through better than around?

[maxmistretta]

Hello everyone,I'm new here and would like to thank you for having me.I'm a 45 year old A.S.E. master certified tech with many hours of G.M. training. I just got a 93 civic dx and plan on "playing" with it. After seeing all the ( I'm sorry) ugly fender skirts It seems to me air could be ducted out of the fenders, through the rear bumper and out the sides of the front fenders late 70's trans am style. Has anyone tried anything like this and if so how does it work?

[elhigh]

Hi.

I don't remember exactly who made this thing, it was either Renault or Peugeot, and it was called either VERA or VESA or something similar. I don't know about venting out the sides of the fenders - I tend to think about fender-top venting, CanAm style through rear-facing louvers. But I remember Renault or Peugeot's design study that had carefully sculpted front wheelwells that let the air out smoothly along the flanks of the car. I'll look for a picture.

[elhigh]

Here we go. Let's see if I can figure out how to add a picture.
Peugeot, BTW, in case you couldn't guess by the styling.

It's not the best image but you get the idea. They also did a partial wheelskirt, dropping the rear wheelwell opening down nearly to the level of the top of the wheel.

This was in the late 70s IIRC, gas mileage being the motivation then as now.

[Bicycle Bob]

Certainly, it is good to use a smooth duct for rad exit air, and to consider how it will affect the other flows. In general, it is better for air to go around rather than through, because adding ducts increases surface area. Cars are so far from being pure shapes that changes often have surprising results, due to interactions of flaws.

[aerohead]

Originally Posted by maxmistretta

Hello everyone,I'm new here and would like to thank you for having me.I'm a 45 year old A.S.E. master certified tech with many hours of G.M. training. I just got a 93 civic dx and plan on "playing" with it. After seeing all the ( I'm sorry) ugly fender skirts It seems to me air could be ducted out of the fenders, through the rear bumper and out the sides of the front fenders late 70's trans am style. Has anyone tried anything like this and if so how does it work?

The present wisdom is to let all the air "pool" above the lowest suspension components,trapped in by the perimeter of the body.The air flowing below will sort of ricochet off this stagnant air.
By opening up the fenders or bumper you create a torture chamber for the air.Subaru published an SAE paper on R&D of a sport coupe they built and it shows a definite benefit of closing off the rear and actually dropping a valance panel down from the bumper to trap even more air until it reaches the "diffuser angle,then they provide a smooth under-belly panel to guide the flow.
GM wind tunnel R&D of the Trans Am Firebird revealed that the aft wheelhouse ducts on the front fenders INCREASED drag.They remained as a styling cue,but actually degraded the cars performance.

[Peter7307]

Welcome to the place to begin.

Since air is going to go through the car anyway ducting the exit point to an area of relative negative pressure makes sense but ensuring it does not disturb the flow already in that region , thus causing more drag , is the trick.

Interesting topic for sure.

Cheers , Pete.