Flow characterization of an array of finite-span synthetic jets in quiescent ambient

An experimental study on the flow characteristics of an array of finite-span Synthetic Jets (SJs) issuing at different conditions in a quiescent ambient was carried out by means of hot-wire and phase-locked planar Particle Image Velocimetry measurements. The actuator comprises twelve slots with aspect ratio 15 fed by a common resonant cavity and off-centered from the axis of the cavity. The frequency response indicates that the SJs are formed in the range of Stokes numbers between 4 and 12.5, in which two operating conditions were inspected yielding the SJs issuing either at Reynolds (Re) and Strouhal (St) numbers of Re = 40 and St = 0.84 or Re = 213 and St = 0.50. It is found that, for the case at Re = 40 and St = 0.84, the flow field undergoes the asymmetries of the actuator. The axis switching persists in the very-near field of the SJ array, while further downstream the spreading of each SJ becomes more pronounced promoting the jet interaction. For the case at Re = 213 and St = 0.50, the main flow direction along the cross-sectional plane tilts of 14.8° towards the side where the cavity extends. The formation of a recirculation region promotes the enhancement of turbulent dissipation mechanisms. The phase-average flow fields reveal that, similarly for both cases, the imprint of the vortical structures exhibits symmetric organization during the ejection phase.