Experimental Research On Dynamic Model Of Single Bubble Rising Near The Vertical Wall

In-depth analysis of bubble motion and kinetic mechanism near vertical wall surface is of great theoretical significance and engineering application value for understanding the heat and mass transfer mechanism between gas and liquid.Using high speed photography technology in combination with shading and particle image technology,the static and glycerine aqueous solution of vertical wall rising near the single bubble motion experiment research,compare the bubble size and bubble initial dimensionless distance between nozzle and the wall(S*)to the movement characteristics of bubble rising influence,analysis of interaction between bubble and vertical wall,and wall before and after the collision dynamics mechanism of bubble and explore the vertical wall near oscillation around the bubble liquid wake vortex structure.Using the image processing technology,the characteristic parameters of single bubble movement near the vertical wall were analyzed,and it was found that:the bubble was stabilized by the wall effect near the vertical wall,and the bubble trajectory was transformed into the two-dimensional zigzag movement perpendicular to the wall under the unconstrained conditions.When the bubble approached the vertical wall surface,it was found that there was a layer of lubrication film on the wall surface,which led to the decrease of bubble velocity.The drop of vertical velocity before the bubble collides with the wall surface can be predicted by the correlation between the distance between the bubble center and the wall surface and the modified stokes number formula.A prediction model for the average drag coefficient of bubbles near the vertical wall surface(S~*<2 or S~*≤0.55)in distilled water(Re≈580～1100)and glycerol solution(Re≈170～660)with repeated bouncing on the wall surface was proposed,and the calculated results were in good agreement with the experimental values.The instantaneous interaction between the rising bubbles and the wall near the vertical wall surface was calculated,and it was found that the interaction between the bubbles and the wall surface inhibited the degree of deformation,and had little influence on the instantaneous drag of the bubbles,while the instantaneous lift force first increased and then decreased with the increase of the distance between the bubbles and the wall surface,and presented an elliptical periodic change.Its significance lies in the quantitative discussion of the interaction between the bubble and the vertical wall surface,and the definition of the movement and dynamic mechanism between the bubble and the wall surface.The stereo-PIV system was used to measure the liquid-flow field distribution around the bubble and obtain the time series distribution of the vortex structure around the bubble.When the bubble approaches the wall surface,the fluid movement around the bubble will be restrained by the wall surface near the wall surface.Two counter-rotating eddies will be formed at the upper and lower parts of the bubble surface.As the bubble leaves the wall surface,the two counter-rotating eddies will gradually fall off at the tail of the bubble.The wake of the bubble will alternately generate and fall off in vortices,resulting in the periodic change of the bubble movement path.