Study on the Subgrid Scale Modeling for Particle-Laden Turbulent Flows

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We carried out a direct numerical simulation (DNS) of fluid-solid two-phase turbulent flows to consider the subgrid scale (SGS) modeling in the large-eddy simulation (LES) of particle-laden turbulence.First, we developed a finite-difference scheme to resolve the interaction between fluid turbulence and particle motion.In our method, the flow around a solid particle having a length scale several times larger than the spacing of computational grid, is directly simulated.The particle motion is governed by the surface integral of pressure and viscous stress together with the body force such as gravity.This scheme includes no models in fluid turbulence, particle motion or interaction between them.Then, we examined our new method by applying it to the three-dimensional flow past a sphere fixed in a uniform stream.As for the drag coefficient as well as the unsteady vortex shedding, numerical results agreed with experimental results.When the vortex shedding took place, turbulence energy induce … More d through wake was not fully dissipated in the region near a particle.This non-equilibrium nature was enhanced just after the change in drag force of a particle.Next, we simulated a forced isotropic turbulence and turbulent flow in a plane channel including sphere particles.Particles formed larger structure such as clusters, resulting in an additional scale of energy source for fluid turbulence.In an another setup, the relative position of particles was fixed to observe the turbulence modulation without particle clusters.In this case, total energy was sometimes reduced due to the shift of energy spectra into high wavenumber range, even though particles induced extra.In the wall turbulence, particles were distributed non-uniformly in the channel.In this case, the shed vortices was stretched into the streamwise direction due to the velocity gradient, resulted in the production of Reynolds shear stress.These DNS results of particle-laden turbulent flows suggested some important characteristics to be accounted for in SGS modeling.They are non-equilibrium nature due to unsteady vortex shedding, multiple scale of energy injection to fluid turbulence, the modulation in turbulence length scale by particle distribution, and the Reynolds stress production due to the stretch of shed vortices, for example. Less