# Effects of \"S\"-Type Bowed Guide Vanes on Unsteady Flow in 1.5-Stage Axial Compressors
## 3 Results and Discussion
### Unsteady Aerodynamic Results under Near-Blockage Conditions
Compared with the design condition, the mean value of the tangential force increased slightly, the mean value of the axial force decreased, and the amplitude of the exciting force under each model increased compared with the design condition. It can be seen that, compared with the \(a=0\) mm model, the aerodynamic exciting force amplitude of the \(a=5\) mm model increases, in which the tangential exciting force amplitude increases by 19.09% and the amplitude of the axial exciting force increases by 17.19%. The aerodynamic exciting force amplitudes of the other models decreased, of which the \(a=-10\) mm model decreased the most, the tangential exciting force amplitude decreased by 85.84%, and the axial exciting force amplitude decreased by 86.58%. Figure 16: Tangential force–time domain distribution under near-blockage conditions. Figure 17: Axial force–time domain distribution under near-blockage conditions. Figure 19 shows the Mach number distribution for the \(a=0\) mm model under the near-blockage conditions. The overall Mach number of the near blocking condition is higher than that of the design condition. At the position of \(h=0.25\) H, the Mach number of the stator outlet is almost the same as the inlet Mach number of the guide vane in the near-blockage condition, which is different from the design condition. In addition, at the position of \(h=0.75\) H, the Mach number in the stator passage is not much higher than that in the guide vane and moving vane passage. The Mach number difference of different blade heights is reduced in the near-blockage condition compared to the design condition. At the time \(t=0.25\) T, the exciting force on the moving vane is the largest, and the leading edge of the moving vane is at the position just passing the guide vane trailing edge. At the time \(t=0.75\) T, the exciting force on the moving vane is the smallest, and the leading edge of the moving vane is at the position near the trailing edge of the next guide vane. The relative position of the moving vane and guide vane is consistent with that under the design condition. Under the near-blockage condition, the aerodynamic exciting force amplitude of the \(a=5\) mm model is the highest and the aerodynamic exciting force amplitude of the \(a=-10\) mm model is the lowest. Figures 20 and 21 show the Mach number distributions of \(a=5\) mm and \(a=-10\) mm under near-blocking conditions. The Mach number distribution of different models is not much different. It shows that the \"S\"-type bowed guide vane will not have a great impact on the overall aerodynamic performance under near-blockage conditions. The reason for the increase and decrease of the aerodynamic exciting force amplitude is the same as that of the design condition, which is determined by the relative position of the moving vane and the guide vane of different blade heights. The reason for the change of the aerodynamic exciting force amplitude is the same as that of the design \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Bending Coefficient \(a/\)mm** & \(-\mathbf{10}\) & \(-\mathbf{5}\) & \(\mathbf{0}\) & \(\mathbf{5}\) & \(\mathbf{10}\) \\ \hline tangential exciting force mean value/N & 138.2 & 136.1 & 137.3 & 137.9 & 136.1 \\ axial exciting force mean value/N & 169.7 & 167.2 & 168.3 & 168.7 & 166.6 \\ tangential exciting force amplitude value/N & 0.719 & 3.114 & 5.081 & 6.051 & 5.223 \\ axial exciting force amplitude value/N & 0.823 & 3.641 & 6.133 & 7.184 & 6.010 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Exciting force under near-blockage conditions. Figure 18: Frequency domain distribution of the aerodynamic exciting force under near-blockage conditions. (**a**) Tangential aerodynamic exciting force; (**b**) Axial aerodynamic exciting force. condition, which is determined by the relative position of the moving vane and the guide vane at different blade heights. Figure 19: Mach number distribution of the \(a=0\) mm model under near-blockage conditions.