A new-type of cylindrical spiral dry gas seal was employed in gas turbine with large vibration. In order to investigate the performance of the cylindrical gas seal

the approximate analytic solution of the gas pressure was obtained by the methods of PH linearization and iteration

which was deduced from the steady micro-scale cylindrical Reynolds equation with the slip boundary conditions. According to the related formulas

the dimensionless buoyancy

leakage and friction torque of cylindrical spiral gas film were analyzed with the different operation conditions and groove structural parameters. Furthermore

part of the optimized structural parameters of spiral groove was proposed based on the comparison of the steady characteristics. It is indicated that the influence of pressure difference on the steady characteristic is more significant than the eccentricity ratio. The influence of the groove number(n) on the buoyancy is not obvious. The friction torque increases with the increase of the groove number but the leakage decreases to a stable value when n=12. The buoyancy decreases with the increase of the groove depth

which is opposite to the friction torque and leakage. With the increase of the seal width(L)

the leakage get stable at L=0.035 m. The increase of the spiral angle leads to the decrease of the buoyancy but the increase of the friction torque and leakage. The friction torque increases with the structural parameters under the pressure difference. The increase of the groove number leads to the decrease of the buoyancy

which is opposite to the influence of groove depth. The buoyancy decreases at L=0.04 m then increases with the increase of the seal width

which is opposite to the influence of spiral angle. The increase of the groove number and seal width lead to the robust decrease of the leakage. Optimized structural parameters are obtained: n=12-18

L=0.03-0.045 m

a=40°-50°.