Homogeneous turbophoresis of heavy particles in turbulent flow
Dispersed particles suspended in turbulent flows are commonly encountered in natural and industrial settings, taking the form of droplets, dust, or sediments. When these particles are denser than the surrounding fluid, they possess inertia and are propelled by centrifugal forces away from the most intense vortical structures of the flow. Over time, as these particles follow their individual paths, this small-scale mechanism results in a significant large-scale drift. This drift leads particles out of the highly agitated turbulent regions, causing them to accumulate in the calmer zones to form uneven spatial distributions. This fundamental process, known as turbophoresis, has been extensively utilised to explain the tendency of particles transported by non-homogeneous flows to concentrate near the minima of turbulent kinetic energy.
In this talk, we demonstrate that turbophoretic effects are just as crucial in statistically homogeneous and isotropic flows. Despite their uniform average, instantaneous spatial fluctuations of the turbulent activity trigger local fluxes that fundamentally influence the emergence of inhomogeneities in particle distribution within the inertial range. Direct numerical simulations are employed to thoroughly probe and depict the statistics of particle accelerations, particularly their scale-averaged properties conditioned on local turbulent activity. These simulations affirm the importance of local energy dissipation in describing instantaneous spatial fluctuations in turbulence. This analysis yields an effective coarse-grained dynamics model, incorporating the detachment of particles from the fluid flow and their expulsion from excited regions through a space and time-dependent non-Fickian diffusion process.
Caption : 2D slice of the instantaneous energy dissipation field (coloured background) for Re_𝜆 = 460, together with particle positions for St = 1 shown as black dots.
Contact Nathanael Machicoane for more information or to schedule a discussion with the seminar speaker.