# Influence of Inflow Turbulence on the Flow Characteristics around a Circular Cylinder
## 4 Drag Coefficient  
The drag coefficient \(C_{D}\) of the circular cylinder was estimated based on the measured wind pressure coefficient. The drag coefficient was then computed for both smooth and turbulent incident flows by integrating the measured pressure distribution according to the relationship:  
\[C_{D}=\int\limits_{0}^{2\pi}C_{P}cos\theta d\theta \tag{2}\]  
where \(C_{P}\) is the wind pressure coefficient measured in the wind tunnel test and \(\theta\) is the angle between the test point and wind direction. Figure 15 shows the mean drag coefficient \(C_{D}\) of the circular cylinder in the smooth flow as well as the results of previous studies. When the Reynolds number is less than \(1.0\times 10^{5}\), \(C_{D}\) is basically unchanged; \(C_{D}\) then decreases with the increase of the Reynolds number. When the Reynolds number is between \(3.0\times 10^{5}\) and \(3.6\times 10^{5}\), \(C_{D}\) decreases rapidly, then increases gradually when the Reynolds number is between \(3.6\times 10^{5}\) and \(4.0\times 10^{5}\). When the Reynolds number is between \(5.0\times 10^{5}\)-\(8.0\times 10^{5}\), \(C_{D}\) gradually becomes stable. The test results in this paper are closer to those obtained by [PERSON] [29], [PERSON] and [PERSON] [30] and [PERSON] and [PERSON] [24] when the Reynolds number is less than \(2.0\times 10^{5}\), and smaller than the results obtained by [PERSON] et al. [13]. When the Reynolds number is between \(2.0\times 10^{5}\) and \(3.0\times 10^{5}\), the test results in this paper are smaller than the results obtained by [PERSON] [29], [PERSON] et al. [31] and [PERSON] et al. [13]. In the region of rapid decline in the drag coefficient, the results are very close to other results. When the Reynolds number is greater than \(4.0\times 10^{5}\), the test results are greater than the results obtained by [PERSON] [29], [PERSON] et al. [31] and [PERSON] et al. [13]; however, it is closer to the result obtained by [PERSON] and [PERSON] [32]. The drag coefficients \(C_{D}\) of the smooth circular cylinder with a Reynolds number for different turbulence intensities and Reynolds numbers are shown in Figure 16 and the results were compared with those obtained by [PERSON] and [PERSON] [22]. In the three different turbulent flows, the critical Reynolds number moves to a smaller Reynolds number and the critical regime of the Reynolds number is inconspicuous compared to that number in the smooth flow. This is consistent with the result of [PERSON] and [PERSON] [22]. In the supercritical regime, the influence of turbulence intensity on \(C_{D}\) of the circular cylinder is not obvious and \(C_{D}\) is basically the same in the four different flows, all of which are approximately 0.5. In the smooth flow, the results in this paper are close to those obtained by [PERSON] and [PERSON] [22]. In the subcritical and critical regimes, however, the results in supercritical are larger than those obtained by [PERSON] and [PERSON] [22]. In the case of similar turbulence, the testresults in this paper are slightly smaller than those obtained by [PERSON] and [PERSON] [22], but the varying trends with the Reynolds number are consistent. The standard deviations of the drag coefficient \(C_{D}^{\prime}\) of the smooth circular cylinder for different turbulence intensities and Reynolds numbers are shown in Figure 17. In different turbulent flow, \(C_{D}^{\prime}\) decreases with the increase in Reynolds number, which is consistent with the results obtained by [PERSON] and [PERSON] [22]. In the smooth flow, there is a sudden change in \(C_{D}^{\prime}\) at \(Re=3.5\times 10^{5}\) because there is no simultaneous transition of laminar separation to turbulent separation on both sides of the circular cylinder. When \(Re=1\times 10^{5}\)-\(2.7\times 10^{5}\), \(C_{D}^{\prime}\) in the smooth flow is generally larger than that in the turbulent flow, consistent with the results of [PERSON] and [PERSON] [22].