Resaerch On Vortex Identification Method Based On Flow Field Measurement Of PIV

In this paper,PIV particle image velocity is used to measure the eddy current field of the grid flocculation tank.By comparing third-generation vortex identification methods,themethod with the best identification effect is selected.Then use Tecplot,Origin,Image-Pro Plus and other post-processing software to conduct statistical analysis on the flow fieldvelocity,vortex distribution,intensity,quantity,scale and other information under different working conditions to explore the flow field vortex characteristics of the grid flocculation tank.The following conclusions are summarized through experimental measurement and calculation analysis:1.When the water flows through the grid plate,a jet will be formed behind the mesh,and the water flow state after the block is relatively stable.The width of the jet behind the grid plate mainly depends on the size of the mesh.The jet is in a stable state in the early stage and fluctuates until the jet disappears in the later stage.There is no obvious difference in the flow field shape under different flow rates after the same grid plate;under the same flow rate,the width and the range of the yet will increase with the increase of the mesh size,and the earlier and larger the fluctuation range of the yet will be.2.The absolute intensity of the vortex gradually decreases along the longitudinal direction,and has a periodic trend along the transverse direction;under the same mesh size,as the flow rate increases,the absolute strength of the vortex increases;under the same flow rate,the mesh size hardly affects the absolute intensity range of the vortex;flow rate and mesh size can reflect that the absolute intensity of the vortex at different distance behind the grid plate increases first and then decreases.3.The relative intensity of the vortex can better characterize the number and distribution of the vortex.In the area where the jet exists behind the grid plate,the vortices are mainly distributed on both sides of the jet behind the block and the forward vortex and the reverse vortex appear in pairs.There is mainly a forward vortex on the left side of the jet,and a reverse vortex on the right side.The number and distribution of vortices under the same mesh size and different flow rates are very similar;at the same flow rate,as the mesh size becomes larger,the number of vortices will decrease.4.The vortex core are mainly distributed on both sides of the jet after the grid plate,from the beginning of the jet to the end area where the jet ends,and exist in pairs on both sides of the jet.The distribution of vortex cores under the same mesh size and different flow rates is very similar and the vortex core sizes are also very similar.The area of??the vortex core is mainly about 2mm~2and about 4mm~2,which has a very clear boundary and grows stepwise.The area of??the vortex nucleus produced under a small flow is larger;at a fixed flow,the mesh size of the grid plate is increased,and the distribution range of the vortex nucleus is larger and the number is larger.5.The vortex area is periodically distributed along the X direction,which is mainly because the vortex mainly exists on both sides of the jet behind the grid plate;The vortex area increases first and then decreases along the Y direction,which is mainly due to the vortex behind the grid piate has a process of growing and then dissipating.Under a small flow rate,the main factor affecting the size of the vortex area is the mesh size of the grid plate.The larger the mesh size,the larger the vortex scale produced;Under a large flow rate,the size of the vortex area will be affected by the mesh size of the grid plate.The larger the mesh size will promote the formation of large-scale vortex,and the larger the flow will weaken the formation of large-scale vortex;the larger the flow rate,the earlier the flow behind the grid will become turbulent,and the large-scale vortex appeared early.