Experimental investigation of two way coupling in particle laden turbulent flow

The primary goal of the proposed research is the analysis of the small scale interactions between suspended heavy particles and turbulent flow. Most of two phase turbulent flows are characterized by two-way interaction mechanisms between particle motion and carrier fluid, which manifest themselves both in the modification of turbulence on all scales and in the distribution of dispersed particles in the flow. The basic interaction of the carrier fluid flow with the particles occurs at the scale of the
particle size or the scale of particle clusters i.e. small scales. Indeed it is now established that the macroscopic behavior of multi-phase systems depends strongly on small-scale phenomena.

The methodology is based on an expansion of the 3D Particle Tracking Velocimetry (3DPTV) system available at IHW Measurements of the 3D velocity field of the carrier fluid are obtained simultaneously with the 3D positions and velocities of the suspended particles. The fluid phase is marked by passive tracers, in order to be distinguishable from the heavy particle phase. To maintain optical transparency for sufficiently high
particle concentrations of the suspension, it is necessary to apply refractive index matching between fluid and suspension.

The first experimental milestone is the implementation of the methodology in a suspension of dispersed particles in a refractive index matched fluid. The second milestone will be the optimization of the whole system to be able to resolve the fluid phase to the Kolmogorov scale to obtain the Lagrangian evolution of the velocity gradient tensor. This, together with the trajectories of the heavy particles will allow us to model the interaction terms.

The significance of the proposed research lies in the elucidation of basic physical mechanisms underlying the main phenomena of particle laden flows. Up to now most of the insights into such flows result from numerical simulations and models based on strong hypotheses, which have to be validated in real physical systems. This need is underscored in view of the differences in existing explanations of basic effects such as preferential concentration and turbulence modification reported in the
literature.

The expected output comprises establishment of a new experimental technique and the identification and quantification of the particles-turbulence interaction effects on the small scales on a statistical basis. The proposed research aims to become a benchmark for future theoretical and numerical investigations.