The Coanda Effect

The Coanda effect is a convincing explanation for the lift of an aircraft wing. It is the tendency for a stream of fluid, such as air or water, to cling to nearby surfaces. The effect is sometimes wrongly used to explain some phenomena. To illustrate the effect try the demonstration pictured below, yourself.

If you use a straw to blow across the side of a jar the jet clings to the side and curls around it. You can see that the dimple on the water, in picture 1, is below the jar.

Picture 1

In the same way the stream of air clings to the paper in picture 2. The paper lifts because the stream of air clinging to the surface is deflected down and the opposite reaction force pushes the paper up.

Picture 2  The stream of air lifts the paper

The Coanda Effect is the tendency of a stream of fluid (liquid or gas) to cling to a surface. First demonstrated by Thomas Young in 1800 in the same way as shown in the first picture (thanks Wikipedia) but more systematically recognised and used by Henri Coanda in about 1910.

There is a greater in depth explanation in the video below.