Abstract
Abstract
An experimental investigation was conducted to comparatively quantify mixing phenomena between crossflow and high-speed jets emitted from different types of fluidic actuator arrays. Three different types of actuators, namely Sweeping jet (SWJ, high-speed unsteady oscillating jet with large spanwise influence area), Rectangular jet (REJ, low-speed steady jet with large spanwise influence area), and Square jet (SQJ, high-speed steady jet with limited spanwise influence area) actuators, were implemented on a flat plate with the nozzle exit intersecting the plate surface orthogonally. During the experiments, both planar and stereoscopic Particle Image Velocimetry (PIV) were utilized with a low-speed wind tunnel at the University of Alabama in Huntsville to quantify streamwise interaction between the free stream and the emitting jet, and spanwise mixing between crossflow and adjacent actuators. The experimental results demonstrate that three actuator types produce distinct mixing mechanisms tied to their jet properties. Under quiescent air conditions, the oscillating SWJ jet is the only actuator type exhibiting noticeable actuator-actuator interaction due to the large sweeping motion of each jet. Under cross-flow conditions, the SQJ penetrates deepest into the boundary layer and forms the strongest counter-rotating vortex pairs (CVPs), with the time-averaged vorticity roughly twice that of the SWJ and REJ. The REJ, with a low exit-velocity ratio, stays coupled to the lower boundary layer and mixes primarily through weak CVPs and jet spreading. The SWJ, with the strongest spanwise mixing effect, instead develops two distinct rows of time-averaged vortex topology, caused by jet oscillation and multi-actuator interaction. This time-averaged flow structure results from the aggregation of a substantially larger population of strong instantaneous unsteady vortices over a broader spanwise region. These findings indicate that jet oscillation, rather than exit velocity or penetration depth, enhances spanwise flow mixing and momentum redistribution in fluidic actuator arrays, informing actuator and array design for flow-control and heat-transfer applications.