6,834 research outputs found
Application of the exact regularized point particle method (ERPP) to particle laden turbulent shear flows in the two-way coupling regime
The Exact Regularized Point Particle method (ERPP), which is a new inter-phase momentum coupling ap- proach, is extensively used for the first time to explore the response of homogeneous shear turbulence in presence of different particle populations. Particle suspensions with different Stokes number and/or mass loading are considered. Particles with Kolmogorov Stokes number of order one suppress turbulent kinetic energy when the mass loading is increased. In contrast, heavier particles leave this observable almost un- changed with respect to the reference uncoupled case. Turbulence modulation is found to be anisotropic, leaving the streamwise velocity fluctuations less affected by unitary Stokes number particles whilst it is increased by heavier particles. The analysis of the energy spectra shows that the turbulence modulation occurs throughout the entire range of resolved scales leading to non-trivial augmentation/depletion of the energy content among the different velocity components at different length-scales. In this regard, the ERPP approach is able to provide convergent statistics up to the smallest dissipative scales of the flow, giving the opportunity to trust the ensuing results. Indeed, a substantial modification of the turbu- lent fluctuations at the smallest-scales, i.e. at the level of the velocity gradients, is observed due to the particle backreaction. Small scale anisotropies are enhanced and fluctuations show a greater level of in- termittency as measured by the probability distribution function of the longitudinal velocity increments and by the corresponding flatness
Three-Dimensional Multi-Relaxation Time (MRT) Lattice-Boltzmann Models for Multiphase Flow
In this paper, three-dimensional (3D) multi-relaxation time (MRT)
lattice-Boltzmann (LB) models for multiphase flow are presented. In contrast to
the Bhatnagar-Gross-Krook (BGK) model, a widely employed kinetic model, in MRT
models the rates of relaxation processes owing to collisions of particle
populations may be independently adjusted. As a result, the MRT models offer a
significant improvement in numerical stability of the LB method for simulating
fluids with lower viscosities. We show through the Chapman-Enskog multiscale
analysis that the continuum limit behavior of 3D MRT LB models corresponds to
that of the macroscopic dynamical equations for multiphase flow. We extend the
3D MRT LB models developed to represent multiphase flow with reduced
compressibility effects. The multiphase models are evaluated by verifying the
Laplace-Young relation for static drops and the frequency of oscillations of
drops. The results show satisfactory agreement with available data and
significant gains in numerical stability.Comment: Accepted for publication in the Journal of Computational Physic
On the Eulerian Large Eddy Simulation of disperse phase flows: an asymptotic preserving scheme for small Stokes number flows
In the present work, the Eulerian Large Eddy Simulation of dilute disperse
phase flows is investigated. By highlighting the main advantages and drawbacks
of the available approaches in the literature, a choice is made in terms of
modelling: a Fokker-Planck-like filtered kinetic equation proposed by Zaichik
et al. 2009 and a Kinetic-Based Moment Method (KBMM) based on a Gaussian
closure for the NDF proposed by Vie et al. 2014. The resulting Euler-like
system of equations is able to reproduce the dynamics of particles for small to
moderate Stokes number flows, given a LES model for the gaseous phase, and is
representative of the generic difficulties of such models. Indeed, it
encounters strong constraints in terms of numerics in the small Stokes number
limit, which can lead to a degeneracy of the accuracy of standard numerical
methods. These constraints are: 1/as the resulting sound speed is inversely
proportional to the Stokes number, it is highly CFL-constraining, and 2/the
system tends to an advection-diffusion limit equation on the number density
that has to be properly approximated by the designed scheme used for the whole
range of Stokes numbers. Then, the present work proposes a numerical scheme
that is able to handle both. Relying on the ideas introduced in a different
context by Chalons et al. 2013: a Lagrange-Projection, a relaxation formulation
and a HLLC scheme with source terms, we extend the approach to a singular flux
as well as properly handle the energy equation. The final scheme is proven to
be Asymptotic-Preserving on 1D cases comparing to either converged or
analytical solutions and can easily be extended to multidimensional
configurations, thus setting the path for realistic applications
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