2012 Exhaust Blowing & Coanda

[Richard]

I've created this thread to consolidate three threads on exhaust blowing, and also tidy up the umpteen posts in car threads discussing the same thing.

[Crucial_Xtreme]

A Technical Directive was issued that stated:

"that any exhaust designs that reingest or redirect exhaust flow for principally aerodynamic reasons will not be permitted."

So aiming the exhaust at the rear brake duct could be illegal. Here's Lotus F1's Technical Directors take on it:

"The rule itself just determines how big the exhaust has to be, where it connects it, what angles it connects it from. But then the directive says you can satisfy the rule, but if we regard the concept of what you have done as satisfying the rule, but nevertheless done principally for downforce generation, then we might have to take a view on that. I think there will be a degree of jostling to work out where the line of acceptable geometries are."

But of course teams will aim there right? Allison says certainly. But it's being used for aero purposes.


"There is the rub! As you probably know, there was something of a spat last year where many teams felt that what we should do was define a black-and-white rule, and then put into the rule a rule that said if you do it to this geometry, then any aero effect will be considered incidental from the point of view of Article 3.15. So, that was an approach. But that was felt by other teams to perhaps open the door to too many unwanted avenues of development. So what we have is a black-and-white rule and a yet-to-be-determined area where the line lies."


There are going to be problems with the "spirit of the rules" this year. Quotes cames from AutoSport Plus interview.

[raymondu999]

I wonder. I think there are several designs that have steered quite well clear of this issue. Renault probably has, seems to just be aimed out under the rear wing and above the crash (into free air?) and Red Bull maybe? Though I'm not sure of that.

[Crucial_Xtreme]

I wonder. I think there are several designs that have steered quite well clear of this issue. Renault probably has, seems to just be aimed out under the rear wing and above the crash (into free air?) and Red Bull maybe? Though I'm not sure of that.

Same as Red Bull

[raymondu999]

Is that Autosport Plus? I saw there was a feature with James Alison but I haven't read it yet

[Ian P.]

A Technical Directive was issued that stated:

"that any exhaust designs that reingest or redirect exhaust flow for principally aerodynamic reasons will not be permitted."

This is the first time (surprising too) that there has been any mention of "reingest". Does this refer to using the exhaust to draw air from internal parts of the car...??
It should be feasable to have the exhaust draw from a duct that is used to pull cooling air from restricted areas or to pull from aero ports on surfaces or at floor edges.

I don't see how the exhaust can be blown out the back of the car WITHOUT having an aero effect. Where you blow it may change the magnitude of the effect.
What is all the fuss about anyway.?? Leave the teams to work inside the rules as written and quit stifling creativity.

[Coefficient]

@Coefficient
My view is that McLaren are trying to mimic the edge sealing of the diffuser as with last year's EBD. The EBD is designed to help prevent the dirty air from the tyre ruining the flow under the diffuser. In effect it acts as a skirt to seal the diffuser and make it work harder.

The thing about the diffuser is that it's job is to get the flow below the floor to meet the flow above in the nicest way possible in order to reduce drag and improve efficiency. Ironically, this works best when the pressure difference across the diffuser is low. By having a region of high pressure above the diffuser you actually reduce its efficiency.

Look at the designs of the cars - they are all designed to get air to flow over the top of the diffuser - this flowing air will reduce the pressure above the diffuser and so make it more efficient. If you wanted to maximise the pressure difference across the diffuser you would have bodywork between the rear wheels in order to have a volume of still (and thus relatively higher pressure) air in this region. The teams don't do that - they want air to flow over the top of the diffuser. And flowing air has less pressure than still air.

So, are they attempting to aim the exhaust plume between the edge of the diffuser and the Wheel assembly and also hoping the exhaust flow will augment the flow over the diffuser's upper surface?

I'd be interested to know:

1. How quickly the exhaust plume reverts to a lower energy state
2. Is the oncoming airflow over the car enough to assist the Exhaust plume to maintain adequate energy?
3. Would a significant tail wind have a disrupting effect on the overall principle?

[Coefficient]

@Coefficient
My view is that McLaren are trying to mimic the edge sealing of the diffuser as with last year's EBD. The EBD is designed to help prevent the dirty air from the tyre ruining the flow under the diffuser. In effect it acts as a skirt to seal the diffuser and make it work harder.

The thing about the diffuser is that it's job is to get the flow below the floor to meet the flow above in the nicest way possible in order to reduce drag and improve efficiency. Ironically, this works best when the pressure difference across the diffuser is low. By having a region of high pressure above the diffuser you actually reduce its efficiency.

Look at the designs of the cars - they are all designed to get air to flow over the top of the diffuser - this flowing air will reduce the pressure above the diffuser and so make it more efficient. If you wanted to maximise the pressure difference across the diffuser you would have bodywork between the rear wheels in order to have a volume of still (and thus relatively higher pressure) air in this region. The teams don't do that - they want air to flow over the top of the diffuser. And flowing air has less pressure than still air.

So, are they attempting to aim the exhaust plume between the edge of the diffuser and the Wheel assembly and also hoping the exhaust flow will augment the flow over the diffuser's upper surface?

I'd be interested to know:

1. How quickly the exhaust plume reverts to a lower energy state
2. Is the oncoming airflow over the car enough to assist the Exhaust plume to maintain adequate energy?
3. Would a significant tail wind have a disrupting effect on the overall principle?

I’d also be interested to know if as the exhaust plume exits the pipe and begins to lose energy, does it then lose energy exponentially if it meets obstructions such as wishbones? The reason I ask is because if this were so would it be better to focus the exhausts initial energy at the point of obstruction as Red Bull have done rather than allow some energy loss prior to the obstruction only then to be further depleted by the obstruction?

[PlatinumZealot]

I think Ferrari and Mclaren are using the exhaust gases to heat the tyres. This I suspect they combine with gentler camber and pressure settings to increase tyre life in the long stints. I believe it also assists with qualifying. Notice Mclaren have not used any temperature indicators on the wings of the car. Ferrari has tried blowing both wings and tyres - using temperature indicators when they blow the wings.

I was apprehensive towards making this topic as I do not want Mclaren's advantage to be lost... But I know Newey has spotted it already so it makes no difference. Or maybe I am just poking around some I deas.. don't take this topic too seriously.

[Caito]

Why would you heat the tire during a race? I mean.. constantly.

Aren't the rear tires already hot enough dealing with 700+hp?

If the problem with tire wearing is lack of heat, that'd be a good idea. But I have no source to tell if they need more, or less temperature in the rear tires. Do they need more heat in the tires?

[PlatinumZealot]

Lack of heat doesn't have to be a requirement. I would like to establish:


1. How adjusting the suspension and air pressure reduce tyre temperature.

2. How adjust the suspension and air pressure increases tyre life

3. How increasing the temperatures increases grip

4. How increasing the temperatures increases/reduces life

5. How to tune the engine to affect Exhaust gas temperature

5. Any other parameters that affect tyre life

There might be a cross over point when you can adjust 1,2, for long life and use 3 and 4 to increase performance. Of course track to track there will be differences.

[Just_a_fan]

One of the issues that the teams think they saw in the RB7 was that the exhaust appeared to be being used to heat the tyres during qualifying and, perhaps more importantly, during the formation lap prior to the start. The engine map was tuned to use the EBD to heat the rear tyres so that, when Vettel did his usual "slow them down, make them cold" routine at the start, he lost much less tyre temp. So he got a better launch and had more faith in the first few corners. The result was that he'd stick half a second on the rest of the field in the first half lap.

McLaren stated that they had designed the -27 to improve qualifying performance. One might therefore assume that they are trying to tune their engine maps accordingly.

If McLaren can pull it off then they have the drivers to maximise the benefits: one perhaps more in qualfying (LH) and one more in the race itself (JB). Getting in to the first corner first is important enough to risk some race pace through having to maybe make an additional tyre stop in marginal conditions. We saw Vettel make extra stops last year because the rears were going off quicker than most other cars. And still he won the races.

The fact they have done plenty of laps (121 today?) and have good high speed corer performance suggests that their strategy hasn't led to a loss of reliability / tyre issues.

Whether it can be transfered to the races themselves, well, we'll have to wait and see...

[PlatinumZealot]

I am doing some simple CFD studies on this..

All I can say so far is that the exhaust is deflected as it comes out the cowl.

The Coanda effect is not so prominent as there is a good amount of air to come between the exhaust stream and the side pod surface.But it is there. The exhaust gas is also too fast to attach to the side pod surface.

The deflection leaves the exhaust coming out in the shape of an eccentric cone. The top side of the cone is horizontal and the bottom side of the cone pointing down at about 10 degrees. So some deflection there.

I will position the exhaust more accurately and see where it is really going. As I see it now it is hitting just about everywhere outboard of the rear wing endplate - the tyres, the suspension arms, the brake ducts. It is not as low as the diffuser and it does not touch the beam wing. Again I will position it more accurately.

I think I might have to discard this tyre blowing theory.. but inspite of that the tyre is playing a critical role in deflecting the exhaust gas INWARDS.

Lets also say the endplate is also forming a low height vertical air curtain...

I will update as soon as I position the exhaust more accurately. I can provide a picture or two.

[Just_a_fan]

How much of the car are you modelling? I think that to get a true feel for what's happening, you'd need the entire package including the front wing and barge boards too which might limit your model.

But having said that, I'm really looking forward to seeing your results =D>

[tok-tokkie]

I am very interested in what you are doing Smikle. I am puzzled by the interaction between the air flowing around & over the sidepod & the exhaust plume trying to cross it at about 15°. The flo-viz we saw in an arc on the floor was surely too low down to have been shaped by the exhaust - so I presume that is where it was painted on. But I am very unsure about it all so would like to see your CFD. Ringo's CFD of the Renault FEE last year was very interesting even if it was much disputed.