PIV Experimental Study On The Effect Of Grid Plate Position On Vortex Field Of Grid Flocculation Tank

In this paper,the particle image velocimetry?PIV?is used to measure the flow field of the grid flocculation tank,and the flow field information behind the grid plate is obtained under different shaft height,different?random,characteristic?sections,and different flow rates.Based on the flow field information measured by PIV,the flow field characteristics and different points of the grid flocculation tank under the factors of height,flow and cross-section difference are analyzed by using Tecplot and Origin software.Then,the change rules of turbulent energy and turbulent energy dissipation rate in the flow field are calculated and analyzed with the large eddy PIV method,and the vortex intensity method(?_ci)is used to analyze the vortex in the flow field The rotation was identified.The effects of different geometric conditions on the velocity,turbulent kinetic energy,dissipation of turbulent kinetic energy and vortex shape in the flow field were explored,so as to further explore the formation mechanism of grid vortex and provide a reference for the reasonable and effective study of grid vortex flocculation dynamics.Through the specific experimental measurement and calculation analysis,the following conclusions are obtained:?1?In the random flow field behind the grid plate of different heights in the shaft,the chaos of the flow field gradually becomes stable along the flow direction,especially in the flow field behind the third grid plate;in the flow field behind the grid plate's mesh center,mesh edge and mesh center's characteristic section,strong jet signs can be formed in the flow field in the mesh center,and the flow field It is stable,but the jet sign is weakened in the flow field at the edge of the mesh,and there is no jet sign in the flow field at the center of the grid,and the flow field becomes very chaotic;?2?In the random flow field behind the grid plate at different heights of the shaft,the velocity fluctuation of the flow field behind the first grid plate and the second grid plate is relatively large,and the velocity of the flow field gradually tends to be stable along the flow direction.Within 20 mm behind the grid plate,the main fluctuation is the longitudinal velocity,while within 20?30 mm behind the grid plate,the main fluctuation is the transverse velocity;in the transverse direction of the grid plate,the main fluctuation is the transverse velocity In the three characteristic cross-section flow fields,the longitudinal velocity mainly fluctuates at the center and the edge of the mesh,but the transverse velocity mainly fluctuates at the center of the mesh;?3?In the random flow field behind the grid plate at different heights of the shaft,from the first grid plate to the fourth grid plate,the turbulent kinetic energy and turbulent energy dissipation rate in the flow field gradually decrease with the flow direction,and the fluctuation amplitude is large within 30mm behind each grid plate;in the flow field behind the grid plate at three cross-sections of the grid plate,the position at the center and the edge of the mesh hole The turbulent kinetic energy and energy dissipation rate generated by the device are larger than those generated by the center of the grid;?4?In the grid flocculation tank shaft,the distribution of vortices in the random flow field behind the grid plate gradually becomes uniform along the flow direction,and the distribution of vortices in the flow field becomes scattered due to the change of flow rate.The trend between the number of vortices in the flow field behind each grid plate and the flow rate is almost the same,which is gradually increasing with the increase of flow rate,but The average radius of the vortex is gradually decreasing.In the flow field behind the grid plate at the three transverse characteristic sections of the grid plate,the distribution of the vortex is mainly concentrated in the two sides of the jet and the flow field at the end of the jet,and the vortex produced in the flow field at the center and the edge of the mesh is the most,and the average radius of the vortex is also the largest,so in the flow field of the grid flocculation pool,the main If the vortex is generated by the mesh center and the mesh edge of the grid plate,the flow field will fluctuate disorderly.