The wind's velocity exerts pressure on objects in its path. Designing wind-resistant structures--for example, wind turbine towers--requires calculating how much wind they can handle without breaking. Wind force calculations also determine the size, strength, shape and expected kilowatt output of a turbine's rotor blades. Calculate how many pounds of pressure a wind of a given speed exerts on a stationary surface using a formula.
Obtain wind speed from an instrument, wind map or other source. Convert miles per hour to meters per second if necessary. Multiply the wind speed in meters per second by 0.06, a constant derived from the density of air, at 20° degrees Celsius and average relative humidity. This calculation results in the wind velocity Vp expressed in pascals.
Multiply the result for Vp by a factor of 1.45 raised to the e-4 power. This is the force (pound-force, abbreviated “lbf”) exerted by one pascal on one square inch of surface. This calculation results in the pound force per square inch exerted by the wind velocity Vp calculated in Step 1.
Multiply the number obtained in the second step by the object's total surface area to arrive at the total pressure in pounds that the wind at the given speed brings to bear on the whole object.
Example: A wind with a speed of 44.45 meters per second acts on a total surface area of 1,200 square inches.
Vp = [0.6 x (44.45 m/s)2] = 2370.4 pascals Pound-force = [2370.4 x 1.45e-4] = 0.3435 lbf/in2 Total force exerted = [1200 x 0.3435] ? 400 lb.
For a quick-and-dirty, non-math-intensive wind force reading, observe wind action on man-made or natural objects, such as trees and bodies of water, and read the relative wind force off a Beaufort Wind Scale. For more-refined wind force formulas, see Resources.
Use a wind map to obtain prevailing wind speeds anywhere in the United States. You can examine one in the Small Wind Electric Systems Guide in Resources.