| Particle-laden flow exists widely in nature and various industrial processes including energy and power fields.Studying the modulation of particles on turbulence can better understand related natural phenomena and optimize industrial equipment.Due to the complexity of the interaction between turbulent and particles,the simultaneous the experimental measurement data of turbulence is not rich enough,so the current understanding of the turbulent modulation of particles is not sufficient.In this paper,particle image velocimetry(PIV)is used in the horizontal oscillating double-grid turbulence system,combined with relevant turbulence theory and statistical analysis methods,by calculating the root mean square velocity,turbulent kinetic energy,dissipation rate,vorticity,turbulence intensity,Statistical characteristic parameters of turbulence,such as isotropy ratio,length and time scale,energy spectrum,etc.,as well as the distribution law in space,conduct experiments on the change law of turbulence characteristics of horizontal oscillating double grid system and the modulation of dissipative scale particles on isotropic turbulence.The main conclusions of the study are as follows:(1)Under the conditions of grid stroke of 1.6-5 cm,oscillation frequency of 0.5-2.5 Hz,and grid spacing of 9-21 cm,the horizontal oscillating grid system can produce a homogeneous and isotropic turbulence of 4 cm × 4 cm in the central area.In the turbulent region,the horizontal root mean square velocity,turbulent intensity,turbulent kinetic energy,energy dissipation rate,characteristic Reynolds number,etc.of the turbulence generated by the system are larger in the large stroke,high frequency and short spacing,and the corresponding turbulent length and time scale are larger.The system can generate turbulence with a dissipation scale between 188 and 1358 μm.(2)When the particle volume fraction is 0～0.1%,the enhance of particles with diameters of 150,270,and 500 μm on characteristic parameters such as root mean square velocity,turbulent intensity,turbulent kinetic energy,and turbulent scale varies with the particle volume fraction.increases and increases.The enhance of largediameter particles on turbulence is more and more significant.When the grid Reynolds number is in the range of 805 to 3220,the particles have an enhanced effect on turbulence.The presence of particles causes significant fluctuations in the velocity around the particles,resulting in additional turbulent small eddies,thus forming a modulation on turbulence.(3)In the turbulence with dissipation scale ranging from 227 to 719 μm,largediameter particles will increase the root mean square velocity,turbulent intensity and energy dissipation rate of turbulence,and reduce eddy turnover time,while smalldiameter particles tend to reduce turbulence.With the increase of the ratio of particle diameter to dissipation scale,the enhancement effect of particles on turbulence intensity and turbulent kinetic energy is greater.The maximum enhancement effect on turbulence intensity and kinetic energy is 135.6% and 439%,respectively,and the maximum weakening effect is 74% and 87.1%.For 270 and 500 μm particles,after the ratio of particle diameter to dissipation scale is greater than 1,the particle has a larger enhancement effect.In this paper,PIV is used to verify the good isotropy of the turbulent flow in the horizontal oscillating double grid system and the variation law of characteristic parameters,and the modulation of dissipative scale particles on turbulent characteristic parameters under different volume fractions,grid Reynolds numbers and turbulent dissipation scales is obtained.As well as the fine flow field distribution around the particles,it provides a certain experimental data reference for the development and verification of the Particle-laden flow interphase interaction model. |
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