热耗散变形下干气密封角向摆动稳定性的研究

Analysis on the angular wobble of a dry gas seal system with thermal dissipation

干气密封系统角向摆动对密封端面造成磨损和影响密封的稳定性,通过数值求解和试验测试来探究密封角向摆动的稳定性规律。基于非线性振动理论,建立了气膜-密封环系统角向摆动模型,同时考虑热耗散变形对气膜厚度和刚度的影响。将气膜刚度和阻尼表示为含有摆角的多项式变量代入振动方程并设置无外激励,利用Floquet指数对非线性振动微分方程进行求解。在热耗散变形下的螺旋角为75°48'32″和无热耗散变形下的螺旋角为75°42'55″时,密封将会发生Hopf分岔,表明考虑热耗散变形下系统稳定运行时的螺旋角范围更大,热耗散变形对螺旋角和分岔点位置有一定影响。选取75°50'和75°两种螺旋角测试热耗散变形下角向摆动对密封端面和泄漏量的影响,发现考虑热耗散变形下螺旋角75°50'的干气密封端面擦痕严重,泄漏量不断增加,无法稳定,相比较螺旋角75°的泄漏量更大,说明热耗散变形对干气密封角向摆动有一定的影响,为干气密封的动态优化设计提供了理论指导。

The contact and wear between seal faces were caused by the angular wobble of a dry gas seal system and then will influence the stability,therefore,both the theoretical calculation and experiment were applied to study the stability. According to the theory of nonlinear vibration in consideration of the heat dissipation effect on the gas film thickness and stiffness,an angular wobble model of the gas film-sealing ring system was set up. In specific cases,the gas film stiffness and damping were expressed as multiple variables involving the wobby angle in order to obtain the differential equation of nonlinear vibration. Without external incentives,the system bifurcation was found through the Floquet index,and the influence of spiral angle of dry gas seal on the system stability was analysed. The hopf bifurcation will occur when the spiral angle reaches 75° 48＇ 32″ in consideration of thermal dissipation deformation and the spiral angle 75° 42＇ 55″without consideration of thermal dissipation deformation. The spiral angle stable ranges were acquired for the cases of under thermal dissipation or non-thermal dissipation. The spiral angle range to stabilize the system under heat dissipation and deformation is larger than that of no heat dissipation,which indicates that changes will happen for the bifurcation when considering the heat dissipation and deformation. Finally,the spiral angle 75°50＇and 75° were chosen to process the specimen and an experiment was designed to observe the effect of angular wobble on the sealing faces and leakage. The dry gas seal with 75°50＇ spiral angle presents a bad serious abrasion face and continuall leakage. The experimental results were compared with those of the theoretical calculation to show that the spiral angle has certain interference on the sealing stability under thermal dissipation deformation,which provides a theoretic guidance for optimizing the dynamic design of dry gas seals.