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Old 08-11-2020, 12:07 AM   #1 (permalink)
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Tuft testing with a leaf blower

Has anyone used a leaf blower for tuft testing on aero mods?
Can it be reliable or accurate enough?
I thought of this because I don't have anyone to drive alongside with a camera. And I have a powerful electric blower I could set up towards the car.

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Old 08-11-2020, 11:17 AM   #2 (permalink)
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I am curious as well, but I think it wouldn't be accurate because of "dispersion" (not sure if thats the best description) since it will accelerate in all directions once it leaves the blower and therefore the velocity against the car would be considerable less just a few feet away from the blower. Since you have to consider the car from front to back I don't think this would provide accurate results. Consider side mirror testing. Since you have to have the windshield and fender to have realistic flow, then by the time the air reaches the mirror you would be 2-3 ft away already.

Just thoughts from the arm chair though. Would be awesome to see a comparison.
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Old 08-11-2020, 11:54 AM   #3 (permalink)
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The problem is a leaf blower will produce wholly turbulent flow. To properly test aero modes you need laminar flow.
Testing in turbulent flow will make objects appear more aerodynamic than they really are.
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Old 08-11-2020, 01:54 PM   #4 (permalink)
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The other issue is the scale of the air flow vs the whole vehicle.

I used 4 (I think?) leaf blowers with a quarter scale model of my CarBEN project.
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Old 08-12-2020, 11:19 AM   #5 (permalink)
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leaf blower

In 'real' flow, any alteration to an automobile body would affect downstream as well as upstream flow. It wouldn't be isolated to any specific region of the body.
I've taken high static pressure, high velocity blowers to a car, and while the results are 'way out ahead of nothin',' I never had any expectation that what I observed could be repeated in a laboratory.
As to 'laminar' and 'turbulent' flow............. if the tufts aren't going crazy, jumping all over the body panel, you might as well presume that you've got laminar flow based on a turbulent boundary layer from the blower blast. It only takes a 20-mph 'wind' to achieve a turbulent boundary layer ( whole car ).
If a neighbor or friends can drive a chase car, and videograph of photograph tufts, that's better, as long as they're not so close as to alter the airflow them selves.
MetroMPG has, for years, solved the 'lack of chase car' syndrome, by attaching a GoPro or similar device to a stand-off strut on the test car itself, allowing autonomous capture of the tuft flow by himself. Clever!
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Old 08-13-2020, 04:37 PM   #6 (permalink)
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I advocate for a drone [follow me feature] pivoting at the center of a 100ft circle, since they typically can't do 30-40mph.

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