Wind Force on Flag Pole Cylinder Formula and Calculator

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Wind Force on Flag Pole Cylinder Formula and Calculator

Fluids Engineering and Design
Civil Engineering and Design

Wind Force on Flag Pole Cylinder Formula and Calculator (Airflow around a Cylinder Formula)

The characteristic drag coefficient plot for cylinders placed normal to the fluid flow is similar to the plot for spheres. The plot shown in Fig. 1 is for infinitely long cylinders, since there is additional wake drag at the cylinder ends. In calculating the Reynolds number, the cylinder diameter should be used as the characteristic dimension.

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Fig. 1 - Drag Coefficient for Cylinder

Density of air
Eq. 1,
ρ = p / ( R T )

Kinematic Viscosity
Eq. 2,
v = µ /ρ

The characteristic dimension of a cylinder is its diameter. The Reynolds number is
Eq. 3
Re = L v / ν = Dv / ν

Frontal area of the flagpole
Eq. 4
A = DL

Drag Force on the flagpole is
Eq. 5
F_D = C_D A ρ v² / 2

Where:

F_D = Drag Force on the flagpole, N
D = Pole or cylinder diamater, m
L = length of pole, m
µ = absolute viscosity (1.709 x 10^-5 Pa · s)
C_D = drag coefficient based on Reynolds number - see Fig. 1
ρ = density of air ~ 1.276 kg/m³ (temperature dependent)
v = Wind speed, m/s
ν = Kinematic viscosity, m²/s
p = pressure, kPa
R = Specific gas constant for Air 287.03 J / kg·K
T = Temperature, K
Re = Reynolds number,dimensionless
A = Frontal area of pole, m²

Reference:

Civil Engineering Reference Manual, Fifteeth Edition