CMS-Flow:Wind Pressure

Wind

In CMS-Flow the wind shear stress is calculated as

${\tau }_{Wi}={\rho }_a{C}_d|W|W_i$

(1)

where $W$ is the 10-min average wind speed at a height of 10 m, $C_d$ is the drag coefficient, and ${\rho }_a$ is the atmospheric density (~1.2 kg/m^3).

The wind drag coefficient $C_d$ is calculated using the Hsu (1988)

$C_d=(\frac{\kappa }{14.56-2\ln W}{)}^2$

(2)

For measurements of wind speed made at heights other than 10 m, an approximation of the 10-m wind speed is (Shore Protection Manual 1984)

$W=W_z(\frac{10}{z}{)}^{1/7}$

(3)

Pressure

The atmospheric pressure is included in the momentum equations as an additional pressure gradient term

$\frac{1}{{\rho }_0}\frac{\partial p_a}{\partial x_j}$

(4)

Symbol Index

Symbol	Description	Units
${\tau }_W$	Wind shear stress	Pa
${\rho }_a$	Atmospheric density (~1.2 kg/m^3)	kg/m^3
$C_d$	Wind drag coefficient	none
$W$	10-min averaged wind speed at 10 m above the sea surface	m/sec
$\theta$	Wind direction	m/sec

References

• Hsu, S.A. (1988) Coastal meteorology. Academic Press, San Diego, CA.

• Shore Protection Manual (1984) 4th ed., 2nd Vol, U.S. Army Engineer Waterways Experiment Station, U.S. Government Printing Office, Washington, DC.

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