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Nozzle configuration may offer the possibility of a passive control technique to provide high mixing and heat transfer rates. Thus, numbers of investigations have been carried out to reveal the influence of nozzle configuration on the flow characteristics. However, very few papers in the scientific literature have focused on orifice jets. Despite the evidence indicating that orifice jets improve the mixing and heat transfer characteristics, we were unable to find a systematic study of them that focused on the contraction area ratio. The effects of varying the contraction area ratio CR from 1.00 to 0.11 on the flow characteristics of a free jet issuing from an orifice nozzle were examined. The large vortex structure of a submerged orifice water jet was visualized by the tracer method, which indicated the coherent vortex structure was highly affected by the CR value. The mean and fluctuating velocities of the orifice air jet were also measured using a single hot-wire and the effects of CR on them were demonstrated. It is found that the normalized centerline maximum velocity could be expressed by uc/um= 1.9CR3 - 3.55CR2 + 1.38CR + 1.53, showing a maximum value of 1.7 at CR = 0.27. In addition, the high spreading and entrainment rates were obtained for smaller value of CR indicating that the potential of an effective passive control technique.

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International Journal of Flow Control

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