Vortex Identification Based On PIV In The Flow Field Of Grid Flocculating Tank

In this paper,Particle image velocimetry(PIV)was applied to measure the flow filed of grid flocculation tank,based on the measurement results of PIV,an appropriate vortex identification method is selected to identify the flow field of the grid flocculation under different conditions.In order to reserach the flow field of the grid flocculation tank further,the location?number?scale?velocity and intensity of vortex generated in the flow field were studied and analyzed under different conditions with Tecplot and Origin software.Through PIV measurement of flow field and vortex identification of grid flocculation tank,the following main conclusions can be drawn:1.After the water flow passes through the grid plate,the flow field pattern of jet and vortex alternates behind the grid plate.The jet formed behind the mesh and the vortex appeared on both sides of the mesh.Under fixed grid plate conditions,when the flow rate increases,the number of vortex increases and the jet range decreases.At the same flow rate,when the mesh size increases,the number of vortex decreases and the jet range increases.2.Under fixed grid plate conditions,when the flow rate increases,the vortex radius tends to decrease to some extent;Under the same flow rate conditions,the vortex radius increases with the increase of mesh size;The influence of mesh size on vortex radius is greater than that of flow rate.3.Under fixed grid plate conditions,when the flow rate increases,the vortex intensity increases gradually,and the numerical values of vortex intensity at different flow rates differ greatly;Under the same flow rate conditions,when the mesh size changes,The vortex intensity is basically at the same level.The influence of flow rate on vortex intensity is greater than that of mesh size.4.The longitudinal velocity of the vortex has a tendency to decrease in the longitudinal direction,and has the characteristic of waveform in landscape orientation;The vortex has no fixed motion direction in landscape orientation,and its transverse velocity distribution is chaotic.The longitudinal velocity of the vortex is obviously greater than the transverse velocity under the same flow rate,indicating that the movement of the vortex in the flow field is mainly in the longitudinal direction of the main flow.Both longitudinal and transverse velocities are closely related to the flow rate.Under the condition of the same grid plate,the larger the flow rate is,the greater the vortex velocity is.5.Under fixed grid plate conditions,when the flow rate increases,the vorticity increases gradually,and the numerical values of vorticity at different flow rates differ greatly;Under the same flow rate conditions,when the mesh size changes,The vorticity is basically at the same level.The influence of flow rate on vorticity is greater than that of mesh size.