SOUND-SCATTERING ON A TURBULENT, WEAKLY HEATED JET

We report an experimental study of the scattering of ultrasonic plane waves on a turbulent jet in air (Pr = 0.7). The jet is weakly heated s o that the temperature fluctuations act as a passive scalar. In the ba ckscattering geometry one measures the Fourier components of the tempe rature field (T) over tilde(q,t). The time averaged characteristics ar e analyzed in detail; in particular we observe a Kolmogorov ''-5/3'' p ower law behavior for the passive scalar spectrum in the inertial rang e of scales. The study of the time fluctuations shows that the histogr ams of (T) over tilde(q,t) remain close to a Gaussian at all scales.