Concept for regulations to improve overtaking

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jjn9128
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Concept for regulations to improve overtaking

Post by jjn9128 » Sat May 13, 2017 2:03 pm

So I recently finished a Ph.D. looking into the composition and effect of F1 wakes. Inspired by Willem Toet's Linkedin articles I tried to write a similar article explaining what I would do to reduce the effect of a wake and why, but it's about 2000 words long and I'm nowhere near as good as Toet at finding the balance between explaining the topic while also making it accessible. I wrote an article in racecar enigineering in the past that had the same problem so I don't know if it will ever see the light of day. Anyway I thought I'd present the cliffnotes here to try to dispell some myths that I see a lot in topics on overtaking.

I do not like the term 'wake turbulence' when describing the wake of an F1 car, I prefer 'dirty air' as it is a much more encompassing term implying that there are many features. Namely, pressure deficits (total, static and dynamic), non-linearity (in the form of localized up-wash/down-wash and in-wash/out-wash) from vorticity from the rear wing endplates, diffuser endfences, various vanes and winglets... etc around the car which break down in the wake to form turbulence, as well as turbulence from boundary layers.

The key effect of the wake is from the dynamic pressure deficit (proportional to streamwise velocity squared) not turbulence or up-wash. Turbulence has been shown to be beneficial in some cases, and it's effect significantly reduces when boundary layers are turbulent, as in the case of F1 cars. The effect of dynamic pressure is that it squeezes the static pressure on the surface of the car towards Cp=0; as neagative pressure under the car sucks the car into the ground, increasing the pressure in turn reduces the downforce. Dynamic pressure deficit at the base of the car is localised around the rear wheels and underbody, hence why 2017 cars are finding it harder to overtake with bigger tyres and larger diffusers. Low velocity in the wake also increases the angle of the up-wash vector which effectively reduces the angle of attack of downforce producing surfaces.

The effect of a wake is not necessarily proportional to quantity of downforce created, if you create the downforce in the right way you can have high downforce with less wake effect BUT increasing the proportion of downforce from the floor is not the solution. Instead increasing the proportion of downforce from the rear wing is better. I did some experiments to quantify the contribution of rear wing and floor on the wake and found downforce generated by the floor drags the wake downwards and affects a following car more (another reason the effect of a 2017 wake is greater as the contribution of the floor has increased from ~50% to north of 60%), whereas the rear wing drives the wake over a following car. Increasing the rear wing vorticity also helped to draw in higher velocity flow from around the car while pushing the wake further up.

So onto my car concept. I would limit the total car length and therefore the space available between the wheels and ultimately downforce generated by the floor. The rear wing length is increased to 500mm with a span of 1m to increase its downforce and drive vorticity. This is draggy as a solution so I would have a totally active car; active wings, active suspension, and active cooling. The active wings would reduce drag on straights, which would also reduce up-wash in the wake meaning that as well as being able to follow in corners there would still be a slipstream effect. The active suspension should allow for slightly simplified aerodynamic surfaces as a lot of the effort in current designs is to produce consistent downforce as the car attitude changes around a lap. The front of the chassis is projected down to the ground allowing for a less compromised suspension set-up. Also the front wing joins the nose, removing the Y250 vortex and it's importance. Active cooling obviously allows a low drag package for running in free air but then allows the cooling to open when behind another car.

While there is a contoured underbody, this isn't to increase downforce of the floor but to reduce the effect of the wake on car balance. At the moment the floor design means there are two low pressure peaks under the car, and the front one is more affected by the wake than at the diffuser (as the wake becomes weaker further from the back of the car), where a wing shaped underbody will have a single low pressure peak and balance would remain consistent. Also a longer diffuser should produce less dynamic pressure deficit, especially if vanes and strakes are banned. Currently the short diffusers are over expanded with the multile channels and vortex producing vanes used to keep aiflow attached and generate a lot of downforce from the surface, to the detriment of a following car.

Sorry for the long post. I hope I explained this in a way which is understandable. Happy to answer any questions on my research if anyone's interested.

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Just_a_fan
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Re: Concept for regulations to improve overtaking

Post by Just_a_fan » Sat May 13, 2017 2:32 pm

Excellent post! Thanks for writing that up - I'm sure there others who would join me in welcoming your longer article if you decided to share it. =D>
Turbo says "Dumpster sounds so much more classy. It's the diamond of the cesspools."

Tommy Cookers
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Re: Concept for regulations to improve overtaking

Post by Tommy Cookers » Sat May 13, 2017 3:22 pm

agreed !

Ogami musashi
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Re: Concept for regulations to improve overtaking

Post by Ogami musashi » Sun May 14, 2017 10:58 am

jjn9128 wrote:
Sat May 13, 2017 2:03 pm
So I recently finished a Ph.D. looking into the composition and effect of F1 wakes. Inspired by Willem Toet's Linkedin articles I tried to write a similar article explaining what I would do to reduce the effect of a wake and why, but it's about 2000 words long and I'm nowhere near as good as Toet at finding the balance between explaining the topic while also making it accessible. I wrote an article in racecar enigineering in the past that had the same problem so I don't know if it will ever see the light of day. Anyway I thought I'd present the cliffnotes here to try to dispell some myths that I see a lot in topics on overtaking.
....

Hello jjn9128,
Nice post. Your findings are in lines with other studies (see my post viewtopic.php?f=1&t=26055&p=688090#p688090).

Some remarks and questions:

- You assert that "turbulence" is not the main culprit. Actually i think this is a problem of vocabulary. "Turbulence" is indeed usually used as a reference to the boundary layer state. In this rigorous definition, yes "turbulence" has nothing to see with "dirty air". This where other studies differ from yours, but again it may be due to the use of "turbulent air" by everybody which is ambiguous: There are two effects, the pressure deficit as you say, but also the changes in angle of attack due to vorticity (and its instability). And according to the same studies, front wing is mainly affected by that. You allude to that also, so you have probably noticed that in your results.

- You bring a very good point about the aerodynamics being made to work with the different attitude of the car and that active suspension would help.
This where i would like to have your point of view: There is a opinion that simplifying the aerodynamics would lead to more "dirty air" tolerance for the following car (i.e: a following car with simplified front wing would better tolerate "dirty air"). Since all the winglets are made to work in different attitudes (thus different angle of attack), and that the wake itself has a profound angle of attack instability effect on front wing, i'm not convinced about that argument.
What is your take on this?

- Also, some studies have shown that tyres are the main source of vortices instability in the wake, did your results show that?

Thank you!

P.S: don't spare me the technical details, i'll handle them :)

jjn9128
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Re: Concept for regulations to improve overtaking

Post by jjn9128 » Sun May 14, 2017 11:17 pm

Tommy Cookers & Just_a_fan maybe once it's gone through a few more drafts I'll post it somewhere.

Ogami musashi
Your findings are in lines with other studies
I should hope so. One of the papers you cite is mine! :lol:

With regard to 'turbulence' there are two distinct uses of the term. One in relation to boundary layer state and the other in relation to wakes/freestream which is then split into 'intensity' and 'length scale'. Where intensity (TI) describes fluctuations from the mean velocity and is normally presented as a percentage and length scale is the length/frequency of those turbulent eddies. The surfaces on F1 cars work the air quite hard, i.e. large pressure gradients, so boundary layers are highly turbulent and you get a thick wake, especially from the floor and rear wing. For reference freestream turbulence intensity in a F1 wind tunnel will be less than 0.15% while TI in the wake of a car can exceed 40% in places - this is from the work of Mike Wilson who has been at Force India since the late 2000s. So where I say TI in the wake has little effect is because what it serves to do (depending on length scale, for the most part the TI in a F1 wake is relatively high frequency) is force boundary layer transition to turbulence. As the operating Reynolds number of a F1 front wing is at the very least transitional, wake turbulence is going to have a very small effect on flow state, again there are a number of papers investigating the effect of turbulence on aerofoils including Wilson.

These front wing pressure distributions are from my work, the model I used is 25% scale so flow state at the trailing edge will be laminar even considering the pressure gradient. It is safe to say that the effect of wake turbulence on this wing will be greater than at higher Reynolds numbers. What the plots show is the baseline (clean air) compared to the effect of the wake at a 1 and 2 car separation. The dashed line is then the baseline scaled by the dynamic pressure deficit in the wake - which clearly forms a high percentage of the wake effect. And this is true for all the surfaces on the car.
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As the effect of the wake is from dynamic pressure I do not see simplified wings as being better/worse at generating downforce in a wake, all that's happening is a scaling of forces. A complex and simple front wing need to produce the same downforce to balance the rear of the car. Where I see simplified surfaces as an advantage is in the importance of the structures they produce. For example the Y250 vortex, is something everyone knows well, is formed by pressure difference at the tips of the flaps where the downforce generating wing joins the FIA neutral section. This has a very important role down the car to divert wheel wakes and help 'seal' the floor (there's a great SAE paper from Nakagawa of TMG showing the use of the vortex in 2009 and it's even more integral now). The reduced surface pressure on upper and lower wing surfaces in a wake means this vortex will be weaker, which has a knock-on effect down the car. Of course front wheel wakes are weaker too so flow ingress under the floor is less detrimental.

Not sure what you mean about the tyres... exposed wheels produce big, unsteady wakes.

turbof1
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Re: Concept for regulations to improve overtaking

Post by turbof1 » Mon May 15, 2017 12:23 pm

Interesting =D> . I'm glad we now have some academic research to denounce the myth that increased emphasis on floor/diffuser and small wings improves overtaking.

I was wondering though: Aside any ethical objections, would wheel covers decrease dirty air coming from the rear wheels and therefore ultimately improve overtaking?

everythingisawesome
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Re: Concept for regulations to improve overtaking

Post by everythingisawesome » Mon May 15, 2017 12:29 pm

I don't get it. You guys don't like watching the drivers dive and dice with each other during a race?

What's more exciting at the end of the race, those couple of epic battles, or the amount of overtakes?
This was never something that was discussed last year, never did I hear anyone say ' oh wow there were a lot of ovetakes during that race'

I feel like a lot of the F1 fans start concerning themselves with 'problems' in the sport, not by their opinion, but by what the media has told you to worry about.

turbof1
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Re: Concept for regulations to improve overtaking

Post by turbof1 » Mon May 15, 2017 12:45 pm

everythingisawesome wrote:
Mon May 15, 2017 12:29 pm
I don't get it. You guys don't like watching the drivers dive and dice with each other during a race?

What's more exciting at the end of the race, those couple of epic battles, or the amount of overtakes?
This was never something that was discussed last year, never did I hear anyone say ' oh wow there were a lot of ovetakes during that race'

I feel like a lot of the F1 fans start concerning themselves with 'problems' in the sport, not by their opinion, but by what the media has told you to worry about.
I don't believe you made a good effort to read the first post... . What is being proposed here, are not artificial overtaking aids, but aerodynamic optimisation for following eachother closely, setting up for epic battles.

Steven
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Re: Concept for regulations to improve overtaking

Post by Steven » Mon May 15, 2017 12:46 pm

Wonderful post jjn9128, welcome at F1T!

everythingisawesome wrote:
Mon May 15, 2017 12:29 pm
I don't get it. You guys don't like watching the drivers dive and dice with each other during a race?

What's more exciting at the end of the race, those couple of epic battles, or the amount of overtakes?
This was never something that was discussed last year, never did I hear anyone say ' oh wow there were a lot of ovetakes during that race'

I feel like a lot of the F1 fans start concerning themselves with 'problems' in the sport, not by their opinion, but by what the media has told you to worry about.
The thing is, if we would find a way to properly enable cars to chase each other down again, we could get rid of DRS. There used to be some "epic battles" before there was DRS, you know ;) The latter was only introduced because it had become nearly impossible to overtake without it (and because the adjustable front wing didn't help at all :mrgreen: ).

Just_a_fan
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Re: Concept for regulations to improve overtaking

Post by Just_a_fan » Mon May 15, 2017 1:14 pm

everythingisawesome wrote:
Mon May 15, 2017 12:29 pm
I don't get it. You guys don't like watching the drivers dive and dice with each other during a race?

What's more exciting at the end of the race, those couple of epic battles, or the amount of overtakes?
This was never something that was discussed last year, never did I hear anyone say ' oh wow there were a lot of ovetakes during that race'

I feel like a lot of the F1 fans start concerning themselves with 'problems' in the sport, not by their opinion, but by what the media has told you to worry about.
Some of us enjoy the racing and the technical side equally.

Does knowing how a rainbow forms make it less beautiful? No. Indeed, knowing the science behind it, for me, makes it even more beautiful.
Turbo says "Dumpster sounds so much more classy. It's the diamond of the cesspools."

everythingisawesome
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Re: Concept for regulations to improve overtaking

Post by everythingisawesome » Mon May 15, 2017 2:20 pm

I'm not knocking the science, engineering, or what you're suggesting here.
Whatever you do to 'help' your competitor follow you closely is not racing. It's an artificial way of making things more 'exciting'.
By writing something like that into the rules, you are doing just as much harm as DRS.
Let the teams build the fastest cars, and work around the challenges as they come.

P.S I agree with you Steven, back in those days.. there was no 'overtaking strategy group'. Teams just raced!

jjn9128
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Re: Concept for regulations to improve overtaking

Post by jjn9128 » Mon May 15, 2017 2:33 pm

everythingisawesome wrote:
Mon May 15, 2017 12:29 pm
What's more exciting at the end of the race, those couple of epic battles, or the amount of overtakes?
I 100% agree. I think we were robbed of a better battle between Hamilton and Vettel in Barcelona by the DRS. Sadly Vettel just couldn't defend against the Vmax advantage. The point of this is that we are being robbed of the capability of drivers to have those battles by the aerodynamic effect of the wake - which has definitely increased this year. To this end what I am suggesting is not necessarily an increase of overtaking frequency but rules which allow the drivers to follow around a lap and then use their skill to overtake. While also being able to defend rather than have to contend with a 15-20kph overspeed. It's not just aerodynamics which affect this though. In recent memory the most epic battles we see are between teammates because (with the exception of Rosberg/Hamilton) they don't drive each other off the track on corner exit and the battle can continue onto the next straight/corner. There is certainly an argument for having a driving etiquette rule to facilitate battling. It's difficult to come up with a concise title to express this...


turbof1 wrote:
Mon May 15, 2017 12:23 pm
I was wondering though: Aside any ethical objections, would wheel covers decrease dirty air coming from the rear wheels and therefore ultimately improve overtaking?
This is a tricky one. I certainly cannot see wheel covers/fairings becoming a part of F1 for quite a while, especially as some form of cockpit protection is being promised for 2018.

Wheels are bluff bodies (compared to the fairly sleek upper bodywork) and so create large wakes. This plot is from the Perrinn 2017 car (so I think it's okay to use) showing total pressure in the wake (i.e. static + dynamic). The more blue the heat map the lower the velocity of the airflow - you can see the wake is really concentrated behind the wheels and diffuser. This car generates ~75% of the downforce of the top teams this year so the diffuser exit on a top car will be even lower energy. I think it is obvious that fairing the wheel with an aerodynamic profile will reduce the size and strength of this wake but there could well be a conflicting effect.
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Wheels are also rotating and produce a lot of unsteadiness (low frequency turbulence) from the various vortices shed from the tyre, wheel and hub. Unsteadiness is not necessarily bad though, I did some experiments making the wake steady state which had a 7-8% greater effect on following vehicle downforce than a time varying wake. This is because the mean (velocity squared) in the wake is not the same as the (mean velocity) squared . e.g. if velocity varies between 9 and 11m/s, the mean velocity is 10m/s so the (mean velocity) squared is 100m/s BUT the mean (velocity squared) is 101m/s meaning the dynamic pressure effect is 1% less. Between 8 and 12m/s (more unsteady) the mean (velocity squared) increases to 104m/s or a 4% reduction of the Pdyn effect. Ultimately though, I think fairing the wheel would reduce the impact of the wake more significantly than wake unsteadiness does.

The short answer is I think it would be beneficial - but wake from the floor/diffuser is as bad as the wheels on a current car which is why I also suggested a contoured underbody without strakes/vanes.

turbof1
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Re: Concept for regulations to improve overtaking

Post by turbof1 » Mon May 15, 2017 2:33 pm

everythingisawesome wrote:
Mon May 15, 2017 2:20 pm
I'm not knocking the science, engineering, or what you're suggesting here.
Whatever you do to 'help' your competitor follow you closely is not racing. It's an artificial way of making things more 'exciting'.
By writing something like that into the rules, you are doing just as much harm as DRS.
Let the teams build the fastest cars, and work around the challenges as they come.

P.S I agree with you Steven, back in those days.. there was no 'overtaking strategy group'. Teams just raced!
Then racing and close racing is artificial on its own, as it exists ultimately only to entertain. The breaking point with DRS is that you purposely give one driver an uncompetitive advantage over the other.

Let's not turn this into a philosophical debate. If you don't like this debate: nobody is forcing you to participate. Rather, that would require a topic on its own.

Dynamicflow
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Re: Concept for regulations to improve overtaking

Post by Dynamicflow » Mon May 15, 2017 3:00 pm

Many thanks for sharing your findings, jjn9128.

I was wondering if you have run your concept car in various drafting scenarios and checked if it is any better than the current situation?

jjn9128
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Re: Concept for regulations to improve overtaking

Post by jjn9128 » Mon May 15, 2017 3:44 pm

Dynamicflow wrote:
Mon May 15, 2017 3:00 pm
I was wondering if you have run your concept car in various drafting scenarios and checked if it is any better than the current situation?
Not yet. I am no longer at my institution so don't have access to commercial CFD or a nice big/fast HPC. I just downloaded a port for running openfoam on windows so I'm going to see if my laptop can handle a simple 1/2 car simulation.

I did run a simple case with a low aspect ratio rear wing added to the test car from my PhD. Unfortunately those tests are in a paper which is currently in review (journals own the copyright of images once submitted) so I can't share any plots from it. But it does indicate what I have said about increasing the downforce contribution of the rear wing using a low aspect ratio wing.