A vortex is a portion of fluid rotating about an axis line. Vortexes or vortices exist in nature in a number of forms such as tornadoes, hurricanes, whirlpools, etc. A vortex can also be observed in real life easily by spinning a water bottle, draining the sink, swirling the cup of tea, etc.
The Shape of a Vortex
A vortex is wider on the top and narrows gradually while moving towards the bottom. This is because of the pressure difference. The pressure is less on the top and is maximum at the bottom. The direction of a vortex is generally determined by the Coriolis effect.
Formation of a Vortex
A vortex is generally formed when there exists a significant difference in the fluid speed. The difference in velocity develops a sheer force that swirls the water around. The swirling water maintains its angular momentum by continuously rotating around a central point while simultaneously losing a portion of energy due to the force of friction existing between the moving and the stagnant water. For instance, if you dip a ceramic or metallic plate into the pool of water and push it forward along a straight line, a vortex or multiple vortexes get formed. This is because the water that comes in contact with the plate experiences motion and the water present away from the plate remains still. The water around the boundary of the plate tends to move forward and get pushed around the sides. At the same time, the water present on the back of the plate gets sucked in the forward direction. Now, even if you remove the plate, the water in motion keeps spinning and forms vortexes that are easily visible to the naked eyes. The two vortexes formed as a result move forward at the same speed and contain a curved line of axis. This means that both the vortexes are connected to each other and form a half-ring of the vortex. A piece of matter added to one vortex ring gets transferred to the other vortex ring. According to Helmholtz law, a vortex line cannot start or end in a fluid. This means that a vortex ring either gets closed in a loop or at two separate boundary points. Similarly, in the case of gases, fast wind moving over the slow wind is responsible for the formation of vortex smoke rings, hurricanes, or other types of vortexes in the air.
Spinning Speed of a Vortex
The spinning speed of a vortex is higher at the bottom as compared to the top. This is because the vortex is wider on the top and narrows while moving towards the bottom. The fluid present at the bottom tends to move in a narrow circular pathway, which is why it must have a high number of rotations per minute to match the speed of the fluid rotating about the same axis on the top of the vortex.
Applications of a Vortex
The principle of a vortex serves to be the basis of the construction of a number of appliances such as a washing machine, milk/cream separators, etc. The concept of the vortex is also used in the medical and defence domain to run various tests on a blood sample and to design special suits for fighter jet pilots. Fighter jet pilots usually undergo sharp curves and turn at high speed. This throws the blood towards the outer boundary of the vessels, which might cause severe medical conditions.