Abstract:

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 (C_zz, C_αα, C_αβ) 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.

Key words: spiral groove dry gas seal, dynamic characteristics, real gas, choked flow, numerical analysis

摘要：

以Chen等提出的氢气实际气体状态方程描述氢气的实际气体行为，以气体出口速度达到音速作为产生阻塞效应的条件，确定出口压力边界条件，采用小扰动法分析了干气密封操作参数对螺旋槽干气密封动态特性的影响规律，并与理想气体、强制出口压力边界模型中的动态特性系数进行了对比。结果表明：研究高压螺旋槽干气密封的动态特性时应当考虑实际气体效应和阻塞流效应。两种效应使氢气螺旋槽干气密封的直接动态气膜刚度减小，使直接动态气膜阻尼增大。随着压缩数、进口压力的增大，两种效应对动态气膜刚度的影响逐渐增强。以频率比为变量时，两种效应主要影响气膜刚度，对气膜阻尼的影响作用较小。针对所研究的工况，与理想气体和强制压力出口边界条件相比，考虑实际气体效应和阻塞流效应，以压缩数为变量时，动态气膜阻尼（C_zz、C_αα、C_αβ）的平均偏差分别为2.28%、1.93%、2.79%；以进口压力为变量时，3种气膜阻尼的平均偏差分别达到4.08%、2.07%、1.82%。

关键词: 螺旋槽干气密封, 动态特性, 实际气体, 阻塞流, 数值分析