This paper presents a detailed investigation on the flow characteristics and the bed-shear-stress distribution around a finite circular cylinder at a fixed Reynolds number (Re $=$ 2 $\times$10⁴) and seven aspect ratios (AR $=$ 0.5$\sim$6) by solving the Reynolds Averaged Navier–Stokes (RANS) equations. It is found that, for a moderate Reynolds number and a relatively large boundary-layer thickness, the time-averaged streamwise vortex structure will be transformed from the ‘Dipole Type’ at AR$\le$3 to the ‘Three-Pairs Type’ at AR$\ge$4. It is the first time that the ‘Three-Pairs Type’ vortex structure has been reported, which consists of Time-Mean Streamwise Tip Vortices, Time-Mean Streamwise Base Vortices and Time-Mean Streamwise Bottom Vortices. Besides, this study indicates that, with increasing AR, the maximum time-averaged bed-shear-stress amplification magnitude upstream of the cylinder will first decrease and then increase, with the minimum occurring at approximately AR $=$ 3.0, due to the influence of AR on the horseshoe vortices. Additionally, this study manifests that different critical AR values can be obtained for various flow variables. For instance, in terms of the total lift coefficient of the cylinder and the transverse fluctuating velocity in the symmetry plane at the mid-height of the cylinder, the critical AR is equal to ${\mathit{AR}}_c=3.0$ and ${\mathit{AR}}_c=2.0$, respectively.

本文对固定雷诺数（Re）下有限圆柱周围的流动特性和床切应力分布进行了详细的研究。 $=$ 2 $\times$10 ⁴）和七个宽高比（AR $=$ 0.5$〜$6）通过求解雷诺平均纳维-斯托克斯（RANS）方程。发现，对于适中的雷诺数和较大的边界层厚度，时间平均流向涡旋结构将从AR处的“偶极子类型”转变$\le$3到AR的“三对类型”$\ge$4.这是首次报告“三对型”涡旋结构，其结构包括时间均值流向顶部涡流，时间均值流向基本涡流和时间均值流向底部涡流。此外，这项研究表明，随着AR的增加，汽缸上游的最大时间平均床剪切应力放大幅度将先减小然后增加，而最小值在大约AR处出现 $=$3.0，由于AR对马蹄涡的影响。此外，这项研究表明，可以针对各种流量变量获得不同的临界AR值。例如，根据气缸的总升力系数和气缸中间高度处对称平面中的横向波动速度，临界AR等于${\mathit{增强现实}}_C=3。0$ 和 ${\mathit{增强现实}}_C=2。0$， 分别。