Journal Bearing Sommerfeld Number & Film Thickness Calculator

Determine dimensionless Sommerfeld number (S), journal eccentricity ratio (ε), and minimum hydrodynamic oil film thickness (h0) per Raimondi-Boyd.

Bearing Geometry & Operating Load

Journal Diameter D (mm):

Bearing Length L (mm): L/D Ratio = 1.0 (Standard)

Radial Clearance c (μm): Typical: ~0.75 - 1.0 μm per mm diameter

Shaft Speed N (RPM):

Radial Static Load W (kN):

Dynamic Viscosity μ (cP / mPa·s): ISO VG 46 at ~50°C: ~22 cP

Hydrodynamic Film Performance

Sommerfeld Number (S):

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Eccentricity Ratio (ε):

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Min Film Thickness (h₀):

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Mean Bearing Pressure (P):

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Lubrication Regime Status:

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Frequently Asked Questions

What is the Sommerfeld number in hydrodynamic lubrication?

The Sommerfeld number S is a dimensionless parameter that characterizes the hydrodynamic performance of journal bearings, combining bearing geometry (R/c), lubricant viscosity, shaft rotational speed, and specific unit load.

What is an acceptable minimum oil film thickness (h0)?

In high-speed turbomachinery, minimum oil film thickness h0 should generally exceed 15 to 25 μm to avoid contact with surface roughness asperities and particulate contamination. Values below 8–10 μm risk wipe-out and catastrophic bearing seizure.

What is the eccentricity ratio (ε)?

The eccentricity ratio ε = e/c is the distance between the shaft center and bearing center divided by radial clearance. As load increases or speed drops, ε approaches 1.0 as the shaft sinks closer to the bearing wall.