arXiv subjects

Piero Olla

Publications and source records attributed to Piero Olla.

40 records · Page 3Linked to original sources

arXiv1997

The lift on a tank-treading ellipsoidal cell in a bounded shear flow

The lift on a strongly non-spherical vesicle in a bounded shear flow, is studied in the case the membrane moves with a velocity, which is a linear function of the coordinates. The magnitude of the induced drift is calculated as a function of the axes lengths, of the distance from the wall, and of the ratio of the cell to the solvent viscosity. It appears that the main mechanism for lift, in the presence of tank-treading motions, is the fixed orientation of the vesicle with respect to the flow. Tank-treading vesicles in suspensions, flowing through narrow gaps under small Reynolds number conditions: $Re=Lv/ν< 1$ (with $L$ the gap width, v the flow velocity and $ν$ the viscosity) migrate away from the walls, with a velocity that is $Ø(Re^{-1})$ larger than predicted by inertia.

chao-dyn↗

arXiv1996

The role of tank-treading motions in the transverse migration of a spheroidal vesicle in a shear flow

The behavior of a spheroidal vesicle, in a plane shear flow bounded from one side by a wall, is analysed when the distance from the wall is much larger than the spheroid radius. It is found that tank treading motions produce a transverse drift away from the wall, proportional to the spheroid eccentricity and the inverse square of the distance from the wall. This drift is independent of inertia, and is completely determined by the characteristics of the vesicle membrane. The relative strength of the contribution to drift from tank-treading motions and from the presence of inertial corrections, is discussed.

chao-dyn↗

arXiv1995

Sample to sample fluctuations in fragmentation and agglomeration processes

The fluctuations in the particle size distribution for processes of fragmentation and aggregation are studied for stationary state regimes. The system is described in terms of a stochastic process over an adequate tree structure. The RMS fluctuations appear to scale with the square root of the mean distribution, as in the case of sums of statistically independent events. Implications for the applicability of a mean field description to fragmentation and agglomeration processes, and possible relation with intermittency phenomena in three dimensional turbulence are discussed.

chao-dyn↗

arXiv1994

A closure model for intermittency in three dimensional incompressible turbulence

A simplified Lagrangean closure for the Navier-Stokes equation is used to study the production of intermittency in the inertial range of three dimensional turbulence. This is done using localized wavepackets following the fluid rather than a standard Fourier basis. In this formulation, the equation for the energy transfer acquires a noise term coming from the fluctuations in the energy content of the different wavepackets. Assuming smallness of the intermittency correction to scaling allows the adoption of a quasi-gaussian approximation for the velocity field, provided a cutoff on small scales is imposed and a finite region of space is considered. In this approximations, the amplitude of the local energy transfer fluctuations, can be calculated self consistently in the model. Definite predictions are obtained on the scaling of the wavepacket energy moments.

chao-dyn↗