My Findings...

[subsonicluv]

Basically, texturing the surface of a port will create a turbulent boundry layer, which promotes adhesion of the airstream and overall more flow linearity.

This will lower some localized velocities that were caused my turbulent mass flow, however it equates to a higher controlled velocity because energy is not lost due to chaotic tumbling. Also you get more net flow/energy transfer.

Correct me if I'm wrong but isn't it simply stated that the turbulence created by dimpling creates something of a cushion of air for air to flow around... thereby decreasing friction.

Not unlike a maglev?

I was kind of thinking the same thing and in some cases where there needs to be a turn sharper that the above stated 14deg, larger dimples (or cavities) may cause the air to swirl inside it. Basically creating a ball bearing of air....for the air that is flowing across it. (just thinking out loud here)

[bbeljefe]

Yeah, I would think that's a pretty good way to explain it. But then... I'm a speaker nerd, not an air nerd, lol.

[Krakin]

I know that when you drive a pickup, the tailgate allows for a "cushion" of air to be created. And if you let the tail gate down to "increase air flow" you get rid of that cushion and create more drag.

But then again, I only drive in one direction, I don't tend to go back and forth rapidly too often.

[CleanSierra]

Krakin, I know that when I used to take my truck to the track, I was SLOWER with the tailgate down. I got advice from everyone to put my tailgate down to get faster and I had my doubts. I threw the gatedown and turned a .2 second slower ET through the traps. Tailgate up was a consistently quicker pass.

Those idiots were also taking their street tired trucks through the burnout box to "heat up" their radials. I didn't have the heart to tell them that they were just flinging water up into the wheel wells, only to drip down onto that "sticky" tire through staging. I staged quick too, so by the time they figured out that they were up in smoke, I was through the 60 ft light and on my way to the win

[Krakin]

I did a big science fair project on the airflow for pickups. If I can find my sources I'll try and post them up on here, but I did this project over two years ago lol.

It goes along the lines of this, when you open the tail gate the "pool" of air that has been set behind the windshield has just "spilled" out of the bed. Then when you drive with it down, the air has an eddy current under the, now in the down position, tailgate that pulls the truck backwards.

I saw a huge test done on this, and they ended up getting, IIRC, Ford '04 to get about 50% less drag at 70mph with a special bed cover that followed the contour of the air in the above picture.

Edit: To further add on, I remembered those "aerodynamic tailgates" such as the netted or slotted ones. Those create even more drag than having no tail gate at all. Imagine dragging a solid object and a fishing net through water. The net is going to require more muscle. Bug deflectors, and rain guards also increase the drag on the truck and can increase noise.

The biggest misconception is that it’s all about single components. But a certain side mirror design doesn’t create a certain amount of drag, its interaction with the rest of the vehicle does

Things that help better the airflow, and create less drag, are Tonneau covers. Most would think the hard tops are better than the soft top covers, however the soft tops are the better ones. They will form in the fashion that the air wants to be in.

Round tube side steps also decrease drag for trucks.

[bbeljefe]

That makes me wonder something... we know the effect of divots but divots aren't easy to create in a wood shop. So... all of us box builder who finish with bedliner have been masking ports and keeping them slick.

I wonder what effect bumps would have relative to divots and if positive, where do they need to be?

OP... GIT IN HERE! Please.

[Krakin]

Could that affect the phase shift, as in the wider bandwidth at a being closer to being in phase?

As well as extend the bass shelf a little further, and then have a sharper roll off?

I really wish I had the means to stimulate myself other than hope someone else can document it....

[Krakin]

I've got access to a 3d printer, I could mock up different parts to be assembled for a port with divots throughout the entire port. Then if it doesn't cost me my left nut I might be able to print one.

[bbeljefe]

Well that kinda takes us full circle to the question of how much air flow is "good" air flow? If we can move it fast enough that the back wave is in (or nearly in) phase with the front wave before it decays much, we have a burp box.

That would be good in the lanes but for music, not so much.

And with that, I think I'm speaking out of turn because I don't understand everything I know about acoustics. Plus, I don't know that much to begin with.

[bbeljefe]

I've got access to a 3d printer, I could mock up different parts to be assembled for a port with divots throughout the entire port. Then if it doesn't cost me my left nut I might be able to print one.

That would be awesome man.