Dynamics of rotors on hydrodynamic bearings

Rob Eling Mitsubishi Turbocharger & Engine Europe

Comsol Conference, October 24, Rotterdam, NL

Rotors on hydrodynamic bearings

The problem: instability of the rotor-bearing system

Fluid

Shaft

Pressure

X

Y

X XXX XY

Y YYX YY

F FK K

X Y

F FK K

X Y

Modeling approach

Fluid dynamics

Rotordynamics

Thermodynamics

Modeling approach

Analysis of the rotor Analysis of the hydro-

dynamic bearings Analysis of the coupled

rotor-bearing system

Analysis of the rotor: modal analysis

Analysis of the rotor: reduction

un

θn vn ψn

kij cij kij cij

75.000 volume elements 10 beam elements

Analysis of the bearing: thin film approach

CFD analysis: Comsol Thin Film Module: Assumptions always need to be checked

dp

dt

Vg

3 31( )

2 12 12

h p h ph hU

t x x x z z

Coupling

u,v u,v

h(ex1,ey1) h(ex2,ey2)

ex1,ey1

Bearing 1 Bearing 2

ex2,ey2

Analysis of the coupled rotor-bearing system: the effect of unbalance

Analysis of the coupled rotor-bearing system: sub-synchronous vibrations

0 500 1000 1500 2000

400

600

800

1000

1200

1400

1600

1800

2000

Frequency [Hz]

Waterfall plot of shaft displacement on the bearing location

Rota

tion s

peed [

Hz]

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1x 10

-5

Conclusions

• Rotors on hydrodynamic bearings show self-induced vibrations due to fluid-structure interaction

• The response of the non-linear rotor-bearing system can be analyzed using run-up simulations over the full operating range, and shows many interesting/dangerous non-linear vibration phenomena