# Effect of Baffle Board on Aerodynamic and Stealth Performance of Double S-Duct Caret Intake
## 3 Results and Analysis
### Effect of Corrugated Baffle Board  
In order to further improve the radar stealth performance of the double S-duct intake under the horizontal polarization condition, four corrugated baffle boards with different corrugation numbers were designed to replace the curved board. The location and orientation of the four corrugated boards were all the same as those of the curved board in Model C-2. Figure 11 shows the RCS values of the four intakes with the different corrugated boards. The stealth performance and aerodynamic performance parameters are calculated in Table 6. According to Figure 11, under both polarization conditions, the RCS values of the four intakes were significantly different at the same incidence angle when the angle is less than 20\({}^{\circ}\). Precisely in this range of the radar incidence angle, improving the stealth performance of the double S-duct intake is extremely important. Therefore, it is necessary to study the effect of the corrugated baffle board shape on both performances of the intake. Figure 10: Flow field results of intakes with different curved baffle boards. According to the data in Table 6, under the horizontal polarization condition, the average RCS values of the four intakes with the corrugated boards reduced to below \(-1.45\) dBsm, and the LSA values also increased to more than 38, compared with Model C-2. Except for Model D-1, the maximum RCS values of the other three models were all reduced to about 7 dBsm. However, under the vertical polarization condition, the stealth performance parameters of the four models had generally deteriorated. Therefore, it could be concluded that the corrugated baffle board can effectively reduce the gap between the intake stealth performances under the two polarization conditions, which was caused by the curved board with vertical orientation. Under the horizontal polarization condition, with the corrugation number of the baffle board increased, the maximum and average RCS values of the intake both decreased first and then increased, while the LSA value increased first and then decreased. Among these, the stealth performance of Model D-3 with the corrugation number of 6 was the best. Under the vertical polarization condition, the stealth performance of the intake was improved with increased corrugation number. In terms of the aerodynamic performance, the flow field results of the four intakes are shown in Figure 12. When the corrugation number of the baffle board was less than seven, there was no obvious difference among the Mach number distributions in the diffusers of the three models and the Model C-2, except for the shape of the low-speed zone on the side of the supersonic flow. Similarly, the outlet pressure distributions of the three intakes were only slightly different in the shape of the high-pressure zone, compared with the results of the model C-2. Therefore, according to the data in Table 6, although the flow coefficients were still around 0.9950, the TPR coefficients of the three intakes were all reduced and the DC60 values all increased, compared with the parameters of the Model C-2. Figure 11: RCS values of intakes with different corrugated baffle boards. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Polarization** & **RCS/(dBsm)** & **Model D-1** & **Model D-2** & **Model D-3** & **Model D-4** \\ \hline \multirow{3}{*}{horizontal} & average & \(-1.47\) & \(-1.71\) & \(-2.01\) & \(-1.82\) \\  & maximum & 7.82 & 7.04 & 6.77 & 7.34 \\  & number of LSA & 38 & 39 & 40 & 39 \\ \hline \multirow{3}{*}{vertical} & average & \(-1.38\) & \(-1.46\) & \(-1.56\) & \(-1.61\) \\  & maximum & 6.95 & 6.49 & 6.41 & 6.33 \\  & number of LSA & 37 & 37 & 39 & 40 \\ \hline \multirow{3}{*}{flow coefficient} & 0.9952 & 0.9949 & 0.9949 & 0.9946 \\  & TPR coefficient & 0.8144 & 0.8131 & 0.8128 & 0.8141 \\ \cline{1-1}  & distortion index DC60 & 0.2694 & 0.2498 & 0.2582 & 0.2610 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: RCS and aerodynamic characteristics of intakes with different corrugated baffle boards.