Effect Of Film Inertia On The Film Force Of Damper Bearing

Reducing shaft Weight and using elastic bearing are a main technology for increasing shaft speed, making machines work under super-criticality. Since squeeze film damper bearings (SFD bearings) have excellent damping, they in various damping methods for bearing high speed shafts have the widest application. In dynamic design of high speed rotor-bearing system, dynamic coefficients of SFD bearings are basis ones for calculating the stability, critical speed and unbalance response of the rotor-bearing system. Continuous increase of machine working speed and use of low viscosity oil have made fluid inertia affect film-dynamic characteristics more and more evidently. Under such a situation, practice shows that effects of fluid inertia must be considered to analyze film-dynamic coefficients. This brings out a research topic that based on considering effects of fluid inertia, film-dynamic characteristics of SFD bearings are studied.Navier—Stokes equation (N—S equation) of fluid dynamic mechanics shows that velocity profile of the bearing film is a foundation for studying film dynamic characteristics. From a N—S equation that contains fluid inertia terms, based on three dimension Navier—Stocks equation, present work develops a mathematical model for numerical calculation of inertia velocity profiles of squeeze film damper bearings (SFD). The studies effects of fluid inertia on film velocity profile, and non-linear problem in the N—S equation is solved by successfully using linear recursive method, developing an inertia profile of film velocity. The profile shows the effects of fluid inertia on film velocity. The calculated results show that SFD inertia velocity profiles along radial direction are parabola distribution. When Reynolds number and radial eccentricity are small (Re 8,0.35), effects of fluid inertia on film velocity profiles are not large. Therefore, under the above conditions, traditional inertialess velocity profile is reasonable. However, with increases of Reynolds number and the eccentricity, tluid inertia action becomes large and ingluences film velocity profiles greatly. Thus, for the conditions of large Reynolds number and eccentricity, traditional inertialessvelocity profile is not reasonable. Numerical calculations show that when time step length t reaches to 0.006, the algorithm developed by present work is still stable and convergent. And with the increase of t, convergent speed rapidly increases. For Navier—Stocks equation, present work develops inertia velocitiy profile of short SFD for the first time.Numerical calculation show that the developde profile is reliable and correct.Based on the inertia profile, this paper studies effects of fluid inertia on film dynamic coefficients. The study overcomes the drawback that the influence of fluid inertia on film velocity is neglected in traditional theory. A new film dynamic coefficient model for short SFD bearings are developed.Experimental results show that the new model is evidently better than the traditional theory of analyzing film coefficients, especially improving analysis theory of film damping force. The new model shows in theory non-linear relation between film damping force and oil viscosity, solving the contradictory between the traditional theory and experimental data in large Reynolds number. The research based on the inertia profile confirms that in large Reynolds number, it is not reasonable that traditional theory relies on non-inertia velocity profile (that is effects of fluid inertia on film dynamic coefficients is studied under neglecting the influence of fluid inertia on film velocity). In large Reynolds number, traditional theory will cause large errors for analyzing film coefficients.For centred, circular whirl in SFD bearings, present work develops a improved Reynolds equation based on the three-dimension N—S equations. The improved Reynolds equation contains effects of fluid inertia.Using the improved equation, this paper studies film dynamic properties from long short SFD bearings, developing mathematics models for film dynamic coefficients.Experimental data and numerical analysis show that the models are correct. The analysis develops a new way for studying film dynamic properties.