%A Mi Jian-Chun(米建春) and Du Cheng(杜诚) %T Influences of initial velocity, diameter and Reynolds number on a circular turbulent air/air jet %0 Journal Article %D 2011 %J Chin. Phys. B %R 10.1088/1674-1056/20/12/124701 %P 124701-124701 %V 20 %N 12 %U {https://cpb.iphy.ac.cn/CN/abstract/article_112510.shtml} %8 2011-12-15 %X This paper assesses the suitability of the inflow Reynolds number defined by ReoUoD/$\nu$ (here Uo and D are respectively the initial jet velocity and diameter while $\nu$ is kinematic viscosity) for a round air/air jet. Specifically an experimental investigation is performed for the influences of Uo, D and Reo on the mean-velocity decay and spread coefficients (Ku, Kr) in the far field of a circular air jet into air from a smoothly contracting nozzle. Present measurements agree well with those previously obtained under similar inflow conditions. The relations KuUo and Kr ∝ 1/Uo for Uo < 5 m/s appear to work, while each coefficient approaches asymptotically to a constant for Uo > 6 m/s, regardless of the magnitudes of Reo and D. It is revealed that Reo may not be an appropriate dimensionless parameter to characterize the entire flow of a free air/air jet. This paper is the first paper that has challenged the suitability of Reo for turbulent free jets.