Investigation of impinging sweeping jets through Particle Image Velocimetry

Sweeping jets are particular jets characterized by an oscillating motion. Such an oscillation is caused by the fluidic oscillator device, whose geometrical internal characteristics influence and govern this sweeping phenomenon. The most interesting characteristic of these devices is the absence of moving parts and piezo-electrical elements, making them a candidate for application in flow control and heat transfer fields. Many experimental studies and numerical simulations have focused on the application of sweeping jets for the control of air flow along aerodynamic surfaces while lower attention has been paid to their impinging flow field, fundamental to have a deep physical understanding of their heat transfer performances.

In order to characterize the mean flow field, the oscillating coherent flow field and the turbulent statistics of impinging sweeping jets phase-locked particle image velocimetry (PIV) measurements are carried out. Three fluidic oscillators devices have been studied. These devices are characterized by different mixing chamber lengths (2.5w, 3.5w and 4.5w). The issued sweeping jets have been investigated at a Reynolds number equal to 17,000 and for a nozzle-to-plate distance (H) ranging between 2 and 10 nozzle width (w).

The main results highlight that the fluidic oscillator mixing chamber length has a strong influence on the sweeping jet flow field in terms of time-averaged velocity components, coherent and uncoherent fluctuations distribution. In particular, this geometrical parameter also governs the presence or absence of the jet oscillating motion. In addition to that, the phase-locked measurements allow to reconstruct the oscillating motion of the jet flow field and the related turbulent fluctuations and to observe the presence of a vortex structure near the impingement plate moving coherently with the sweeping motion of the jet itself.