# Effect of Baffle Board on Aerodynamic and Stealth Performance of Double S-Duct Caret Intake
## 3 Results and Analysis
### Effect of Curved Baffle Board Locations  
Figure 9 presents the RCS values of the four double S-duct intakes with curved baffle boards installed at different locations. The stealth performance and aerodynamic performance parameters are displayed in Table 5. According to Figure 9, the RCS values of the four intakes varied similarly with the incidence angle, indicating that the baffle board played a relatively minor role in the RCS characteristics of the intake. However, the RCS values of the four intakes differed significantly at the same incidence angle, especially at angles like 9\({}^{\circ}\) and 18\({}^{\circ}\) with the vertical polarization condition. Figure 8: Flow field calculation results of two intakes. Figure 9: RCS values of intakes with different curved baffle boards. Table 5 shows that compared with Model B, the RCS values of the four intakes were generally reduced, and the LSA numbers were generally increased, demonstrating that the baffle board coated with low-scattering material could be highly effective in improving the stealth performance of the intake. Additionally, the average RCS values of Model C-1 and Model C-3 under at the horizontal polarization condition were both below \(-1.7\) dBsm, while the values under the other condition both exceeded \(-1.5\) dBsm, indicating that the horizontal board was more effective under horizontal polarization. Similar conclusions can be drawn from the values of the other two models. Under the horizontal polarization condition, the average and maximum RCS values of Model C-3 were both greater than those of Model C-1. However, under the other condition, there was little difference between the parameters of the two intakes. Similarly, under the vertical polarization condition, the stealth performance of Model C-2 was obviously better than that of Model C-4, but there was no difference under the other condition. Therefore, it could be concluded that the baffle board in the front diffuser was more effective in reducing the RCS of the double S-duct intake than the board in the rear diffuser. Notably, the LSA number of Model C-1 still needs to be increased under the vertical polarization condition, and the RCS values of Model C-2 at some angles also need to be reduced under the horizontal polarization condition. In terms of aerodynamic performance, the flow field results of the four intakes are shown in Figure 10. According to Figure 10b, a significant difference occurred between the flow zones on the two sides of each baffle board, inevitably leading to changes in the outlet total pressure distribution and enhancing the flow mixing effect. Therefore, compared with the values of Model B, the DC60 values of the four intakes all increased above 0.24, and the TPR coefficients were all reduced. There was an obvious low-speed zone in the rear diffuser of Model C-3 and Model C-4, respectively, indicating that the baffle board in the rear diffuser could aggravate boundary layer separation. Due to the decrease in the actual flow area caused by the low-speed zone, the flow coefficients of the two models both reduced below 0.99. However, the baffle boards of the other two models had no effect on the flow coefficients. Additionally, due to the short distance between the outlet and the baffle board in the rear diffuser, the downstream flow mixing effect had little influence on the suppression of the low-speed zone and the discontinuity between the flow at the two sides of the board. Therefore, with the same orientation of the baffle boards, the DC60 values of Model C-3 and Model C-4 were respectively higher than those of Model C-1 and Model C-2. It could be concluded that the baffle board in the front diffuser has a lesser adverse effect on the aerodynamic performance of the double S-duct intake, compared with the board in the rear diffuser. Additionally, because the flow distribution along the \(Y\)-axis direction was more uneven than along the \(Z\)-axis direction in the double S-duct intake, the DC60 value of Model C-2 was 0.06 lower than that of Model C-1.