CONTACT VELOCITIES OF SMALL ELLIPSOIDS SETTLING IN TURBULENCE etc15 Tracking Number 63Presentation: Session: Multiphase and non-Newtonian flows 2 Room: Room D Session start: 10:30 Thu 27 Aug 2015 Christoph Siewert c.siewert@aia.rwth-aachen.de Affifliation: Institute of Aerodynamics, RWTH Aachen University, Aachen, Germany Rudie P. J. Kunnen r.p.j.kunnen@tue.nl Affifliation: Fluid Dynamics Laboratory, Eindhoven University of Technology, Eindhoven, The Netherlands Wolfgang Schröder office@aia.rwth-aachen.de Affifliation: Institute of Aerodynamics, RWTH Aachen University, Aachen, Germany Topics: - Transport and mixing, - Turbulence in multiphase and non-Newtonian flows, - Lagrangian aspects of turbulence Abstract: Collisions of small and heavy non-spherical particles settling in turbulence are very important for systems such as ice clouds and proto-planetary disks where the particle spectra evolution is strongly dependent on the collision induced growth rate. Still, the influence of the particle shape on the collision probability is virtually unknown. Building on our recent investigation on the collision rate of monodisperse suspensions of ellipsoidal particles (Siewert et al., J. Fluid Mech. 758, 686-701, 2014), we show theoretically and by direct numerical simulations that the behavior of ellipsoids subject to turbulence and gravity is different from the behavior of spheres. Due to the dependence of the particle settling velocity on the particle orientation, the relative velocity at contact is influenced by turbulence. When ellipsoids differ either by mass or shape, their contact velocity is randomized by the randomized particle orientation. For particles much heavier than the fluid these orientation dependent settling velocity differences are larger than the relative velocities directly induced by the turbulent fluctuations. |