Has anyone tried this type of air deflector?

[djwarner]

I was reading a 2001 post by Michael regarding aerodynamics and exhaust fumes and spoilers. His in depth description of why 240z aerodynamics were so poor got me thinking.

 

NACA scopes are effective because they roll a vortex into the duct to help break up the laminar flow. I got to thinking about the low pressure area over the rear hatch and the relatively higher pressure on the sides of the cockpit. It occurred to me we could put a curved air deflector over the sail directing air onto the hatch to help to detach the laminar flow coming over the top.

 

I envisioned a deflector like those used on station wagons to keep the rear glass clean. Attached is a picture suggesting my idea. the air deflectors are colored gray.

 

Comment from the more aerodynamically literate among us would be appreciated. 

[BluDestiny]

Can you post a picture of said station wagons? I can't exactly picture what you're saying.

[djwarner]

I was thinking about a station wagon air deflector running across the top, but I found this picture on the web

[260DET]

Those sort of deflectors would create a lot of drag and noise? at high speed. How about a row of vortex generators along the top of the roof at the back?

[JMortensen]

Agree with Richard. FWIW, when you see these deflectors on Blazers and wagons, I think the idea there is to keep the rear window from getting dirty, rather than to lessen the separation of flow on the hatch.

 

As far as solutions to the flow separation, you could look at WRX vs EVO. The WRX had a roof mounted deflector along the top that did the same basic thing. If I recall, the EVO's VGs were the better solution, but those were sedans with a pretty steep rear window angle. Since the angle of the hatch isn't that severe, I don't think you would want these things on the side directing side air across the window. Seems like the side deflectors would be high drag.

[ctc]

Tape some 1-2 inch pieces of yarn to the back window in rows equally spaces.  Stick a go-pro camera in the back and video the air flow over the hatch.  Will give you  a much better image of what is going on.  Yell out your speed so you get it on the video.  Bet what you will find is a large area of reverse flow starting about halfway down the glass where it runs out of energy.  VG's energize the flow so in less then technical terms, the energized flow will push father down the glass.  Reverse flow means more drag and other bad things.  Main issue is any surface ahead of were you are interested will take energy out of the flow.  Your deflectors would need to stick out into the free air, about 2 inches away from the body.

Edited February 14, 2014 by ctc

[260DET]

Just remember that the squared off back of a station wagon is way different to that of a Z. In aero terms that is black and white, with aero for us amateurs it's best to stick with what actually works rather than trying to work out what an entirely different setup will do. But what ctc suggested is the go if you want to experiment.

Edited February 14, 2014 by 260DET

[Hypertek]