ELFT HÍRADÓ

[StatFizSzeminar <statfiz AT glu.elte.hu>]

                   #    #    #    #    #    #

                   ELTE Institute of Physics
                SEMINARS IN STATISTICAL PHYSICS


                       16 September 2015
                       Wednesday, 11 a.m.

                         Ksenia Guseva

 Institute for Chemistry and Biology of the Marine Environment,
 Carl von Ossietzky University of Oldenburg, Oldenburg, Germany

            "History effects in the sedimentation of
     light aerosols in turbulence: the case of marine snow"


We analyze the effect of the Basset history force on the sedimentation of 
nearly
neutrally bouyant aerosol particles, exemplified by marine snow, in a
three-dimensional turbulent flow. Particles are characterized by Stokes 
numbers
much smaller than unity, and still water settling velocities, measured in 
units
of the Kolmogorov velocity, of order one. The presence of the history force in
the Maxey–Riley equation leads to individual trajectories that differ
strongly from the dynamics of both inertial particles without this force, and
ideal settling tracers. When considering, however, a large ensemble of
particles, the statistical properties of all three dynamics become more 
similar.
The main effect of the history force is a rather slow, power-law type
convergence to an asymptotic settling velocity of the center of mass, which is
found to be close to the settling velocity in still water. The size of the
ensemble, the variance, increases diffusively, after the large eddy turnover
time of turbulence. We demonstrate that the settling of the center of mass for
such light aerosols is best approximated by the settling dynamics in still 
fluid
found with the history force, on top of which fluctuations appear which follow
very closely those of the turbulent velocity field.


                          Room 2.54
     1117 Budapest, Pázmány P. sétány 1/A (Northern Block)
              home page: http://glu.elte.hu/~statfiz


                   #    #    #    #    #    #