Effects of Fluidic Oscillator Nozzle Angle on the Flowfield and Impingement Heat Transfer

Experimental and numerical investigations were performed to evaluate the effects of the exit nozzle configuration of a fluidic oscillator on the flowfield and impingement heat transfer performance downstream on a flat plate. A conventional wall-attachment-type fluidic oscillator with a fan-shaped exit configuration was studied. Eight different exit fan angles (0 deg <= theta <= 130 deg) were considered, and the effects of each nozzle configuration on the theta(jet) oscillation frequency, average fluid fan angle theta(jet), and discharge coefficient C-d were studied. Results show that the exit fan angle has a significant effect on the average fluid fan angle. Initially, theta(jet) increases along with the fan angle up to (theta <= 70 deg); beyond which, theta(jet )eventually plateaus with further increase in theta. The jet oscillation frequency appears to be independent of nozzle configurations. A case study was performed that includes sweeping jet impingement heat transfer in order to assess the practical implication of the exit geometry. Heat transfer experiments were performed for each nozzle configuration at a jet-to-wall spacing of HID = 5 and three coolant mass flow rates (<(m)over dot> = 0.97, 1.48, and 1.97 g/s). The average heat transfer tends to deteriorate with increasing fan angle. However, a pronounced improvement in cooling uniformity zeta was observed at large-fan-angle configurations (theta >= 70 deg). The time-resolved velocity field obtained from an unsteady Reynolds-averaged Navier-Stokes simulation revealed that separation bubble starts to appear at the diverging wall of the nozzle exit when theta > 70 deg that prevents the lateral motion of the jet, thus reduces the average fluid fan angle.