# Computational Fluid Dynamics-Aided Simulation of Twisted Wind Flows in Boundary Layer Wind Tunnel
## 4 Development Stage
### Optimization of Guide Vane Configuration
#### 4.2.3 Distance between Trailing Edge of Guide Vane and Center of Turtable  
As can be readily observed from Figures 11 and 12, the flow significantly accelerates in the lateral direction after it passes the leading edges of the vanes, forming a long and narrow area with a lateral wind speed over 1.4 m/s (colored in orange in the figure), referred to as the \"high-speed area\" herein, at the downstream region of each vane. These two so-called high-speed areas begin to merge after a certain distance, and the lateral wind speed becomes more uniformly distributed over the downstream region. Therefore, the distance from the center of the model test region to the trailing edge of the vanes, denoted by \(d_{vane,model}\) herein, needs to be sufficiently long so that the high-speed areas merge before they reach the model test region. Meanwhile, if \(d_{vane,model}\) is too great, it may cause the attenuation of the twist characteristics, as pointed out by [PERSON] et al. [8]. Therefore, it is necessary to balance \(d_{vane,model}\) to ensure a sufficient development of the twist characteristics while avoiding excessive attenuation of these characteristics over distance.  
Based on the numerical simulation results, Figure 13 illustrates the profiles of the longitudinal wind speed, the lateral wind speed, and the twist angle. The X-axis in Figure 13 originates from the inlet boundary of the numerical wind tunnel illustrated in Figure 9, and the vanes were set up with their leading edges at X = 6 m and trailing edges at X = 7 m. The wind profiles in the downstream region of the vanes at X = 8 to 12 m, with intervals of 1 m, are plotted in Figure 13 to demonstrate the flow propagation over distance. In addition, the wind profiles in the upstream region at X = 5 m are also plotted in the figure as a reference. It is observed that the longitudinal wind speeds at all heights were approximately 12 m/s while the lateral wind speeds and twist angles were zero, which is desired because the inflow was set to be uniform in the simulation. As shown in Figure 13a, the wind speeds at heights below 0.5 m dropped due to the blockage caused by the vanes, whilst those above 0.5 m maintained the same amplitude as in the upstream region. The  
Figure 12: Distribution of lateral mean wind speed at z = 0.3 m: (**a**) \(d_{vane,vane}\) = 700 mm; (**b**) \(d_{vane,vane}\) = 800 mm; (**c**) \(d_{vane,vane}\) = 900 mm; (**d**) \(d_{vane,vane}\) = 1000 mm.  
lateral wind speeds and the twist angles, as observed from Figure 13b,c, became evident at heights below around 0.6 m due to the guide vanes. Since the profiles at X = 11 m are similar to those at X = 12 m, this indicates that the high-speed areas generated by the two vanes have been merged and created a stable TWF field uniformly distributed over these distances. Hence, it is concluded that X ranging from 11 to 12 m, or, equivalently, \(d_{eane,model}\) ranging from 4 to 5 m, is the optimal value for the present wind tunnel setup.  
Figure 13: Wind profiles at different locations on the X-axis: (**a**) longitudinal mean wind speed; (**b**) longitudinal turbulence intensity; (**c**) twist angle.