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The physics of settling spheres - Still many unknowns

The problem of spheres settling in a fluid (the simplest paradigm of drifting particles) underlies a whole hierarchy of rich imbricated phenomena, summarized in the table above. The TurBullet project aims at answering 4 important questions related to the individual and collective dynamics of small passive drifting particles and active particles (which embrace the fascinating class of self-propelled particles, such as bacterial suspensions and oceanic plankton) interacting with a turbulent background :
  • Q1. Can we disentangle the role of gravity (drift) and inertia on particle/turbulence interactions ?
  • Q2. When and how does turbulence enhance/inhibit the individual settling (drift) of inertial particles ?
  • Q3. When and how do collective effects (promoted by clustering and/or particle-particle interactions) enhance/inhibit the settling of an ensemble of particles.
  • Q4. How is the dynamics of active particles influenced by the presence of background turbulence ?