# Effect of Surface Roughness on Aerodynamic Loads of Bluff Body in Vicinity of Smoothed Moving Wall
## 3 Results and Discussion  
The integrated quantities and the frequency of vortex shedding due to the turbulent flow around the cylinder, i.e., \(C_{D}\), \(C_{L}\), and \(\text{St}\), were obtained to verify the responses of the coupled methods. The Strouhal number, \(\text{St}\), was estimated by performing a fast Fourier transform on the \(C_{L}\) time history. The results of the computer code were previously validated by our research group [15] in comparison with experimental findings [29; 41; 42] from the literature. A good approximation of the experimental data was obtained. The intrinsic characteristics of the turbulent flow around the cylinder away from the moving wall can be explained physically by interpreting the instantaneous distribution curve of the pressure coefficient on the discretized surface of the body using [PERSON]'s interpretation [6], which conjectures that a growing vortex gaining circulation from the shear layer, which forms from the boundary layer separation on one side of the cylinder, becomes intense enough to attract the opposite shear layer through velocity induction. Conversely, the approaching flow with opposing vorticity, with a certain intensity, ceases the circulation supply of the growing vortex, and thus, it is disconnected from the shear layer and subsequently thrown downstream of the body, incorporating into the viscous wake. The points indicated in Figure 4a correspond to times A (t = 46.95), B (t = 48.70), C (t = 50.60), D (t = 51.75), and E (t = 52.50), and the respective instantaneous distributions of the circumferential pressure coefficient are shown in Figure 4b. Point A indicates that a clockwise vortical structure is shedding at the top of the cylinder, where a maximum positive lift force and a drag force that is still increasing acts (Figure 4b). The drag force will increase until the moment when the clockwise vortical structure starts to be incorporated by the wake (point B). Point B indicates the imminence of an inversion in the lift coefficient, as can be seen in Figure 4a. This inversion means that the clockwise vortical structure, shedding from the cylinder surface at point A, begins to be incorporated by the wake formed downstream of the body. In Figure 4b, a zone of low pressure is recognized to be approximately constant between \(\theta=57^{\mathrm{o}}\) and \(\theta=280^{\mathrm{o}}\). At point C, an anti-clockwise vortical structure is shed at the bottom of the cylinder, where a maximum negative lift force and a drag force that is still increasing act, as can be seen in Figure 4a. This drag force will increase until the moment when that vortical structure starts to be incorporated by the wake (point D). In Figure 4b, a low-pressure zone between approximately \(\theta=190^{\mathrm{o}}\) and \(\theta=320^{\mathrm{o}}\) is noted. At point D (Figure 4a), there is again the imminence of an inversion in the lift coefficient, which will pass from a negative to a positive value. This inversion indicates that the counterclockwise vortical structure, shed from the cylinder at point C, begins to be incorporated by the wake. In Figure 4b, a zone of low pressure, approximately constant, is detected between \(\theta=70^{\mathrm{o}}\) and \(\theta=287^{\mathrm{o}}\). Figure 4: Cylinder with a smooth surface—\(\mathrm{Re}=1\times 10^{5}\) (\(\mathrm{Nc}=104;\ \sigma_{\mathrm{o}}=0.001;\ \mathrm{t}_{\mathrm{S}}=100\)): (**a**) time history of the aerodynamic coefficients; (**b**) instantaneous distribution of the pressure coefficient over the cylinder. At time t = 52.50, corresponding to point E (Figure 4a), a maximum positive lift force and a low-pressure zone between approximately \(\theta=46^{\rm o}\) and \(\theta=178^{\rm o}\) are identified in Figure 4b. At this moment, in a manner analogous to what happened with point A, a new clockwise vortical structure is shedding from the upper part of the cylinder. At this stage of numerical simulation, there are 109,200 vortex blobs constructing the viscous wake.