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Formula One exhausts

A year ago, the topic of discussion in the corresponding article to this one was how Formula One engineers might compensate for no longer being allowed to ‘blow the floor’ with exhaust gas. In 2011, much of the technical discussion, as far as exhausts were concerned, centred on the use of the energy in the exhaust gas flows to create extra downforce. ‘Hot blowing’ and ‘cold blowing’ were bywords in a season that culminated in a rule change being agreed which outlawed the blowing of the underfloor and diffuser. With the knowledge that exhaust gas energy could be used to great effect in improving the car performance, it was unlikely that the genie could be returned to the bottle, so to speak, despite the best efforts of the FIA.

The new FIA regulation for the 2012 season stipulated that the exhaust system exit must be on the top deck of the car. A year ago I wrote that “there is no reason why the engineers involved won’t try to do something clever with the exhaust mass flow with aerodynamic surfaces on the top deck of the car, or to influence the flow over the rear wing”, although I wouldn’t have predicted that the pace of exhaust development would be as swift as it turned out to be.

The buzzword this year in terms of exhausts was ‘Coanda’. Put simply, the Coanda effect is the tendency of a fluid flow to be attracted’ and to ‘stick’ to a solid surface. In general, a stream of gas tends to entrain and mix with its surroundings. When a solid surface is brought close to the moving stream of gas, entrainment is limited from that direction; in reaction to this the jet accelerates and moves towards the surface. Once attached, the flow will tend to adhere to the form of the surface, even if it curves away from the original flow direction.

Its industrial uses are varied and it finds application in aircraft, air conditioning and fluid separators. However, we might claim, with some justification, that the Coanda effect is most ‘at home’ when applied to exhaust exits. Very aptly, the Coanda effect is named after an aircraft engineer who noted the effect of adjacent surfaces on the flow of gas from an engine he had designed more than a century ago. Coanda designed, and possibly briefly flew, the first aircraft not deriving its thrust from a propeller but from a jet of air.

In terms of the 2012 Formula One season, a number of teams designed exhaust exits that encouraged the exhaust flow to adhere to the top surface of the sidepods of the car which then sloped downwards toward the diffuser. As noted elsewhere, the deflection of the exhaust flow is due to a combination of the Coanda effect and ‘downwash’, where the upstream flow of air over the car’s sidepods is already well adhered to the bodywork surfaces and its direction of flow relative to the car has a downward component.

The Coanda exhausts were designed into some cars from the beginning of the season, with others adopting the technique later in the season with varying degrees of success. Playing catch-up is never easy and requires a lot of effort, with additional programmes of mid-season development consuming time and money.

Written by Wayne Ward

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