Analysis of the characteristics of a squeeze film damper by three-dimensional Navier-Stokes equations: A numerical approach and experimental validation.

摘要

The squeeze film damper is widely used in turbomachinery due to its ability to reduce vibration, help transition through the critical speed (resonance) and diminish the force transmitted to the support frame. Instead of the commonly used Reynolds equation modeling technique, this dissertation employed the three-dimensional Navier-Stokes equations. These equations are coupled with a homogeneous cavitation model, Gumbel (π-film) or full Sommerfeld (2π-film) cavitation strategies in dealing with the flow field and pressure development in a squeeze film damper. The characteristics of the pressure distribution, velocity field, dynamic force and the associated damping and inertia coefficients were investigated by the parametric studies using either lubricant properties such as the gas concentration, viscosity and density or damper geometry.;The equation of motion for a rigid or flexible rotor model was employed in the stability analysis for the rotor-damper operating system. The dynamic coefficients were introduced into the equations to determine the rotor trajectory and stability through the source term. By analyzing the eccentricity, rotor deflection and transmissibility response, this dissertation has pointed to a methodology of finding the ‘preferred range’ of both one- and two-phase squeeze film dampers. Further, parametric studies on the rotor-damper system evaluate the effects of the lubricant dynamic viscosity, density, gaseous or vaporous cavitation, gas concentration, static eccentricity, whirling speed, rotor flexibility, retainer spring stiffness, the lumped mass distribution and the amount of imbalance. These parameters are necessary in optimizing the design of a damper.;Except for the analysis based on the equations of motion, the direct numerical simulation for the determination of the journal orbit was performed by the coupling of flow, grid deformation and stress module in CFD-ACE+. The close match of the two sets of results strengthened the confidence of the simulation results.;The experimental portion of this study was designed to validate qualitatively and quantitatively the numerical simulations in pressure distribution, cavitation visualization and the damper vibration. The damper vibration was measured by means of proximity sensors located circumferentially around the supporting frame; the pressure evolution was measured by pressure transducers and the gaseous and vaporous cavitation was visualized by both a digital camera with strobotac lighting and a high speed (5000fps) camera. The experimental results corroborated the theoretical analysis.