Heat transfer performances of an impinging synthetic jet-controlled sweeping jet

The current work deals with the experimental analysis of the heat transfer performances of a synthetic jet-controlled jet. Specifically, this study focuses on a novel device consisting of two synthetic jets, driven in opposition of phase, controlling a main steady jet issued through a square exit nozzle, which results into a sweeping jet. Infrared thermography and a heated thin foil heat flux sensor are used to experimentally investigate the cooling performances of the jet, both in the baseline (i.e. without control) and in different controlled configurations. The synthetic jets are operated at several amplitudes and actuation frequencies, for a total of nine control configurations, characterized by different values of the momentum coefficient Cμ and the Strouhal number St. All the experiments are carried out at the same jet Reynolds number, equal to 5.79×103, while six different nozzle-to-plate distances H/D are taken into account. The time- and phase-averaged results suggest that the angle swept by the main jet widens with the increase of the synthetic jet control parameters, specifically the momentum coefficient. Consequently, at low impingement distances (H/D≤2), the configurations characterized by the largest value of Cμ outperform the steady jet in terms of heat transfer rates nearby the centre of the target surface. Differently, as the impingement distance increases (H/D≥4), the baseline configuration offers the highest heat transfer rates, although the controlled configurations yield regions of maximum convective heat transfer with greater uniformity. Furthermore, the Strouhal number affects the curvature of the jet, and consequently the shape of the region of high convective heat transfer.