Fr.: hélicité cinétique
In fluid mechanics, a quantity that describes helical flow. It is defined by the integrated scalar product of the velocity field and the → vorticity: KK = ∫ dVu . (∇ x u). In the absence of magnetic field, this quantity is conserved by the → Euler equation. See also → magnetic helicity.
Fr.: hélicité magnétique
A quantity that measures the extent to which the magnetic field lines wrap and coil around each other. It is closely related to field line topology. Magnetic helicity is defined by: HM = ∫ A . B dV, where A is the vector potential of the magnetic field and the integration is over a volume V. → helicity; → kinetic helicity