Study Of Dynamic And Thermal Characteristics In Particle-laden Turbulent Channel Flow

The study of particle-laden flows is very important,and particle-laden flows consist of a fluid carrier phase and a solid or liquid dispersed phase.The momentum and thermal interactions between the particles and turbulence are the key problems which are attended by many researchers.Direct numerical simulation of a turbulent channel flow combined with the Lagrangian point-particle tracking under the condition of two-way coupling is applied to study the interactions between the particles and turbulence in this paper.1.The characteristics of heat transfer in particle-laden turbulent flow are studied.It is found that,with the increase of Prandtl number,the modulation of velocity field induced by the particles has a smaller influence on turbulent temperature field,and thermal feedback of the particles to turbulence becomes weak.That results the particles have a smaller effect on the turbulent thermal field for larger Prandtl number.With the increase of the particle specific heat,the efficiency of heat transfer in particle-laden flow increases gradually.In comparison with the particle-free flow,the large specific heat particles strengthen the efficiency of heat transfer while the small specific heat particles weaken it.With the increase of particle momentum Stokes number,the thermal feedback of the particle to turbulence increases and the contribution of the particles to heat transfer strengthens,that results in the increase of heat transfer efficiency.2.Characteristics of turbulence transport for momentum and heat in particle-laden turbulent flows are investigated.The flow drag and the capacity of heat transfer decrease with the increase of the particle momentum Stokes number which can be contributed to the decrease of the turbulent contributions to flow drag and heat transfer.Furthermore,under the condition of the same particle thermal Stokes number,the feedback contributions to flow drag from particles increase as the particle momentum Stokes number increasing while the feedback effect of the particles on heat transfer is opposite.In addition,the possibility of increasing heat transfer and suppressing flow drag simultaneously by the addition of particles with different specific heat is investigated.It confirms that under the constant particle momentum Stokes number condition,drag reduction,and heat transfer enhancement can be achieved at the same time when the particles have large specific heat capacity.3.The modulations of multi-component droplets on flow drag and heat transfer in the turbulent boundary layer are studied.It can be found that the total drag coefficient increases with the increase of the droplet mass loading,which can be contributed to the increase of turbulent drag coefficient and the droplet force feedback drag coefficient.The high inertial droplets have a dominant contribution to momentum exchange between the multi-component droplets and turbulence though the fraction of high inertial droplets in the multi-component droplets system is very small.The evaporation of the droplets has little influence on the flow drag of turbulence though for high droplet mass loading.However,the gravity of the droplets increases the total drag coefficient.In addition,with the increase of the droplet mass loading,the total Nusselt number first decreases and then increases.The total droplet thermal feedback to turbulence mainly derives from the high inertial droplets.Both the droplet evaporation and droplet gravity result in the increase of heat transfer capacity with the increase of the droplet mass loading.