Quote:
Originally Posted by ecomodded
I was watching this video (from the Yoshi link) when Yoshi mentioned the wind speed he would be using is 40 to 50 mph to simulate a full size car going 100 mph.
It appears that you reduce speed to simulate a real car.
I had also thought I would need to increase the wind speed.. it just got easier to construct by a few fans at least and several mph.
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No, he said it would simulate a real car going about 2 mph.
Ideally, you want the Reynolds number of the model to be the same as the vehicle you are simulating. But since the car is 1/32 size, you would have to run the wind speed up to 32 times the real car speed that you want data for, which is not practical for most people.
But you can find out what the relative impact is for changes to the shape. Just try to make the model as big as possible and the wind speed as fast as possible.
FYI, a quick approximation for Reynolds number for objects in air at sea level is
Re = Length in feet X Speed in mph X 10,000.
So a 15 ft long car at 50 mph would have a Reynolds number of 15 X 50 X 10,000 = 7,500,000.
A 1/32 scale model in a 50 mph wind tunnel would have a Reynolds number of 15 X 1/32 X 50 X 10,000 = 234,375, or 1/32 of the full-size car. If you double the wind speed in the tunnel to 100 mph, the Re would be 1/16 of the full-size car. See the relationship?