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

摘要: 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.

Abstract: 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.