Influence of leakage flow through labyrinth seals on rotordynamics: numerical calculations and experimental measurements

Abstract

An extensive investigation of the influence of the leakage flow through a labyrinth seal at supply pressure of 12 bar on the rotordynamics was performed by using numerical calculations and experimental measurements. Toward this end, an experimental rotor setup was established in Shanghai Jiao Tong University. Two labyrinth seals were chosen for comparison, e.g., an interlocking seal and a stepped one. The numerical calculations based on the bulk-flow theory and the perturbation analysis were accomplished. Simultaneous acquisitions of the fluctuating static pressure at the stator wall and the displacement of the whirling rotor were made. The influence of the aerodynamic forcing on the rotor was analyzed in terms of the axial distribution of the mean static pressure, the circumferential distribution of the fluctuating pressure, the fist critical speed and the destabilization rotating speed of the rotor. The experimental results demonstrated that the sinusoidal distribution of the fluctuating static pressure on the stator wall was closely related to the whirling motion of the rotor. The first critical speed of the rotor was reduced by the aerodynamic forcing, resulting in intensified destabilization of the rotor system. Furthermore, the numerical analyses were in good agreement to the experimental measurements. List of symbols AUnsteady cross-sectional area of the cavity (m 2 ) A n Steady annular flow area (m 2 ) [C]Damping matrix C 0Orifice contraction coefficient C 1 Kinetic energy carry-over coefficient C r Steady radial seal clearance (m) C x x , C yy Damping coefficients (N-s/m) C xy , C yx Cross-couple damping coefficients (N-s/m)

A nonlinear model of flow-structure interaction between steam leakage through labyrinth seal and the whirling rotor

“…The unsteady static pressure in cavities of the interlock seal, which was numerically calculated by employing perturbation analysis, was demonstrated to be in favorable agreement with experimental measurements by Liu et al [10]. The above-mentioned linear model was reduced from a preconditioned track of the whirling rotor, which slightly deviates from the statically balanced position; otherwise, the nonlinear behaviors of the whirling rotor, e.g., lock-on frequency and kick amplitude, could not be accurately captured by the linearized force-displacement model [2][3][4][9][10][11]. Hua et al [12] and Cheng et al [13] carried out nonlinear analysis of the rotordynamics associated with leakage air flow through a simple annular seal by using the Muzynska model [14].…”

“…Subsequently, the rotordynamics coefficients associated with the leakage air flow through various labyrinth seals were numerically determined, e.g., the straight-through seal [1, 2, 7 and 8], the stepped seal [3,4] and the honeycomb seal [9]. The unsteady static pressure in cavities of the interlock seal, which was numerically calculated by employing perturbation analysis, was demonstrated to be in favorable agreement with experimental measurements by Liu et al [10]. The above-mentioned linear model was reduced from a preconditioned track of the whirling rotor, which slightly deviates from the statically balanced position; otherwise, the nonlinear behaviors of the whirling rotor, e.g., lock-on frequency and kick amplitude, could not be accurately captured by the linearized force-displacement model [2][3][4][9][10][11].…”

Influence of steam leakage through vane, gland, and shaft seals on rotordynamics of high-pressure rotor of a 1,000 MW ultra-supercritical steam turbine

“…The in-depth evaluation of the rotordynamics of the high-pressure rotor of a 1,000 MW ultra-supercritical steam turbine associated with steam leakage through labyrinth seals was made according to the first critical speed, ω cr , and the logarithmic decrement of the rotor vibration, δ, which was determined from Eq. (11). The destabilization of the rotor system associated with steam flow through the labyrinth seals is fundamentally analyzed in terms of the radial force and the frictional force, which are the major components of the aerodynamic forcing on the rotor.…”

“…The destabilization of the rotor system associated with steam flow through the labyrinth seals is fundamentally analyzed in terms of the radial force and the frictional force, which are the major components of the aerodynamic forcing on the rotor. The radial force entails deformation of the rotor and is equalized by the elastic force of the rotor, while the frictional force accelerates the whirling motion of the rotor [11]. When the positive work exerted on the rotor by frictional force is larger than the dissipation energy consumed by the external damping force, destabilization of the rotor is triggered [12].…”

Computation of rotordynamic coefficients associated with leakage steam flow through labyrinth seal

“…Further more, a set of differential equations were employed to allow the clear flow structure of the leakage air flow through a straight-labyrinth seal [13,14]. Recently, Liu et al [15] convincingly demonstrated deterioration of the rotor stability due to aerodynamic forcing of the leakage air flow through an interlocking labyrinth seal. Recall that the major concern of most previous experimental and numerical endeavors was related to leakage air flow through labyrinth seal.…”