Performance of Floating Seal Dam Compliant Foil Face Gas Seal under Different Foil-Dam Positions

Dry gas seal is widely used in the shaft seal of middle and high speed rotating machinery. However, when the shaft vibrated violently or the working conditions change obviously, the dry gas seal is liable to failure due to the brittle solid structure of the sealing ring which is easy to be rubbed and crushed. Besides, it is poor in heat dissipation. Therefore, it is difficult to adapt to extreme working conditions such as ultra-high speed, high temperature and high vibration. In order to solve the above problems, this paper presented a new type of compliant foil face gas seal with floating seal dam (FSD-CFFGS) which was based on gas foil thrust bearings and existing compliant foil face gas seal structure. The bump foil was set at the bottom of the rigid seal dam. When the film thickness or the working conditions were changed by disturbance, the sealing performance and the anti-impact ability of seal dam could be improved by adaptive floating. In addition, the bottom hollow structure formed by the bump foil was conducive to the heat dissipation of the foil area and the floating seal dam area, and could effectively avoid the heat crack of the sealing ring caused by the high temperature. Taking this as the research object, the theoretical model of elasto-aerodynamically coupling was established. The steady Reynolds equation was discretized by the finite difference method. After that, the convergent film pressure, foil deformation and film thickness distribution were solved by numerical method. Exploring the working principle and sealing mechanism of FSD-CFFGS under three kinds of foil-dam positions: the position of foil plane was higher than, equal to and lower than the position of seal dam plane and then the influence of supporting foil compliance coefficient on the film pressure, deformation and sealing performance was systematically studied. Comparing the opening force, film stiffness, leakage rate and stiffness-leakage ratio under different supporting foil compliance coefficients. Self-adaptability, opening performance and leakage control performance were considered comprehensively, the optimal range of supporting foil compliance coefficient and initial height difference between the position of foil plane and seal dam plane were determined. The results showed that FSD-CFFGS had good self-adaptability and sealing performance through the coordination of film pressure, film thickness, foil deformation and seal dam floating. when the position of foil plane was higher than the position of seal dam plane and the initial height difference was larger, the dynamic pressure effect of sealing fluid was significant and the opening performance was better. The larger the supporting foil compliance coefficient, the stronger the self-adaptability of FSD-CFFGS, but the worse the opening performance. Furthermore, the leakage rate increased with the increase of the supporting foil compliance coefficient of floating seal dam. When the initial height difference was between 1.5~2.5 μm, the supporting foil compliance coefficient of foil area was between 0.05~0.15, the supporting foil compliance coefficient of floating seal dam was between 1×10⁻⁵~1×10⁻³, FSD-CFFGS not only had certain self-adaptability but also could ensure good opening performance and leakage control performance. The research of this paper provided some theoretical guidance for the sealing performance evaluation and engineering design of FSD-CFFGS.