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[Pup]

Tell me you don't have a burning desire to prove me wrong?

You know, I don't.

[hardingfv32]

Surely the exhaust plume flares after it has left nozzle to fill the channel

Well, first we need to state what an effective Coanda Effect is in this application. It would be my opinion that you would need to see the center axis of the exhaust flow bend downward. That is one possible way to describe the situation.

Now as you state, the exhaust plume expands and follows the contour of the channel. No need for the Coanda Effect. Now is the Coanda Effect going to augment this flow once it gets to the bottom of the channel, not clear. I would claim that the 'center axis of the exhaust flow' has not been bent in this situation.

Why do we not mention Coanda Effect when discussing the flow around the side pod? What is different in that case?

Brian

[wesley123]

Which really makes everyone want to joint that debate, doesn't it?

We don't learn anything from you saying it is not true, you have to explain why.

Brian

I know I am nothing better then you in these situations but you ask everyone to explain, but you do not do yourself. You merely go by asking obvious question even my toe could answer and then start claiming others are wrong, with no reason from yourself to state why they are. I 100% am behind Pup on this one and understand him

[hardingfv32]

but you ask everyone to explain, but you do not do yourself.

I disagree. I have clearly stated why the Coanda Effect is not applicable, it is there for you to responded to.

Are you asking for my understanding of the channel duct? I think it just a duct restricting the exhaust plume on the sides, curved at the bottom to allow the expanding plume to escape downward and open at the top to meet the rules, unfortunately allowing exhaust to also escape upwards.

Brian

[ForMuLaOne]

In this case you can observe many effects at the exhaust exit with its bodywork around. It is not very constructive to pull out a law that might suit the desired function of these exhaust solution. There is a lot going on, and it is for sure that the exhaust gases have another direction than the exhausts are pointing at. The bodywork surely effects the airflow downwards. If it was not, we were observing highly skilled aero engineers wasting time for a concept that neither works in theory, nor on the car.

[ForMuLaOne]

Mr. Bernoulli would be very disappointed if he knew he was not mentioned in this context

[Pup]

Are you asking for my understanding of the channel duct? I think it just a duct restricting the exhaust plume on the sides, curved at the bottom to allow the expanding plume to escape downward and open at the top to meet the rules, unfortunately allowing exhaust to also escape upwards.

Brian

Exhaust plumes don't expand. They contract as they cool. This was mentioned a few pages back.

[Shrieker]

Exhaust plumes don't expand. They contract as they cool. This was mentioned a few pages back.

Whoa - really ? I was under the impression that if you open a box full of heated air, the gas inside would expand when exposed to the ambient air surely, no ?!?

[Pup]

I know enough about it to know I don't know enough. But take a look at the photo of my kitchen torch, and you see that the plume contracts. The rest of it has to do with ambient air pressure and the nozzle shape, which is why a rocket plume will change shape as the rocket gets higher, so, yes, I think that the plume could expand, but my limited understanding is that for what we're talking about here the expansion has already taken place before the gas exits the tail pipe. The other thing is that the exhaust isn't totally like a jet, since it's a series of pulses. I'm guessing it looks a little like a supersonic plume (with the mach diamond pattern) but for a totally different reason.

Actually, if you look at the torch photo, you'll see that the plume is somewhat overexpanded and so you see how it contracts immediately as it leaves the nozzle. Kind of cool, huh?

[beelsebob]

Exhaust plumes don't expand. They contract as they cool. This was mentioned a few pages back.

Whoa - really ? I was under the impression that if you open a box full of heated air, the gas inside would expand when exposed to the ambient air surely, no ?!?

If you open a box full of pressurised air, sure, and of course, heated, and pressurised often go hand in hand. Convection will also have a certain effect of spreading the hot air out too, but that doesn't really apply when you have a highly energetic source like an exhaust, there are far bigger factors involved.

The effect of pressurised air expanding though is short lived – as it rapidly reaches the same pressure as the air around it.

If you're then dealing with cooling it down, and hence reducing its pressure, it'll contract again slowly. You can see this in the shape of the flame seen on the blow torch above - the air expands rapidly at the exit, as it's under high pressure, but as the flame cools, it contracts again down to a point.

Note though, like pup, I don't know exactly how all this works, so I'm merely giving my intuition here.

[Shrieker]

I'm still a bit sceptical, but;

for what we're talking about here the expansion has already taken place before the gas exits the tail pipe.

this makes a lot of sense.

@beelsebob,

Cheers

[Pup]

The thing that we're used to seeing, of course, is exhaust overrun, where we get the big flame out the tailpipe. But in that case, the fuel is being ignited in the tailpipe itself and so I'd guess is still expanding a good bit as it exits.

And another thing is what I was talking about with the flowvis on the floor maybe getting baked - there's the plume and then there's the air around the plume. The exhaust gas of course is cooling, but doing so by heating the air around it. So that air will expand. Take a look at this photo, and you can see both the contracting exhaust, but an expanding cone of air around the exhaust.

[Gridlock]

OK kitchen blowtorch and martini shaker is one thing, buying an F22 is a bit of overkill

Nice shock diamonds though.

Funnily enough you've posted exactly the effect I thought of not when I saw the McLaren but the RB8, where the suspension member would move in and out of the flow as the car's velocity changed.

[Pup]

OK kitchen blowtorch and martini shaker is one thing, buying an F22 is a bit of overkill

It was the only way I could convince Brian.

[strad]

Really??