Virvellegemene

Virvellegemene is a term used in fluid dynamics to describe an idealized, localized region of rotating fluid that functions as a single vortex element within a larger flow. It is characterized by a finite circulation Gamma around its core and a finite core size to avoid singularities in the mathematical description. In vortex methods, the flow is represented as a set of virvellegemene whose velocity field is obtained by summing the Biot–Savart contributions of all elements. Physically, a virvellegeme does not correspond to a solid body; it is a region in the fluid with concentrated vorticity that can translate and deform under the influence of other elements and boundaries.

The main properties include circulation, core radius, and position. Interaction laws derive from fluid dynamics; the motion of each virvellegeme is influenced by the velocity field produced by others and by external boundaries. Conservation of circulation and vorticity is a guiding principle in inviscid approximations, while viscosity in real fluids leads to diffusion and decay of vorticity over time.

Uses include numerical simulation of incompressible flows, wake modeling behind wings (vortex particle methods), and pedagogical illustrations of vortex interactions. Limitations include the idealized nature of a point-like or finite-core vortex; singularities in pure line-vortex models; dependence on smoothing lengths and discretization.

Etymology: Dutch virvel = vortex; legeme = body. See also vortex, Biot–Savart law, vortex method.