Bernoulli's theorem is a law which quantitatively shows the relationship among the velocity, pressure and height of flowing fluid, and is induced from the fact that the sum of the potential energy and the kinetic energy of a fluid is constant in the case that the fluid is an ideal fluid that is inviscid and incompressible and flows regularly. Bernoulli's theorem states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure and vice versa. In modern everyday life there are many observations that can be successfully explained by application of Bernoulli's theorem.
FIG. 1 shows an aircraft wing as a typical example of the application of Bernoulli's theorem, wherein in a sectional view, the wing has a bottom surface formed in the shape of a straight line and a top surface formed in the shape of a curve that is concave upwards. In other words, the same fluid flows on a first point where the wind is first applied to the wing and a last point where the fluid gathers again. In order to reach a same point in a same time, air on the top surface of the wing has to move a relatively longer distance that air on the bottom surface of the wing so that the air on the top surface of the wing increases in velocity rather that the air on the bottom surface.
Then, due to the difference in velocity, the pressure on the surfaces of the wing will be relatively lower above than below and this pressure difference results in an upwards lift force, which enables the aircraft to lift.
However, a general aircraft wing using Bernoulli's theorem as discussed above is in close relationship with the generation of lift force that enables the aircraft to lift, but has nothing to do with the thrust increase operations of transfer means such as vehicles and ships except aircraft.
FIG. 2 is a view for explaining the vortex flow of cavity flow that is generated in a flow station.
FIG. 3a shows a state that the flow of a fluid rotates in position and generates an unstable vortex flow when the fluid flows forwards, and FIG. 3b shows a state that the flow direction of a fluid may be stably induced in a direction as desired by a user in the case that a change in angle is applied to the flow of the fluid at a side.