In fluid mechanics, Helmholtz's theorems, named after Hermann von Helmholtz, describe the three-dimensional motion of fluid in the vicinity of vortex lines.
These theorems apply to inviscid flows and flows where the influence of viscous forces are small and can be ignored.
Helmholtz's three theorems are as follows:[1] Helmholtz's theorems apply to inviscid flows.
In observations of vortices in real fluids the strength of the vortices always decays gradually due to the dissipative effect of viscous forces.
However Helmholtz's theorems were published in 1858,[3] nine years before the 1867 publication of Kelvin's theorem.