Question 15.9: A circular disc of diameter 2 m is positioned normal to the ......
A circular disc of diameter 2 m is positioned normal to the direction of flow of wind at 20 m/s. If the coefficient of drag of the disc is 1.12, fmd the force required to hold it at rest. The density of air is 1.2 kg/m³.
Given data:
Diameter of disc D = 2 m
Velocity of wind U_{\infty}=20 \mathrm{~m} / \mathrm{s}
Coefficient of drag C_D=1.12
Density of air ρ = 1.2 kg/m³
Area of disc is A=\frac{\pi}{4}(2)^2=3.142 \mathrm{~m}^2
The drag force acting on the disc is given by Eq. (15.14) as
F_D=C_D A \frac{1}{2} \rho U_{\infty}^2
=1.12 \times 3.142 \times \frac{1}{2} \times 1.2 \times 20^2=844.57 \mathrm{~N}
The force required to hold the disc at rest is equal to the drag force exerted by wind on the disc.