The exit pressure boundary was determined by Chen's real gas equation of hydrogen and choked flow condition of gas exit speed reaching to the sound speed. Then

dynamic characteristics of spiral groove dry gas seal (S-DGS) at various operating parameters was analyzed by perturbation method

and compared to those of ideal gas and coercive exit pressure boundary models. The results show that real gas and choked flow effects should be taken into account for studying dynamic characteristics of S-DGS at high pressure. Both effects reduced direct stiffness coefficients of hydrogen S-DGS but increased direct damping coefficients. The influence of these two effects on dynamic gas film stiffness gradually enhanced with the increase of squeeze number and inlet pressure. In addition

when frequency ratio was varied

these two effects had a significant influence on gas film dynamic stiffness but minimal influence on gas film dynamic damping. Compared to models of ideal gas and coercive pressure boundary condition at the studied operating circumstance

these two effects caused three gas film dynamic damping coefficients (Czz

Cαα

Cαβ) by mean standard deviations of 2.28%

1.93%

2.79% when squeeze number is variable and 4.08%

2.07%

1.82% when inlet pressure is variable.