In this post I want to share to you how to estimate wind speed as function of height. Wind velocity plays a significant role in influencing the dispersion of released fluids. Wind speed rises with altitude above the earth’s surface, so reference height should be specified. Typically, 10 m is used as the meteorological standard unless noted otherwise.
Wind speed is also a function of weather stability and on the terrain.
Weather stability relates to vertical temperature gradients and atmospheric turbulence. The Pasquill-Gifford (P-G) classes are commonly used, with class G excluded from dispersion modelling.
The turbulence may depend on amount of incoming solar radiation as well as other factors. Figures below illustrate each stability class.
Regarding the terrain, wind speed is also a function urban and rural areas.
Equation below can be used to estimate wind speed as function of height and terrain:
where:
u10 is the wind speed at 10m height
p is an exponent which depends on weather stability class and on the terrain
y is height
u (y) is the wind speed at y height
The value of p is tabulated below.
I made a simple spreadsheet on how to estimate wind speed. You can freely download here. It is very easy to use. Here is the screenshot of an example.
I hope you find this simple post useful as always!
References:
[1] Aloha Help
[2] Process Safety Calculations, Second Edition. Renato Benintendi