I agree -- thing is, a golf ball is round, bodywork surfaces are not. Drag reduction is the only thing a golf ball is after and the dimple created boundary layer works in the case of the golf ball.

Aero vehicles and associated aerofoils need boundary layer control (VG's) to work efficiently -- its all about the L over D relationship. Surface separation on a wing's working surface is a bad thing -- it limits L and add's D.

 

Here is a shot of flow-visualisation I did at a track test - -this one of the VG at the tunnel entrance -- interesting stuff indeed..

 

what is that your are using to create those flow marks. Some sort of paint I would guess. What apply drops and let the air flow move cuase them to "flow".

 

Cover one side and leave the other uncovered and see if it pulls to the uncovered side.

 

Here is a good article about dimples used in racing.
Basically, they can be effective in the same way that vortex generators can be used. this article talks about use on the wheels. Use on the body will probably not work or decrease drag.

http://www.racecar-engineering.com/a...-surfaces.html

and about different types of dimples on golf ***** and their effect on lift and drag.


http://ecomodder.com/forum/showthrea...mics-6263.html

 

Those are some great shots and a great technique to show flow direction and stagnation. A few dabs of whiteout or water colors and hit the road at 120mph and see how they streak????

mk

 

Agreed, especially on that track (MSR Cresson). Maybe at TWS or VIR or Road America, but not MSR.







Professional Racing and Driving Coach

 

Chris, interesting photos. How do you identify when the air separates?

Mark my point was your reference to needing only 50 HP to overcome drag. Friction is a component but most of the work being done by the engine is to overcome drag once the car is at top speed.

I'm not saying the dimples work but the idea is certainly novel. I don't think we'll see it in F1 mind you, those guys massage every component to minimize drag and create the downforce they want with minimum loss.

Best,

 

I would guess if there is no paint on the bodywork, the air has separated.

 

Yes, its only about 50hp to overcome drag aero drag at 100mph. Friction is still a component, but its relatively constant. Its built into this drag number if we look at 4-500hp to go 200mph. I remember hitting 120mph with my moms100 rwhp hp toyota in high school. If most of the power required is for drag, its easy to see that at 100mph, power required would be 60rwhp.

The point is, we are not eliminating all of the drag, right? Maybe only a percentage of it, even if it did work, and lowered drag Cd, and most think it will not, what percentage could it help? 1, 2, 5%?? not enough power here to save enough power to help lap times by any measurable amount.

Lets put it in perspective. I added a cup car wing and tilted it about 5 degrees. It creates about 200lbs of downforce at 100mph. Do you think the dimples could save this much drag????? Drag force for this wing will be about 20lbs.
(these kind of efficient wings have a 10:1 lift to drag ratio)
Through a 4.5:1 gearing, and 100mph, the net effect on the car's engine might be 4ft-lbs assuming a 24" diameter drive tire. (assuming a 5600rpm it would be near 5hp). 5HP cost for a wing that is creating 200lbs of downforce! Do you think this bubble wrap dimple wrap can save more drag than a wing can create?? and even if it did, its ..................4hp. 4hp is not worth 2 seconds a lap.

Sure, at 150mph, its a lot more, but assuming aero curves, the cost at 150mph would be 16hp. Still not enough to improve lap times much if the losses were gains through the use of dimples.

Now, if you doubt this, all you need to do is plug the drag coefficients into the drag formula and get your answer for total drag force. (based on speed, air density, Cd and frontal area).

mk

PS (Edit) This could be answered with some quality time in a wind tunnel. Instead, they got a B rated driver to conduct a driving test comparison and used smokers and wind to determine air separation. What they really needed was a test in a wind tunnel to determine if the "dimple wrap" actually lowered the drag coefficient. Im pretty sure it would not. the golf ball handles separation of the flow off the ball with the dimples and also uses them to create lift. our cars use rear wings and spoilers to reduce separation. I guess if you really wanted a race car application, it might be on cars with no aero additions. like maybe the entire back of a stock car could be peppered with dimples. It might have the same effect as a rear spoiler.

 

Interesting video to be sure. All valid, drag reduction, etc. My daughter wears a fast suit with this technology in the pool as do Olympians. Pretty sure an Olympian can benefit from it, the handful at that level anyways, we know airfoils do. For the rest of us and for cars, etc, I would bet the advantage comes from "thinking" you will be fast.
The mind is a powerful thing and it is pretty well proven that prepping yourself mentally can help lap times a lot. If someone wrapped my car with a state of the art material and told me it would make me quicker I bet it would make me "think" quick and drive as such.
I do know my money would be better spent on new rubber

 

Don't buy 2 seconds unless it's the Nurburgring. And still iffy then. If it's wind tunnel tested, the wind tunnel results would tell us all we needed to know. Maybe they left that part out because they wanted to focus on the lap time, maybe there is wind tunnel data posted elsewhere. If not, serious black mark on them IMO. Just give the concrete data. Even do a long road trip and then replicate it on a similar day, see how many more miles you get.

If they had the concrete data, seems they would have shown it though, which makes me doubtful.

 

As an avid student of aerodynamics, I can tell you that this idea on a car absolutely does not work.

The small dimples on a golf ball do work because of it's spherical shape and the pocket of air that encases the ball as it travels through the area. Because a car has so many different angles and shapes, the dimples do not work as they would on a golf ball.

Formula 1 teams and their aerodynamicists studied if the same dimple effect would work on their cars many years ago and found that it was actually slowing the cars down. This was tested in wing tunnels as well as the track.

Because of the aforementioned multi-angular cars, smoother surfaces actually work better. In fact, many F1 teams no longer paint the leading edge of their wings and body work on their cars because of the tendency of the paint to get chipped up during the course of a race from debris of other cars that they are following or their own exposed tires. As a result of the chipped paint at the leading edge, aerodynamicists found that their vehicles were actually less efficient and had more drag because of the uneven edges to their wings.

A few things come to mind when I saw that film:

1. The testing was less than scientific in that the 15 lap runs in the morning with the wrap were probably is cooler temps than in the afternoon sans the wrap. In Texas where this was conducted, that could be a big difference.

2. There was never any mention made of the subsequent 15 laps run with fresh tires. If they ran the tests with the same set of say Hoosiers, the grip level of say A6s will not be the same as the first 15 laps as they are always faster when new. Once again, nothing was said about tires and we're assuming the tires were new to begin with, but they could have been corded for all we know.

3. When in doubt, follow the money trail. This was a good PR piece for this guys wrap business, but there is not a huge market for track cars with dimpled wrap. However, what the owner is angling for is expanding his business to the almost never ending trucking business where if this wrap thing took off, it could make him and others in the business multi-millionaires.

 

Mark I am realy intrigued. If it only takes 50 HP or so to overcome drag how come my 415 HP car cannot exceed 193 MPH? I'm missing something here.

 

50 hp to overcome how much drag? There has to be a quantifiable amount to determine how much hp is needed to overcome it.


But on another note, who would put that ugly mess on their car to begin with? If they could make it all the same color it would probably still look like crap, but that looked aweful on there.