical wavefronts such as laser beam wavefronts through turbulence or optical imaging through turbulence. In this study, the structure of turbulent refractive interfaces and aero-optical interactions along laser beam propagation paths, in unforced and forced separated compressible shear layers, are examined through use of direct imaging and pulsed plasma actuators. Dielectric-barrier discharge (DBD) pulsed plasma actuators are used to excite the flow prior to separation. Our interest is in searching for the frequencies and amplitudes of the forcing that produce direct suppression of the large scale turbulent interfaces and, thereby, direct reduction of the laser wavefront aberrations. Whole-field shadowgraph imaging of pure-air separated shear layers is conducted for control off vs. control on cases at various forcing frequencies, in order to explore the effects of plasma forcing on the large-scale flow behavior. Direct profiling of forced vs. unforced turbulence-aberrated laser wavefronts propagated transversely through shear layers is conducted using high-resolution Shack-Hartmann microlens arrays. Evidence is presented showing significant reduction of the turbulence-induced laser aberrations, for forced vs. unforced shear layers, indicating the presence of a mechanism of suppression, i.e. disorganization, of large-scale organized structures by high-frequency pulsed plasma forcing.