After an attempt to ban exhaust blown diffusers for 2012, Formula 1 teams rushed to the start of the season with a workaround to achieve the same effect – the Coanda exhaust. Here is how they came about and how they worked …
Prior to the 2012 Formula 1 season, the FIA had made many changes to counter the growing trend to use exhaust fumes to affect the car’s aerodynamic performance.
This followed the ban on double diffusers, which was then reinforced in their second year by the use of exhaust blowing solutions – which the FIA also tried to stop.
As explained in the previous edition of banned, the crackdown has not been effective – presumably, the tighter restrictions have actually led to more teams developing their own exhaust blowing solutions. With particularly strict dimensional criteria implemented for 2012, the FIA intended to put an end to this practice.
However, blown floors being such a good avenue for increasing car performance, the designers were not going to sit down and pass up any opportunity.
The “Coanda” effect
At its core, the Coanda effect is the phenomenon where a jet of fluid can attach to and follow a curved surface, developing a region of low pressure.
By being able to use this effect, F1 teams could use the car body to bring the exhaust gases to the ground and create the blown diffuser in this way.
F1’s technical working group (TWG) meetings, during which the teams’ technical directors would negotiate with the FIA on the direction of the new regulations, have included attempts by Red Bull and McLaren to manipulate the exhausts – both having experienced the effect in the wind turbine. – in a position in which they wanted.
“At McLaren, we brought in our first exhaust blowing solution in 2010, and it didn’t work! So we did an R&D charge to determine what was going on, and we found that the exhaust had gone wrong and we’d discovered an effect called Coanda “ Paddy Lowe
“There were quite a few constraints on this part for 2012 with the [engine] the cards, “says Paddy Lowe, then technical director of McLaren,” but I think they realized that everything was very difficult with the cards, so the final solution was going to be geometric or physical in the sense of the tailpipes.
“There’s a pretty interesting story about it. At McLaren, we brought our first exhaust blowing solution in 2010, and it didn’t work! We launched this new floor at Silverstone and didn’t got support.
“So we did a lot of R&D to figure out what was going on, and we found out that the exhaust went wrong and we discovered an effect called Coanda.
“When we advanced towards Hungary in 2011, while the FIA was trying to impose a final solution on the positioning of exhaust gases, there were many people who were trying to negotiate what these constraints would really be and who would put the exhausts at the top and things like that, and there was an angle constraint.
“So, walking around that, we settled on pointing it between 10 and 30 degrees. And we had this conference call with all the technical directors on the team, actually the TWG on the phone, and I was sending a message to Paul Monaghan, my counterpart at Red Bull, because we both knew Coanda and we already had in mind to get around this problem.
“So we were trying to keep them from pointing too high, and we agreed on a number that was really difficult, but we felt we had to take on the challenge. So when we came out with the car 2012, we made everything Coanda work really well, and we were ahead of the game.
“Because we did a lot of work in 2010 trying not to have Coanda, we knew the score and we developed the tools that helped us reproduce these effects in the wind tunnel.”
McLaren’s solution was most widely adopted for 2012, extending the rear of the side posts outward to help the exhaust plume produce the Coanda effect.
The jet of exhaust gas expelled from the engine attracted the nearby air flow towards it, ensuring that it took the desired path to the space between the sidewall of the tire and the outer wall of the diffuser, just as c was the case with the blown exhaust diffuser solutions used in 2011.
The critical thinking behind the design of the McLaren solution was that with the exhaust mounted in a nacelle that overlooked the side deck, the air flow would still circulate around the pontoon and in the “ coke bottle ” area.
It was a key issue that users of a ramp solution like Sauber had to contend with. The exhaust gases would mix with the flow normally intended for the coke bottle area – diluting the effect of both.
Red Bull, however, wanted a solution that brought the best of both worlds. It was a more complex perspective and needed a tunnel to help the two effects intersect. However, this would not be without complications, as the team had to try to make it work in the real world after the simulations offered promising potential.
Red Bull was so convinced that he was on something special, he actually used a mild exhaust during pre-season testing in an effort to delay anyone able to copy his arrangement.
He finally released his transition ramp solution on the penultimate day of testing and ran into problems, as he suddenly found that there was unstable flow with the tunnel that made the car inconsistent at the corner, but the team continued its development.
The regulatory changes for 2012 not only had an impact on the position of the exhaust but also on the surrounding bodywork. As such, many models seen from top to bottom of the grid that used this Coanda-style solution had bodywork with a trough-like appearance.
This was limited by the new regulations and most opted for a simple mailbox type bin. However, Red Bull has pursued many ways to manipulate this shape to influence the trajectory of the exhaust plume and has tried different solutions, some of which hoped to manipulate the flow in the tunnel below.
The amount of work Red Bull did in 2012 to make its solutions work was monumental
For the Chinese Grand Prix, Sebastian Vettel even returned to the pre-season test solution because he thought it would not only solve some of the problems he had with the car, but also help the team understand where these problems could be found.
The tinkering continued, now with a renewed effort to reshape the entrance to the crossing tunnel in order to facilitate the passage of air flow in the tunnel and beyond. This meant a complete overhaul of the sidepod, including the movement of the exhaust pipe. There was also an extension of the tunnel, the shape of the tunnel entrance being enlarged and a vertical separation slot mounted inside.
At this point, it appeared that the team had finally overcome its aerodynamic instability problems and that the car had behaved in a more predictable way, which means that it could now seek additional performance. This would come from a continuous push to refine the crossover tunnels and the bodywork that surrounded the shape of the exhaust and a renewed effort by Renault to find ways to stabilize the exhaust flow.
During this time, the team understood that the plume created by the shape of the exhaust, itself imposed by the new regulations, had a harmful effect. In order to soften a damaging vortex that formed, he worked on using a Helmholtz resonance chamber – a noise control device that absorbs any excess energy – to minimize the amount of drone inside . In doing so, Red Bull has successfully dampened the exhaust primarily to create a more uniform distribution of exhaust gases.
The amount of work Red Bull did in 2012 to make its solutions work was monumental, but that doesn’t mean that others on the grid were resting on their laurels either.
Sauber, who did not have the luxury of being able to bring new parts to each race and had started with the ramp solution, had a brief allusion to the crossover solution before realizing the level of development that would be necessary to do so function. As such, he rather switched to a Coanda McLaren-style solution during the season.
Ferrari has remained an outlier throughout, preferring to try to modify its “ Acer ” cladding solution on an ad hoc basis while it has found the best way to maximize the Coanda solution that it finally introduced.
The FIA has let the use of these Coanda style exhausts slip for 2013 knowing the financial burden that the teams had to bear to develop them. He was fully aware that with the new hybrid rules coming into play for 2014, the possibility of blowing the diffuser with the exhaust would no longer be viable.
Thus, although it was never specifically prohibited by a new target rule, the regulation was modified to take it into account. With the exhaust coming out along the center line of the car, the days of blown floors were over.
