## dimensionless group

(Also nondimensional number, dimensionless number.) A dimensionless combination of several physical variables (e.g., velocity, density, viscosity), usually with a physical interpretation.

Dimensionless groups arise naturally in the scale analysis of equations. The sixth edition of the McGraw–Hill Encyclopedia of Science and Technology lists 12 pages of dimensionless groups.

*See*Boussinesq number, Cauchy number, Grashoff number, Mach number, Nusselt number, Péclet number, Prandtl number, Rayleigh number, Richardson number, Rossby number, Strouhal number, Taylor number;*see also*dimensional analysis, similarity theory, Buckingham Pi theory.