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Old 01-02-2010, 06:32 PM   #50 (permalink)
Rokeby
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Quote:
Originally Posted by Christ View Post
...The idea is similar, but slightly different. The wheel deflectors are similar
because they're a leading object which opens a wake for the tire to travel in,
but different in that they're only really there to prevent the tire from
compressing air under and around it, creating potential traction issues and
instability.
Same principle, different application, I suppose.
The OEM wheel deflectors have their major axis parallel to the ground. To be
congruent with the experimental set up in the OP cite, they should be
perpendicular to the ground, or perhaps more to the point the underbody
of the car. And I suppose there should be a flat and level "ground plane"
under the car as well. The OEM deflectors sort of hang down out of nowhere.
Deflected air is free to go up, down, or around them.

The paper cited in my OP was a set of lecture notes. As such, the material in
it is probably snippets of stuff from many places. There is indication that
identical masking effects on the main body can be achieved with either a
plate or a cylinder.

As noted above, to be consistent with the experiment cited in my OP, the
up-stream plate should be perpendicular to a "ground plane." I suppose it
would hang down to ~ an inch from the ground. It would have to be able to
handle being impacted by stuff; speed bumps/humps, debris, etc.

I'm thinking that a cylinder might fair better than a flat plate hanging own in
front of the wheels... something like a short length of swimming pool
"noodle."

Ultimately though, I suspect that identifying the contribution of the wheel
deflectors to overall fuel efficiency would be difficult for backyard
ecomodder experimenters. I thought that I've read, but can't find, figures
from Volvo that might be that detailed.

Quote:
Originally Posted by Bicycle Bob View Post
...Has anyone considered the power used to create the drag reduction? I
think the leading object is being given a free ride. Motor paced bicycle
records are set using a motorized fairing to set up a pressure differential on
the bike, and pedaling to hold position.
Bob,

I'm not sure what you are saying here. The original experimental set up
involved a simulation of a building and an upstream "deflector." There was
no consideration of energy inputs to create/sustain the wind. In thinking
about the use of an upstream deflector -- either for a wheel or the whole car
-- energy inputs, that is moving the vehicle, are of interest.

If I understand what you're saying, there should be an expectation that there
will be additional energy needed to move the car with the plate/cylinder
attached. But if the plate/cylinder works, more energy would be saved due
reduced drag from the main body,, whether it is a wheel or the whole car.

Am I even close?

Last edited by Rokeby; 01-02-2010 at 09:32 PM..
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