In a three-dimensional two-phase flow, accessing the velocity fields of the two phases simultaneously is challenging. Nevertheless, information about the local relative motion between the two phases is particularly valuable to quantify the inter-phase interactions. In this article, the dynamics of neutrally buoyant finite-sized particles embedded in a three-dimensional turbulence is investigated using a simultaneous particle image velocimetry (PIV) and particle tracking velocimetry (PTV) measurement technique based on optical discrimination of the two phases prior to image acquisition. The implementation of this dual whole-field velocimetry technique is presented and detailed. With this technique, we were able to measure the instantaneous and local velocity differences between the particles and the underlying fluid. Our results show that, whereas the single-point velocity statistics of the two phases are very similar, the particles often have different local velocity than the velocity of the neighboring fluid. The relative velocity increases with the relative size of the particle to the Kolmogorov scale. In addition, the relative velocity exhibits an intermittent distribution.
['Mehdi Elhimer', 'Olivier Praud', 'Moise Marchal', 'Sébastien Cazin', 'Rudy Bazile']
Simultaneous PIV/PTV velocimetry technique in a turbulent particle-laden flow