Sommerfeld Number


In the design of fluid bearings, the Sommerfeld number (S), or bearing characteristic number, is a dimensionless quantity used extensively in hydrodynamic lubrication analysis. The Sommerfeld number is very important in lubrication analysis because it contains all the variables normally specified by the designer.

The Sommerfeld number is named after Arnold Sommerfeld (1868–1951).

Related formulas


SSommerfeld Number or bearing characteristic number (dimensionless)
rshaft radius (m)
cradial clearance (m)
μabsolute viscosity of the lubricant (pascal*s)
Nspeed of the rotating shaft (1/s)
Pload per unit of projected bearing area (N/m2)