Digital Wind Tunnel Video Shows Aerodynamics Of Tesla Model S

MAR 8 2015 BY MARK KANE 12

Exa software was used to explore the flow field around the Tesla Model S. Areas of higher drag are shown in red.

Exa software was used to explore the flow field around the Tesla Model S. Areas of higher drag are shown in red.

Tesla Model S has a drag coefficient of just 0.24, one of the lowest among cars available today and very important to the extend range of the car.

Now we find out that  Tesla was developing the Model S using computer simulations. Without these simulations and the incremental improvements that came from this, the Model S’ aerodynamics likely wouldn’t have been refined so quickly and possibly wouldn’t be at the impressive level we see today.

In an article from 2013, we read that everything begins with a conventional steady-state CFD code that uses the Reynolds Averaged Navier Stokes (RANS) approach to define the eddy viscosity on all scales of turbulent motion.

Rob Palin, Lead Aerodynamicist at Tesla Motors stated:

“The results did not match our expectations, so we switched to PowerFLOW, which uses a fundamentally transient solver and sophisticated lattice-Boltzmann physics models to directly resolve anisotropic turbulence scales. We had confidence based on validation and prior correlation with physical tests that PowerFLOW simulations were an accurate representation of the aerodynamics.”

Then, Exa’s PowerFLOW tool came into game:

“We used Exa’s PowerFLOW transient solver that directly resolves very large eddies to deliver superior accuracy compared to conventional CFD codes. This approach is especially beneficial in areas where flow physics are complex such as in the rear of a curved vehicle. The result is a full-size electric sedan with a drag coefficient of 0.24.”

Wheels alone can generate up to 20% of the drag on the vehicle, while rear-view mirrors another few percent. This would indicate that cameras can extend range by up to about 5%, but at the moment we’re thinking it will be hard to get rid of the wheels.

“The drag coefficient of early design concepts of the Model S was 0.32. The major shape changes reduced the drag to 0.27, and the smaller changes provided further improvement to 0.24. These numbers were validated with wind tunnel testing using standard SAE International procedures, and extended using CFD modeling to add in factors that are not traditionally included, due to practical limitations in experimental testing, but do contribute to the on-road drag of the car.”

Source: SAE International, Teslarati

Categories: Tesla

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12 Comments on "Digital Wind Tunnel Video Shows Aerodynamics Of Tesla Model S"

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There’s nothing really new here.

This isn’t state of the art CFD or science.

This is how industry works. Every company from your local architecture firm to General Electric works like this.

Some less effectively than others, it seems . . .

For reference:

We’ve been able to achieve Cd~0.2 since the 1930’s on great big sedans. Incredibly aerodynamic vehicles aren’t particularly attractive or have appropriate trunk space.

electric-car-insider.com

+1 Philip. Tesla manages a low CoD, great looks and loads of trunk space.

Not sure why, with 100 years of experience, the legacy OEMs can’t manage it.

I think it has something to do with intention.

Well the electric drivetrain is a big advantage for Tesla. Lack of exhaust system, flat bottom, etc. are all helpful.

Tesla keeps bragging about their efficient AC motor drive and great aerodynamics, but the best they can get is 100 MPGe for 85D. It’s a good rating for big car, but far behind 124 MPGe of i3, 119 MPGe of Spark and 116 MPGe of e-Golf. Even the brick shaped Kia Soul EV has 105 MPGe rating.

They are a lot lighter… Thats the reason. Remove 2/3 of the battery, take small tires, reduce the size and Model S will be around 116-120 MPGe.

For example:
S85: 89 MPGe combined
S60: 95 MPGe combined
S40: not rated… Probablly around 101-110 MPGe

And the improved S85D is already at 95 MPGe. Imagine the 60D. This version should already be over 100 MPGe. To bad tesla doesn’t offer the 60D any more.

Exactly. The Model S weighs 4,647 lbs. The Kia Soul EV weighs 3,289. HUGE difference there.

This leaves room for them to get the CD down in the Model 3, plus the total CdA (Coefficient of Drag x Area) could well be less than 80% of the model S!

Model 3 should be shooting for at least 125 MPGe on it, at least to be better than the i3, and if they really work at it – they might be able to hit 130 MPGe out of the gate!

Not sure how my plain Electricfly EV conversion (Lead Acid, 96V) compares in MPGe, but it used about 13,700 Watts at 100 Kph, or about 137 Wh/Km. Extreme hard and gentle driving tests showed extremes of – on the high end, of 277 – 285 Wh/Km; but on the gentle driving tests, as low as 67 – 100 Wh/Km!

This is with NO Regent – GE Series Wound DC Forklift or similar motor, friction brakes only, at a 2,000 Lb Curb Weight.

OK, found a website listing the conversion formula as MPG = 25125 / (Wh/Km) assuming Petrol fuel, so that makes my formula: 25125 / 137 = 183.39416 MPGe. Nice! And that was with a 400 Lb Lead Acid Battery Pack.

http://www.seai.ie/Renewables/EV_support_programme_launched/Electric_Vehicles/How_to_Compare_with_a_Petrol_or_Diesel_Vehicle/

What this article does not mention is the aero wheels that were offered at one point. What happened? Was their benefit too small? What was it, anyway? It was never really quantified in terms of cd. And they were available such a short period of time that they never got a chance to be popular.

Bjron Nyland managed to score a set for his Model S (you can see them here: https://www.youtube.com/watch?v=yIUwLv5yTsU), and even Musk mentioned them at one point. Then, nothing.

I’d love to see InsideEVs investigate what happened with that wheel option.

I too am curious why this option disappeared… brake cooling issues? No one wanted them… (I did) How about rear wheel skirts… even transparent ones so the car style doesn’t have to change. Would love to see effects of that.

Those are too ugly, nobody wants them.