Red Bull RB8 exhaust diagram

How the Red Bull RB8’s exhaust feeds its diffuser

F1 technologyPosted on | Author John Beamer

To no-one’s surprise the race-specification exhaust for the Red Bull RB8 appeared on the penultimate day of the last pre-season test.

The team went to considerable lengths to cover it up, as the video above shows. But now the design has been seen we can get a look at how it works.

As the FIA has restricted where teams can place their exhausts, designers are striving to continue using the hot air to make their diffusers more powerful.

Red Bull’s approach is similar in principle to McLaren’s exhaust concept in that it tries to pull the exhaust plume downwards from the exhaust exit over the side of the diffuser to create a sealing effect.

The Red Bull design appears quite different and more elegant. But we won?t know until Melbourne whether it is more effective.

The Red Bull RB8 exhaust

Red Bull RB8 exhaust diagram
Red Bull RB8 exhaust diagram
The first illustration shows Red Bull?s new set-up. I?ve left out the pull-rod suspension arm and lower wishbones to make the image a little clearer.

The grey zone where the exhaust exits is covered in heat-resistant paint to prevent damage to the carbon fibre. The exit contains a channel indent to drag the plume downwards using the Coanda effect, as described in the McLaren exhaust article.

This area is shaped to continue to drag the exhaust gas downwards towards the diffuser. In addition, air coming over the sidepod is also used to create a high pressure zone around the exhaust exit, further helping the Coanda effect and shaping the exhaust plume. The red lines show the exhaust flow.

The issue designers face is that this potentially interferes with how the undercut sidepod works.

Over the past couple of years teams have aggressively undercut the sidepod to feed fast-flowing air to the coke bottle zone. This helps the diffuser to be more effective by creating a low pressure zone above it, which in turn reduces flow separation in the diffuser.

Dragging the exhaust plume to the floor will reduce the effectiveness of the coke bottle zone. The bulge in McLaren’s exhausts is designed to direct the exhaust gas over this flow.

Red Bull have adopted a different solution which is visible in the image. They have carved a duct at the bottom of the sidepod for the undercut airflow to go through. This duct exits in the coke bottle zone, missing the exhaust plume.

Replicating the exhaust-blown diffuser effect

Red Bull RB8 exhaust diagram
Red Bull RB8 exhaust diagram
The second illustration shows a similar picture of the RB8’s exhausts in plan view.

The exhaust exit is circled in yellow and again I’ve added the exhaust flow (red) and undercut flow (blue).

From this angle it is possible to see the shape of the exhaust indent in the bodywork. It is built in such a way that the exhaust gas appears to split – one stream spills over the side towards a vane on the floor ahead of the inner part of the rear tyre.

This will create a vortex and is primarily aimed at sealing the diffuser – this part replicates the effect of last year’s exhaust blown diffuser.

The second stream adds energy over the diffuser, which will help reduce the pressure gradient above the diffuser exit and hence reduce the risk of airflow separation under the car.

It is thought by some that the exhaust flow may partly feed a duct in the floor that houses the starter motor hole. However, it is unclear at this point whether this is for exhaust gasses or air flowing through the sidepod duct. Given the restrictions on starter motor hole size the effect is likely to be small.

As exhaust solutions are developed we’ll get a feel for the most effective solution. Last year teams quickly converged on Red Bull?s solution to optimise the exhaust blown diffuser.

Ferrari technical director Pat Fry suggested the same could happen again this year, assuming Red Bull’s design is considered legal, telling Sky: “It comes down to what re-ingested exhaust gas is really and that’s a question for Charlie [Whiting].

“I think it’s the obvious direction to go in. We gave it a shot; we didn’t quite get it right. The issues we had, we weren’t going to solve for at least the first four races, so that’s why we had to back up and change course.”

At this point the Red Bull solution is visually neater but doesn?t completely eliminate the exhaust/undercut interaction. McLaren?s solution likely does a better job in this respect but could face trade-offs on drag or quality of exhaust flow to the diffuser. The first weekend of running in Melbourne will yield more clues.

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Illustrations ?? John Beamer for F1 Fanatic