2012 Exhaust Blowing & Coanda

[aral]

Nice and easy way to see the effect is taking a round glass and hold it under the tap with water running.

I think you will find that the exhaust gasses are exiting the pipes at a very high speed and pressure. Totally different to holding a glass under a stream of low presure water.

[Pup]

Where were you guys when we were doing show and tell months ago?

Kitchen torch, cocktail shaker, 0 kph:


As for Jenson - I've never seen exhaust smoke from any car in the pits, regardless of where they place the pipes. Jenson's exhaust was broken, and was probably burning something under the bodywork, and the smoke from that is coming out of the big vent at the back.

[hardingfv32]

Pup's demo is rubbish when related to F1 exhaust flows. Here is a experiment with more correct parameters. You will note that the nozzle outlet hits the drum at a tangent point and not somewhere below the tangent point as in the 'other' example. This better complies with the F1 regs. Also note how little Coanda Effect there is. This is a pure low pressure acetylene flame.

Brian



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[Pup]

Butane more closely models exhaust flow than acetylene. And my cocktail shaker is silver, like the car.

[Chuckjr]

I think these two examples of coanda working and not working are a microcosm of the macrocosm of the complexity these engineering teams are facing and why resolution is so difficult to find. Great examples guys. Thanks.

[omar2726]

Doesn't the downwash from above the sidepods push the otherwise upwards-angled exhaust plume down, THEN the Coanda effect happens? (Based on the notion that they are indeed using the Coanda effect) I don't think a 10 degree upward angle exhaust, coupled with the downward slope of the sidepod will induce a Coanda effect right away, without the downwash.

This is how I understand it: IF they are using the Coanda effect, they are trying to use the downwash (thus forward motion is necessary) to change the upward angle of the exhaust to a more tangent path to the bodywork. This is when the Coanda effect takes effect. Thus, without forward motion, the exhaust doesn't attach to the bodywork.

I hope I made some sense here.

[hardingfv32]

T Thus, without forward motion, the exhaust doesn't attach to the bodywork.

Your are probably right. That is why the smoke off the car in the pits is probably a correct representation for the non-moving situation.

Brian

[Nando]

I think you will find that the exhaust gasses are exiting the pipes at a very high speed and pressure. Totally different to holding a glass under a stream of low presure water.

It´s the same principle. In this case the water will attach to the glass and follow it slightly.

It´s just to get the coanda effect, not simulate an exhaust at 18.000rpm

[omar2726]

I think the tyres play a role on how where the exhaust flow . Working the sidepods , exhaust position and the tyres together is a possible way to direct the gases to the top of the diffuser.

Not that I am discounting this possibility, but I don't think they'd risk working the exhaust with the tyres. Aside from high temps, working with rotating tyres is very unpredictable. That's why they work so hard to direct the airflow away from the tyres right?

Cheers
Omar

[MIKEY_!]

Coanda effect does not depend on downwash however the downwash is useful (not vital) for good performance. Remember in this system the exhaust has to flow diagonally downward and at high speed (without downwash sidepods) might not make it to the floor. The downwash sidepods fix this problem. Also the acetylene flame got wider as only the bottom of the plume (nearest the surface) was dragged down. This effect gets less and less the further the particle is from the surface. Downwash will push the plume down from the top maintaining it's original shape and probably helping to prevent the plume separating from the surface as the acetylene did. Hope that was all logical [-o<

[omar2726]

Coanda effect does not depend on downwash however the downwash is useful (not vital) for good performance. Remember in this system the exhaust has to flow diagonally downward and at high speed (without downwash sidepods) might not make it to the floor. The downwash sidepods fix this problem. Also the acetylene flame got wider as only the bottom of the plume (nearest the surface) was dragged down. This effect gets less and less the further the particle is from the surface. Downwash will push the plume down from the top maintaining it's original shape and probably helping to prevent the plume separating from the surface as the acetylene did. Hope that was all logical [-o<

I think I got your point there, but does that mean, that even without downwash [from forward motion], even with the exhaust pointed upwards, that Coanda effect is still possible? What I was thinking was that downwash is needed in order for the exhaust gases to have a more tangential path.

Cheers

[raymondu999]

You may have a point there Omar. Obviously we don't know how the exhausts are pointing, but it could be a design where the downwash helps point the exhausts down, when coanda takes over - but at a standstill there might not be coanda because the exhaust path is angled up. Coanda itself is working without any motion on the sidepod's part, but the exhaust direction might not even come close to the sidepod bodywork.

[MIKEY_!]

Omar: coanda effect is absolutely possible without downwash, mclaren didn't have downwash in pre-season testing and it seemed to work fine (but not as well as now). Anyway that smoke and gas going over the monkey seat definitely did not come from the exhaust exits.

[raymondu999]

Mikey - coanda is indeed possible without downwash, but I think omar's question was about the angle the exhausts are pointing. Without downwash, the exhausts will point at least 10 degrees upwards. If this just sends it up, at no point touching any bodywork (angling away, in fact), there's nothing to "coanda" if that makes sense. The downwash helps push the plume down onto the bodywork, THEN coanda effect comes into play.

[shamikaze]

In simple terms you could state that the forward lotion causes the the downwash and that in turn is guidinf the exhaust-plume down from its up- and outward angle in order to enable the coanda-effect to take place.