## 1 Introduction  
The flow around a bluff body has attracted widespread attention due to its various engineering applications [1; 2; 3]. Initially, the investigation of flow characteristics began with a two-dimensional bluff body or an infinite cylinder. The seemingly simple model contains a variety of complex phenomena, including flow separation, vortex shedding, wake instability, etc., resulting in changes in the pressure coefficient, Strouhal number, and force coefficient. The research methods usually consist of general experimental study [4; 5; 6; 7; 8], numerical study [9; 10; 11; 12; 13; 14], or 3D flow [15; 16]. Among all bluff bodies, the circular cylinder is one of the most representative due to its unique flow characteristics, which are substantially influenced by Reynolds numbers (\(Re\)). In practical engineering, circular structures have a finite height, and are immersed in the boundary layers, such as chimney stacks, cooling towers, lamp posts, oil tanks, etc. These structures are generally free at one end, and fixed on the ground at the other. Therefore, many different mechanism vortices exist in the flow around a finite circular cylinder. The interaction of these vortices makes the flow three-dimensional, and changes the mechanism of wind-loads simultaneously [1]. Apart from the \(Re\), aspect ratio \(AR=H/D\) (where \(H\) and \(D\) are the height and diameter of the cylinder, respectively) is also a key factor affecting the wind-load characteristics of a finite circular cylinder. The majority of previous research has focused on the analysis of finite cylinders with \(AR>1\)[17; 18; 19; 20; 21; 22]. [PERSON] and [PERSON] [23] conducted a wind tunnel test in the \(Re=2.82\times 10^{4}\)-\(1.69\times 10^{5}\) range with cylinder \(AR\) ranging from \(1\) to \(6\). As a result of the study, it was observed that the mean drag coefficient increases with \(AR\), and the rate of increase remains fairly large for \(AR<1.5\), while the fluctuating drag and lift coefficient reaches their maximum value at \(AR\approx 1.5\), and then rapidly decreases with \(AR\). [PERSON] et al. [24] also observed similar results in their experiments; for \(AR=3\), the mean drag coefficient is lower than that of \(AR=5\), 7 and 9, and the vortex shedding peaks are mostly absent or broad-banded along with the cylinder height. Among the results obtained, there is a critical aspect ratio \(AR_{cr}\), and when \(AR\leq AR_{cr}\), the downwash from the tip extending to the ground plane may have a mechanism for the suppression of Karman vortex shedding. In subsequent research, [PERSON] et al. [25] investigated the behavior of mean aerodynamic forces and vortex shedding in cylinders with \(AR\) ranging from 0.5 to 11, and proved that \(AR_{cr}\) is related to boundary layer thickness, and also provided a more exact range of \(AR_{cr}\). Moreover, the research also confirmed and expanded upon the existence of a second change in behavior of wind-loading and vortex shedding at higher aspect ratios. As for numerical simulation studies, [PERSON] et al. [26] used LES (large-eddy simulation) to study the flow and force characteristics of cylinders with \(AR=6\) and 10 at \(Re=2\times 10^{4}\). Regular vortex shedding was found in the wake of the higher \(AR\) cylinder, along with a strong downwash originating from the free end, while irregular and intermittent vortex shedding occurred in the lower \(AR\) cylinder. This phenomenon resulted in differences in the wind pressure, force, and \(St\) of the two cylinders. [PERSON] et al. [27] also used LES for cylinders with \(AR=2.5\) and 5 at \(Re=4.3\times 10^{4}\) and \(2.2\times 10^{4}\), respectively. By comparing results with experiments, detailed information of the complex flow near the free end and flow structure in the wake of two cylinders was described. Considering finite circular cylinders with lower aspect ratio (\(AR\leq 1\)), the flow and wind-load characteristics may be similar to those of \(AR\leq AR_{cr}\).