The Sub-grid Scale Effect On Particle Collisions In Homogeneous Isotropic Turbulence

The internal mechanism of the interaction between fluid and solid particles is a verycomplex issue and needs to be studied in depth. In the context of the framework oflarge-eddy simulation, the study of the effect of the subgrid fluid on particle motion andcollision under the influence of turbulence is present multiphase flow hot issues in thisfield.Under the background of homogeneous isotropic turbulence flow field In this paper, weconduct corresponding research works on the impact of subgrid fluid on the particlecollision in this paper. Firstly, based on the direct numerical simulation of flow field with2563grids, the dependence of the radial distribution function g(R) and the radial relativevelocity between particles on the particle s inertia was accessed under the condition ofsteady-state collision statistics. Next, filtered-DNS field was obtained through a filteroperation on the DNS field and then an analytic compare of collisional variables can becarried out between this two conditions. It s known that g(R) varies in the opposite waywith different Stk number after filtering, for particles with low inertial g(R) decrease withthe filtering, while for particles Stk number above2.0, g(R) will be slightly larger than thecorresponding DNS value. For the terms of radial relative velocity <|w(r)|>, filteringoperation could cause its decrease within the whole range of inertial zone, especially forparticles with small Stk number. Meanwhile the PDF distribution and high moment ofrelative velocity along with Stk number were studied which verified the close connectionbetween g(R) and <|w(r)|>, also it has been proved that the negative radial relative velocityis the main cause of particles clustering.Finally, with the basis of two-point PDF theory, we verified its capacity of prediction inthe range of limited inertial particles and also extended our research focus to particle-pairdrift-diffusion issues by access to the characteristic structure variables in the flow field andthe exponential rate of collision statistics which variation with particle Stk number. Also wehave briefly introduced the implementation of one-point sub-grid Lagevin model withattention of its influence on the collision results, it s referred that one-point PDF model cannot predict reasonable collision rate under large-eddy simulation.