End plates for rear flip-ups

[AeroGT3]

Also make sure the nose cone has a virtually flawless join with the monocoque bodywork, i.e. no obtuse angles, which i have seen on some formula student cars lol. Also joins etc become less critical the further you go back, and keep it very clean, to avoid tripping the boundary layer and generating turbulent regions of flow. Any more help lemme know Regards.

Unless the nose angles are REALLY big, there's no reason to worry. You're talking about tiny separation regions which re-attach. Also, transition to turbulence is DESIRED for automotive applications. Why would you want a laminar BL? So your wings stall out faster? Laminar BL's have the advantage of lower skin friction drag, but that's irrelevant on a car. Avoiding tripping the BL is bad advice.

[Aerodynamicist#1]

Aero GT3,

Avoiding tripping the BL is bad advice.

I disagree about tripping the boundary layer, i think that you need to keep the flow as clean as possible unless you are specifically trying to re-energise the flow, which you will probably only try to do if you have an advanced aero package. Also please explain how keeping a laminar bl helps to stall the wing faster?? I don't follow this at all, surely with a laminar bl on the wing, the flow will stay attached longer, hence preventing the onset of stall. Please explain this to me.

Regards

Aero#1

[ReubenG]

it is to reduce the lift effect produced by the rear wheel. It may sound strange unless you have studied aerodynamics, but rotating cylinders (i.e. a tyre) produce lift, because the rotation moves the separation point on the upper half further back and so a pressure gradient is set up producing lift. .

Rotating cylinders / spheres in a fluid stream do produce a lift / downforce perpendicular to the flow (Magnus lift). My understanding was that there had to be flow on either side of the cylinder (otherwise there is no fluid pressure gradient) - so how does this work with a tyre where clearly there is no flow under the tyre? Also the direction of the lift / downforce depends on the direction of rotation: with a golf ball, back spin helps add lift. With tyres, the direction of rotation should give a downward force...

So if the rear wheel is producing lift / reducing downforce, I don't believe that the rotating cylinder analogy is the correct one.

[AeroGT3]

I disagree about tripping the boundary layer, i think that you need to keep the flow as clean as possible unless you are specifically trying to re-energise the flow, which you will probably only try to do if you have an advanced aero package.

No offense, but you are way wrong on this, you're reciting a college lecture without understanding the content.

Race cars are dominated by flow separation, not viscous drag. If you have laminar flow over your wheels/body/wings, they're going to separate sooner. Sure, a laminar BL will save you drag on skin friction, but that's a REALLY small percentage of your drag on a racecar or road car.

On a nice clean aircraft wing where viscous drag is about HALF your drag, sure, keep things laminar, it saves you drag. On a racecar that theory will drive your drag way up.

Also please explain how keeping a laminar bl helps to stall the wing faster?? I don't follow this at all, surely with a laminar bl on the wing, the flow will stay attached longer, hence preventing the onset of stall. Please explain this to me

Turbulent flows stay attached longer. This is a classic, basic Aero example. Ever heard of dimples on a golf ball? The famous Cd of a sphere/cylinder drag vs Re plot where drag drops dramatically at the transitional reynold's number? Dig up an aero textbook, surely this stuff is in there somewhere.

[MMUK]

[Aerodynamicist#1]

Race cars are dominated by flow separation, not viscous drag. If you have laminar flow over your wheels/body/wings, they're going to separate sooner.

You still didn't explain why you get separation sooner if you have laminar flow over a wing. I think it is probably you who doesn't understand the physics very well, what you are saying is contradictory to Ludwig Prandtls theories. I am guessing that you have a mechanical background and not an aeronautical background.

So if the rear wheel is producing lift / reducing downforce, I don't believe that the rotating cylinder analogy is the correct one.

I think you may be right about the flow being over both top and bottom, but i am not entirely sure, I am tending to trust the Autosport technical article on this one! The contact of the tyre on the lower surface is equivalent to having zero pressure there hence since there will be a reduction in pressure on the upper surface due to the flow having to negotiate the circular arc camber of the rear wheel, a -ve pressure will occur on the upper surface possibly giving a small lift force and of course a large drag force.

Regards,

Aero#1

[AeroGT3]

You still didn't explain why you get separation sooner if you have laminar flow over a wing.

Are you joking? It just does. That's life. It's been repeated in HUNDREDS of experiments for DECADES across the whole world. I cannot believe a Uni student doesn't know this. The laminar/turbulent separation example is fundamental. This link is from a children's site, but maybe it will help:
http://wings.avkids.com/Book/Sports/ins ... lf-01.html

Why does drag so suddenly drop at exactly the Reynold' number where turbulent transition typically occurs?

what you are saying is contradictory to Ludwig Prandtls theories.

That's probably because you're talking about academic theories (which I think you're misreading) while I'm referring to things I see from wind tunnel and CFD data at my job and industry rules of thumb and textbooks that have existed for decades. Go to your first interview and tell them a turbulent flow separates sooner.

And BTW, which theory are you referring to?

I am guessing that you have a mechanical background and not an aeronautical background.

Actually I've an MSc aero. But even a electrical engineer probably understands this stuff.

[Aerodynamicist#1]

Msc Aero? Haha i think i'm maybe just a wee bit more qualified. Ever heard of stratford pressure recovery? you need to have a laminar flow to be maintained for as long as possible in order for a descent pressure recovery and maximum downforce, because the alpha effective change is not large enough to cause the maassive stall associated with large alpha effective angles when stratford recovery is used for say an aircraft wing. All F1 car rear wing aerofoils are designed with Stratford pressure recovery. The more laminar flow, the greater the pressure differential. The flow is sometimes tripped by some mechanism about 3/4 chord to initiate the recovery but you want to maintain laminar flow up to this point, however for the fella who asked the question, he isn't going to have the resources to work that one out, not even with CFD unless he has allot of time! I think he's gonna want to avoid bumps ripples, parasites etc on his bodywork as best he can I'm sorry but you couldn't even name an aero text - go read Anderson's Fundamentals of Aerodynamics. By the way

It just does.

what a poor arguement, i'm sure that one gets you far! Haha

[Gecko]

Both laminar and turbulent flows are desireable, but both in different regions of the flow.

Laminar flow is indeed desireable in the areas of flow acceleration along the surface (favourable pressure gradients). Any obstructions in these areas should be removed if skin friction is important. Turbulent flow in these areas doesn't help at all.

The laminar flow, however, starts to separate in the areas of large enough adverse pressure gradients. In the places where the flow starts to slow down, you want a very swift transition to turbulence which helps bring some more momentum close to the surface and delays the flow separation. In this regime, the Stratford pressure recovery shape is designed such as to minimize turbulent skin friction while keeping the turbulent flow still attached. You might actually want to err on the side of more skin friction, as the explained situation is very marginal, often causing laminar airfoils designed with such a philosophy in mind to become quite useless due to increased separation when the flow conditions aren't ideal.

In the sphere example; ideally you want the flow to remain laminar up to the middle of the sphere, at which point you want it to transition to turbulence in order to keep the boundary layer attached for longer.

[AeroGT3]

Msc Aero? Haha i think i'm maybe just a wee bit more qualified.

Really? Your profile says you're a 4th year student. So either, you are VERY slow at getting your advanced degree (...), or you have no degree at all. Also, asking questions this basic makes me think you aren't qualified at all: viewtopic.php?f=6&t=6011&p=84700#p84700 You do realize your posting history and profile are viewable by all? Might want to make posts with the coherance of a bachelor's degree holder before claiming you've got degrees beyond an MSc. BTW, how's your multi gridding report going?

Ever heard of stratford pressure recovery? you need to have a laminar flow to be maintained for as long as possible in order for a descent pressure recovery and maximum downforce, because the alpha effective change is not large enough to cause the maassive stall associated with large alpha effective angles when stratford recovery is used for say an aircraft wing.

I suggest you return the books to the library and go get a job.

All F1 car rear wing aerofoils are designed with Stratford pressure recovery. The more laminar flow, the greater the pressure differential. The flow is sometimes tripped by some mechanism about 3/4 chord to initiate the recovery but you want to maintain laminar flow up to this point, however for the fella who asked the question, he isn't going to have the resources to work that one out, not even with CFD unless he has allot of time!

Any gains from these small increases in pressure differential provided by the laminar flow are erased by the HUGE decreases in pressure differential when the wing STALLS EARLIER. RACECARS ARE NOT AIRCRAFT.

You are applying ways of decreasing drag on aircraft in cruise conditions to race cars. Guess what? F1 rear wing CL = 4. Aircraft cruise CL's are ten times smaller or more. Laminar flow on a nose that separates WILL re-attach, so the advice to keep it smooth at the expense of enormous cost and manufacturing difficulty is pointless. You're worrying about laminar flow for tiny amounts of pressure recovery on a rear wing which also has MASSIVE total pressure losses due to the wake of the car and driver in front of it? At a Formula student level, he is MUCH better off just getting it all turbulent and having it stall later than gaining 0.00000001% from keeping the nose laminar instead of accepting small separation and re-attachment.

I suppose you also believe us CFD users are wasting our time because we haven't heard the theories of 12th order accurate DNS schemes

I think he's gonna want to avoid bumps ripples, parasites etc on his bodywork as best he can

Pure bullshit. Can you defend that and substantiate how a ripple on the nose will ever make a significant difference?

I'm sorry but you couldn't even name an aero text - go read Anderson's Fundamentals of Aerodynamics. By the way

It just does.

what a poor arguement, i'm sure that one gets you far! Haha

I guess you skipped the part of Anderson's book where he explains that a turbulent boundary layer stays attached longer. Or the decades of Boeing and Airbus conclusions. Or every book/paper on high lift aero ever written. Or the complete EXISTENCE of vortex generators, who's sole purpose is to keep flow attached longer than it would were it left laminar. Looks like YOU need to be doing some reading, kid.

What are you, a 19 year old student?

[Scotracer]

Aerodynamicist#1 I really am perplexed by your arrogant claims at being the "#1" in this field. I am a final year Mechanical Engineering student and plan to go on for an MSc in Automotive Aerodynamics or Aeronautical eng and at no point have I ever claimed to be all-knowing in the subject

If you think the boundary layer stays attached longer on a surface during laminar regime...why do golf-balls have dimples? Go ask your high school physics teacher if you must

AeroGT3, do you have any specific papers on the effects of a road wheel in fluid flow? I can only find one SAE paper; I do need to get a bit more background on this particular topic for my Formula Student car. I tried asking my Fluid Dynamics Prof but he didn't have anything off-hand to suggest.

Cheers,

Scott

[AeroGT3]

AeroGT3, do you have any specific papers on the effects of a road wheel in fluid flow? I can only find one SAE paper; I do need to get a bit more background on this particular topic for my Formula Student car. I tried asking my Fluid Dynamics Prof but he didn't have anything off-hand to suggest.

Cheers,

Scott

A. F. Skea and P. R. Bullen,
CFD Simulations and
Experimental Measurements of
the Flow Over a Rotating Wheel
in a Wheel Arch, SAE Paper No.
2001-01-0487, 2000.


It references other papers you might want to check out.

I'd mesh a simple wheel up and solve it though, then you can take out of the results what you are looking for.

[Ciro Pabón]

Sorry for intruding in this interesting and abstruse conversation.

I just wanted to say that the previous posts show, patently, why in engineering discussions is such a bad idea to claim authority. I thought about it when I saw the first arguments of that kind.

Cicero said something that I think all engineers should learn by heart:

... in discussion it is not so much authorities as determining reasons that should be looked for.

In fact the authority of those who stand forward as teachers is generally an obstacle in the way of those who wish to learn, for the latter cease to apply their own judgment, and take for granted the conclusions which they find arrived at by the teacher whom they approve.

Nor am I in the habit of commending the custom of which we hear in connection with the Pythagoreans, of whom it is said that when they affirmed anything in argument, and were asked why it was so, their usual reply was “the master said it,” “the master” being Pythagoras, and the force of preconceived opinion being so great as to make authority prevail even without the support of reason

On the nature of the gods", I, V

And that's why every time somebody says that he knows more than some other person, engineers should become suspicious. If he has so much experience, surely he can explain the reasons, instead of claiming authority. In the end, authority comes from your ability to explain things. It's something other people think about you, not something you can claim about yourself.

Besides, I think it's bad taste and it's against the Code:

Engineers shall not maliciously or falsely, directly or indirectly, injure the professional reputation, prospects, practice or employment of another engineer or indiscriminately criticize another's work.

ASCE Code of Ethics

Of course, as Barbosa would say: "And thirdly, the Code is more what you’d call ‘guidelines’ than actual rules."

Please, don't answer this post, which is totally OOT. I can take any nagging about it by PM...

[Scotracer]

AeroGT3, do you have any specific papers on the effects of a road wheel in fluid flow? I can only find one SAE paper; I do need to get a bit more background on this particular topic for my Formula Student car. I tried asking my Fluid Dynamics Prof but he didn't have anything off-hand to suggest.

Cheers,

Scott

A. F. Skea and P. R. Bullen,
CFD Simulations and
Experimental Measurements of
the Flow Over a Rotating Wheel
in a Wheel Arch, SAE Paper No.
2001-01-0487, 2000.


It references other papers you might want to check out.

I'd mesh a simple wheel up and solve it though, then you can take out of the results what you are looking for.

Thank you, Aero.

Will look more into this in the coming week.

[alelanza]

Sorry to revive this one, but can anyone confirm that a forward rotating tyre on an open wheel car would produce downforce as the flow over it slows down/pressure increases?
And if so, is it significant?
TIA