# Effect of Baffle Board on Aerodynamic and Stealth Performance of Double S-Duct Caret Intake
## 1 Introduction  
A non-significant RCS value plays a very important role in the safety of an advanced fighter. It has been proven that the forward radar echo intensity of an aircraft could be significantly influenced by the intake [1]. Therefore, understanding how to effectively reduce the influence of intake on the RCS characteristics of a fighter is very important. The compression section of the caret intake is designed according to the waverider principle [2] and has an uncomplicated structure, with excellent aerodynamic performance [3] and non-significant RCS characteristics. Therefore, the caret intake is highly applicable for use in advanced stealth fighters. By using computing technologies and a variety of suitable turbulence models, the efficiency and precision of computational fluid dynamics (CFD) methods in simulating the complex flow field of intake have been fully developed [4; 5; 6]. Therefore, in addition to experimental methods [7], CFD methods have become another common approach for analyzing the aerodynamic performance of intake. [PERSON] [8] used a field velocity method to numerically simulate the flow field of a serpentine intake exposed to non-stationary horizontal sinusoidal gusts, and proved that the gusts could cause the deterioration of outlet distortion. [PERSON] [9] used the SST k-\(\omega\) turbulence model to investigate the aerodynamic performance of a supersonic intake, and proved that the boundary layer bleed could reduce the outlet distortion. [PERSON] [10] simulated the airflow field of a supersonic intake by using the SST k-\(\omega\) model, and proved that the interaction between the shock wave and the boundary layer could be the main reason for the buzz onset. In radar stealth research, the larger the RCS value of the object, the stronger the scattered radar echo intensity, and the worse the stealth performance. According to thefinite element method, the RCS value can be investigated by obtaining the surface current, and a variety of computational electromagnetic methods have been developed to solve this problem [11]. By directly solving the coefficient matrix derived from [PERSON]'s equations, the precision of the method of moment (MOM) in analyzing the RCS characteristics of objects with different materials has been verified [12]. However, due to the too large matrix, this method is inefficient in investigating the RCS value of objects sized much larger than the radar wavelength, such as the intake. In order to solve these problems, the MLFMM has been developed and is widely used. [PERSON] [13] used the MLFMM to investigate the RCS characteristics of various fighters, and proved that the RCS characteristics of intake could be greatly affected by the compressor blades. In order to suppress the radar echo intensity of intake, two methods have been proven to be effective. The first one uses the S-duct diffuser [14], coating the wall with low-scattering material [15]. A study on the aerodynamic and RCS characteristics of the double S-duct caret intake has proven that this method can be effective, but it could also lead to multiple boundary layer separations [16]. These separations could cause deterioration of outlet distortion [17]. Model parameters which could improve the stealth performance generally cause the loss of aerodynamic performance. Using the boundary layer bleed system can effectively suppress separation in the S-duct intake, but it could also lead to deterioration in the stealth performance [18]. Therefore, comprehensive analysis of the aerodynamic and stealth performance is necessary both for the design of S-duct intake [19] and for evaluating the effects of additional structures. Another method utilizes additional structures, such as the baffle board studied in this article, to increase the consumption of radar waves. Based on theoretical analysis of the supersonic intake, the baffle board could inevitably interfere with the high-speed airflow, resulting in the loss of aerodynamic performance.