Rotordynamic Performance of the Interlocking Labyrinth Seal With a Tilting Rotor

The interlocking labyrinth seal leaks less due to its more tortuous flow path compared with the conventional see-through labyrinth seal designs. Meanwhile, shaft misalignment between the stator and the rotor exists in most rotational machines. Rare publications studied the rotordynamic performance of the interlocking labyrinth seal, particularly with consideration of different shaft misalignments due to a tilting rotor. Numerical analysis model of an interlocking labyrinth seal, including 6 seal cavities and 7 seal teeth (3 teeth on the rotor, 3 teeth on the stator), is established for studying the effect of tilting rotor on its rotordynamic characteristics. The dynamic characteristic identification method based on infinitesimal theory is applied to solve the dynamic force coefficient of the annular seal with arbitrary elliptical orbits and eccentric positions under field conditions. The paper investigated the dynamic characteristics of the interlocking labyrinth seal with various misalignment angles (θ = 0, 0.1°, 0.2°, 0.3°, 0.4°, 0.5°, 0.6°), different pressure ratios (P_in = 6.9 bar, PR = 0.5, 0.8). Results show that the tilting rotor could minimize the leakage of the interlocking labyrinth seal, and a higher pressure ratio shows a more obvious effect. When the misalignment angle θ = 0.6°, the mass flow rate can be reduced about 2.5%. The tilting rotor causes the geometric deformation of the interlocking labyrinth seal cavity and the changes in the seal radial clearance, which results in an increasing pressure drop. Each seal cavity has a different effect on the system stability. The seal cavity with the inlet close to the rotor and the outlet away from the rotor helps to improve the system stability, otherwise, the system stability will be reduced. The cross-coupled stiffness coefficients of the cavity C1, C2 and C3 are negative, which improves the stability of the system. While they become to be positive for C4, C5, C6, and the system stability will be reduced. The direct damping coefficient, cross-coupled stiffness coefficient, and effective damping coefficient of the entire interlocking labyrinth seal increase as the misalignment angle goes up. The effective damping coefficients for all studied whirling frequencies are positive, and decreases with increasing whirling frequencies. The effective damping coefficient also shows a high frequency-dependent variation for low whirling frequency (<~160Hz). And it almost keeps a constant when the whirling frequency is more than 160Hz. The tilting rotor or shaft misalignment behavior is beneficial to the stability of the interlocking labyrinth seal.