Numerical Simulation Of Convective Diffusion Of Pollutants On The Wall Surface Of Ocean Pillar Structure

As offshore wind power technology gradually matures,offshore wind power projects have become an important part of the development of green energy.The construction and maintenance of offshore wind farms will inevitably produce environmental pollution problems.In the marine environment,offshore wind farms have to face the load of the waves.Usually,marine anti-corrosion paint is sprayed on the surface of the column.The protective coating of the cylinder will fall off from the cylinder surface into the sea under certain conditions,causing pollution to the marine environment.Therefore,;it is of great significance to study the convective diffusion effect of pollutants on the wall surface of the marine pillar structure for the offshore wind power project pollution assessment and improvement of pollutant prevention and control systems.In order to study the diffusion effect of pollutants on the wall surface of the marine cylinder structure in the tail flow area,this paper uses fluid simulation methods to first simulate the dynamics of the flow around the single cyliner and the flow around the multi-cylinder,analyze the flow law.On this basis,the concentration field generated by pollutants on the cylindrical wall under different conditions was simulated,and the convection and diffusion law of pollutants in the tail flow area was analyzed.Finally,the stress of the cylinder under the wave conditions and the diffusion of pollutants on the wall are simulated.The results shows:(1)For the problem of flow around cylinder,When the Reynolds number is between 3 ×105-1 × 106,the vortex shedding is random and the law is not obvious.For the flow around tandem double cylinders,there is a critical spacing ratio value between 3-3.5,so that the drag coefficient of the downstream cylinder suddenly changes.For parallel double cylinders,when the spacing is relatively small,the wake interaction between the two cylinders is strong,and the frequency of vortex shedding is greater than that of a single cylinder.When the distance is relatively large,the interaction can be basically ignored.(2)For the problem of convection and diffusion of pollutants on a single cylindrical wall,in the wake area,the diffusion of pollutants is basically consistent with the change of the vortex field.Due to the influence of the vortex,the pollutants are not easy to convect in the flow field.In the low Reynolds number range,as the Reynolds number increases,the cumulative effect of pollutants will show a downward trend.In actual working conditions,the problem of pollutant diffusion on the cylindrical wall surface with low Reynolds number can be properly increased by artificial methods to increase the Reynolds number and reduce the concentration of pollutants.For the problem of convection and diffusion of pollutants on tandem double-cylindrical walls,When the distance is relatively small,the lateral diffusion degree of pollutants at the front end of the wake area is small,and the concentration peak is high.At the rear end,the lateral diffusion degree gradually increases and the concentration peak gradually decreases.When the spacing is relatively large,the overall lateral diffusion range is expanded.For the problem of convection and diffusion of pollutants on the walls of parallel double cylinders,when the distance is relatively small,the two cylinders can be regarded as an ellipse with double width,and the wake falls off in a double-peak structure;when the distance between the two cylinders is relatively large,the interaction between the vortex streets is getting weaker and weaker,and two separate vortex streets are formed,so the pollutants have a broad peak structure in their wake areas.As the spacing ratio increases,the interaction between the wakes of the two cylinders continues to weaken,and the pollutants diffuse along their respective vortex streets,reducing their aggregation.This shows that in the parallel double cylinder problem,the farther the separation distance between the two cylinders,the greater the degree of diffusion of pollutants,and the less likely it is to form a cumulative effect.(3)Under the effect of the focused wave,the concentration of pollutants in the tail flow area of the cylinder gradually decreases along the direction of water flow,and the lateral diffusion range decreases first and then increases.When there is a wave factor in the flow field,the double-peak structure of pollutant diffusion is not obvious.The reason may be that the action of the wave will slow down the wake-off effect of the wake vortex,thereby forming a single-peak structure.Due to the characteristic that the focus wave will suddenly increase at the focus time and focus position,the wave height will peak here,and the pollutant on the cylinder wall will also reach the maximum value at the focus position.