Science -- Your Future, Scotland's Future
SCI-FUN Roadshow Exhibits -- Coanda Effect
In this exhibit you learn about how moving air clings to curved surfaces.

When moving gas (or liquid) is directed at a curved object, such as a ball, the airstream (or stream of liquid) will follow the surface of the object, and will have a tendency to pull the object into the airstream. This is called the Coanda Effect.

The Coanda Effect is often used in engineering. It can be used to more successfully move vehicles through air or water, or to move gases or liquids through a system.

Aeroplane wings are often designed to curve the air over the top of the wing, and lift the aeroplane up. This type of wing has been used on various aircraft, and they sometimes use fans to provide high speed air to move over the wing surface.

The Coanda Effect is used to make more effective air conditoners. Because cold air falls, air conditioners are usually mounted near the ceiling. Air can be pumped so that it moves along the ceiling for a while, before it drops to the ground. This means that the cold air can spread out to cool more of the room.

We can also apply our knowledge of the Coanda Effect to weather systems. It has been shown that winds can curve around mountains, and winds show interesting effects in mountain ranges.

Our bodies also make use of the Coanda Effect. The curved surfaces in an unborn baby's (foetus') heart cause the blood flow to be split in two, so that it can go to two different places. In people with damaged heart valves, we can see that the blood follows the curves of the heart, due to the Coanda Effect.

The Coanda Effect can sometimes be a problem. Large boats use propellers on either side of the bow (front of the boat) to turn. These propellers push water out to the side, causing the boat to turn in the opposite direction. However, if the boat is moving quite fast, the water flow from the side propellers will just follow the hull of the boat, so it won't turn.

1 When moving gas is directed at a ________ object, the airstream will follow the ________ of the object.
2 How do aeroplanes use the Coanda Effect?
3 Why are air-conditioners often placed near the ceiling?
4 How does the blood flow get split in two in the heart of a foetus?
5 What do propellers on either side of the bow of a boat do?
6 Can you think of any other circumstances when the Coanda Effect might occur?

1 Recreate the Coanda Effect exhibit with a ping-pong ball and a hairdryer. On the cold setting, point a hairdryer upwards to keep a ping-pong ball in the air. Then slowly tilt the hairdryer to the side, and you'll see that the ping-pong ball stays up in the stream of air.
2 Place a can in front of a lit candle. Blow directly onto the can. Your breath will curve around the surface of the can, and put out the candle on the other side.