Vortex is an object that appears due to a gusty circular motion of liquid or gas. Any vortex motion is aimed at the energy isolation in a closed field by creating a dense boundary envelope. The vortices are classified into toroid vortex (or vortex ring) and spiral vortex. Toroid vortex is observed, when the flow pattern takes on the shape of a toroid. The spiral vortex appears as a result of rise of warmer liquid or gas or of descent of colder gas or liquid from the surface.
In any gas, force is a result of the pressure difference in two close layers. In case of interaction of a vortex with a flow the pressure difference is explained by the Bernoulli equation:
It follows from this equation that static pressure increases, when velocity decreases, and vice versa, static pressure decreases, when velocity increases. On one side of the vortex, the flow velocity is subtracted from the velocity of the vortex surface; therefore, the total velocity decreases, and pressure increases. On the other side of the vortex, the flow velocity is added to the velocity of the vortex surface; therefore, the total velocity increases, and pressure decreases. The force is directed towards the minimum pressure.