Wind effect on noise propagation

[aesoton]

Hello All,

Does anybody have a formula that would enable me to calculate the attenuation upwind of an noise source due to wind speed and distance? Similarily, enhancement of the noise level downwind.

Thanks
Andrew

 

[Rob45]

Be careful when trying to use a formula for this that you don't have any interaction between the source and the wind.

For example, some years ago I learned that the noise level upwind of an exhaust pipe (when the wind is impinging directly on the open end of the pipe) is greater than the noise downwind.

Beranek has a plot, but the testing on which it is based seems rather obscure.

 

[Denial]

I've never thought about this before, but in a totally uniform wind field you might be able to apply the inverse square law, but measuring the "radial" distance from the moving generation point rather than from the actual stationary point.

However no wind field is uniform. In particular, the wind speed usually increases with height above the ground ("vertical wind shear"), and this effect tends to "focus" the sound waves onto ground-level points downwind. Similarly it also tends to "unfocus" the sound waves away from upwind ground-level points.

The severity of the vertical wind shear depends upon many factors, including the roughness of the terrain upwind of the point in question.