Taycan CT vs Hummer EV

JimBob

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Model what?
Hypothetically, you want to design a car and try out different geometries. Instead of building a full size car, you build a quarter size model. Test that in the wind tunnel. Providing the geometries don't change, scale it up. One of the reasons for dimensionless parameters is to allow scaling. It's done all the time with aircraft and boats.

Do I have to provide authorities on modeling and scaling?

I'm guessing F1 doesn't do this.
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In lifted mode, the top of the Taycan didn’t reach the bottom of the Hummer’s windows. And I was staring up into the wheel well from the driver’s seat. What a mammoth vehicle.
I had an encounter with one at a local EV watering hole. What a comically enormous monster.

Porsche Taycan Taycan CT vs Hummer EV IMG_20220801_204246


Porsche Taycan Taycan CT vs Hummer EV IMG_20220801_204356


It's amusing but also is kind of embarrassing that this is how some US OEMs think is the only way they can sell an EV to a certain segment of our population.
 

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I like the look of the Hummer the same way i like the Ford Raptor! I'd never get one in the UK! It wouldn't fit😂. Its like a giant loppy dog😂
 

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I like the look of the Hummer the same way i like the Ford Raptor! I'd never get one in the UK! It wouldn't fit😂. Its like a giant loppy dog😂
It's a comic spectacle that's for sure and for now they amuse me more than they disgust me. Hopefully I won't see them in the numbers that they'll clog up roads and parking garages everywhere.
 

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Hypothetically, you want to design a car and try out different geometries. Instead of building a full size car, you build a quarter size model. Test that in the wind tunnel. Providing the geometries don't change, scale it up. One of the reasons for dimensionless parameters is to allow scaling. It's done all the time with aircraft and boats.
You may have implied this in the above, but just to be clear-
In that example, it isn't necessary to know the Cd. A quarter scale model has one sixteenth of the surface area of the full sized thing being modeled. Measure the actual drag force of the model under specific conditions, and multiply it by 16 to get the expected drag force of the full sized thing under those same conditions. The Cd (derived from actual drag force measurement assuming the shape isn't a simple shape that has an already known co-efficient) is more useful for comparing different designs or shapes, because it enables comparison without having to take account of their surface dimensions.
 


Murph7355

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....there is an embarrassing amount of the cheapest plastic known to the auto industry...
tbh I have yet to sit in an American car and not be able to find something of this description included :) It's never a great surprise to see them so cheap compared to other makes.
 

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I have thousands of hours experience wind tunnel and CFD testing cars, mainly Formula 1 but some road car too.

A frequent simplification is often made, which is not to rotate the wheel but IME the flow field around stationary wheels and the ground not moving relative to the car makes big flow field changes which are probably not correctable by a fudge factor.
On one road car I tested with the wheels rotating the cooling air went through the radiator and then under the car with the wheels stationary the radiator exit air came out of the wheelarch so the force data from the non rotating wheel case is obviously not comparable with reality.

I long ago (30+ years) concluded aero testing without rotating wheels and moving ground was a waste of money since I needed real information.

The road car industry was and is massively behind the racing car industry in accurate aero knowledge since until recently (and probably still today) aero is trumped by styling and marketing.

The study you link is a thorough and expensive one but from my experience the starting assumptions mean the results are of questionable use.
Why not put the car in the wind tunnel on a giant treadmill? The difference between the speed of the wind and the treadmill would be the "simulated wind conditions". You could even face the car with the treadmill backwards to simulate tail wind conditions ;)
 

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Why not put the car in the wind tunnel on a giant treadmill? The difference between the speed of the wind and the treadmill would be the "simulated wind conditions". You could even face the car with the treadmill backwards to simulate tail wind conditions ;)
Been doing that since the 1970s in Formula 1 but road car companies either have never done a test to discover the magnitude of the error or have, looked at the costs, and decided not to bother.
There is very little aero data for road cars I would be impressed by.
 


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Been doing that since the 1970s in Formula 1 but road car companies either have never done a test to discover the magnitude of the error or have, looked at the costs, and decided not to bother.
There is very little aero data for road cars I would be impressed by.
Racing surfaces are more uniform and predictable. Road cars face many different surfaces, often deteriorated with holes and pits which more than likely affect air flow above them. That said, I don't know specifically what Mercedes is doing, but they seem to be making good progress in aero of their EV's, even if it results in a rather bland/boring appearance. Their concepts are supposedly getting more and more range out of the same batteries. Of course EV's may go the way of the ICE car, once the charging becomes commonplace enough, customers will forget about range anxiety, and car companies will deprioritize optimizing efficiency.
 

f1eng

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Racing surfaces are more uniform and predictable. Road cars face many different surfaces, often deteriorated with holes and pits which more than likely affect air flow above them. That said, I don't know specifically what Mercedes is doing, but they seem to be making good progress in aero of their EV's, even if it results in a rather bland/boring appearance. Their concepts are supposedly getting more and more range out of the same batteries. Of course EV's may go the way of the ICE car, once the charging becomes commonplace enough, customers will forget about range anxiety, and car companies will deprioritize optimizing efficiency.
The big influence in simulating the moving ground is that it rotates the wheels.
With the wheels not rotating, as is the case with most full sized wind tunnels without simulated road, the flow field is wrong in a way not correctable by a correction factor.

The full size Pininfarina tunnel does not have a moving road simulation byt does have a system to rotate the wheels which sorts the flow field shortcoming, I am told.
 

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The big influence in simulating the moving ground is that it rotates the wheels.
With the wheels not rotating, as is the case with most full sized wind tunnels without simulated road, the flow field is wrong in a way not correctable by a correction factor.

The full size Pininfarina tunnel does not have a moving road simulation byt does have a system to rotate the wheels which sorts the flow field shortcoming, I am told.
It's probably worth noting that computer simulations are getting better and better too. Fluid dynamics simulations today are significantly more powerful than even 5-10 years ago, as processing power is still scaling up at a pretty good pace (we continue to build more and more powerful supercomputers, some of it driven by autonomous driving but the same hardware can do some rather amazing fluid dynamics simulations when the AI geeks are not monopolizing the supercomputer time ;) ).
 

f1eng

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It's probably worth noting that computer simulations are getting better and better too. Fluid dynamics simulations today are significantly more powerful than even 5-10 years ago, as processing power is still scaling up at a pretty good pace (we continue to build more and more powerful supercomputers, some of it driven by autonomous driving but the same hardware can do some rather amazing fluid dynamics simulations when the AI geeks are not monopolizing the supercomputer time ;) ).
Indeed CFD is much closer to accurate than it used to be.
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