Numerical Simulation Of Suspended Motion And Spatial Distribution Of Particles In Wall Turbulence

Suspended motion of particles in wall turbulence widely exists in nature and engineering applications,such as suspended dust in sandstorms,wind dust removal from solar panels or other devices.Numerical simulation is an important tool to study two-phase particle-laden flows,which can effectively reveal the transport mechanism of particles under the effect of turbulence.In this paper,direct numerical simulation(DNS)of wall turbulence and one-way coupled Lagrangian point-particle method are leveraged to investigate the suspended motion of particles jumping from a wall in an open channel turbulent flow.The main objective is to study the spatial distribution characteristics of particles and the effects of inertia and Saffman lift on their motion and spatial distribution,and investigate the role of turbulent structures on the vertical transport of particles.Spatio-temporal transport process of three kinds of particles with particle Stokes numbers of 5,25 and100 were calculated in a turbulent flow with a friction Reynolds number of 400.In the computations,two different cases are considered,i.e.,one in which particles are subjected to fluid drag force only,and the other particles are subjected to both fluid drag force and shear-induced Saffman lift force.Initially,particles are uniformly distributed on the surface,and a stochastic dynamic model is applied to simulate the process of particle resuspension from the wall.The results of this study show that: the Saffman force has a weakening effect on the preferenntial distribution of particles in both vertical and horizontal planes,and the larger the particle inertia,the stronger the weakening effect;the Saffman force increases the average streamwise velocity and streamwise fluctuation velocity of particles with large inertia in the near-wall region,which affects the force acting on the particle,and the effect of the Saffman force on particle vertical velocity is small;the Saffman force weakens the average transport flux of particles in the streamwise direction and enhances the average transport flux in the vertical direction;the Saffman force weakens the fluctuating transport flux of particles in the near-wall region.On the other hand,the effect of particle inertia on the probability distribution of particles in the vertical direction is non-monotonic without considering the Saffman force,and particles with moderate inertia have the highest probability residing in the near-wall region;particle inertia has a weak weakening effect on the mean velocity of particles in the streamwise direction and vertical direction,while there is a more significant weakening effect on the fluctuating velocity and a significant enhancement effect on the fluctuation of flow and particle slip velocity;particle inertia has certain enhancement effect on the mean transport flux in both the streamwise direction and vertical direction;the effect of particle inertia on the fluctuations of transport flux is non-monotonic,and the fluctuations of transport flux are strongest for particles with moderate inertia.In addition,it is found that particles generally tend to live in the low velocity streaks of flow streamwise velocity,where particles moving upward(away from the wall)tend to reside in Q2 events(positive streamwsie fluctuating velocity and negative vertical fluctuating velocity),and conversely particles moving downward tend to locate in Q4 events(negative streamwise fluctuating velocity and positive vertical fluctuating velocity).Furthermore,particles also prefer to be found in stable focus/stretching flow region with high strain rate and low vorticity,and both Saffman force and particle inertia weaken these tendencies;particle inertia significantly weakens the correlation between fluctuating velocities of particles and fluid,while Saffman force only weakens the correlation of the streamwise and vertical components near the wall.In this paper,we have applied a stochastic dynamic model for particle resuspension and investigate the effect of the Saffman lift on the distribution and transport of suspended particles,which enriches the research and fills the gap on the suspension motion of particles.The differences between the suspension and deposition of particles are compared,and the understanding on the effect of the Saffman lift on the suspension motion of particles is deepened.