Vanagon EV (Vanabolt) high top

[yabert]

Hi

I have a electric Vanagon since almost 5 years now. Details in my signature.
It is awesome with lot of power and nice regen to save brakes downhill. It cost almost nothing to ride with electricity rate of hydropower here around 0.05-0.08$ US/kWh
We like it a lot and we use it as battery backup for our house in case of long outage.

But the fiberglass pop-top is in terrible shape and we want to build an hightop to replace it. Stand up in the van would be nice.
Of course I would like to shape the hightop to have a good aerodynamic in order to have the same range or even better. The actual pop-top have terrible aerodynamic.
I can design in 3D almost any simple shape and build it out of laser cut aluminum, but the thing is to know what is a good aerodynamic shape.
Below, some rapid shapes I designed + some old data about hightop for Vanagon.

I keep in mind that it could be easy to integrate a 400-500w panel in this hightop with a 2-3 kWh 12V storage battery, but it's not the main goal at this moment.

So, where to start?
Thanks

 

[RV8R]

That is some DIY Project @yabert

I like the idea of semi non proprietary Design / Build.

Congratulations !!

 

[eXodus]

I like option number 3 it seems like it follows the contour of the windshield.

The slopped back should help the air to follow the contour of the Bus.







When you look up different Bus and RV designs - It seems that following the windshield slop at least for a while is key.

In the German Pictures you posted - the black Vanagon with the rounded high top - it also has a close match to the windshield line.

 

[eXodus]

Create some black and white drawings of you design - with the front facing to the left and run them with Flowsquare.

Flowsquare | The free, handy, integrated, Computational Fluid Dynamics software

flowsquare.com

That should give you some baseline. 700x500 pixel is decent 30-40.000 frames. Depending on your computer might take a day or so to run.

 

[yabert]

Ok, black and white BMP file. And blue and green line for other parameter.
But then, what? I click and drop the BMP to open flowsquare. Is it supposed to start something?
No sure to understand the steps.

 

[eXodus]

tossing one more option for free CFD http://flowsquare.com/

@AndyRonLI and @curiouscarbon @justgary could you guys chime in and help with another solar aero simulation?

Some disclaimers: Like @AndyRonLI and @curiouscarbon both said, this should be taken for its entertainment value only. You are getting free advice from your "best internet friend" who is neither an aerodynamic engineer nor a structural engineer. Do not mistake any of this for actual engineering. These diagrams show airspeed only, and not pressure.

@eXodus, if you don't see these kinds of results, perhaps you didn't rename one of the .bmp files as "bc.bmp".

With that said, I still hesitate showing you the first results because I think it has a problem.

RV_Nopanels at 100KPH (62.2 MPH):
View attachment 79257

RV_Panels at 100KPH (62.2 MPH):
View attachment 79258

The problem? It looks to me like the flow gets very distorted when it hits the top of the calculation frame, causing it to build pressure and break free. In other words, I don't think the calculation area is large enough to keep it from interfering with the answer. I am running another one now with a 400x200 calculation space, but it won't be done for hours.

 

[yabert]

Ohhh sh*t!
Things evolve slowly with Flowsquare software. I want few hours just to finally see my van in the software
I bet I have now many other hours to play with this in order to expect to don't only have garbage in / garbage out results...

 

[eXodus]

actually not bad.
Now you just need to place is on the ground or at least very close to.

You also need to make the frame higher - the "ceiling" aka the frame of the simulation is solid on Flowsquare - so like driving through a tunnel

 

[justgary]

actually not bad.
Now you just need to place is on the ground or at least very close to.

You also need to make the frame higher - the "ceiling" aka the frame of the simulation is solid on Flowsquare - so like driving through a tunnel

Sorry I missed the party. I always like how the people who make commercial products to help reduce wind drag only show the air flow at the front of the vehicle, yet the big contributor is what happens behind the vehicle. Generally, any sort of boattail should help reduce the vortex that forms behind. Dragging a huge air swirl behind you takes a lot of energy. A lot of semi trucks have extension panels at the back to help shape the airflow behind the trailer.

Making the Flowsquare frame tall and very long (maybe five or more vehicle lengths long) can help you see the vortex. You also need to run the simulation long enough to see the steady-state solution. If you see a big wagging tail, you might be able to help shape it. I have been in large vans before at highway speeds, and I could feel the tail wagging as the vortex whipped around behind.

With all of this said, take the solution you see as a "serving suggestion" and don't place too much weight on what that means when you drive your actual vehicle. A few smoke wands on the vehicle would show you what is really happening, but would be a bit pesky to set up.