Time Resolved Particle Image Velocimetry and Infrared Thermography are used to investigate the behaviour of a round jet impinging on a flat plate for a Reynolds number 28 000, for orificeto- plate distances of 3 or 5 nozzle diameters and for two different nozzles, a contraction and a long tube. The contraction nozzle reveals a different heat transfer distribution on the impinging plate compared to the long tube case, more often used in the literature. The jet is excited by a loudspeaker at Strouhal numbers 0:26, 0:51 and 0:80. This acoustic forcing changes the jet velocity structure, modifying annular vortex rings in the shear layer of the jet and increasing the turbulent values in the whole domain of the jet, including the potential core. The heat transfer is therefore modified, resulting in an increase of the Nusselt number near the jet axis and an alleviation or a shift of the secondary peak. 時間分辨粒子成像測速系統(tǒng)(TR-PIV)