Roof Spoiler on Pick-Up Truck Cab - Phase-1

[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:

[kach22i]

Forgive me if I don't see a huge difference in the overall. I see a tiny bit more yellow hitting the rear spoiler, but not much.

Would it help to bevel the leading edge of the roof wing (down) as I did in real life?

I think it's 3/16" thick.

The rear spoiler is 45 degrees or greater.

7" to 8" gap under the front chin spoiler.

I can tell you that there are depression wells in the bed cover fabric while at speed, mostly between the last spar and tailgate but some in the middle one too.

I'd really like to see those corner vortex's forming. That is my next modification, to tame those suckers.

[viio]

The red is where the air is at it's lowest velocity (i.e. most dragged). The roof spoiler is keeping that slow air out of the truck bed and actually directing it to (and over) your rear spoiler. If you didn't have that rear spoiler at all you'd have less drag as the roof spoiler would be sending air into the wake rather than into another object (rear spoiler).

[viio]

I don't think you'll be getting vortexes by the way, at least not like the big blue ones you drew on. There's too much laminar airflow coming down the sides of the vehicle, it'll just push the air into the truck bed. 3d model coming up to show you what I mean.

[viio]

It's hard to see in the 3d view, but those vortexes are just getting swamped by airflow down the side and over the top of the vehicle.


These 3 give a better picture of whats going on in the truck bed:

[kach22i]

Originally Posted by viio

The red is where the air is at it's lowest velocity (i.e. most dragged). The roof spoiler is keeping that slow air out of the truck bed and actually directing it to (and over) your rear spoiler. If you didn't have that rear spoiler at all you'd have less drag as the roof spoiler would be sending air into the wake rather than into another object (rear spoiler).

This is the opposite of what I've experience though.

My roof wing is actually directing air downward, doing so (I theorize) by removing the boundary level air though the slot and drawing the air above it down with it. This flow goes into the rear spoiler sooner and with more mass than without the roof wing. And yes, this means more drag, but I love the extra safety in bad weather.

This is the only way I can explain all the extra down force.

I'd be getting some lift and less drag according to the computer flow diagrams, this matches all the other data on "garnish" I've read. I think you did an accurate enough job, still wonder if the cant to the leading edge of the wing is responsible for extra redirecting of surface/boundary air.

I will have to tape some tuffs or longer strings in that area and film what's going on.

There must be a safe way to generate a small amount of smoke in front of the wing to record what is happening. Any ideas?

[redorchestra]

smoker can for bee hives?

[viio]

Well if nothing else you've got a bit more science to look at there. Want me to do another version with the roof spoiler aimed down some?

[SvdM]

I'd like to see that too (I vote for spoiler aimed down ~ 12°?)

[kach22i]

Originally Posted by viio

Well if nothing else you've got a Lot more science to look at there. Want me to do another version with the roof spoiler aimed down some?

From what I've read a 10 or 12 percent downward angle on the "garnish" will net a +20% reduction in drag, but a +30% increase in lift. This is one of the reasons I never angled it down.

I would be interested if your "science" can measure this reported "lift", or at least graphically represent it.

I think for the most part your program underestimates the suction/flow of air though the small air gap between the end of the roof and the beveled leading edge of the wing. I do need to find a way to measure this alleged flow, smoke bomb in a coffee can on the roof?