Jérôme Laviéville

On the spatial distribution of heavy-particle velocities in turbulent flow: from continuous field to particulate chaos

The effect and modelling of the spatial correlation between particle velocities is investigated in two-phase turbulent flows. A statistical model based on the joint fluid-particle probability distribution function kinetic equation is introduced, which accounts for the modification of the collision probability due to the correlation of the velocities of colliding particles. To study the long-range spatial correlation of the particle velocities, a conditional average, for a given fluid turbulent flow, is introduced. This approach allows us to separate the instantaneous velocity of any particle into two parts: a turbulent contribution, from an underlying continuous velocity field shared by all the particles, and a random contribution obeying the ‘molecular chaos’ assumption. This article was chosen from selected Proceedings of the Second International Symposium on Turbulence and Shear Flow Phenomena (KTH-Stockholm, 27-29 June 2001) ed E Lindborg, A Johansson, J Eaton, J Humphrey, N Kasagi, M Leschziner and M...

A penalization method for the simulation of bubbly flows

Abstract This work is devoted to the development of a penalization method for the simulation of bubbly flows. Spherical bubbles are considered as moving penalized obstacles interacting with the fluid and a numerical method for ensuring the shear free condition at the liquid–bubble interface is proposed. Three test-cases (curved channel, inclined channel and 3D translating bubble) are used to validate the accuracy of the discretization ensuring the slip condition at the interface. Numerical simulations of a rising bubble in a quiescent liquid are performed for moderate Reynolds numbers. Considering bubble terminal velocities, initial accelerations and wake decay, the effect of the penalization viscosity used to ensure a uniform velocity in the penalized object is discussed. Finally, simulations of bubble swarms have been carried out in a fully periodic box with a large range of void fractions from 1% to 15%. The statistics provided by the simulations characterizing the bubble-induced agitation are found in remarkable agreement with the experiments.