Paper detail

Study on preferential concentration of inertial particles in homogeneous isotropic turbulence via Big-Data techniques

We present an experimental study of the preferential concentration of sub-Kolmogorov inertial particles in active-grid-generated homogeneous and isotropic turbulence, characterized via Voronoï tessellations. We show that the detection and quantification of clusters and voids is influenced by the intensity of the laser and high values of particles volume fraction $ϕ_v$. Different biases on the statistics of Voronoï cells are analyzed to improve the reliability of the detection and the robustness in the characterization of clusters and voids. We do this by adapting Big-Data techniques that allow to process the particle images up to 10 times faster than standard algorithms. Finally, as preferential concentration is known to depend on multiple parameters, we performed experiments where one parameter was varied and all others were kept constant ($ϕ_v$, Reynolds number based on the Taylor length scale $Re_λ$, and residence time of the particles interacting with the turbulence). Our results confirm, in agreement with published work, that clustering increases with both $ϕ_v$ and $Re_λ$. On the other hand, we find new evidence that the mean size of clusters increases with $Re_λ$ but decreases with $ϕ_v$ and that the cluster settling velocity is strongly affected by $Re_λ$ up to the maximum value studied here, $Re_λ= 250$.