Optimizing Aerodynamics of a Truck: Part 1

[freebeard]

At 04-12-2022, 01:00 PM (#5 Permalink) I was responding to:

Originally Posted by cRiPpLe_rOoStEr

Have you never considered blocking the grill from the outside instead of the inside? Wouldn't it lead to a greater aerodynamic benefit?

...everyone here's, adopted (for simplicity) ideal body shape...

Not everyone, I'd given up the battle a decade before 2022-08. (Reducing an elliptic curve to a 12 degree angle).

Imagine vertical up DBD (Dielectric Barrier discharge = surface wind) from the vertical bit of the 'leading edge', where the air is (normally) unavoidably stagnant...

Is this not logical..?

I don't know. "Imagine vertical up DBD from the vertical bit..."? It appears the stagnation point in the example is where the positive and negative arrows meet around the headlight area.

[Logic]

Originally Posted by freebeard

Not everyone, I'd given up the battle a decade before 2022-08. (Reducing an elliptic curve to a 12 degree angle).

Stop trying to (mentally) implement the shape from the roofline down over the nose.
Just implement, smaller, it to the nose.

Originally Posted by freebeard

I don't know. "Imagine vertical up DBD from the vertical bit..."? It appears the stagnation point in the example is where the positive and negative arrows meet around the headlight area.

I see the stagnation point at the point/s or line which are/is perpendicular to the oncoming air.
ie:
Where the air cant pick a direction to flow based on the angle of oncoming surface and just sort of mills about undecidedly.
If the angle is decided for it by a DBD flow; that's the way it will go.
So what used to be stagnation now has a direction picked for it by the DBD.
The DBD basically 'says":
"Flow up. The surface will curve back soon enough, giving you a nice direction to flow in.

So you should end up with an extra forward facing arrow in the pressure graph pic.
Also less air headed under the car.

[freebeard]

Stop trying to (mentally) implement the shape from the roofline down over the nose.

At the time the mantra was "It's not how you open the hole in the air, it's how you close the hole in the air".

I take it that your describing a forward-facing DBD.

[Logic]

Originally Posted by freebeard

At the time the mantra was "It's not how you open the hole in the air, it's how you close the hole in the air".

Yep. Yet there that high pressure stagnation point is: Direction undecided air due to hitting a perpendicular surface. with a 50/50 chance of being jostled either way.

Don't get me wrong; keeping the flow attached where the body begins to and is converging to a tail (or not/cam) is high on the list too.

The problem that certain people have with DBD for attaching flow is you can't (apparently?) to a non existent boat tail:

ie: Imagine an ice-cream cone with a starting to melt (slippery) cone of ice in it.
Squeeze on the cone and the ice/body will pop up/forward.

So those long tails are all about giving air/pressure time to actually 'squeeze the cone', rather than get vacuumed into chaos.
The 'cone' is NOT going to happen as most cars spend all their time in cities and towns where weight and being able to park are more important than aero...
Get over it!

But IMHO well placed DBD adds to air pressure's slow/belated effort to gain 'in the way again' momentum and neatly fill the 'hole'.
That and well placed exhaust gas will (at least) decrease that vacuum/chaos/wake which = less drag for less weight and inconvenience.

[Vman455]

Originally Posted by freebeard

It appears the stagnation point in the example is where the positive and negative arrows meet around the headlight area.

No! Stagnation = isentropically-decelerated flow to 0 velocity relative to an inertial reference frame. In this case, the reference frame is the car, so 0 velocity relative to the car = highest static pressure/longest arrows pointing into the car surface in that image.

[freebeard]

Thanks. I guess...

Edit:
I seek your opinion. I've felt for some time that Blender will be able to do CFD on par with OpenFOAM. That's because for some time Blender has implemented OpenVDB.

What's coming is node-based editing of volumetrics.

Grids! The epic new Blender 5.0 feature

I have a basic understanding of node editors, but don't know how the specific node types apply to CFD. Most are common, but Sample Grid and Get Named Grid are specific.

Does this appear useful?

[Logic]

Originally Posted by Vman455

No! Stagnation = isentropically-decelerated flow to 0 velocity relative to an inertial reference frame. In this case, the reference frame is the car, so 0 velocity relative to the car = highest static pressure/longest arrows pointing into the car surface in that image.

Quite so.
And the ground means air low down cannot get out of the way as easily as moving out of the way downward not an option.

But a nudge form the top of where that "0 velocity relative" to the car air starts is pretty much where the body is vertical to air direction.

What if you give that high pressure stagnant air a nudge upward, to follow the top curve where high pressure over the nose turns to low and the 'suction' is...?
Add speed in the desired direction...
You can most likely lower/lessen that static high pressure bit in the graph/picture..



Putting DBD where the stock, 'downstream' bit of the car body, where it begins to converge quite sharply seems to help and the onboard generation of DBD power showed a net positive.
IIRC
I'd add some to the vertical front curves too! And follow the curve! Out of curiosity!

https://ecomodder.com/forum/showthre...n-41356-3.html

There's lots of research in that direction. Not so much on leading edge DBD.

[freebeard]

Bluff forebodies rule.

[Logic]

Originally Posted by freebeard

Bluff forebodies rule.

OK...?
Are you sayin Beetle hoods have an almost perfect leading edge profile for creating 'suction'?
Or did you feel a change of subject to avoid... shall we say controversy, was in order?

[freebeard]

No, I said "Bluff forebodies rule."

The picture was a distraction, I guess. I wanted a row of Beetle noses, but the first ones I found lacked fenders. The point was the lack of a corner that needs a DBD band-aid to fix.

In another sense it was a pro-aerohead troll.

It all falls apart at the windshield, of course; but at least these examples have peep mirrors.