Wednesday, March 21, 2012

What is Coanda effect and its use in Formula 1

Another blog post on a things related to Formula 1, this time I'll try to explain with simple words what "Coanda Effect" is. I got the inspiration from Joe Saward's blog, and particularly an article here.

First, a bit of history.
A Coanda Effect is named after Romanian aerodynamics pioneer Henri Coandă (7 June 1886 – 25 November 1972) - there are several commercial applications based on it, as well as few patents
What exactly it is:

Ability / tendency of a fluid or gas to stay attached to a surface if the shape of the latter allows it.

That's my personal simple explanation to a very complex phenomenon. Coanda effect can be seen in many forms, mostly involving jet and wings. 
Caveat: the example that you've seen in YouTube with the spoon and the water flow is not a Coanda effect, it's caused by a surface tension.
You can demo the Coanda effect for yourself trying to extinguish a candle by placing a bottle in front of it, and yourself on the other end of the chain, e.g.
You -> blow small amount of air from your mouth towards the bottle -> bottle -> candle burning.

The candle will eventually be extinguished. This is a Coanda effect - because the air that came from your mouth was able to stay attached to the curved surface of the bottle and both streams coming from the left and the right side of the bottle reunited back together to execute the final job - the candle is shut down.

Why is that happening? The Bernoulli's principle is also here, playing its role: 
An increase in the velocity of any fluid or gas is always accompanied by a decrease in pressure.  
Since the pressure around the air is being decreased, the outside area respectively has a higher pressure, which pushes the gas to the surface.

How F1 teams are using that effect? By making the exhaust gases to follow the natural contour of the bodywork, driving more of them towards the trailing edge of the diffuser and sealing it was lot more easier and thus beneficial, as opposed to neutral solution, such as early Mercedes or Lotus.

Red Bull's development iterations:

Image courtesy Jason (@Crucial_Xtreme)

Update of the recent implementation of the different teams:

RB8, third revision of exhaust configuration

Ferrari F2012

Mclaren MP4-27
Mercedes AMG W03
Lotus E20, tested in Korea FP
Image credit:


The 2012 F1 rules actually 'created' the Coanda exhausts by limiting severely what could be done with exhaust plume towards diffusers. Generally, the previous efforts were a pursuit of having the hottest gases possible through the pipes, which will increase the velocity flow. The mass flow rate remained the same, dictated by engine maps and essentially amount of fuel and air coming to the engine. This meant to carry greater momentum - as a sum of velocity and mass flow rate.

In 2012 teams put lots of efforts to make the pipes smaller and more curved, which meant some initial loss of power, most recently experienced by Lotus, which were the final team to introduce this solution. 
These smaller pipes, however, helped to increase the velocity of the flow by some considerable amount, which really made a difference, and this was evident by teams' choice to run similar solutions.