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The Coanda effect states that a fluid or gas stream will hug a convex contour when directed at a tangent to that surface. This was discovered in the 1930s by a Romanian named Henri-Marie Coanda. What is unusual about the Coanda effect is the fact that the fluid or gas flow is pulled so strongly by a curved surface. A concave curve will naturally push the flow, but the fact that a convex one would react so strongly to fluid or gas is unusual. This property is particularly relevant to aircraft design.
This principle was discovered and tested by Coanda on an airplane. He studied his aircraft for more than 20 years to prove that air along the wing of the plane will be deflected downward due to the wing's shape. The air leaves the wing, pushing the plane upward and giving it lift. This motion naturally results in a Coanda effect.
A Coanda effect can be applied to modern day aircraft as well. With a Coanda thruster, air is ejected from the front of the body and attaches to the surface before flowing toward an upper surface. Attached air that flows in a sheet is called a Coanda jet, which flows toward the back of the thruster. This results in the suctioning of a large amount of air from the surrounding atmosphere. Instead of positive air pressure on the front and negative pressure on the rear, the opposite of drag occurs, which is also known as thrust.
Another important application of a Coanda effect is in circulation control wing technology. A Coanda surface is formed from the short, flat surface of a levitating device. The goal of circulation control wing technology is to use the surface and slot blowing to replace the lift devices on the edges of a wing. The first use of this application was on a Boeing 707.
Since all applications of a Coanda effect involve a fluid object flowing over a solid one, the science behind this effect is known as fluid dynamics. Fluid dyanamics represents the motion of liquids or gases. Studying this science can lead to many consequential discoveries like the Coanda effect.