中文摘要：

针对菱形和圆形2种不同出口形状的孔板自由射流，在出口雷诺数Re=72000（速度使用射流平均出口速度以，特征长度使用当量直径De）的情况下应用粒子图像测速（particle image velocimetry，PiV）技术对空气射流在初始段和过渡段的流场进行测量，并对2种不同形状出口的射流流动特性进行对比分析。结果表明：与圆形自由射流相比，菱形自由射流有更强的混合和卷吸周围流体的能力，具体表现在菱形自由射流的势流核更短，速度衰减和扩散更快以及湍流强度更大；另外，在菱形射流中还出现了长短轴半值宽变换的现象。

英文摘要：

Detailed mean flow and turbulence measurements were made in the near field and the transition field of two air/air turbulent jets issuing from a diamond orifice plate and a circular counterpart. Particle image velocimetry （PIV） was used for the measurements of the flow field with the exit Reynold number （ 72 000）, based on the exit mean velocity Ue and the equivalent diameter De. Compared with the circular jet, the diamond jet is found to have a superior mixing capability. This is reflected by a shorter potential core, higher decay and spread rates of the jet and also the faster turbulence intensity growth. In addition, the phenomenon of axis switching is also found to occur in this jet.