中文摘要：

利用 PIV 对高宽比为7的有限长正方形棱柱尾流和二维方柱尾流进行了测量。实验中雷诺数为9300。对流场进行了本征正交分解（POD），并分析了各阶模态对湍动能的贡献。基于瞬态流场重建中各阶模态的系数，比较了有限长棱柱尾流和二维柱体尾流的瞬态流动特性。结果表明：在二维柱体尾流中，代表着卡门涡街的1、2阶模态对湍动能的贡献占支配地位，达到了73．6％，而在有限长柱体尾流中，1、2阶模态的贡献仅为45．9％。后者的尾流中存在两种典型的流动形态：一种是1、2阶模态占主导的卡门涡街形态，类似于二维棱柱尾流；另一种是3阶或更高阶模态占主导的对称形态。

英文摘要：

The near wake of a 2D square cylinder and that of a finite length square cylinder with the as-pect ratio of 7 was measured by PIV.The Reynolds number based on free stream oncoming flow and cylinder width is 9300.Proper orthogonal decomposition （POD）was performed to analysis the contributions of each mode on turbulence kinetic energy （TKE）.Instantaneous flow properties were compared between the near wake of finite length and 2D square cylinders,utilizing the coefficients of POD modes for flow reconstruc-tion.It was found that,in 2D cylinder wake,the first 2 POD modes,which represent the Karman vortex shedding,dominated the near wake and contributed 73.6% of total TKE;while in the finite length square cylinder wake,the TKE contribution from the first two modes was only 45.9%.There were two typical in-stantaneous flow status occur in the finite length cylinder wake：one was the status of Karman vortex shed-ding dominated by the first two POD modes,similar to that in a 2D cylinder wake;the other was symmetri-cal flow status which was dominated by the third and/or other higher POD modes.