title: Transit times in turbulent flows.
abstract: Statistics of the motion of passively convected point particles in turbulent flows are studied. The database used is obtained by direct numerical solution of the Navier-Stokes equation. We estimate the probability distribution of the transit times of such particles through reference volumes with given forms and sizes. A selected position within the reference volume is moving with the local flow velocity, thus determining the motion of the entire surface. The transit time is defined as the interval between entrance and exit times of surrounding particles convected through the volume by the turbulent motions. Spherical as well as hemispherical surfaces are studied. Scale sizes in the inertial as well as in the viscous subranges of the turbulence are considered. Simple, and seemingly universal, scaling laws are obtained for the probability density of the transit times in terms of the basic properties of the turbulent flow and the geometry. In the present formulation, the results of the analysis are relevant for chemical reactions, but also for understanding details of the feeding rate of micro-organisms in turbulent waters, for instance.
authors.affiliation: Department of Physics, University of Oslo, Box 1048 Blindern, N-0316 Oslo, Norway.
authors.forename: H L
authors.initials: HL
authors.lastname: Pécseli
authors.forename: J
authors.initials: J
authors.lastname: Trulsen
mesh_terms: D008962:Models, Theoretical; D009038:Motion; D011336:Probability; D011789:Quantum Theory; D013997:Time Factors; D014783:Viscosity