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How do I go about finding the pressure exerted on a rectangular surface in a free flowing air stream?

I wouldn't imagine that this is directly related to the airspeed / surface area, but have no idea where to start. Is there even an equation, or does one need to do some kind of FEA?

For instance a 1.2m x 2.4m metal sheet suspended some distance above ground level, if I have a gust of wind at 8m/s (directly perpendicular to the sheet), what is the average pressure across the face of sheet?

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2 Answers

up vote 1 down vote accepted

Wind Load Formula:

$F_d = \frac{1}{2} \rho v^2 A C_d$

$F_d$ is the force of drag (or in this case Force Against the flat plate)
$\rho$ is the density of the air
$v$ is the speed of the air against the object
$A$ is the area of the object which the air is blowing against
$C_d$ is the drag coefficient

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Seeing as how I just asked a fluid dynamic question earlier today, I'm probably not the best person to answer this. I think to get you in the right direction you may want to look at Bernoulli's equation for compressible flow. Initial pressure is probably atmosphere. See if that helps.

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