A NUMERICAL PROCEDURE FOR INVESTIGATION OF IMPACTS OF ROTORS SUPPORTED BY CAVITATED LONG FLUID FILM BEARINGS AGAINST THE STATIONARY PART

Abstract eng:
The rotor systems consit of two principal components, of a rotor and of a stationary part, and the fluid film bearings are often used as coupling elements. As the clearance between the discs and the casing is usually very narrow, excessive lateral vibration of the rotor can produce impacts between the discs and the housing. Because up to now influence of the fluid film bearings and the impacts on the rotor behaviour has been investigated separately, it is desirable to develope a procedure which would make possible to analyze their mutual interaction. Into the mathematical models both the hydrodynamic bearings and the contacts are implemented by means of nonlinear force couplings. To determine the contact forces a Hertz theory is applied. The hydrodynamic forces depend on the pressure distribution in the oil film. As the bearing gap is very narrow a classical theory of lubrication can be used for this purpose. If pressure at some location of the bearing gap should drop below a critical level, a vapour cavitation occurs. In the noncavitated part of the lubricant layer the pressure distribution is governed by solution of the Reynolds equation and in the cavitated region it remains constant. The developed procedure for determination of the pressure distribution in the oil film satisfies the continuity of flow through the inlet and outlet edges of the cavitated area. Components of the hydraulic force are calculated by integration of the pressure distribution along the bearing lenght and circumference. For solution of the equation of motion a modified Newmark method is adopted. Applicability of the developed approach has been tested by means of computer simulations.

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