Turbulence attenuation by large neutrally buoyant particles

International audienceTurbulence modulation by inertial-range-size, neutrally-buoyant particles is investigated experimentally in a von Kármán flow. Increasing the particle volume fraction Φ v , maintaining constant impellers Reynolds number attenuates the fluid turbulence. The inertial-range energy transfer rate decreases as ∝ Φ 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. Introducing impurities in a developed turbulent flow has drastic effects on the mechanisms of energy transfer and dissipation. A minute amount of polymer additives causes for instance drag reduction. 1 In such visco-elastic fluids, the coupling between the local flow and the polymers stretching can be modeled in order to quantify the exchanges between kinetic and elastic energies and to interpret turbulent drag reduction as a suppression of large velocity gradients. 2 The mechanisms at play in turbulent suspensions of finite-size spherical particles are much more intricate and turbulence can either be enhanced or suppressed