MIDIT OFD CATS Modelling, Nonlinear Dynamics Optics and Fluid Dynamics Chaos and Turbulence Studies and Irreversible Thermodynamics Risø National Laboratory Niels Bohr Institute and Technical University of Denmark Building 128 Department of Chemistry Building 321 P.O. Box 49 University of Copenhagen DK-2800 Lyngby DK-4000 Roskilde DK-2100 Copenhagen Ø Denmark Denmark Denmark
by Hans L. Pécseli,
University of Oslo, Physics Department, Oslo, Norway,
Wednesday, October 24, 2001, 10.00 h
at OFD Meeting Room Building 130, RISŘ
Abstract: With reference to studies of predator-prey encounters in turbulent waters, the feasibility of an experimental method for investigations of particle fluxes to an absorbing surface in turbulent flows is demonstrated. The analysis is based on data from a laboratory experiment from the Meteorology Department at Risř, where an approximately homogeneous and isotropic turbulent flow is generated by two moving grids. The simultaneous trajectories of many small neutrally buoyant polystyrene particles can here be followed in time. Selecting one of these to represent a predator, while the others are considered as prey, we obtain estimates for the time variation of the statistical average of the prey flux into a suitably defined ``sphere of interception''. The variation of this flux with the radius in the sphere of interception, as well as the variation with basic flow parameters is well described by a simple model, in particular for radii smaller than a characteristic length scale for the turbulence. Also the Eulerian counterpart of the problem has been analyzed, and the particle fluxes from the two studies compared.