2012 Exhaust Blowing & Coanda

[omar2726]

I understand that Coanda is still possible without downwash, but without forward motion, with the exhaust angling at least 10 deg upwards, and the bodywork sloping down, how is it possible? In the preseason testing setup without downwash, I think the forward motion still helps angle down the exhaust gas to at least closer to horizontal, while the new setup with downwash "pushes" it even more down towards the bodywork.

[Crucial_Xtreme]

I understand that Coanda is still possible without downwash, but without forward motion, with the exhaust angling at least 10 deg upwards, and the bodywork sloping down, how is it possible? In the preseason testing setup without downwash, I think the forward motion still helps angle down the exhaust gas to at least closer to horizontal, while the new setup with downwash "pushes" it even more down towards the bodywork.

I think it has to do with the exhaust jet. Wouldn't the speed of the exhaust exiting the pipe cause a reduction in pressure below the plume, thus causing it to be "sucked" down to the tunnel thing McLaren have?

[raymondu999]

That's pretty much coanda in a nutshell. But I think what Omar is contending is that the exhaust points too far away for the exhaust to start any coanda effect, and so McLaren use a bit of downwash to get the exhaust closer to the bodywork first, which THEN initiates the coanda.

[Crucial_Xtreme]

That's pretty much coanda in a nutshell. But I think what Omar is contending is that the exhaust points too far away for the exhaust to start any coanda effect, and so McLaren use a bit of downwash to get the exhaust closer to the bodywork first, which THEN initiates the coanda.

But that's just it, the 10° above horizontal really isn't that much, and then the way the tunnel is built the plume when it leaves the pipe is really close to the surface.
I'm saying, I think it's a mixture of both that help, but I think the downwash is to get the exhaust to the floor, not to necessarily start the effect.

[shamikaze]

That's pretty much coanda in a nutshell. But I think what Omar is contending is that the exhaust points too far away for the exhaust to start any coanda effect, and so McLaren use a bit of downwash to get the exhaust closer to the bodywork first, which THEN initiates the coanda.

So actually they apply the coanda effect 2 times...

First time with the downwash into the exhaust-tunnel and then the 2nd time when the exhaustflow exits the tunnel in order for the flow to attach to the bodywork / floor in order to be dorected towaeds the dode of the diffuser to seal it


ps: sorry for the many typo's, caused by freak'n spellcheck on Windows-phone... :S

[shelly]

What is not evident from tha availabel pictures is if there is a small slot under the exhaust pipe, between the pipe and the ramp inside the bodywork cutout. If there is such a slit, then the control flow for the coanda effect (the flow tht gets accelerated and narrowed against the convex surface) would be provided by the sidepod's internal flow.

[Nando]

Do the Mclaren really use the Coanda effect though?

To me it looks like Mclaren´s solution uses airflow to push the exhaust gases down and slightly inwards.

While RBR or Sauber uses the coanda effect almost from where the exhaust starts.
Or possibly that none of them uses the Coanda effect at all but simply uses the airflow to guide the exhaust gases down the right path.

I don´t know much about aero though,

I´m pretty sure you would have to point the exhaust gases towards something solid for the effect to take place.

[Pup]

I think the major difference between Brian's example and mine is the velocity of the airflow. I do think that the slower flame more closely matches the exhaust flow.

And while I wouldn't be surprised if the surrounding airflow does help, I think the exhaust is primarily dependent on coanda.

I also suspect that McLaren's curved cutout increases the effect.

I remember from my little experiment that as the flame came closer to the cylinder, that I could feel the heat wrapping around the curve before the visible flame began to bend.

So perhaps its a matter of degree.

[Nando]

Edit: Pup was quicker,

A bit like this, again most lines are probably wrong but you get the idea.
Could anyone tell me where the coanda effect takes place?

Again im no aerodynamicist but from my ignorant point of view i would say there´s no coanda effect at all, just airflow pushing the exhaust gases down and slightly inwards.

[omar2726]

I guess I see Mikey's and CX's point more clearly now. But the downwash does help the exhaust come down right?

Looking at Nando's example, it led me to think: is the downwash, or the airflow from the sidepods and tunnels enough to influence the path of the exhaust gases? These exhaust gases are at a high speed and pressure, right? Compared to the flow of surrounding air, is the surrounding airflow (due to forward motion) enough to control the exhaust plume? Or is it really influenced more by the Coanda effect, then helped by the downwash/airflow?

[Nando]

Could anyone explain where the coanda effect takes place?

From my understanding the exhaust gases would have to be pointed towards something for the effect to take place.

Like the pictures Pup and some other guy posted.

[raymondu999]

It doesn't have to be aimed AT something. 10 degrees is the exhaust minimum angle. Add a bit of sidepod downwash to decrease the angle to the horizontal, and then it's close enough for coanda effect to dictate the exhaust will follow the sidepod.

[GrizzleBoy]

Edit: Pup was quicker,

A bit like this, again most lines are probably wrong but you get the idea.
Could anyone tell me where the coanda effect takes place?

Again im no aerodynamicist but from my ignorant point of view i would say there´s no coanda effect at all, just airflow pushing the exhaust gases down and slightly inwards.

I thought I was the only one on this forum who didn't think the RB8s exhaust flow magically drifted downwards at a sharp angle towards the floor immediately after exiting the tubes!

I also cant help but feel that McLaren is waiting to add some kind of upgrade to where that tape is on the floor.....it just doesn't fit in with their desire to have their car be pretty and perfect(at least aesthetically) for it to be something that's going to be there for the rest of the season.....

[hardingfv32]

I also cant help but feel that McLaren is waiting to add some kind of upgrade to where that tape is on the floor.....it just doesn't fit in with their desire to have their car be pretty and perfect(at least aesthetically) for it to be something that's going to be there for the rest of the season.....

1) Have you ever seen any discoloration of this tape?

2) What better way to misdirect the competition with a falsely placed piece of tape. The body prep department probably smiles every time they put the tape in place.

Brian

[Nando]

It doesn't have to be aimed AT something. 10 degrees is the exhaust minimum angle. Add a bit of sidepod downwash to decrease the angle to the horizontal, and then it's close enough for coanda effect to dictate the exhaust will follow the sidepod.

If you don´t aim it at something then you won´t have much of an effect at all.
The gases will reach down a tiny tiny bit but after that go straight.
There´s no magic force that will pull the exhaust gases down to the floor.



To get the exhaust flow down to the floor you need downwash or airflow over the sidepods which will push the gases down to the floor.

and by making the exhaust housing more like the mclaren one ÿou can see it would be even harder for the exhaust gases to magically get pulled onto that surface.

I just can´t see how the shape of the housing can in any way re-direct the exhaust gases downwards. imo it has to be pushed down and be contained by air to reach it´s destination.