Turbulence attenuation by large neutrally buoyant particles

Turbulence modulation by inertial-range-size, neutrally buoyant particles is investigated experimentally in a von Karman flow. Increasing the particle volume fraction Phi(v), maintaining constant impellers Reynolds number attenuates the fluid turbulence. The inertial-range energy transfer rate decreases as proportional to Phi(2/3)(v), suggesting that only particles located on a surface affect the flow. Small-scale turbulent properties, such as structure functions or acceleration distribution, are unchanged. Finally, measurements hint at the existence of a transition between two different regimes occurring when the average distance between large particles is of the order of the thickness of their boundary layers. (C) 2015 AIP Publishing LLC.