More data on smooth wheel covers effectiveness

[California98Civic]

Great pictures. Thx. Noteworthy, too, that these designs are beyond what Porshe deemed safe for brake cooling. It's almost as if maybe Hyundai does not expect its cars to get driven like a Porshe.

[oil pan 4]

With my leaf normally I can stop, get out and put my finger on the brake rotor with out it being uncomfortably hot.
If you have some brake regen, and can keep it under 140mph no need for massive brake cooling.

[JulianEdgar]

Horses for courses, of course. When in my Gen 1 Insight I brake from 125 mph to 60 mph at the end of a local straight, I don't want brake fade.

As I have said, I've never read any formal reference that doesn't mention the importance of brake cooling when developing aero wheels for road cars. They all mention it!

[COcyclist]

OP- Thank you for posting this. I especially liked the color representations in the full paper. There is one thing I would like to point out. In post #1 the graph you posted is from the averaged wind tunnel vs CFD results. I was shocked by the amount that front lift went up in the graph. As I read the whole article I found there was a discrepancy between wind tunnel and CFD results. The wind tunnel did not show such drastic increase in lift with the fully blanked wheel. I copied the following from the conclusions.

"Overall, CFD predicts the trends from the wind tunnel results well; however, in the case with the fully blanked wheels there is a noticeable over-shoot in the drag decrease and the front lift increase. CFD also fails to capture the drag trend for the smallest centre blanking (350mm), though it predicts the rear lift trend well. Based on these two cases, it is thought that CFD over-predicts the effects of the interactions between the onset flow and the flow through the front wheels."

The CFD was done without modeling turning wheels. Great article. Thanks.

[JulianEdgar]

Originally Posted by COcyclist

OP- Thank you for posting this. I especially liked the color representations in the full paper. There is one thing I would like to point out. In post #1 the graph you posted is from the averaged wind tunnel vs CFD results. I was shocked by the amount that front lift went up in the graph. As I read the whole article I found there was a discrepancy between wind tunnel and CFD results. The wind tunnel did not show such drastic increase in lift with the fully blanked wheel. I copied the following from the conclusions.

"Overall, CFD predicts the trends from the wind tunnel results well; however, in the case with the fully blanked wheels there is a noticeable over-shoot in the drag decrease and the front lift increase. CFD also fails to capture the drag trend for the smallest centre blanking (350mm), though it predicts the rear lift trend well. Based on these two cases, it is thought that CFD over-predicts the effects of the interactions between the onset flow and the flow through the front wheels."

The CFD was done without modeling turning wheels. Great article. Thanks.

As I said in Post #2, the graph displays the difference in CFD prediction vs wind tunnel results (ie the error) - not the actual changes in drag. The heading explains that - change of CD from CFD minus change in CD from wind tunnel.

[Vman455]

Originally Posted by COcyclist

The CFD was done without modeling turning wheels. Great article. Thanks.

Also, it should be noted that they did model wheel rotation. Under 18.2 Methodology:

A complete moving ground plane was simulated using the sliding wall boundary condition, and the wheel rotation was included using a sliding mesh representation on all parts of the wheel except for the tyres, which had a rotating wall boundary condition applied.

And in the conclusion, they point out the error in the modeling of tire rotation specifically:

The obvious discrepancy between the experimental setup and the computational is the axisymmetric modelling and lack of true rotation of the tyres in CFD. As no account is taken to the rotational shape changes, it will invariably have an effect on the computational results.

[aerohead]

Originally Posted by oil pan 4

Typical wheel found on US cars trucks and SUVs through the 1990s. Now resides on my trailer.


Auto makers put vents on wheels because they look cool and make the wheel lighter, they don't really start to make any functional difference until you are on a race track.

From a safety standpoint,wheel porosity/aspiration as a function of brake heat flux dissipation,has been an issue for a century.
Worse-case scenarios would be factored into design, in order to prevent brake fade,especially descending extended mountain grades while pulling at gross vehicle weight load.Engineers must anticipate motorists operating right at the edge of the envelope.Fatalities are bad for marketing.

[aerohead]

Originally Posted by JulianEdgar

Brake cooling has been part of road car wheel design for at least 50 years. For example, a textbook I have on brake design that was published in 1967 mentions it.

In a current context, a recent Porsche paper I was reading on the development of an aerodynamically slippery wheel spends over half that section on the difficulties of developing an aero wheel that doesn't too adversely impact brake cooling. In fact, you can see exactly how much extra drag they accepted in order to achieve adequate brake cooling.

I think every reference (text or paper) that I read when writing the section in my book on wheel drag mentions the importance of brake cooling.

No kidding! There's a whole train of product-liability attorneys who'd love to take on class-action lawsuits against any auto maker who inadvertently overlooked brake compromise/failure during R&D.
In the 1970s,heading eastbound into Chattanooga,Tennessee,one might notice the 'orange landscaping' at the bottom of mountain valleys,from all the ROADWAY tractor-trailer rigs who's brakes burned up,while failing to find a runaway truck ramp in time to save itself.

[aerohead]

Originally Posted by Tahoe_Hybrid

i thought they had asbestos brake pads back then
I saw a set of pads that said "now without asbestos". that my grandpa had in the garage that was sitting there for ages..

The medical injury,class-action lawsuit against John-Mansville Corporation, for asbestosis and mesothelioma drove clutch disc and brake shoe/pad technology away from bonded asbestos friction surfaces.A friend's husband died from his job remanufacturing clutch discs.Dead worker.Dead husband.Dead father.Not good.

[aerohead]

Originally Posted by California98Civic

Great pictures. Thx. Noteworthy, too, that these designs are beyond what Porshe deemed safe for brake cooling. It's almost as if maybe Hyundai does not expect its cars to get driven like a Porshe.

Bear in mind that,there remain sections of the Autobahn and Autostrada, which are posted for unlimited speed.And since Porsche cars are capable of significant velocity,in a 'panic' situation,the cars must be capable of dissipating tremendous quantities of heat energy to avoid collisions,something Hyundai might not have to design for.
Hyundai's track version of the Veloster may have high-porosity wheels,with enhanced load-shedding capacity.Same for Honda's Type-R.A few others.