# Effect of Baffle Board on Aerodynamic and Stealth Performance of Double S-Duct Caret Intake
## 3 Results and Analysis
### Corrugation Shape Optimization of Baffle Board  
To investigate the influence of corrugation shape on the effect of the corrugated baffle board, three corrugated boards with the same corrugation numbers but different shapes were designed and installed at the same positions on the front diffuser as above. The large-curvature zones of the corrugated boards in the three models were designed, respectively, near the upper wall, at the middle part of the board, and near the lower wall. Figure 13 shows the RCS values of the three intakes. The stealth performance and aerodynamic performance parameters are calculated in Table 7. Compared with the Model D-3, the stealth performances of the three intakes all deteriorated under the horizontal polarization condition and were all optimized under the other condition, which was consistent with the comparative conclusion regarding the effects of the curved board and corrugated board mentioned above. According to Figure 13a, under the horizontal polarization condition, there was almost no difference between the RCS values of the three intakes at the same incidence angle, except that the values of the Model E-3 were significantly greater than those of the other two models when the angle was less than 5\({}^{\circ}\). Therefore, with the same LSA number, the maximum and average RCS values of the Model E-3 were both the largest, while the performance parameters of the other two models were generally similar. Additionally, the performance parameters of the Model E-3 were also generally similar to the Model C-2, in which the curved board was installed. It could be concluded that the curvature of the middle part had only a slight influence on the effect of the baffle board in improving the intake stealth performance under the horizontal polarization condition. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Polarization** & **RCS/(dBsm)** & **Model E-1** & **Model E-2** & **Model E-3** \\ \hline \multirow{3}{*}{horizontal} & average & \(-1.46\) & \(-1.52\) & \(-1.18\) \\  & maximum & \(7.32\) & \(7.25\) & \(7.65\) \\  & number of LSA & \(38\) & \(38\) & \(38\) \\ \hline \multirow{3}{*}{vertical} & average & \(-2.04\) & \(-1.75\) & \(-1.89\) \\  & maximum & \(5.44\) & \(5.88\) & \(5.77\) \\  & number of LSA & \(40\) & \(39\) & \(40\) \\ \hline \multirow{3}{*}{flow coefficient} & \(0.9950\) & \(0.9950\) & \(0.9950\) \\  & TPR coefficient & \(0.8128\) & \(0.8142\) & \(0.8139\) \\ \cline{1-1}  & distortion index DC60 & \(0.2596\) & \(0.2382\) & \(0.2405\) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: RCS and aerodynamic characteristics of intakes with shape-optimized baffle boards. Figure 13: RCS values of intakes with shape-optimized baffle boards. Under the vertical polarization condition, there were obvious differences among the RCS values of the three intakes at the same incidence angle when the angle was less than 15\({}^{\circ}\), meaning that the corrugation shape had a significant influence on the effect of the corrugated baffle board. The closer the large-curvature zone of the corrugated board was to the upper wall, the smaller the maximum and average RCS of the model, and the better the intake stealth performance. In terms of the aerodynamic performance, the flow field results of the four intakes are presented in Figure 14. By comparison, the flow field distribution and the aerodynamic performance parameters of the Model E-1 were generally the same as those of the Model D-3. Similarly, there was not much difference between the calculated results of the Model E-2 and the Model C-2. The aerodynamic performance of the Model E-3 was between those of the other two models. The reason for this phenomenon was that the boundary layer separation in the supersonic zone was aggravated as the curvature of the corrugated board near the upper wall increased. Therefore, it could be concluded that the closer the large-curvature zone of the corrugated board is to the upper wall, the worse the intake aerodynamic performance. I.