Acoustical technique for Lagrangian velocity measurement

Ultrasonic transducers array can be used to track solid particles advected by a turbulent flow. The simultaneous use of four linear antennas of transducers gives the 3D position of the particles. The extraction of the Doppler frequency shift gives a precise estimation of velocity components. We describe the principle of the technique, the signal conditioning and the acquisition schemes. We show briefly the performances of the technique applied to a turbulent flow at high Reynolds number. The dynamical range of the measurement is over 55dB and the frequency response spans over 2decades. These performances allow us to investigate the inertial time scales of Lagrangian turbulence.