Old Spice

Well-known member
First Name
Ben
Joined
Nov 15, 2019
Threads
61
Messages
162
Reaction score
601
Location
Katy TX
Vehicles
F-150, Polaris RZR
Country flag
https://electrek.co/wp-content/uploads/sites/3/2022/07/1657882323685.mp4

Tesla Cybertruck electric pickup surprises in aerodynamic performance simulation

Now a new study of the Tesla Cybertruck’s aerodynamic performance shows that the electric pickup truck has a drag coefficient of about 0.39 Cd.

Aleix Lázaro Prat, a CFD Engineer for Numeric Systems, used the company’s aerodynamic simulation technology to produce the study that they released on LinkedIn.




The engineer shared the positive aspects of the design from his study:
Contrary to what many people would think, the sharp edge of the roof does not produce a big detachment! It is true that the flow it is not attached, but in fact the air follows down the slope quite seamlessly. The boundary layer does not substantially grow. This is quite remarkable and a big aerodynamic advantage compared to other pick-up trucks. Moreover, the diffuser makes a substantial effect in the center of the vehicle’s rear-end! It creates suction and reduces the wake.
However, he also saw plenty of room for improvement:
On the other side, our results show clear turbulent structures created by the front edge which connects the bumper and the bonnet, the vertical edge right behind the front lights, the wheel arches’ “protectors”/surrounding edgy geometry, the rim styling and the geometry of the a-pillar and c-pillar. The generation of the turbulent structures is caused by the sharpness of these edges. These geometrical features increase the drag of the vehicle, which ultimately reduce the range the CYBERTRUCK. Furthermore, due to the sharp rear end, the flow instantly detaches and creates a considerably big low energy area (wake), mostly noticeable behind the top and side rear-end edges.
It’s important to note that Numeric Systems don’t have the final geometry of the Cybertruck, and therefore, it shouldn’t be completely representative of the final product.

There are factors like the lack of side mirrors that we don’t know if or how will be implemented in the production version of the truck next year.

 

Coolbreeze704

Active member
First Name
Bruce
Joined
Nov 23, 2019
Threads
1
Messages
41
Reaction score
79
Location
Troutman,NC
Vehicles
2022 Model Y, Ram 1500, CyberTruck (someday)
Occupation
GM Sales
Country flag


rr6013

Well-known member
First Name
Rex
Joined
Apr 22, 2020
Threads
48
Messages
1,346
Reaction score
1,291
Location
Coronado Bay Panama
Website
shorttakes.substack.com
Vehicles
1997 Tahoe 2 door 4x4
Occupation
Retired software developer and heavy commercial design builder
Country flag
“Low pressure” at the rear? IDU

Any fluid guys that can explain whether that’s detrimental or clean separation is a drag?
 

firsttruck

Well-known member
Joined
Sep 25, 2020
Threads
74
Messages
1,384
Reaction score
1,971
Location
mx
Vehicles
none
Country flag
It's a good design... optimized for range.
*All* electric trucks should be optimized for range. Sadly they are not. Other companies care more about the look of their truck matching some old paradigm.

Yup, like designing cars to look like horse & buggy because that was what was before even though current capabilities are different.
 

GnarlyDudeLive

Well-known member
First Name
Darin
Joined
Aug 26, 2020
Threads
8
Messages
318
Reaction score
718
Location
Chicago
Vehicles
2004 F350 Dually (Tri-CT reservation)
Occupation
Database Administrator
Country flag
Redesign the CT so that it has such a bad Cd that pulling a trailer actually improves the Cd. :) This allows full bragging rights of how much more efficient the truck is vs other competitors for towing. LOL
 


firsttruck

Well-known member
Joined
Sep 25, 2020
Threads
74
Messages
1,384
Reaction score
1,971
Location
mx
Vehicles
none
Country flag
https://electrek.co/wp-content/uploads/sites/3/2022/07/1657882323685.mp4

Tesla Cybertruck electric pickup surprises in aerodynamic performance simulation

Now a new study of the Tesla Cybertruck’s aerodynamic performance shows that the electric pickup truck has a drag coefficient of about 0.39 Cd.

Aleix Lázaro Prat, a CFD Engineer for Numeric Systems, used the company’s aerodynamic simulation technology to produce the study that they released on LinkedIn.




The engineer shared the positive aspects of the design from his study:


However, he also saw plenty of room for improvement:


It’s important to note that Numeric Systems don’t have the final geometry of the Cybertruck, and therefore, it shouldn’t be completely representative of the final product.

There are factors like the lack of side mirrors that we don’t know if or how will be implemented in the production version of the truck next year.
-----------------------------------


This guy's number seems high & is much higher than Tesla's goal for Cybertruck.

The boxy front & horizontal tonneau covered bed Rivian R1T claims a .3 drag coefficient so the aero nosed and sail panel angled tonneau covered Cybertruck should have at least as low drag coefficient ( Cd ). The high boxy front & horizontal tonneau covered bed 2019 Ram 1500, the most aerodynamic model in the high capacity ICE truck market had a coefficient of around 0.36.

Elon said goal was for production Cybertruck to be better than prototype.

----------------

Elon Musk @elonmusk 9:16 PM · Nov 30, 2019 Replying to @IntEngineering

With extreme effort, Cybertruck might hit a 0.30 drag coefficient, which would be insane for a truck. Requires tweaking many small details.


----------------

Cybertruck drag analysis with Ansys Fluent. Coefficient of Drag = 0.34 (2.8m poly-hexcore cells, k-omega SST turb. model)
Posted by u/pkrcm
2021

----------------

The Rivian R1T is Electrek’s 2021 vehicle of the year
By Seth Weintraub
Dec. 17th 2021
https://electrek.co/2021/12/17/rivian-r1t-electrek-vehicle-of-the-year-2021/

.....
Rivian executives brag about its ultra-low .3 coefficient of drag that is more slippery than many sports cars and gives the vehicle an impressive 314-mile range.

----------------
 
Last edited:

JBee

Well-known member
First Name
JB
Joined
Nov 22, 2019
Threads
3
Messages
1,555
Reaction score
1,611
Location
Australia
Vehicles
Cybertruck MY Prius Merc VW
Country flag
“Low pressure” at the rear? IDU

Any fluid guys that can explain whether that’s detrimental or clean separation is a drag?
Well if it would be a high pressure it would actually create forwards thrust and push it along. Don't laugh it's actually possible to do. 😎

The clean separation is positive if it is off the end of the vehicle. (which is why it has a Kammback rear end aka Prius, Insight, Citroen CX, GT40) You don't really want separation (non-laminar flow) along any other surfaces though, as separating the boundary layer increases turbulent flow before it gets to the edge which in turn increases turbulence around the vehicle and effectively increases frontal area and drag.

How Turbulent Is The Airflow Over Your Wings? | Boldmethod

Generally, you want to change the airflow direction gradually to separate it and then gradually bring it back together so that the airflow speeds match again. That's why rounded edges matter, because airflow can stay attached whilst going around them without separating the boundary layer. (think of the boundary layer as very thin air layers that gradually increase in speed with each layer until they match vehicle velocity)

Boundary Layer


Obviously, the CT a and c pillar structures are fairly sharp and don't gradually change airflow direction, but you don't always need round edges to achieve gradual airflow direction changes, you can also use other things like an air curtain or wing. These can sit in front or to the side of the vehicle, and although they look like part of the vehicle design are really only there to manipulate airflow around the vehicle. The CT really needs more of these elements IMHO, like the airflow around the front of this Porsche using an air curtain design around the wheels.

b-P19_0686_a3_rgb.jpg


Especially if you look at the wheel aero slice from that CT simulation where you can see just how bad the wheels look:

CT Wheel Aero.PNG

CT Wheel Side Aero.PNG

In comparison to the full vehicle aero:

CT Aero H.PNG


CT Side Aero.PNG


The wheels, wheel arches and the height above the ground really don't help the CT aero at all. It needs to be lower, and tuck those wheels into the body as best it can, with the smallest possible wheel well space. This is where an air curtain could keep the air from interacting so much around the outside of the vehicle. Remember airflow is in 3D, and seeing the CT has fairly high side walls, it also matters how the air flows around the sides of the CT.

I'm not sure what they mean with rear diffuser, the CT hasn't got much of one, but what you really want is an active one like this hanging off the rear bottom end:

Mercedes EQXX.PNG


The reason why "active" is important is that airflow shape is dependent on vehicle speed, so depending on how fast you go the air actually flows differently, sometimes to the point that at one speed it is good, but at a higher speed it's completely rubbish. (think of flaps and spoilers on aircraft wings) So what you really want to do is change airflow depending on speed, so you need an active system that moves depending on vehicle speed. A solid non moving form is only really the best at one speed, the rest is a compromise. This matters more for vehicles that are going to do higher average speeds, like long range country or highway cruising.

Anyway the bottom rear diffuser would be particularly important for the CT, especially if it is driving around that far off the ground. By changing it's angle and length you can reduce the overall wake.

There are two other interesting elements, (which I've mentioned before elsewhere) there is a air cushion in front of the CT that helps separation at the front, even though the CT has a fairly blunt nose, and air flows around the sides of the windows and back around the top of the vault cover. This actually helps maintain the rear laminar flow off the Kammback.

In either case I don't think they will release a CT with a Cd over 0.30, without otherise having to load quite some more batteries to get the advertised range.

Hope this helps.
 

electricAK

Well-known member
Joined
Mar 5, 2020
Threads
5
Messages
153
Reaction score
368
Location
Haines, Alaska
Vehicles
Cybertruck dual-motor
Country flag
The wheels, wheel arches and the height above the ground really don't help the CT aero at all.
This is why the adjustable air suspension is so important. Crank it down to the lowest level for highway cruising to increase range. Crank it up when you go off-road. Super important in an EV Truck!

Rivian executives brag about its ultra-low .3 coefficient of drag that is more slippery than many sports cars and gives the vehicle an impressive 314-mile range.
It seems as though the published Cd values for other trucks are minimum values achieved at ideal airflow, not an average Cd across all speeds. While Cd is generally expected to be independent of air speed, in practice Cd changes when airflow detaches in various places at various speeds (think Stall for an airplane wing). So, comparing the Cd from these random Cybertruck simulations to the published Cd of other trucks is a false comparison.

The turbulent low pressure in the bed of a typical truck is a massive drag on the vehicle. Cybertruck removed it entirely with its wing-shaped tonneau cover. Keep that cover closed!
 

rr6013

Well-known member
First Name
Rex
Joined
Apr 22, 2020
Threads
48
Messages
1,346
Reaction score
1,291
Location
Coronado Bay Panama
Website
shorttakes.substack.com
Vehicles
1997 Tahoe 2 door 4x4
Occupation
Retired software developer and heavy commercial design builder
Country flag
This is why the adjustable air suspension is so important. Crank it down to the lowest level for highway cruising to increase range. Crank it up when you go off-road. Super important in an EV Truck!



It seems as though the published Cd values for other trucks are minimum values achieved at ideal airflow, not an average Cd across all speeds. While Cd is generally expected to be independent of air speed, in practice Cd changes when airflow detaches in various places at various speeds (think Stall for an airplane wing). So, comparing the Cd from these random Cybertruck simulations to the published Cd of other trucks is a false comparison.

The turbulent low pressure in the bed of a typical truck is a massive drag on the vehicle. Cybertruck removed it entirely with its wing-shaped tonneau cover. Keep that cover closed!
Funny. I’ve read that tests with open bed pickup trucks effected no-adverse aerodynamics. None at all. Zero loss.
1C90DE71-44FF-4189-9B22-2EDA510BD321.jpeg

Results here
 

electricAK

Well-known member
Joined
Mar 5, 2020
Threads
5
Messages
153
Reaction score
368
Location
Haines, Alaska
Vehicles
Cybertruck dual-motor
Country flag
Funny. I’ve read that tests with open bed pickup trucks effected no-adverse aerodynamics.
I think you may be misreading things. I see the following in your links:
"As expected, we could see massive flow separation behind the cabin space and then again flow separation at the end of the cargo bay. " and " The basic shape of a pickup truck is not the most rewarding one when it comes to aerodynamics, with a large frontal area, large open wheel spaces, a chopped-off cabin and an open cargo bay. "

Your second link analyzes the difference between *tailgate* open and closed. It concludes that the closed tailgate is better since it creates a trapped vortex in the bed, which does help things. But inside that area is turbulent flow. At least in every truck bed I've ever ridden in. And it takes energy to move that air around, plus a larger area of low pressure behind the vehicle which pulls the vehicle backwards. I don't think they did a good simulation or analysis. And their conclusion is NOT that pickup trucks are aerodynamic, just that it is better to have the tailgate closed.

 

 
CYBERBACKPACK
Top