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So, one would expect the air to flow out of the fan horizontally in all directions, but due to the Coanda effect; the air bends down, to almost 90 degrees

The airflow is being pushed down by the air above, because the pressure of the air in between the flow and the curved surface, is reduced by the suction of the airflow.

Next, an other example of the Coanda effect, where I used smoke to make the flow visible.

Air is being accelerated down, and part of the upper surface is in touch with reduced air pressure. This action gives the object a force up, thrust, that can lift the object.
Henri Coanda realized this, and then designed a flying disc based on this effect, in 1932!

We hope you enjoy the video.