Open wheels and aero............

[Sumner]

 

We have wondered about the air around an open wheel/tire.  Jon posted pictures of the 66 car at El Mirage that are good shots of the dust around the wheels/tires.  I blew them up and I'm interested in anyone's' thoughts.



c ya,

Sum

[Graham]

A friend of mine that's now working at Toyota F1 is just finishing his PhD in a topic closely-related to open wheel aero.

There's been a fair bit of research done in this field over the years, including on the drag/wake properties... Fackrell and McManus are two names that spring to mind. Fackrell will certainly have been cited by dozens of others by now, his wind tunnel experiments were done in the 70's I think. I know technical papers can be a bit hard to get hold of if you're not at a university or company that pays for access, but google or scholar.google often turns up freely-available stuff.

[Rex Schimmer]

Sum,
Always an interesting subject for the "open wheel" guys. Looking at the picture I think that the dust shows pretty much what is expected and that is attached flow over the top of the tire to about the 20 degree mark and then seperation with a turbulent flow pattern for the remainder of the back of the tire. This area is low pressure and makes up most of the tires drag as pressure drag.I think that you also see some dust being kicked up by the bottom of the tire as it runs over the lake surface and this goes directly into the low pressure area behind the tire.  I have often considered using some sort of "turning vane" to take air that is passing the wheel and turn it into the low pressure area behind the wheel. I think that as long as the vane did not pass the verticle plane of the tire it would be legal. I have seen something like this on the McLeish Brother's car when they run it as a lakester. They have a small turning vane below the front axle that turns the air to the back of their front tires. The question is always " Does turning the air to fill this void behind the tire reduce drag more than the drag of the turning vane?" Which probably means that the actual shape of the turning vane should be some sort of cambered airfoil section with a very low drag coefficient. Great thing to try at a wind tunnel!

Rex

[John Burk]

The tops of Joe Law's and Fast Freddy's tires are near sonic .

[Dynoroom]

The tops of Joe Law's and Fast Freddy's tires are near sonic .

That's very interesting John. What do you think that means to airflow? I know we don't want are engine intake ports to go sonic, but you can't do anything with the tire going sonic.
What about in a streamliner, does the tire going sonic have some type of effect?

Rex, I think you have a valid point but in the picture could we be seeing something similar to what happens to a fuel dragster tire? The air comming up from the bottom of the tire being sucked back up creating a pressure wall? Not sure how to put it into words. I think I might like your hypothesis better anyway.

[sabat]

Here's a couple figures I found digging around teh internets that might be relevant. Cover the top half of the wheel is the gist I guess, Kent Riches could have told us that, eh?

Fackrell;


Regert et al;

[Dean Los Angeles]

The speed of sound in dry air at seal level is 761 mph. Half of that is 380 mph. Any car going over 380 mph has the forward air speed meeting the tire going the other way at 380.

So Fast Freddy and Joe Law might be close, but there are others that are over! Because it is a rotating surface the interactions may prevent exceeding the speed of sound until higher speeds, but very interesting.

Ok, so you had to know that the flow would look something like that. What can you do about it?

[Sumner]

The question is always " Does turning the air to fill this void behind the tire reduce drag more than the drag of the turning vane?" Which probably means that the actual shape of the turning vane should be some sort of cambered airfoil section with a very low drag coefficient. Great thing to try at a wind tunnel!  Rex

After seeing some of the F1 cars and what they have done, I've thought about the "vane" thing for a couple years and would like to try it some time in the future after I have some base data, since I don't have that "wind tunnel" thing  .

c ya and sabat thanks for the illustrations,

Sum

[John Burk]

On Don Vesco's fastest run the tops of the tires were going well over 900 m/h but the air in the tire well was moving with the car so no sonic boom . Hasn't Freddy had an exit of around 370 ? If so , tops of the tires were going 740 , mach .97 .

[Graham]

Due to altitude, the speed of sound at Bonneville is likely to be more like 750mph, maybe slightly less depending on the weather.

The question of sonic flow on the wheel is an interesting one. The displaced air accelerates over the wheel such that its peak speed above the wheel is significantly higher than the speed at which the car is travelling, but the air the wheel is hauling around with it only has the wheel speed right at the wheel surface. There will be a mixing zone between the wheel surface and the air flying over the top, but it's hard to say what will happen there, if there will be any actual supersonic flow. I would doubt it. Googling supersonic cylinders might throw up some information on what could happen though!

You would never hear a "sonc boom" from it alone though - that's created by a completely different mechanism.

[Rex Schimmer]

The fact that the top of the tire is going sonic for cars over 380 mph is only valid for cars with exposed wheels. On a streamliner the wheel/tires are enclosed and on the good ones they are in a well sealed enclosures to minimize air pumping effects.

Rex

[Stan Back]

I don't think you'd hear it over the other noises made by Fast Freddy's car, any way.

[wolcottjl]

A little google tonight found the following.  Might help - Might not

Race Car Wheel flows   http://www.cranfield.ac.uk/automotive/research/projects/aerodynamics/page24160.jsp

Race car Wheel flows F1 flow using laser doppler




A.J. Saddington, R.D. Knowles, and K. Knowles, "Laser Doppler Anemometry Measurements in the Near-wake of an Isolated Formula One Wheel", Experiments in Fluids, 2007, 42(5), pp 671-681. [ISSN 0723-4864 (Print), 1432-1114 (Online), DOI 10.1007/s00348-007-0273-7]

R.D. Knowles, A.J. Saddington, and K. Knowles, "On the Near Wake of Rotating, 40%-scale Champ Car Wheels", SAE 2002 Transactions - Journal of Passenger Cars: Mechanical Systems, 2003, 6, pp 2245-2253. [ISBN 0-7680-1290-2]

R.D. Knowles, A.J. Saddington, and K. Knowles, "Simulation and Experiments on an Isolated Racecar Wheel Rotating in Ground Contact", 4th MIRA International Vehicle Aerodynamics Conference, Warwick, UK, 16-17 October 2002.


Using a detailed semi-truck scale model in its wind tunnel in Indianapolis, ARC found that there was a 12.4% increase in aerodynamic drag with the rolling road, compared to a stationary road.

http://trailer-bodybuilders.com/trailer-oem/aerodynamic_breakthrough_rolling_road_testing/

"I wish I had done my degree at the Imperial College; the resources and academics were excellent and there were good workshops and backup. What one gains there is a proper understanding of the building blocks of aerodynamics. The flow around an open-wheel racing car is very complex: the front wheels generate rotating turbo-machinery type flows and right near them is the vortex inducing tip of a wing. An understanding of embedded vortices is essential to analyse the flow in an objective manner. I have learned that for this type of work it is necessary to recruit people with the right kind of background, people who are academically solid, good at experimental aerodynamics and who are prepared to get their hands dirty. The Imperial College attracts and hones engineers and researchers with the right characteristics."

PHD Opportunity at Durham College - Air flow about an exposed racing car wheel RDDBS2


Contact is
r.g.dominy@durham.ac.uk

The wheels of an open-wheel racing car provide a major source of aerodynamic lift and drag. It is therefore essential that engineers have a thorough understanding of the air flow about those wheels and of the interaction of those flows with other parts of the car. However, reliable experimental techniques to achieve these measurements have proved to be elusive and numerical simulations have as yet failed to provide accurate simulations. The purpose of the proposed research is therefore to investigate existing and novel alternative measurement techniques in order to perform detailed studies of the flow physics associated with the air flow about a rotating wheel.

Contact is
r.g.dominy@durham.ac.uk

[sabat]

So wind tunnels without a rolling road maybe be misleading for open-wheel vehicles... Huh.

Quoting Auto Research Center Ops Mgr Mike Camosy;

"He says the rolling-road concept is nothing new. Previous research by ARC with vehicles ranging from passenger cars to open-wheel racecars has shown that rotating wheels play a key role in aerodynamic performance. In many tests at the ARC, it has been found that changes made to a vehicle may show a drag decrease in a fixed-floor tunnel test, yet show an increase when the wheels are rotated.

The opposite effect has also been witnessed. Camosy says this highly non-linear interaction of rotating wheels with the overall air flow around the vehicle must be considered carefully when designing aerodynamically optimal vehicles. He believes ARC's study confirms that this is also the case for tests conducted with rotating wheels on both standard production vehicles and Class 8 trucks.

“Each evaluation yields similar dependency trends, which emphasizes drag reductions found with fixed non-rotating wheels are at times drag increases once the wheels are rotated and vice versa,” he says."

[SPARKY]

Mike and Rex---is this what you are refering to?