The effect of nozzle geometry on the flow and heat transfer of pulsed impinging jet on the concave surface

The main aim of this paper is to investigate the effect of nozzle geometry on the flow and heat transfer from a pulsed jet into a concave surface. Experiments have been carried out for pulsed circular jet and numerical simulations were done for circular, elliptical, rectangular and square geometries. Numerical solution was performed for the frequency ranges of 25 Hz to 100 Hz, the jet Reynolds number of 7000, the dimensionless nozzle distance to concave surfaces of 2 and 5. Numerical results show a consistent agreement with experimental results and previous works. Accordingly, the geometry of nozzle directly affects the air entrainment ratio. In addition, with the increase of aspect ratio of the nozzle, average Nusselt number (Nuave) decreases. By pulsating the inlet jet with pulse frequency of 100Hz, the average Nu number for circular/square and elliptical/rectangular jets increases 22% and 15%, respectively. Generally, the pulsation causes a reduction and an increase of the Nuave at low and high frequencies, respectively, compared to that of the steady jet. At low frequencies, the Nuave of circular jet decreases significantly in comparison to that of the square and elliptical jets. However, at high frequencies, circular jet shows higher Nuave compared to other ones. As the distance between the jet and the concave surface increases, the effect of the nozzle shape on Nuave decreases.