Investigation on the Leakage and Static Dynamic Characteristics of Rotating Seals at High Eccentricity Ratios

To evaluate the influence of rotating annular seal with eccentric rotor on the operation efficiency and stability of turbomachinery, a novel 3D mesh generation method and a numerical approach were adopted to solve the static gas response forces and static stiffness coefficients for the rotating annular seal at high rotor eccentricity ratios based on the mesh deformation technique and steady RANS solutions. An investigation on the leakage and static destabilizing characteristics of rotating annular seal at high rotor eccentricity ratios was conducted. The leakage flow rate, static gas response (exciting) forces, static stiffness coefficients and flow field characteristics of a fully-partitioned pocket damper seal (FPDS) were computed at three pressure ratios (0.17, 0.35, 0.50), two inlet preswirl ratios (0, 0.5) and seven eccentricity ratios (0.0,0.1,0.3,0.5,0.7,0.8,0.9). The results showed that the leakage flow rate increases with the eccentricity ratio. The rotor eccentricity and inlet preswirl result in a significant destabilizing cross-coupling stiffness, which may give rise to a risk of rotor whirling instability. The FPDS has a positive static direct stiffness as long as it operates at subsonic exit flow conditions, no matter the eccentricity ratio is high or low. For the choked exit condition, the FPDS shows negative static direct stiffness at low eccentricity ratios and then crosses over to positive value at the crossover eccentricity ratio 0.5, following a trend indicative of a parabola. The negative static direct stiffness may result in a full rotor eccentricity and rapid wear of seal due to rubbing contact. © 2017, Editorial Office of Journal of Xi'an Jiaotong University. All right reserved.