Adding curved form to roof - good or bad??

[Frank Lee]

Straight-on wind will be just as rare in the UK, yet Don-Bur get good results on their bulged trailers.

As previously noted, I'm highly highly suspicious that they work at all.

This top will allow for some optimized radii along the sides that will Improve
crosswind performance!

Depends on what's up there now... regardless, seems such a small detail I can't imagine it showing up in the gas logs.

[IsaacMTSU]

You could try the bump spoilers like on the back of the Mitsubishi Evo Like These

[Frank Lee]

We've been down the vortex generator road almost as much as the HHO road.

[Tesla]

I have looked at the vortex generators, questionable, what's the HHO road so I can avoid it?
I agree with Frank in that a little bump on the roof won't do much on it's own, but as mentioned by Skyking if it allows for a shorter sharper boattail design, then it may well be worth a look at.
While on the subject, looking at the sides, the wheel guards come out quite a bit from the body, especially at the sills, where the sidesteps (running boards are), so I was thinking of a rubber skirt that hung off the doors, with the bottom just below the sidesteps. That would give a straight line from the front to the rear wheel arches, but if I cover the rear wheel arch it will need to stick out about 2", would it be better just to curve out the rear wheel arch cover on its own, mainly in the middle or run the line all the way from the front wheel arch?
So I suppose the question is better to have 2 curved obstructions (wheel arches) or have them connected in length, so it is just one long obstruction?
I would assume straight lines or reducing curves would be better than multiple bumps.

[Tesla]

Just scouting around to fine tune my ideas and stumbled on this older thread re the same topic.
http://ecomodder.com/forum/showthrea...ars-16726.html
And I thought I had an original idea.
Nevertheless, good info and discussion, I am leaning more to a positive direction on the roof bubble idea, just want to sort the front, bottom and sides first.

[IsaacMTSU]

You can't say anything unicorn about vortex generators...The way some idiots put them on their cars maybe, but the actual effects of them installed properly are proven.
Mitsubishi Flow Analysis PDF They help the boundary layer of airflow reattach after a downward curve on a roof/back window/wing. You cant put them on every inch of the back of your car and get the Cd of a sports car from an SUV though.

[euromodder]

Originally Posted by IsaacMTSU

You could try the bump spoilers like on the back of the Mitsubishi Evo Like These

This set-up only works on that car, has taken considerable wind tunnel time to get it right, improves Cd only a little.

Small chance a hobbyist would get it right - though I'm still convinced VG can work when done properly, and not truck-sized.

[aerohead]

Originally Posted by IsaacMTSU

You can't say anything unicorn about vortex generators...The way some idiots put them on their cars maybe, but the actual effects of them installed properly are proven.
Mitsubishi Flow Analysis PDF They help the boundary layer of airflow reattach after a downward curve on a roof/back window/wing. You cant put them on every inch of the back of your car and get the Cd of a sports car from an SUV though.

Was the Mitsubishi research not based on a Lancer notchback,with a trunklid/boot present for the air to reattach to,whereas the Toyota SUV has no such structure?
I believe that Hucho mentions,that without a reattachment surface,VG efficacy in three-dimensional flow remains unknown.

[Tesla]

Originally Posted by aerohead

Was the Mitsubishi research not based on a Lancer notchback,with a trunklid/boot present for the air to reattach to,whereas the Toyota SUV has no such structure?
I believe that Hucho mentions,that without a reattachment surface,VG efficacy in three-dimensional flow remains unknown.

Stumbled on this PDF last night,
Don't know much about it, but did get that point, you need to have a surface to reattach to in vehicle applications, so suitable for sedans, but of questionable value on wagons and Kammbacks.
As they do add drag, you need to make sure they are properly suited to the application for a gain.

[IsaacMTSU]

I agree they work best with a surface to reattach the flow to, that's why tons of airplanes use them from the factory to decrease the critical angle of attack and lower the stall speed. They also reduce the size of the turbulence behind the "shape", whether it be a wing or a car, which decreases the drag. (When used properly )