14h30 - 14h55 : Turbulent settling of inertial particles

The transport of particles by fluids is an important aspect for the formation of clouds, spreading of aerosols or dust by wind and mixing of suspensions in industrial applications. The complexity of these systems is indicated by the large number of dimensionless parameters that control their behaviour: the particle inertia (Stokes number), the particle volume fraction, the flow turbulence (Reynolds number based on the Taylor microscale) as well as the influence of buoyancy and drag forces on the particles (Rouse number and Froude number). To disentangle their overlapping influence on important physical aspects, such as preferential concentration or settling velocity alteration, we are performing an experimental study in a water tank. By using different particle populations with diameters of 20 to 200 micrometer (on the scale of or below the Kolmogorov scale) and particle-to-fluid density ratios of 2.5 to 15.6 we are able to cover a large range of the parameter space, accessing regimes which are challenging to investigate and have been rarely considered. Turbulence is generated by two oscillating grids which have been shown to be able to create conditions close to isotropy and homogeneity. The particle motion is measured using particle tracking velocimetry (PTV) in a vertical laser sheet. The flow itself is visualised by rhodamine-coated tracers and evaluated using particle image velocimetry (PIV). This simultaneous double measurement with tracers and particles of similar size is another challenging aspect of our work: two cameras record the experiment, with one only receiving fluorescent light emitted by the tracers and the other being used for the tracking of the inertial particles. The resulting experimental database will be a step forward in quantifying the respective influence of each control parameter while a help in improving theoretical models and accompanying numerical simulations [Monchaux and Dejoan, Phys. Rev. Fluids 2, 104302 (2017)].