Characteristic Number on Bearings

It is also called sommer field number.

The Sommerfeld Number is

S = \left( \frac{r}{c} \right)^2 \frac {\mu N}{P}

Where:

S is the Sommerfeld Number or bearing characteristic number
r is the shaft radius
c is the radial clearance
μ is the absolute viscosity of the lubricant
N is the speed of the rotating shaft in revs/s
P is the load per unit of projected bearing area

... or:

Sommerfeld number> 1 occurs in heavily loaded bearings at the
limit for b/d: 0 < b/d ≤ 2

Sommerfeld number < 1 occurs in high speed bearings at the
limit for b/d: 0.5 < b/d ≤ 2

d : bearing diameter
b : bearing width