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Re-suspension of particles in an oscillating grid turbulent flow

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Particle re-suspension in liquid environments is an important mechanism in a variety of practical applications, such as: particle filtration, oil production, migration of surface contaminants [3] and even particulate transport in respiratory ways. Over the years, different criteria and models have been proposed to define threshold conditions for particle incipient motion. Despite a significant progress in the field during the past decades, description of the mechanisms responsible for the initiation of particle detachment from a surface and re-entrainment into suspension remains a challenge. This is partially due to the technical difficulties to quantify the forces applied on the particles and the collection of high-resolution data of flow measurements and particle displacement simultaneously.
The majority assumes particle-turbulence interaction to have a major influence on the phenomena [6]. Observations led to models that consider turbulent coherent structures with vertical velocity component ,v, exceeding the particle settling velocity, vs , to be responsible for the incipient motion. Since in boundary layers velocity components are proportional to the friction velocity, u*=(τw/ρ)0.5, the critical conditions for the initiation of suspension (pick up or lift off) are defined in terms of friction velocity, i.e. u*/vs >1(Bagnolds' condition) [1]. In flows without mean shear it was proposed that root-mean-square of turbulent fluctuating velocity or turbulent kinetic energy, i.e (u'2+v'2+w'2)/2 characterizes the re- suspension process.

Author(s):

Hadar Traugott    
Turbulence Structure Laboratory,School of Mechanical Engineering,Tel Aviv University.
Israel

Alex Liberzon    
Turbulence Structure Laboratory,School of Mechanical Engineering,Tel Aviv University.
Israel