Near the ground on the upwind side of a busy car park the wind speed increases with…

PHYSICS · Multi-part · Fermi University Physics · Fluids & Continuum Physics · Waves, acoustics and compressible flow · Waves, acoustics and compressible flow

Signal Speeds in Fluids, Ch Sound in a moving, absorbing fluid: sources, refraction and loss

Problem

Near the ground on the upwind side of a busy car park the wind speed increases with height with shear

\mathrm{d}U/\mathrm{d}z = 0.15\,\mathrm{s^{-1}}

, and the temperature is uniform, so

\mathrm{d}c_{\rm eff}/\mathrm{d}z = -0.15\,\mathrm{s^{-1}}

for rays travelling into the wind (taking

c_0=343.2\,\mathrm{m\,s^{-1}}

as the local sound speed). A car alarm and a listener are both

1.5\,\mathrm{m}

above the ground, the listener upwind of the alarm. ((a)) Find the radius of curvature

R

of a nearly horizontal ray travelling upwind. ((b)) Find the distance beyond which the listener lies in the acoustic shadow.

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