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)

$C_{d}={\biggl (}{\frac {\kappa }{14.56-2\ln W}}{\biggr )}^{2}$

(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)

$W=W_{z}{\biggl (}{\frac {10}{z}}{\biggr )}^{1/7}$

(3)

Pressure

The atmospheric pressure is included in the momentum equations as an additional pressure gradient term \begin{equation} \tag{4} \frac{h}{\rho_0} \frac{\partial p_a }{\partial x_j} \end{equation}

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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