In this video, we will analyze the aerodynamic features of the Tesla Semi truck.
First, some context. Lately, heavy-duty transport has been facing increasing pressure: in Europe, trucks, buses, and coaches together produce around a quarter of all road transport CO2 emissions.
On the power consumption side, efforts are made to reduce aerodynamic drag, as it is responsible for more than half of the power required to drive a truck at highway speeds.
But improving truck aerodynamics is not easy: typically, trucks and trailers are bulky objects that have been stretched to make use of every cubic centimeter that is allowed by road regulations, such as maximum length, height & width. It’s not hard to see that trucks are not exactly super streamlined, but exactly how bad is it?
Aerodynamic efficiency is expressed via the drag coefficient Cd. If you want to learn more about the drag coefficient, just watch our separate movie on this. In short, lower is better with the Tesla model 3 at 0.23 and a conventional truck between 0.5 to 1. So when Tesla claimed 0.36 for their Tesla Semi truck, we jumped up and wanted to know more.
We called Elon Musk and asked him to send us a 3D model of the truck within 2 weeks. But he’s not too good with deadlines and we didn’t want to wait, so we asked our partner engineering agency Voxdale to build a 3D model for us instead.
And believe it or not, we got a drag coefficient of 0.35 for the Tesla Semi truck! You can argue that we didn’t use the exact geometry for example, but even compared to our optimistic conventional truck it featured a 20% drop in aerodynamic resistance! That’s over 10% reduction in fuel consumption or 5000 liters of fuel per year!
Let’s start at the front: the vertical frontal face of the boxy conventional truck causes a huge pressure build-up on this entire surface, as the air needs to take a 90° turn to get around the cabin, either over the top or around the sides.
To provide smoother escape routes for the air, the Tesla Semi’s cabin features a strong backward inclination angle and large smooth corners around the sides of the cabin. This allows for a much more gradual evacuation of incoming air and thus a lower pressure buildup.
On road cars, the mirrors make up 2 to 5 % of total drag. On trucks, they are much bigger and Tesla decided to simply replace them with tiny camera’s mounted on aerodynamic wing-shaped beams! It’s quite easy to spot this difference by looking at the wake caused by both mirror setups!
If the roof spoiler is too wide or too high, this can leave a large wake and create unnecessary drag, as we can see at the top of our conventional truck. If it’s too low or narrow, the air will hit the square front of the trailer, causing local pressure to build up and separation downstream. Tesla made sure the Semi cabin fits nicely with its trailer: they were able to do so by extending the side spoilers all the way to the trailer and by leaving just enough space in top view for the trailer to rotate.
The wheels. Covering the front wheels is quite difficult, as they need room to turn in corners, but the rear wheels of the Tesla Semi have been shielded to create a smoother airflow.
Should they stop there? Of course not! The trailer itself can be optimized a lot as well, with side skirts and flaps at the rear for example. There’s plenty of after-market equipment already out there.
You can argue that in the end, it’s the CO2 emission per unit of cargo that matters and that the Semi’s longer cabin reduces the available cargo space in its wake. But then again, this depends on local regulations and it’s not a coincidence that the European Union is increasing the allowable length.
They have already triggered others to come up with innovative concepts, like the Ford F-Vision, for example.
The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).
We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!
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