PIV Measurement Of Particle-laden Turbulent Flow Over Rough Surfaces

It is well known that particle-laden turbulent flow exists widely in nature,human medicine,industrial production and other fields,such as dust storms,the flow of inhalable particles in the human respiratory tract,coal powder pneumatic conveyance,fluidized bed and pulverized coal combustion.However,the surface of the particle-laden flow is not completely smooth due to various defects in the actual industrial production.Therefore,it is of significance for scientific development and practical engineering application to investigate the particle-laden turbulent flow over rough wall.Particle image velocimetry is used to study the characteristics of turbulent gas flow over rough wall.The effect of wall roughness on the gas turbulence characteristic and space structure is analyzed.The rough surface is composed of three-dimensional roughness.It is found that the existence of roughness decreases the mean velocity of gas flow and increases the Reynolds stress,and the effects will be more obvious as the roughness growing,comparing with the gas turbulence over smooth surface.However,the phenomenon of wall similarity is found when these turbulence statistics are characterized by the wall friction velocity.In addition,the wall roughness also reduced the probability density of ejections and sweeps events of gas turbulence,but has little effect on the quadrant events in the outer layer.The analysis of the spatial structure of turbulence shows that the spatial structure in small scale is less affected by wall roughness than that of the large-scale spatial structure,which basically satisfies the similarity hypothesis.On the basis of the single-phase turbulence,a series of experiments were also performed to investigate the influence of particle and wall roughness on the gas turbulence.The results show that the dragging effect of the particles increases the average velocity of gas turbulence.Besides,the Reynolds stress and the probability density of quadrant events will be increased since the existence of particles,and the effects will be more obvious as the particle size growing.The influence of roughness on particle-laden turbulence flow is compared with that of single-phase turbulence flow,it is found that the effect of roughness on the gas turbulence is similar,especially for the average velocity and Reynolds stress.While the difference is that the wall roughness will increase the probability density of quadrant events near the wall when the particles exist.Obviously,the effect of wall roughness on turbulence characteristics will be affected by the presence of particles.Through the statistical analysis of the particle distribution,it is found that the introduction of rough elements will reduce the deposition of particles.Comparing the distribution of two kind of particles can also found that the deposition of larger particles is more significant than the small particles.