Pickup Truck Aerodynamics - CFD Study Chevy S10
 

A few weeks ago I had coffee with a talented Aerodynamist which after years of working with the big automobile manufacturers started to explore some other options, including doing some work independently.

I had an opportunity to see some of his work on the laptop he brought, and he explained how to read and interpret some of the CFD images, what the colors meant and what to look for.

No college credits accumulated, but I felt I was tutored by an expert, especially once he looked at a from scratch design I've been working on and provided helpful commentary.

What brought us together was my Chevy S-10's aerodynamic modifications which are posted here in this forum and on other places across the Internet. We happen to live in the same town so a coffee get together ensued.

In order to quench some of my curiosity regarding how the truck works CFD wise and what that roof wing really does he worked up some studies for me, which I will do my best to share including some of the e-mail comments I managed to add to the images below.

Aerodynamics by George Kachadoorian | Photobucket
http://i184.photobucket.com/albums/x...psxebkuinf.jpg
http://i184.photobucket.com/albums/x...pszsjro5xn.jpg
http://i184.photobucket.com/albums/x...psskp7ojcy.jpg
http://i184.photobucket.com/albums/x...psgewe5pxk.jpg
http://i184.photobucket.com/albums/x...pspki8rpdk.jpg
http://i184.photobucket.com/albums/x...psuh4xugco.jpg
http://i184.photobucket.com/albums/x...ps1mhqbqas.jpg

1. Truck was raised by previous owner by about 2-inches (change made).

2. Roof wing shape is close enough for general discussion purposes.

3. Chin spoiler and rear spoiler look to be accurate and to scale.

4. The Sportside/Sidestep bed verses Fleetside bed is not addressed as it was not a concern at the time.

5. Tonneau cover on bed is included on the images.

I know these might be hard to read, so you can go to my Photobucket account and do a Ctrl+ command to zoom in and read some of the text.

http://s184.photobucket.com/user/kac...?sort=3&page=1

Oh yea, if you want to explore some more images, non-related to this quick/rough study feel free to click on the link below. Not a whole lot there right now, but I assume there will be one day.

http://www.simspade.com/

Pictures of the real truck.
http://s184.photobucket.com/user/kac...?sort=3&page=1
http://i184.photobucket.com/albums/x...pstnmn5khs.jpg

Bodywork and paint thread:
http://forums.pelicanparts.com/off-t...amouflage.html

Lucky you. :thumbup:

Do you know what the simulation ran on?

Did he explain why the front tire contact patch has air squirting sideways but the rear doesn't.

So lucky, that's awesome.i especially like the way the airflow is represented in picture #4. I really miss having access to Autodesk's Project Falcon, I had tons of fun with that. So much better than video games.

My guess... If the simulation was running in the red area on the first picture, you can see it isn't aligned straight from the front to rear wheels. Just a guess though.

Images #5 & #6 are of the flow under the truck and between the wheels, in other words the centerline.

Green is a good color more or less as it is medium pressure or medium velocity depending on the illustration.

I do not remember the software used, I might have been told, just don't recall.

Image #2 with the front wheel, the tiny high pressure red spot on the tire is just below the bottom edge of the front chin spoiler.

S-10
 

Your S-10 was rated Cd 0.42 (middle image)
http://i1271.photobucket.com/albums/...ead2/5-175.jpg
The 1st-gen S-10/S-15 'Syclone' ,modified for Bonneville (bottom image) achieved Cd 0.315 (lower than Corvette for the day).
http://i1271.photobucket.com/albums/...titled28_6.jpg
This GM/Holden Ute has Cd 0.309,lowest for any production pickup.
http://i1271.photobucket.com/albums/...titled27_9.jpg

http://i184.photobucket.com/albums/x...pszsjro5xn.jpg
I tried to answer your question already, but didn't quite get it.

I'm guessing the rear wheel is getting disturbed air flow so the pressures both positive and negative do not reach the same amplitude heights/depths as full free flowing air causes up front. Sort of like the tractor propeller verse the pusher propeller, the air going into the pusher will always be disturbed, causing loss of power or less efficiency.

All that negative pressure (sucking) on the leading edge of the front wheel causes me to wonder if covering the front wheels is more effective than covering the rear wheels.

I found an example of a partial front wheel cover in the forum.

http://ecomodder.com/forum/showthrea...ion-21046.html
http://farm7.staticflickr.com/6152/6...0bcefdd3_z.jpg


A reference to the car below by name is made in that thread:
Ferrari 250 Testa Rossa (#0710TR) '11.1957
http://i.wheelsage.org/pictures/f/fe..._spyder_3.jpeg
Lots of room for improvement, almost anything will make it better.:)

EDIT-1:
I found this in a Volvo forum.

http://forums.tbforums.com/showthread.php?t=287934
http://us1.webpublications.com.au/st...4/2455_2mg.jpg

Looks like the front wheels are double the drag of the rear wheels.

Also in the Volvo forum.
https://www.mech.kth.se/courses/5C12...erg_2012_1.pdf

Ooh I like that last chart. It's crazy how much the front wheels affect drag! Also that chart peeks my interest because it kind of shows me how much affect an underbody could have to each area beneath the car. I'm glad the exhaust seems to hardly contribute, since that is the area I was most concerned about trying to cover without catching anything on fire... I really need to get my hands on some coroplast!

Front wheel wells are more voluminous to accommodate the wheels' steering, so it's logical they'd be dirtier. You see examples at Bonneville of front skirts only, my favorite being Bombshell Betty:

http://ecomodder.com/forum/member-fr...inspection.jpg

IIRC that lateral jet is caused by the tire and road surface coming together. I guess it depends on a clean entry.

I found CFD some images which look like my truck again, seen them before, forgot all about them. One was posted in a snow thread a few years back

"Snow Flow" testing?
http://ecomodder.com/forum/showthrea...ing-27509.html
http://i184.photobucket.com/albums/x...pslagfyaik.jpg





viio's Bucket/ecomodder
bed-flow_intopplane3.png Photo by viio | Photobucket
http://i4.photobucket.com/albums/y14...ntopplane3.png
http://i4.photobucket.com/albums/y14...ntopplane2.png
http://i4.photobucket.com/albums/y14...intopplane.png
http://i4.photobucket.com/albums/y14...r/bed-flow.png
http://i4.photobucket.com/albums/y14...10_spoiler.png
http://i4.photobucket.com/albums/y14...e_wspoiler.png
http://i4.photobucket.com/albums/y14...rightplane.png

EDIT:
I found the post from five years ago.............I'm getting old, don't remember much of this.

http://ecomodder.com/forum/showthrea...a-19525-4.html

I've always found pickup truck aero modifications interesting, because​ I have a Del Sol. It's kind of like a baby truck, the way the roof drops off completely and the trunk is flat like a truck with a tonneau. It stands to reason that if a roof spoiler would work for a truck, it would work for me as well.

Edit: Just realized i posted this on the wrong forum. Sorry everyone!!!!

I see some dimensions in the quick drawing, but no notation for the radius of the arc. Know what it is? Height of the truck (~65") would suggest an arc of about 30' in radius. Are you anything close to that?

Just curious. Looks good...

Welcome to Ecomodder, it sounds like you'll fit right in.

Those people you refer to all started with the minimal (safe from separation) angle of 12.5° and then went searching for a maximum (w/o separation).

kach22i's innovation is to reduce the weight, cost and complexity of a full canopy to that of a full tonneau and half a boogie board. This has attracted attention for two people who invested their own time and energy in documenting the performance in CFD. I say :thumbup:

You might start that thread before the build. A lot of people start a thread with something like "Here's my brick with edges as sharp as a Lego, now how do I slather aerodynamics all over it?" You could avoid that.

You have a single two-dimensional line, where do you go from there? What materials?

What I'm liking lately is wakeboard control arms.

http://ecomodder.com/forum/member-fr...0-100-1101.jpg

These range 5-8ft, I eventually bought most of them. They are very light tempered aluminum. The 5-footers might serve for a rear edge, with the 8-footers longitudinal. I paid (maybe) $10-15 each. Here I'm considering a boat tail on my Superbeetle:

http://ecomodder.com/forum/member-fr...2-100-1120.jpg

Also, considering what you do with that single curve, here's a pickup canopy on the only pickup I had laying around in 3D. It presents additional frontal area at the front to absorb any turbulence or incipient vortexes coming off the cab and maximize interior volume. Not a good fit to the cab, though.

http://ecomodder.com/forum/member-fr...4-10-08-26.png

The solution to that is squircular; but I'm going to give kach22i back his thread now.

Degrees of ease (assuming full cap/ canopy):

1. Build square/flush with upright tailgate.

2. Extend the top plane only.

3. Extend in 3D, open the tailgate and place an aero-box there or build all as one.

Here is example #3- sort of, in diagram form.
http://ecomodder.com/forum/showthrea...hts-22378.html
http://i49.tinypic.com/10d5tee.jpg

Each one of the options above becomes increasingly time consuming and increasing difficult to get right. However if you start with option-1, you can gradually add on. Aerohead's T-100 is an excellent example of this.

I would not try a wing at the tail, it would just be asking to get vandalized. However a "Box Cavity" would be a little more durable. Do a forum search, several examples or at least studies of possible projects have been posted.

The wing would be Okay, just put it at the bottom and add longitudinal fences and a trailer hitch.

http://ecomodder.com/forum/member-fr...80-silver4.jpg

I thought the wing he was talking about was similar to a roof wing, only installed as an extension of the Aero-Cap. See option-2 below.

I was picturing a ricer wing. Carry on.

That poor Lotus...

That's a really cool opportunity you had! Does this aerodynamicist have any aero mods on their car?

Looks like someone has made a roof spoiler for my car, by modifying a Civic EG Hatch spoiler to fit a Del Sol. They were doing it for styling, but wonder if it improved aerodynamics. I would definitely try this if I got my hands on a EG spoiler.

Before:
http://i54.tinypic.com/wioikh.jpg

After:
http://rs1260.pbsrc.com/albums/ii569...h=480&fit=clip

I did not see the car he was driving.

The DelSlow spoiler sure looks interesting. Something four times the size out of a clear material sure would be worth while.

My plastics guy could fab something up, he does all sorts of things for people. Sure would be a change from the typical display stuff he does involving bending plastic using a torch. I bet many local shops would be up to it if provided a template in cardboard or other material.

Yea this is one of those cases where bigger really would be better. I wonder what something like that would cost. I wish I had a plastics guy.

http://ecomodder.com/forum/member-fr...11-5-38-12.png

Take whatever shape you want (shown is Thee Template) and lay out a polygonal mesh, using triangles, diamonds or hexagons as you prefer. Add darts in your layout, one dart per hexagon for instance. Then cut and draw the darts closed or lap them. It would produce an approximately compound curve with minimal seamage.

An interesting means of joining the clear material might be https://books.google.com/books?id=pg...=PA63&lpg=PA63 Radfast memory plastic.