✅ OpenFOAM - Units Tutorial

OpenFOAM – Units

Written by cfd.ninja

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March 19, 2020

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Source: CFD Direct

Dimensional units

In continuum mechanics, properties are represented in some chosen units, e.g. mass in kilograms ( $kg \relax \special {t4ht=$ ), volume in cubic metres ( $3 m \relax \special {t4ht=$ ), pressure in Pascals ( $−1 −2 kgm s \relax \special {t4ht=$ ). Algebraic operations must be performed on these properties using consistent units of measurement; in particular, addition, subtraction and equality are only physically meaningful for properties of the same dimensional units. As a safeguard against implementing a meaningless operation, OpenFOAM attaches dimensions to field data and physical properties and performs dimension checking on any tensor operation.

The I/O format for a dimensionSet is 7 scalars delimited by square brackets, e.g.

[0 2 -1 0 0 0 0]

No.	Property	SI unit	USCS unit

1	Mass	kilogram (kg)	pound-mass (lbm)
2	Length	metre (m)	foot (ft)
3	Time	— — — — second (s) — — — —
4	Temperature	Kelvin (K)	degree Rankine ( $∘ \relax \special {t4ht=$ R)
5	Quantity	kilogram-mole (kgmol)	pound-mole (lbmol)
6	Current	— — — — ampere (A) — — — —
7	Luminous intensity	— — — — candela (cd) — — — —