# Influence of Inflow Turbulence on the Flow Characteristics around a Circular Cylinder
## 1 Introduction  
The flow characteristics over circular cylindrical structures have always been a classic problem in the field of wind engineering. Tubular steel parts are often used in many structures such as TV and transmission towers, steel poles and bridges. Compared to bluff structures (such as square columns) and streamlined structures (such as aerofoils), circular cylinders are usually defined as semi-pneumatic [1], with their flow characteristics and aerodynamic parameters affected by factors such as Reynolds number, flow turbulence and surface roughness [2; 3]. Previous studies have mainly focused on the Reynolds number effect of the drag coefficients of smooth circular cylinders. In the pioneering work of [PERSON] [4], a Strouhal-Reynolds number relationship for the laminar shedding regime was presented for Reynolds numbers from about 50 to 150. Based on the pressure tests of circular cylinders, [PERSON] [5] divided the measured Reynolds number into four regimes: subcritical, critical, supercritical and transcritical. However, not all studiesuse the same terminology for regimes above the critical [6; 7; 8; 9]. In this study, the terminology for the regimes is as defined by [PERSON] [5]. The different phenomena of the different stages of transition from subcritical to transcritical have been clarified in more detail by [PERSON] [10]. [PERSON] [11] measured the wind pressure at the mid-span position of the circular cylinder and found that the flow around circular cylinders appears to be a switching between regular and irregular vortex shedding in a critical Reynolds number regime. [PERSON] et al. [12] studied the flow characteristics of circular cylinders in the regime of the transcritical Reynolds number by artificially stabilizing the steady wake, finding that the drag coefficient is about 0.7. [PERSON] et al. [13] studied the drag coefficient and lift coefficient of a circular cylinder whose diameter was 30 cm under different regimes of Reynolds numbers and found that asymmetric wind pressure distribution appears at a certain wind speed at the regime of the critical Reynolds number. With advances in computer technology, in addition to the study of wind tunnel tests, computational fluid dynamics (CFD) has been applied to the study of the problem by some researchers. [PERSON] et al. [14] presented numerical calculations of laminar vortex-shedding flows past circular cylinders and they found that the Strouhal number and the drag coefficient agreed better with experiments and previous numerical results at the lower Reynolds numbers comparing to these at the higher Reynolds numbers. It is blamed on the initial influence of stochastic fluctuations for the difference between the calculations and measurements for higher Reynolds numbers. [PERSON] [15] provided a numerical solution of vortex-excited oscillations of a circular cylinder based on numerical simulation and found that the results of this investigation agreed well with the experimental evidence, except for the reduced velocities in the lock-in region. [PERSON] [16] studied the three-dimensional flow characteristics of a circular cylinder with a Reynolds number of \(1.4\times 10^{5}\) based on large eddy simulation (LES) and found that the importance of the subgrid scale model significantly increased in the case of the high Reynolds number in comparison with a low Reynolds number. [PERSON] et al. [17] studied the mean pressure distribution by LES for high Reynolds number complex turbulent flows and found that the mean pressure distribution is predicted reasonably well over the Reynolds number regime from \(5\times 10^{5}\) to \(1\times 10^{6}\). Among factors influencing the flow around the circular cylinder--in addition to the Reynolds number--the turbulence intensity also plays an important role. The effect of freestream turbulence in crossflow around a circular cylinder in delaying the separation and reducing its drag at subcritical Reynolds numbers has long been recognized.