what are these stuck on Aero thingies?

[aerohead]

Originally Posted by acparker

Found this while googling:

Aerodynamic Effects of Rear Spoiler and Vortex Generators on Passenger Cars

https://www.researchgate.net/profile...Passenger_Cars

We'd want to look at:
* the blockage ratio of their model/wind tunnel test section
*buoyancy effects
* the Reynolds number based upon model scale and air velocity

[freebeard]

I want to look at

https://www.researchgate.net/publication/290024199_The_COANDA_Flow_Control_and_Newtonian_Co ncept_Approach_to_Achieve_Drag_Reduction_of_Passen ger_Vehicle

But the Read More link starts off down a garden path instead of offering the PDF. This doesn't happen with the previously linked article. I guess I could use TOR to request it.

[gumby79]

If the kick up effects are as I imagine it .the air circulating at the rear of the hatch is allowed to meet the air off the deck lid traveling in the same general angle, instead of at almost right angles. I clicked the "full text " link.they asked for an E-mail to notify me when 1 of the authors release it. This as I understand them from the abstract ,this smoth directional convergence, is what I was trying to promote with the duck bill sticking out behind my tail gate.

[aerohead]

Not to slam their research,but here's some considerations.
*at 1/15-scale,the test section flow velocity would need to be a minimum of 300-mph in order to achieve critical Reynolds number.
*The model's frontal area should not exceed 5% of the test section cross-sectional area.Clearly not the case.
*at 300-mph,transonic flow would be present with shockwaves forming on parts of the body,blocking airflow in those areas.
*at 300-mph,the boundary layer would be thick enough on the walls,ceiling ,and floor of the test section as to choke off the flow,creating a velocity acceleration discontinuity over the length of the model,compounding the blockage effects and supersonic jets.
*at 300-mph,the wheels and lower body of the model could be immersed in the boundary layer,which would never happen at 1:1 - scale.
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If the authors had actually read Hucho's book,they'd know these things before they ever began,and never proceeded.
Another thing,these sorts of body details cannot be examined at this sort of scale level.Maybe 1:2 scale,then 1:1 scale verification later.
I think it's one of those Donald Rumsfeld moments in science,where the investigators didn't know the known knowns.

[freebeard]

They either had an air tunnel and picked an inappropriate scale; or picked a scale and chose air over a water tunnel. Then it's all downhill from there.

[Fat Charlie]

Originally Posted by aerohead

I think it's one of those Donald Rumsfeld moments in science,where the investigators didn't know the known knowns.

Donald Rumsfeld's contributions to scientific thought are greatly misunderstood, and I think incorrectly attributed here.

A true Donald Rumsfeld moment would be deciding that you do aero testing with the scale model you have, not the scale model you might want or wish to have at a later time.

Or perhaps it would be phrased Absurd. We don’t need nearly 1:1. Not that large. Certainly no more than 1/15.

Whichever way you apply him, the result is an abject failure, but the exact reasons why can be fascinating.