The vertical distribution of mean wind velocity was observed, using several Robinson small cup anemometers, in the lower layer over three places in Tokyō.
From the results, the vertical distribution of wind velocity was fitted to the logarithmic law as follows :
U(
Z)=(
U∗/
k) log
e ((
Z-d)/
Z0)………(1)
where
U∗,
k,
Z0 and d denote the friction velocity, Kármán’s const. 0.45, roughness parameter and zero plane displacement (d was chosen to give the best fit in wind profile). The values of d and
Z0 are observed.
Then, the vertical diffusion coefficient (
Kz) is given by (2), from Prandtl’s theory on the turbulence mixing.
Kz=
kU∗ (
Z-d)………(2)
The calculated values of
Kz was the order of 10
4cm
2/sec, for
Uav varying form 3.6m/s to 6.4m/s at height from the ground 10m.
View full abstract