Bagnold number

The Bagnold number, named after Ralph Alger Bagnold, used in granular flow calculations, is defined by

<math>Ba=\frac{mD^2\gamma}{2\gamma_e\mu}</math>

where <math>m</math> is the mass, <math>D</math> is the grain diameter, <math>\gamma</math> is the surface tension and <math>\mu</math> is the interstitial fluid viscosity.

Bagnold conducted experiments with 1 mm wax spheres suspended in a glycerin-water-alcohol mixture were sheared in a coaxial cylinder rheometer. The rheometer was cleverly designed to measure both the shear and normal forces applied to the walls. He identified two distinct flow regimes: the macroviscous and the grain inertia. These regimes can be distinguished using a quantity that is now referred to as the Bagnold number.

External links

• Granular Material Flows at N.A.S.A

bs:Bagnoldov broj