wervelstroom

Wervelstroom is a Dutch term used in physics and engineering to describe two related phenomena characterized by circular or spiral motion. In one sense, it denotes eddy currents: loops of electrical current induced within conductors by changing magnetic flux. When a conductor is exposed to a varying magnetic field—such as a moving magnet or an alternating current in nearby coils—Faraday's law predicts the formation of closed current loops. According to Lenz's law, these currents produce magnetic fields that oppose the change that created them. Eddy currents cause energy loss in the form of heat and can produce magnetic braking or drag. They depend on the material's electrical conductivity, thickness, geometry, and the rate of magnetic flux change; at higher frequencies the skin effect confines currents to the surface.

In another sense, wervelstroom also describes vortical or circular flows of fluids or gases. These eddies arise behind obstacles, at shear layers, or in turbulent wakes. They transport momentum and heat and can affect mixing, drag, and noise. The size and strength of vortices depend on the flow velocity, viscosity, and the Reynolds number; they tend to decay over time and interacting eddies can form complex turbulent structures.

Applications include eddy current testing for nondestructive evaluation, where induced currents reveal defects in conductive parts; induction heating and magnetic braking; and flow control or analysis in hydrodynamics and meteorology. Although the same term is used, eddy currents and fluid eddies describe different physical mechanisms—one electromagnetic, the other mechanical—sharing the common feature of circulating motion.