出口条件对圆形湍流射流远场区自保持性的影响

EFFECT OF EXIT CONDITIONS ON THE SELF-PRESERVATION STATES OF ROUND JETS

报道出口条件对圆形湍流射流自保持性影响的实验研究结果.对来自渐缩和长管两种不同结构喷嘴的射流,在相同雷诺数条件下,沿轴线进行了速度测量;研究的统计量包括平均速度、湍流强度、高阶矩、能谱和积分尺度.实验结果表明,渐缩喷嘴射流比长管射流发展得更快、更容易达到自保持状态.通过对比发现,在两射流的速度(温度)场中,平均速度(温度)、湍流强度、偏斜因子和平坦度因子都存在明显的异同.同时发现两射流的积分尺度随轴向距离的增加都成线性增长,且在渐缩喷嘴射流中增长得更快.通过对比两射流的边界层厚度、径向与轴向湍流强度的比值、湍动能能谱图并结合前人的研究结果,对两射流湍流场所表现出的不同的统计学行为给出了合理的解释.

Centerline velocity measurements are made in two round jet flows issuing with the same Reynolds number （86 000） from a smooth contraction and a long straight pipe, respectively. The influence of exit flow conditions is investigated to induce the different self-preservation states in the far field of the two jets. The smooth contraction jet flow is found to approach more rapidly to self-preservation than the pipe jet. The study suggests that the observed self-preservation states may be related to the underlying turbulence structures in the near field of the two jets.