# Computational Fluid Dynamics-Aided Simulation of Twisted Wind Flows in Boundary Layer Wind Tunnel
## 5 Closeout Stage  
Following the setup in the numerical wind tunnel as discussed in Section 4.3, the passive devices, including the vane system, were implemented in the actual wind tunnel as shown in Figure 17. Considering that the twist angle values at heights below 0.4 m were lower than the desired values, the guide vanes were moved closer to the model test region by 200 mm (i.e., \(d_{vane,model}\) = 3.8 m) to alleviate the attenuation of twist characteristics. Table 2 summarizes the final experimental setup of the guide vanes at the closeout stage, i.e., the optimal guide vane setup obtained following the procedure framework proposed by this study. It is noteworthy that the experimental setups are highly dependent on the specifications of the wind tunnel, and, therefore, modifications of setup parameters may be needed when generating the TWF wind profiles in another wind tunnel.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline No. of vanes & 2 \\ \(\theta_{\text{vane}}(z)\) model & Ekman spiral \\ \(\theta_{\text{vane}}(0)\) & 30\({}^{\circ}\) \\ \(\theta_{\text{vane}}(1)\) & 0\({}^{\circ}\) \\ \(\theta_{\text{vane}}(1.5)\) & 0\({}^{\circ}\) \\ \(H_{\text{vane}}\) & 1.5 m \\ \(d_{vane,wall}\) & 750 mm \\ \(d_{vane,pane}\) & 700 mm \\ \(d_{vane,model}\) & 3800 mm \\ \hline \hline \end{tabular}
\end{table}
Table 2: Summary of optimal experimental setup of guide vanes.  
Figure 16: Wind profiles obtained by optimal setup in numerical wind tunnel: (**a**) longitudinal mean wind speed and turbulence intensity; (**b**) twist angle.  
Figure 18 presents the variations in the profiles of longitudinal wind speed and turbulence intensity obtained from the numerical wind tunnel over time, indicating that the flow simulated by the LES technique became steady within approximately 30 s. In addition, the profiles obtained from the actual wind tunnel tests are also plotted in Figure 18 for comparison purposes, and good agreement between the LES-simulated profiles and the measured ones can be readily observed. Such agreement suggests that the numerical wind tunnel can serve as an efficient and accurate approach to provide useful reference to the actual wind tunnel tests.  
Figure 19 plots the profiles of longitudinal speed, turbulence intensity, and twist angle of the TWF. As presented in Figure 19a, both profiles follow the power law expressed by Equations (4) and (5) with an exponent of \(0.12\) and \(-0.22\), respectively. Furthermore, the profiles of conventional ABL wind flow (CWF) without twist were also generated in the wind tunnel as a reference. Good agreement can be readily observed between the profiles of the TWF and those of the CWF, indicating that the experimental setup for the TWF has produced ABL characteristics that are satisfactory. On the other hand, Figure 19b shows that the maximum twist angle of the TWF reached \(27^{\circ}\), which is only slightly below the \(30^{\circ}\) set for the Ekman spiral model, and the measured twist angles well match the target values with a maximum discrepancy below \(3^{\circ}\). Furthermore, Figure 20 shows that the power spectral densities of the longitudinal and lateral wind speeds, obtained by the Welch and Yule-Walker methods, are in good agreement with the [PERSON] spectrum model. These results indicate that the guide vane system, configured following the procedural framework proposed in this study, has generated the desired TWF with satisfying accuracy.  
Figure 17: Final setup in actual wind tunnel.  
Figure 19: Wind profiles obtained by final setup in actual wind tunnel: (**a**) longitudinal mean wind speed and turbulence intensity; (**b**) twist angle.  
Figure 18: Variations in wind profiles at different locations on the X-axis: (**a**) longitudinal mean wind speed; (**b**) twist angle.