Measurement of Lagrangian Velocity in Fully Developed Turbulence

We have developed a new experimental technique to measure the Lagrangian velocity of tracer particles in a turbulent flow, based on ultrasonic Doppler tracking. This method yields a direct access to the velocity of a single particle at a turbulent Reynolds number $R_{\lambda }=740\mathrm{}$, with two decades of time resolution, below the Lagrangian correlation time. We observe that the Lagrangian velocity spectrum has a Lorentzian form $E^L\left(\omega \right){=u}_{\mathrm{rms}}^2{T}_L/[1+(T_L\omega {)}^2]$, in agreement with a Kolmogorov-like scaling in the inertial range. The probability density functions of the velocity time increments display an intermittency which is more pronounced than that of the corresponding Eulerian spatial increments.