| In the vicinity of a bridge,wharf and other hydraulic structures,vehicles,ships gathered,the traffic situation is complex.It is easy to cause traffic accidents,and lead to environmental pollution,where become a key area of environmental protection.At the same time,the phenomenon of flow around a bridge pier,high pile and other hydraulic structures leads to a large number of vortices in space distribution.The complex flow brings huge challenge to the transport path and the pollution prediction.Study on the effect of cylindrical building for contaminant transport has important theoretical and practical significance for the control of environmental pollution.The main work and conclusions are as follows:(1)Six different turbulence models have been selected to simulate flow around a single cylinder.The computed hydrodynamic force(lift coefficient,drag coefficient and St)and flow field structure were compared with the experiment data of physical model with the same Reynolds number.The results computed by k-? turbulence model and Reynolds Stress turbulence model have a good agreement with the experiment data in pressure distribution;k-? turbulence model has obvious advantages in whole flow field simulation.It provides references for turbulence model choice in numerical simulation of flow around a circular cylinder.(2)Based on the distribution characteristics of the concentration field around a single cylinder under different conditions of flow and pollution sources,the double point-source model is proposed to reveal the mechanism of pollutant diffusion around a single cylinder.The results showed that the distribution of pollutant varies along the flow direction.At first,the lateral distribution form is bimodal structure,then become single broad peak structure,and quasi-normal distribution structure,finally.The paper also analyzed influences of horizontal trailing vortex swing and longitudinal velocity shear strain on concentration distribution.Based on the formation mechanism of pollutant distribution,we established the double point-source model to calculate the concentration of wake area,and unified three kinds of distribution structures theoretically,which provides a new way for research of cylinder wake concentration field.(3)Different arrangement modes of double cylinders show different concentration distribution characteristics of pollutants,which revealed the mechanism of the interaction between the cylinders.Under the condition of double cylinders in parallel with G/D?2,the weak influence can be ignored on pollutant diffusion which generated by double cylinder wake vortex.Under the condition of double cylinders in tandem arrangements with G/D?0.25,two cylinders effect on concentration field can be regarded as a whole.With 0.25<G/D<2,pollutants have the maximum lateral diffusion.(4)Different arrangement modes of three cylinders show different concentration distribution characteristics of pollutants,which revealed the mechanism of the interaction between the cylinders.Under the condition of three cylinders in parallel with G/D=2,the range of pollutant diffusion get the minimum values.Under the condition of three cylinders in tandem arrangements,pollutant transportation and diffusion process is similar to double cylinders in serial.The range of lateral diffusion of pollutants has been increased and then decreased. |
PDF Full Text Request