Visualization of a Sweeping Jet by Laser Speckle Retro-reflective Background Oriented Schlieren

The National Aeronautics and Space Administrations Environmentally Responsible Aviation (ERA) Program is currently investigating the use of sweeping jet actuators as active flow control devices to improve the aerodynamic performances of vertical tails on commercial transporters. Computational Fluid Dynamics (CFD) simulations have shown that the motion of the jet is not a simple sinusoid, but lingers at the extremes of jet deflection. As part of an effort to better understand this non-sinusoidal behavior and validate the CFD, a sweeping jet actuator was tested in the 48-by-32-inch wind tunnel in the Fluid Mechanics Laboratory (FML) at NASA Ames Research Center. The jet was visualized at very high frequencies using a new technique: laser speckle retroreflective background oriented schlieren (RBOS). These measurements confirmed the non-sinusoidal nature of the jet motion. Although measurements were also made by Particle Image Velocimetry (PIV) that resolved the flow velocities in the jet, only the new RBOS technique could provide high enough frequencies to both spatially and temporally resolve the non-sinusoidal motion. This paper presents the laser speckle RBOS method and visualization, as well as a brief comparison to CFD simulations.