Wind Speed & Turbulence Limits Used in Model Calculations
At the time of plume rise calculations the turbulence at stack top (or whatever level the meteorology is selected from in the case of iterative plume rise) will be recalculated as
Dilution of the plume is determined by the wind that corresponds to average over the magnitudes of the wind vectors during a given time interval. But measurements only give us the vector averaged wind, which can be zero, even though the dilution wind is not zero. We can estimate the dilution wind by assuming that the vector wind, uv , can be expressed as
where
is the mean measured wind, and the primed quantities refer to the
turbulent fluctuations. Notice
that, as assumed v
= . If we assume that the measured velocity
fluctuations correspond only to the angular variations of a constant
vector, uv , we can write from
eq.
(138),
In
this simple model, uv , is the dilution wind. If we take 
u
= v , the dilution wind can be written as
This
formulation assures that the dilution wind is not zero as long as
either " or v is not zero. V Similarly, at the time of
dispersion calculations, the effective turbulence and effective wind
speed will be recalculated using eqs. (136), (137) &
(140), where the stack top values will be replaced with w ,v &
u.
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