# Aerodynamic Design and Performance Analysis of a Large-Scale Composite Blade for Wind Turbines
## 2 Aerodynamic Design and Analysis
The constant inflow rate was set as the velocity boundary condition at the inlet area, and the constant pressure was set as the pressure boundary condition at the outlet area. The software used for the blade's flow analysis was ANSYS 2022 R2. In this study, the influence of the nacelle or tower for aerodynamic analysis was not considered. Aerodynamic analysis was performed considering only the blade aerodynamic load. The rotation of the rotor was set as follows: the ambient stationary domain and wind turbine rotating domain were separated. The rotation condition was applied to the rotating domain. The two domains set the interface using the frozen rotor model. Only aerodynamic analysis of the rotor blades was performed. The effect of the ground and tower on blade aerodynamics was not considered because the blade is quite high off the ground and the tower is behind the blade's rotational surface. The lift and drag, which are loads that affect the blade, were previously verified with the power coefficient through blade element theory. CFD analysis was used only to verify the rated power performance. An atmospheric model composed of air and wind turbine models was constructed into grids for CFD analysis. The model was constructed as a periodic model for one blade model to save analysis time and resources. In particular, the atmospheric model was constructed with 10 times the blade length. This is for sufficient mixing of air after the blade rotates the disk. The wall surface of the model subject to analysis is the blade surface. Mesh sensitivity was reviewed based on y+. The mesh was constructed to be y+ \(<\) 50. Table 4  
Figure 3: The curve of the power coefficient and tip speed ratio during the wind tunnel test. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \(V\left(\mathbf{m/s}\right)\) & \(\lambda_{0}\) & \(C_{p}\) & \(P\left(\mathbf{kW}\right)\) & \(P_{c}\left(\mathbf{kW}\right)\) \\ \hline
4 & 21.78 & 0 & 0 & 0 \\
6 & 14.52 & 0 & 0 & 0 \\
8 & 10.89 & 0.33 & 5607 & 5326 \\
10 & 8.7 & 0.42 & 13,937 & 13,240 \\
12 & 7.26 & 0.45 & 25,803 & 24,513 \\
12.5 & 7.00 & 0.46 & 29,813 & 28,322 \\
14 & 6.22 & 0.38 & 34,601 & 32,870 \\
16 & 5.44 & 0.31 & 42,135 & 40,028 \\
20 & 4.36 & 0.14 & 37,165 & 35,304 \\
25 & 3.49 & 0.08 & 41,479 & 39,405 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The result of aerodynamic performance estimation of the tip speed ratio. shows the detailed boundary conditions for CFD analysis. For aerodynamic analysis, mesh independence was evaluated. The numerical analysis was performed for five cases based on Y+. As a result of evaluating the power coefficient, it was an appropriate mesh. Figure 4 shows the result of mesh independence. We analyzed the numerical analysis result for the 25 MW wind turbine blade designed. We examined the power result based on rotational speeds. The rated rotational speed was 6.4 rpm at 12.5 m/s, which is the rated wind speed. As a result of the analysis, this was found to indicate a power of 28 MW at the rated rotational speed. As a result of comparing the theoretical performance analysis results, it was therefore confirmed that the rated power produced similar results. Figure 5 shows the boundary conditions for CFD analysis. The boundary mesh is shown in Figure 6. The mesh generation of the blade surface is shown in Figure 7. Figure 8 shows the y+ contour of the blade surface and Figure 9 shows the pressure contour. The stream line based on numerical analysis is shown in Figure 10.  
This aerodynamic analysis was conducted by referring to the CFX analysis example for a general horizontal wind turbine. Total temperature and normal speed were set as inlet conditions for the wind turbine. The static pressure was applied to the outlet in the direction of airflow and the opening in the vertical direction. The k-Epsilon or SST was used in the turbulence model. In this work, the k-Epsilon model, which makes it easier to construct the grid, was used.