Study On The Turbulence Field Around A Transverse Square Column

The phenomenon of flow around the near wall square column is not only widely used in daily life,but also in civil engineering,chemical industry,machinery and other fields.It is of great theoretical significance and academic value to study the flow around a square column not only because of its wide application,but also because of the complicated characteristics of flow separation,adhesion,vortex shedding and other phenomena under the influence of wall.In this paper,the flow characteristics behind the square column and the flow structure in the boundary layer are studied in detail by wind tunnel test and numerical simulation.The main contents are as follows:First using PIV technology to different clearance ratio(G/D=0,0.3,0.5,0.8,1.0,G for square column and wall spacing,D for square column section size,D=10mm)square column under the wake area measurement,including friction Reynolds number(Re_D=U₀ D/?,? for kinematic viscosity coefficient)for 1900,boundary layer thickness(?)and square column section size ratio(?/D)to 18.By analyzing the time-average velocity field,pulsation field and vorticity field,the influence of the lower wall surface with different clearance on the flow morphology,motion variation and evolution process behind the square column is explained.It is found that the size of the backflow area tends to be stable with the increase of the clearance,and the influence of the square column on the wall flow decreases gradually.At different clearance ratios,vortex structures generated by the wall exist near the wall.The influence of the square column on the flow structure in the turbulent boundary layer was revealed by spatial correlation and POD modal decomposition.It was found that the energy transport carriers in the flow field were different under different clearance ratios,and the lower the order,the higher the energy ratio.Secondly,using the hotline technology for two different section size(D=5mm,D=10mm)square column x=2D position after different high speed measurement,found 5 mm(?/D=36)square column of vortex shedding frequency is greater than 10 mm(?/D=18)square column,contrast has greater boundary layer thickness and square column section size ratio(?/D)square column under the vortex shedding frequency experimental observation results,found that the vortex shedding frequency is influenced by the?/D.By using the software of Fluent software simulation by changing the size of square column(D=5mm,10mm,15mm,20mm)under the condition of different Reynolds number(Re_D=U₀ D/?=950,1900,2850,3800)under different gap(G/D=0.3,1.0)near wall square tail flow characteristics.It is found that the vortex shedding frequency in the simulation results is significantly higher than the experimental results,so the vortex shedding frequency may be affected by the friction Reynolds number,the ratio of the boundary layer thickness to the section size of the square column and the turbulence intensity,and the lift and drag coefficient is also affected by the Reynolds number.