TourTourHydrodynamic journal bearing

 
 Diameter shaft D 10-3 m
 Bearing length L 10-3 m
 Diametric clearance ΔD  10-6 m
 Rotational speed n rpm
 Minimum film thickness h0 10-6 m
 Viscosity η Pa·s
 Density ρ 103 kg/m3
 Specific heat capacity c 103 J/(kg·K)
   
 Bearing length number L /D
 Clearance number D/ΔD
 Eccentricity ratio ε = (ΔR-h0)/ΔR
 Sommerfeld number So
 Attitude angle β
 Flow number Cq
 Friction number μ(R/ΔR)
 Coefficient of friction μ
 Load capacity F 103 N
 Stiffness S = - dF/dh 106 N/m
 Power loss N W
 Side leakage Q 10-6 m3/s
 Frictional heating dT K
 
Contour plot of the hydrodynamic pressure projected on the film contour. The maximum pressure occurs in the converging part of the film while cavitation pressure manifests in de diverging part of the film.

Hydrodynamic journal bearings become unstable with small shaft eccentricity. It's the reason that high speed or relatively low loaded hydrodynamic bearings are to be designed less stiff. Sometimes lemon bore or multi lobe bearings might be an option. These bearings behave stable even with small shaft eccentricity.

The frictional heating is calculated assuming adiabatic boundary conditions for the bearing, i.e. power loss N is drained with the fluid flow Q through the bearing.
 
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