## 1 Introduction
[10] proposed an aeroelastic coupling method by calculating the floating ring's opening force and the effects of rotor rotation direction, sealing ring width, rotor speed, rotor radius and other factors. [PERSON] et al. [11], on the basis of the aeroelastic coupling method and considering the influence of centrifugal expansion, investigated eccentricity and inner/outer rotor speed on sealing performance. Unfortunately, the effects of surface roughness and temperature were not considered. On the whole, few reports of gas film seals between shafts exist. Most face or cylinder gas film seals being studied have problems sealing the rotor and stator interfaces and are generally used in ground machinery under relatively stable conditions. Analysing gas film performance is important for improving the seals that exist between reverse shafts, such as for cylinder gas film seals. [PERSON] et al. [12; 13] proposed a radial adaptive sealing device for cylinder gas film seals and calculated the effects of different gas film gaps and inlet pressure on the gas film's pressure characteristics using the CFD method. [PERSON] et al. [14] proposed a flexible support sealing method and studied the effects of various sealing rings and structural parameters of the T-groove on the sealing performance under stable conditions. Their analysis used computer simulations and the fluid-structure coupling analysis method to reveal gas film thickness, eccentricity and other factors that could affect sealing performance. [PERSON] et al. [15] examined rotor speed, different inlet pressure and gas viscosity effects on gas film stiffness, leakage and T-groove cylinder seal force using the CFD method. [PERSON] et al. [16] examined T-groove cylinder gas film seal groove parameters on sealing performance and concluded that groove depth principally affected the gas seal's performance using orthogonal testing procedures. [PERSON] et al. [17] found that the spiral groove model demonstrates better dynamic pressure effects under identical conditions by calculating and comparing eccentricity, speed and differential pressure effects on the sealing performance with and without a spiral groove. [PERSON] et al. [18] calculated and analysed the effects of seal gap, speed, viscosity and differential pressure on the sealing performance using the CFD numerical analysis method. Most current studies on gas film seals have used numerical calculations or CFD analysis. However, different from the existing seals at the rotor and stator interface, the cylinder gas film seal between reverse shafts studied herein is used between two rotors rotating at high speeds simultaneously, proving that the effect of the direction and size of the sealing interface on the flow and bearing capacity of sealing fluid is an important basic work for the design of seals. Furthermore, when dealing with micron-thick gas films, the roughness of the sealing interface cannot be ignored when vibration causes radial runout in engine rotors. We propose a cylinder gas film sealing structure. First, we established a force balance sealing ring analysis model considering the centrifugal expansion effects of sealing at high speeds. We determined the degree of solid contact between the sealing ring and the inner rotor using the minimum gas film thickness. Finally, we calculated the sealing ring's performance parameters using the average Reynolds equation and the micro-convex contact theory.