# Performance of the Compliant Foil Gas Seal with Surface Micro-Textured Top Foil+
## 1 Introduction  
As an aircraft is susceptible to random uncertainty excitation during operation [1], which may induce seal instability or failure, designing a seal structure with good high-speed stability and strong autonomous adjustment capability is of great importance for the development of aerospace engines. The compliant foil seal (CFS) is a new type of non-contact seal [2]. Compared with the traditional gas film sealing structure, which has a rigid floating ring, the compliant foil can undergo adaptive deformation under load; moreover, there is Coulomb friction between the contact elements [3, 4]. Owing to these advantages, the sealing structure can rapidly adapt to the operating position, spontaneously adjust the balanced relationship between the friction pair, load, and gas film, ensure gas film stability, and prevent friction and collision. Therefore, a sealing structure with a compliant sealing surface or flexible support has considerable potential for application in the sealing components of rocket turbine pumps and aero-engine systems [5, 6]. In the 1990s, [PERSON] and [PERSON] proposed a CFS structure based on the study of foil bearings, and they tested it at 55,000 rpm and 560 \({}^{\circ}\)C [7, 8, 9]. Regarding the theoretical study, they established the governing equation of the film pressure by considering the turbulence effect and analyzed the sealing performance of CFS under high-speed operation conditions using the method of successive over-relaxation [10]. [PERSON] [11] combined the perturbation method for a floating ring seal with the finite element method for a flexible foil to analyze its characteristics and found that the eccentricity decreases while the direct stiffness and damping coefficient increases as the bump foil thickness increases. [PERSON] et al. [12] designeda floating ring seal structure using a bump foil to support the ring, which demonstrated its stability at high speed through eddy current stability experiments. [PERSON] [13] used the PH linear method to study the steady-state flow field characteristics of a cylindrical spiral-groove gas film seal and found that the sealing pressure difference has a significant effect on the steady-state characteristics. [PERSON] [5] analyzed the sealing characteristics and dynamic properties of CFS and tested the effect of different surface roughness values on the start-stop cycle performance of high-speed elastic foil sealing [14]. The results showed that improving the interface surface properties can effectively attenuate the hysteresis effect of the seal. Interface modeling of the friction pair has a significant impact on the flow field, dynamic pressure effect, and friction performance [15; 16]. [PERSON]'s [17] introduction of a series of cavities in the diverging curved walls of a two-dimensional ribbed diffuser or [PERSON]'s [18] application of transverse grooves on both sides of the stern side can produce locally stable flow re-circulation. The textured surface of the diamond-like carbon film is machined on the dry gas seal ring, and its trapping effect contributes significantly to the improvement of friction performance [19; 20]. Moreover, the parameters of pits are the keys to affecting friction performance [19; 21]. The shape design of the texture successfully utilizes the knowledge of biomimicry; for instance, streamlined grooves in dolphin skin were used by [PERSON] [22] and a semi saliva leaf textured face was processed by [PERSON] [23]. With the widespread application of texture, optimization or hybrid processing techniques such as mask deposition and laser cladding are gradually developed [24]. Thus far, research on the surface modeling of friction pairs of the cylinder gas seal has mainly focused on the design of dynamic pressure grooves [25; 26; 27]. Most of these studies have used CFD software, where procedures such as geometric modeling and mesh division are relatively cumbersome. In summary, research on the characteristics of compliant foil gas seals has mainly focused on structural design.