On the Adjusting of the Dynamic Coefficients of Tilting-Pad Journal Bearings

Abstract

This paper gives a theoretical and experimental contribution to the problem of active modiJication of the dynamic coefficients of tiltingpad journal bearings, aiming to increase the damping and stability of rotating systems. The theoretical studies for the calculation of the bearing coeficients are based on the fluid dynamics, specifically on the Rqrnolds equation, on the dynamics of multibody systems and on Premnted aa a Soclety of Triboiogists and Lubrication Engineers paper at the ASMEISTLE Tribology Conference in Lahaina, Hewaii, ~c t o b e r 16-20, 1994 Flnal manuscript approved August 3, 1994 some concepts of the hydraulics. The experiments are carried out by means of a test rig specially designed for this investigation. The four pads of such a bearing are mounted on fourflexible hydraulic chambers which are connected to a proportional valve. The chamber pressures are changed by means of the proportional valve, resulting in a displacement of the pads and a modification of the bearing gap. By changing the gap, one can adjust the dynamic coeficients of the bearing. With help of an experimental procedure for identihing the bearing coef/icients, theoretical and experimental results are compared and discussed. The advantages and the limitation of such hydrodynamic bearings in their controllable form are eualuated with regard to application on the high-speed machines. di,. hi, = damping and stiffness coefficient of oil film -d . . j;.. 'J' 'I = reduced damping and stiffness coefficients of the bearing h ( x , t ) = gap function kt, = hydrodynamic force on the equilibrium position k~ = membrane stiffness 4 = stiffness of the hydraulic chamber, membrane + oil P I~I P z X * P l y . P z Y = hydraulic pressure in each chamber p(%%t) = hydrodynamic pressure distribution Qxl QY = oil flow, hydraulic control 1 = time '+xL"_'Y = control voltage of the servo valve (% y.2) = coordinate system fixed on the pad z j = { A [ , A q , A t p A~p } T j , = displacement of the j th rotor-pad subsystem -4 = amplitude of the motion of the j th rotor-pad subsystem A = membrane area 6 ( 0 ) . E ( 0 ) = reduced damping and stiffness matrices of a tilting-pad journal bearing FpE = hydrodynamic force acting on the pad in the 5 direction s = { F Z F,q Fe Mpq }Ti, = perturbation force Fi = amplitude of the perturbation force = components of the force F, acting over the rotor in the F, and q directions = amplitude of the forces in the 5 and qdirection acting over the rotor = hydrodynamic momentum acting on the pad = pad radius = complex stiffness matrix of the j th rotor pad subsystem = oil volume in the chamber and pipes = inertial coordinate system = rotor displacement in the coordinate systems (X-Y) or (6-q) = pad angle = compressibility module of the oil = position angle of the j th pad = tilt motion of the j t h pad = oil viscosity = oil density = linear motion of the j th pad in the 5 direction = vibration amplitude of the rotor in the 5 and directions = supply pressure of the hydraulic control system = small translation and rotation of...

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Improving stability and operation of turbine rotors using adjustable journal bearings

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On the future of controllable fluid film bearings

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