Pickup Truck Aerodynamics - CFD Study Chevy S10

[kach22i]

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








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


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

[freebeard]

Lucky you.

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.

[Shortie771]

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.

Originally Posted by freebeard

Lucky you.

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.

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.

[kach22i]

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.

[aerohead]

Your S-10 was rated Cd 0.42 (middle image)

The 1st-gen S-10/S-15 'Syclone' ,modified for Bonneville (bottom image) achieved Cd 0.315 (lower than Corvette for the day).

This GM/Holden Ute has Cd 0.309,lowest for any production pickup.

[kach22i]

Originally Posted by freebeard

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

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



A reference to the car below by name is made in that thread:
Ferrari 250 Testa Rossa (#0710TR) '11.1957

Ferrari 250 Testa Rossa

Originally Posted by aerohead

Your S-10 was rated Cd 0.42 (middle image)

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


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

[Shortie771]

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!

[freebeard]

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:



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

[kach22i]

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






viio's Bucket/ecomodder
bed-flow_intopplane3.png Photo by viio | Photobucket








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

Originally Posted by viio

Okay I put a couple of hours on this tonight - please excuse the model it's slightly ghetto but it'll do the job. I re-used a couple of parts from other models. I also couldn't quite get the curvatures of the roof right so I've curved the spoiler instead to create the same gap at the edges. There's a higher quality render running right now and I'll post up pic once thats done.

*** Thumbnails are for the clicking ***

The spoiler I've bodged together:


The velocity in the right plane before:


The velocity in the right plane with the spoiler:

[Shortie771]

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.