Custom Astro van aero high top

[Stacygifford]

Originally Posted by freebeard

If you look at the low pressure area just abaft the windshield header (easier said than done, right?)just filling that void then rising to the height requirement would be optimal

I mean, I could build a jig bolted to the front bumper to hold a few smoke bombs and make a very crappy tunnel-les wind tunnel for probably $70-$100

https://store.enolagaye.com/us/p/rai...-grenade-pack/ and some pvc

[freebeard]

Have you seen this?



The high top has the lowest Cd and CdA. This suggests a slow front rise and rear truncation.

[cRiPpLe_rOoStEr]

Would a pop-up top be totally out of question? You know, sometimes clearance may be an issue while driving through some tight spaces, such as under low bridges for instance, or while stopping at some covered parking areas while buying supplies for a road trip.

[aerohead]

Originally Posted by Stacygifford

Hey guys, it has been a LONG time since my last post.

I am currently building a 4x4 Astro camper van, but my inner ecomodder keeps showing through. the van now has a 6.0 LS with a 6l90 for double overdrive as well as a partial camper conversion.

I have been wanting to buy a high top (from a junk yard) but I'm not sure i can stomach the fuel economy hit with how awful most high tops are. I really want to keep the thing getting over 20mph hwy. (goal of 25mpg @60mph)

So, the logical idea is to build a high top in the Foamy style following the aerodynamic template.

Which of theses 3 do you think will work best? all 3 have been set to the exact same height (13" higher than the factory roofline) Assuming frontal area is the same between all 3.

* The overall height and position of the new roof's apex determines alignment with the 'AST Template.'
* And it must include the 'roadway' in order to protect the pressure gradient along the roofline, and with it, the boundary-layer attachment.
__________________________________________________ _____________
* Additionally, the AST-Template is intended for use with coupes, sedans, and small crossover utility vehicles ( CUVs), where the 'height' of the vehicle is the 'minimum' component of the frontal area.
* With a 'squareback' van, there are aerodynamic 'solutions' better suited for your use, as the 'width' of the van ought to dominate the 'calculus' we'd want to use for streamlining.
* I recommend that we add the 13", determine where the high point to the roof occurs, then place 'that' under the template, and see where it leads.
If we don't include the overall height of the van, we'll end up with a roof-flow deceleration 'overshoot', and impose such an adverse pressure gradient, that the boundary-layer will just 'throw it's hands up and say,'see you later,' triggering separation,losing any drag benefit.

[Stacygifford]

Originally Posted by freebeard

Have you seen this?



The high top has the lowest Cd and CdA. This suggests a slow front rise and rear truncation.

Although not a perfect model, it provides reasonable insights. By using the flow pattern depicted in the image you provided, I constrained the Reynolds number for flow illustrator. Fortunately, the length of the Astro van and the VW are quite similar, 180" and 189" respectively, resulting in a negligible difference. For the VW, a more suitable Re value would be 1.13 to account for the slight variation in length.

Nevertheless, it is evident that there is more upwash in the proposed design than desired, as suggested by other members. While the overall height remains the same, the highest point has been moved toward the back, above the middle of the middle window, rather than toward the front, as in my initial proposal.



I'm not opposed to a pop top, and I may still incorporate that as well, depending on cost.

[aerohead]

1) One could mimic the Don Burr semi roof extension I suppose. There's no 'penalty' for the height, although, if the added height serves no useful function, it's a lot of trouble for nothing.