Modeling Of A Dynamic Nonlinear Rotor System With A Squeeze Film Damper

Rotor system is one of the core components of an aero-engine.Rotating at high speed,a small amount of mass unbalance and external interference may lead to greater unbalance response of the rotor system.Therefore,it is necessary to study the dynamic characteristics of a rotor-support system and to investigate the influence of nonlinear support structure on vibration behavior of a rotor system.Squeeze film damper(SFD)is a passive vibration control structure and an important component of the rotor support,which is mounted between the rotor and the casing for damping.In the high-speed operating state,the numerical simulation of squeeze film damper is difficult to ensure accuracy.The conventional calculation method of damper's oil-film force is deduced from the Reynolds equation based on the classical lubrication theory,ingoring the inertia effect of oil-film.However,with the increase of rotating speed,the Reynolds number increases subsequently.In particular,for high-speed rotor system,it is usually much larger than 1.Therefore,for high-speed rotor system,the influence of oil-film inertia should be considered during numerical simulation of squeeze film damper.A dynamic model of a Jeffcott rotor system is establishd,and the differential motion of equation for the rotor system is deduced using finite element method.On this basis,the calculation algorithm is programmed via Matlab,and verified by the ANSYS results.The expressions of dynamic pressure and velocity distribution of the finite length open-ended oil-film are derived.The fluid inertia terms in Navier-Stokes(NS)equation are retained,and the oil film inertia effect is introduced.On this basis,a new calculation model of oil-film pressure distribution is established to consider the effect of oil film inertia on oil-film forces,and the results of pressure are analyzed.The pressure distribution is solved by finite difference method.The reaction force of oil-film is obtained by numerical integration of the pressure field on the journal surface.To study the influence of squeeze film damper considering the fluid inertia on the rotor-support system,the calculation model of the rotor system considering the inertia effect of the oil film for transient and steady-state responses is established.In this model,Newmark-Hilber-Hughes-Taylor(Newmark-HHT)method is used to combine the oil-film force model with the dynamic calculation method of the rotor system.The transient responses of the rotor system is solved by iteration,and the results are analyzed.The results indicate that in the case of small eccentricity,the influence of viscous force makes the pressure distribution closer to a sinusoidal curve at a small Reynolds number,but for medium and large Reynolds numbers,the phase changes and the pressure curve is converted into cosine waveform.In the case of medium eccentricity,the difference of the results is mainly reflected in the magnitude of pressure at a small Reynolds number,while the shape and phase of the profile of the pressure curve are not affected.However,the temporal inertia is different in the curve profile,which shows that the convection inertia term will greatly affect the shape of pressure curve.When the eccentricity is large,the effect of convective inertia on the pressure is very significant even at a small Reynolds number,and the pressure distribution is sensitive to the fluid inertia.The change of Reynolds number will have a significant impact on the pressure distribution.The fluid inertia effect increases the radial component of oil-film force,but the tangential component is bascially not affected.The response amplitude considering oil-film inertia effect is reduced to a certain extent when compared with that of the system neglecting inertia effect.In addition,the increase of the inertia effect can reduce the response amplitude further.In conclusion,during high-speed operation with large Reynolds number,the influence of fluid inertia on vibration characteristics of squeeze film damper and the unbalanced response of rotor-support system cannot be ignored.