PROPAGATION OF SOUND THROUGH A TURBULENT VORTEX

We report an experimental study of sound propagation in the bulk of a homogeneous flow made of a single intense vortex in air. By using an a daptive-coherent average technique, the mean amplitude and phase of th e distorted wave fronts are reconstructed. A large phase shift is obse rved on the wave fronts on either side of the ''shadow'' region behind the vortex. The shape of the averaged amplitude, as a function of spa ce coordinates, shows that caustics are also formed in the acoustic fi eld. In a nonstationary flow, these effects make it possible to monito r the vortex strength and position.