Technically Speaking: Coanda Exhausts

15/03/2013

We hear a lot about Coanda exhausts but how many of us really understand. Thankfully, Pitpass' technical expert Matt Somerfield can explain.

'Coanda Effect named after Henri Coanda is the tendency of a fluid jet to be attracted to a nearby surface' As with everything in F1 it's not new simply a reinterpretation of aerodynamics based on a new set of regulations.

The energy created by exhausts as we know is something that the teams are eager to use in order to extract additional downforce from the rear of the car. This crusade for additional downforce extraction from exhausts was initially fuelled by the use of Exhaust Blown Diffusers (EBD) in 2010 with the placement of exhausts down on the floor of the car directly in front of the gap between the floor and tyre to 'Seal' the diffuser.

Diffuser Sealing: The premise of 'Sealing' the diffuser is creating an air skirt along the sides of the diffuser to stop Tyre Squirt from impinging on the diffuser robbing it of the downforce it creates which is especially important as the car enters the braking and turning phase. (Tyre Squirt is airflow that is pushed laterally off the tyre into the Diffuser as the wheel rotates)

The teams went one step further in 2011 when Off Throttle Blowing was added to the mix meaning that the teams now had a continuous air skirt even when the driver was off throttle meaning the downforce was retained during the braking and cornering phases.

In 2012 the teams had, had their efforts curtailed by the FIA's rule changes that meant the exhausts had to fit within the specified box shown in Red in the image below. Furthermore the exhaust must be aimed upward (Between +10 to +30O). The FIA also limited the amount of Off Throttle blowing available to the teams further robbing them of the downforce the teams had created throughout 10/11.

Enter 2012 and the 'Coanda' exhausts, McLaren arrived with a solution that most of the field converged upon throughout the year realising the potential for recovering some of the 'Sealing' effect which could have been potentially lost when the FIA banned EBD.

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