2012 Exhaust Blowing & Coanda

[hollus]

Guys, the exhaust slows down by interacting with the surrounding air. The exhaust gas "cylinder" decelerates by accelerating the air around it. Furthermore, just by slowing down it widens (conservation of mass, constant(ish) density) by itself. So what was a narrow and very fast flow quickly becomes a wider and not so fast flow.
Don't let the shape of the flames misguide you, they are surrounded bu much bigger warm areas, just not hot enough for creating a plasma. Take your kitchen torches and put your fingers a bit off the shiny flame if you don't believe me. (Carefully)

Edit: My point being that the exhaust flows are much wider than the exhaust exits.

[Nando]

Nando - Your version 3 hasn't taken into account downwash. Downwash will reduce the angle from 10 degrees. Coanda takes it from there.

Sorry forgot that, here´s one with downwash making the exhaust gases horizontal and a proposed line the exhaust gases will take thanks to the coanda effect according to you.

As you can see, even though exhaust gases are now horizontal thanks to downwash, it is still nowhere near a surface to actually bend the exhaust stream.
I know you said low pressure will do that however i´m not sure the low pressure is great enough to bend exhausts coming out at 360km/h in that short little space.
And bend all of it, not just some fumes at the bottom.


And just so people understand, (some apparently did not as they pm:ed me)
I am no aerodynamicist, i haven´t studied aerodynamics.
I´m just skeptic to the idea but i am completely open minded.
As of right now there are people on both sides of the fence.

What i say should by no means be taken as fact, this is simply my opinion on the matter and it will probably change as we get deeper into the discussion.

[Crucial_Xtreme]

Nando... Yes, you are correct that the Coanda Effect is not going to function under the current design restrictions without the exhaust flow being forced downward by the air flow over the side-pod. There is a possibility that there is no Coanda Effect required. Maybe the flow over the side-pod does a good job of forcing the flow downward into the channel and that the channel is just an aiming mechanism.

Brian

Nobody ever said otherwise. The point is Coanda is being used to start the downward motion of the plume. The downwash then helps to direct the plume further downward. End of story.

Article on the exhaust, Coanda, & downwash. See blue highlighted section


Link to Scarbs Article

Now have a look at the Ferrari exhaust in Jerez. Note the extension on the end of the exhaust pipe for Coanda to start the downward motion of the exhaust plume.




And Brian you've seen the pictures of the heat shield tape being damaged already

[amouzouris]

Here...if u are not patient skip to 0:39...and see how much deflection there is by the coanda effect...
[youtube]http://www.youtube.com/watch?v=k_eDutgh ... re=related[/youtube]

[hardingfv32]

Nando... Your drawing is not representative of the McLaren channel. The floor of the channel is within 3 deg of the exhaust pipe axis. It is aimed upward at the starting point. In your drawing it would be 7 deg above horizontal but also a convex curve.

IF WE ASSUME we can initiate a Coanda Effect with this 3 deg deviation (from axis) then it is possible to get the flow in downward flow direction using the convex curved surface to guide the flow from 7 deg above horizontal to something way below horizontal. That would be the plausible theory.

Brian

[Nando]

Nobody ever said otherwise. The point is Coanda is being used to start the downward motion of the plume. The downwash then helps to direct the plume further downward. End of story.

Article on the exhaust, Coanda, & downwash. See blue highlighted section
PICTURE

Link to Scarbs Article

Now have a look at the Ferrari exhaust in Jerez. Note the extension on the end of the exhaust pipe for Coanda to start the downward motion of the exhaust plume.

PICTURE


And Brian you've seen the pictures of the heat shield tape being damaged already

PICTURE

But how would we know that it´s the coanda effect keeping the exhaust gases attached to the bodywork and simply not downwash?

The Ferrari one was a bad example i think as the system doesn´t even work properly. (yet)

[Nando]

Nando... Your drawing is not representative of the McLaren channel. The floor of the channel is within 3 deg of the exhaust pipe axis. It is aimed upward at the starting point. In your drawing it would be 7 deg above horizontal but also a convex curve.

IF WE ASSUME we can initiate a Coanda Effect with this 3 deg deviation (from axis) then it is possible to get the flow in downward flow direction using the convex curved surface to guide the flow from 7 deg above horizontal to something way below horizontal. That would be the plausible theory.

Brian

Do we have some close ups showing the angle of it that i could look at?

I don´t dis-trust you it´s just that on the page before it was said to be sloping downwards.

If it´s 3 degrees from the 10 degree exhaust then it would still be pointing upwards.

How much of a bend is it? and does it start high then go low or does it start low, then comes up near 3 degrees of the invisible regulation box then comes down again?

a paint picture would be nice

[hardingfv32]

The point is Coanda is being used to start the downward motion of the plume. The downwash then helps to direct the plume further downward. End of story.

My experiment demonstrates there is very little if any Coanda Effect when the flow axis is below the contact object (curve surface). The only way there is any Coanda Effect is if the flow is forced down onto the contact object by the flow over the side-pod.

Brian

[Nando]

Maybe like this?

It includes the 10 degree regulation. A fantasy 3 degree (random guess there)
And a proposed exhaust housing, am i close?



And here is my thoughts (and probably Brian´s) on how much of an effect the Coanda effect would have at most.
Not counting downwash after the exhaust housing.



the airplane video is an extreme case. You are talking about a 90 degree bend which sends the air right down to the ground.

So in a way it nullifies the Coanda theory pushing the exhaust gases down to the floor due to the minimal angle of the exhaust housing.

[hardingfv32]

Sorry, I could fab something faster than I would be able to computer paint.

Your drawing is now correct.

You will have to search for photos on your own, but I do not recall any real tight shoots of the channel.


Another negative to the Coanda Effect thesis. Only the floor of the channel is curved and would provide the Coanda Effect. And the floor is curved at that, for the effect would not be as great as the wall moves to vertical. The floor of the channel should really flat for maximum Coanda Effect.

Brian

[Crucial_Xtreme]

Maybe like this?


So in a way it nullifies the Coanda theory pushing the exhaust gases down to the floor due to the minimal angle of the exhaust housing.

It doesn't nullify anything. To the best of my knowledge you nor Brian, nor myself has a degree in Aeronautical Engineering and we're not privy the the McLaren exhaust specification details. It's your opinion. Same as ours is our opinion. Neither opinion proves or disproves the other. Whats more is people (Scarbs- Mark Hughes- Gary Anderson) who have access to inside information from the teams and are more familiar with the particulars with the latter actually having worked in Formula One say the Coanda effect is in play here. I think I'll go with the opinion of someone who has worked in F1 & those that have direct access to the teams.

[hardingfv32]

I will try and fab an experiment with a channel. I will not be able to photograph a side view of the channel, but we should see what the effect is after the channel.

Some issues to be agreed to first.

1) Was the acetylene flame acceptable? I could juice it up with oxygen.

2) What is the width of the channel? Should it be the size of the visible flame as seen in my photographs?

Brian

[hardingfv32]

I think I'll go with the opinion of someone who ....

As opposed to a physical experiment that I provided? Is that the new scientific method these days?

Can I improve my experiment to make it more convincing, or do you need an actual car sim to sway you?

Brian

[Nando]

It doesn't nullify anything. To the best of my knowledge you nor Brian, nor myself has a degree in Aeronautical Engineering and we're not privy the the McLaren exhaust specification details. It's your opinion. Same as ours is our opinion. Neither opinion proves or disproves the other. Whats more is people (Scarbs- Mark Hughes- Gary Anderson) who have access to inside information from the teams and are more familiar with the particulars with the latter actually having worked in Formula One say the Coanda effect is in play here. I think I'll go with the opinion of someone who has worked in F1 & those that have direct access to the teams.

Do we agree on the angle of the exhaust housing?

Do we agree that you need to angle a wing 90 degrees in order to get air to the ground? As been proven by the video showed.

Do we agree that this gif from wikipedia is correct?

Do we also agree that the angle of that circle far and away exceeds the angle of the exhaust housing on the Mclaren?



Should also mention that i don´t think anyone denies the Coanda effect.

The part where we split sides is the effectiveness of it.

[GrizzleBoy]

Maybe like this?


So in a way it nullifies the Coanda theory pushing the exhaust gases down to the floor due to the minimal angle of the exhaust housing.

It doesn't nullify anything. To the best of my knowledge you nor Brian, nor myself has a degree in Aeronautical Engineering and we're not privy the the McLaren exhaust specification details. It's your opinion. Same as ours is our opinion. Neither opinion proves or disproves the other. Whats more is people (Scarbs- Mark Hughes- Gary Anderson) who have access to inside information from the teams and are more familiar with the particulars with the latter actually having worked in Formula One say the Coanda effect is in play here. I think I'll go with the opinion of someone who has worked in F1 & those that have direct access to the teams.

You dont need any of that stuff if you have a good enough general grasp of physics, especially in the general terms we are speaking.

The coanda effect is in play, but the majority of it is from downwash.

The MAJORITY of the exhaust plume would not be affected by the floor of the exit tunnel.

It's like having a wide stream water jet pushing water out at high pressure. The water closest to the nearest surface intended to create the coanda effect will indeed be affected, but the rest will just shoot straight out due to the pressue and velocity being more of a factor in direction.

As others have explained, the exhaust gases expand outwards when they exit the exhaust, but just as much, if not more of the exhaust will be unaffected by the floor when stationary.

At the velocities the gases come out at, you'd get some downward pull, but nowhere near enough to accomplish any kind of solid or consistant effect.

The downwash when the car is in motion acts like a lid over the top of the exhaust tunnel and focuses the gases into a lower/tighter stream that then helps to bring the gases downwards towards the tunnel floor at the end of the exhuast tunnel, which then helps the gases get closer to the floor of the car.