## 4 Results and Discussion
### Discussion
Then, with the far-field distance further increasing to 20 \(L\), compared with the 16 \(L\) far-field distance results, the error ratio decreased by 94.22%, 2.04%, 7.00%, 7.43%, 9.69%, and 10.85%. Compared with the results of 12 \(L\) far-field distance, the calculation accuracies of 20 \(L\) far-field distance increased by 93.50%, 0.88%, 9.58%, 15.77%, 20.92%, and 23.46%. The above results indicate that the key point is the degree of the far-field distance increases. When the AOA range is small ((0\({}^{\circ}\), 0\({}^{\circ}\)), (0\({}^{\circ}\), 2\({}^{\circ}\))), boosting the far-field distance may not necessarily lead to an increment in simulation accuracy, but may lead to a drop. When the  
Figure 18: The optimal total error ratios of four formula models and the corresponding calculation accuracy improvements. AOA range is large ((0\({}^{\circ}\), 4\({}^{\circ}\)), (0\({}^{\circ}\), 6\({}^{\circ}\)), (0\({}^{\circ}\), 8\({}^{\circ}\)), (0\({}^{\circ}\), 10\({}^{\circ}\))), the greater the far-field distance, the better the simulation accuracy. As the range of the AOA grows larger, the improvement of calculation accuracy also increases, which means the degree of optimization brought by the increment of far-field distance has a positive correlation with the size of the AOA range. In conclusion, a far-field distance of 20 m is suggested. Figure 20 demonstrates the optimal total error ratios of SST k-omega and Spalart-Allmaras under different AOA ranges. At the ranges of (0\({}^{\circ}\), 2\({}^{\circ}\)), (0\({}^{\circ}\), 4\({}^{\circ}\)), (0\({}^{\circ}\), 6\({}^{\circ}\)) and (0\({}^{\circ}\), 8\({}^{\circ}\)), compared with the results of SST k-omega, the calculation accuracy changes with Spalart-Allmaras are \(-25.36\%\), \(-27.06\%\), \(-11.51\%\) and \(-1.29\%\), which means SST k-omega performs better than Spalart-Allmaras. However, at the ranges of (0\({}^{\circ}\), 0\({}^{\circ}\)) and (0\({}^{\circ}\), 10\({}^{\circ}\)), Spalart-Allmaras behaves better than SST k-omega, with corresponding accuracy improvements of 98.66% and 4.57%. Therefore, when the AOA range is small (except (0\({}^{\circ}\), 0\({}^{\circ}\))), SST k-omega is preferred. However, when the AOA range increases, the performance difference between these two turbulence models decreases, and when the range increases to (0\({}^{\circ}\), 10\({}^{\circ}\)), Spalart-Allmaras is preferred. In general, the range of AOA studied determines the chosen turbulence model. Table 19 gives the optimal mean error ratios and the corresponding simulation configurations based on the results of the previous three sections. In summary, if the AOA range is (0\({}^{\circ}\), 0\({}^{\circ}\)), the sharp trailing edge based on the definition formula applying 200 points, combined with SA+20 m, achieves the optimal result, which is (0.00%, 0.00%). If the AOA ranges are (0\({}^{\circ}\), 2\({}^{\circ}\)), (0\({}^{\circ}\), 4\({}^{\circ}\)), and (0\({}^{\circ}\), 6\({}^{\circ}\)), the sharp trailing edge based on 200 points NACA4-digital, combined with SST+20 m achieves the optimal results, which are (0.78%, 1.38%), (2.80%, 1.22%) and (4.98%, 1.11%). If the AOA range is (0\({}^{\circ}\), 8\({}^{\circ}\)), the sharp trailing edge based on the definition formula applying 400 points, combined with SST+20 m, achieves the optimal result, which is (5.75%, 1.54%). If the range of AOA is (0\({}^{\circ}\), 10\({}^{\circ}\)), the sharp trailing edge based on the definition formula applying 400 points, combined with SA+20 m, achieves the optimal result, which is (6.67%, 1.55%). If the applied trailing edge shape is blunt, the suggested corresponding simulation configurations are SST+16 m, SST+12 m, SST+20 m, SST+20 m, and SA+20 m.  
Figure 19: The optimal results of three far-field distances and the corresponding calculation accuracy improvements.