Study On Turbulent Reaeration Induced By Water Velocity Excitation In Urban River

Dissolved oxygen concentration is an important indicator for evaluating water quality.Dissolved oxygen concentration directly affects the survival and reproduction of aquatic plants and animals,and also plays an important role in the protection and management of aquatic ecology.Low dissolved oxygen concentration is inseparable from the problem of eutrophication of water bodies.The sources of dissolved oxygen in water are atmospheric reaeration,and plants produce oxygen through photosynthesis.The atmosphere is the main source of dissolved oxygen in rivers,and it is of great significance to study the gas-water reaeration law to improve river water environment.Former researchers have done a lot of research on the reaeration coefficient to characterize the reaeration rate.However,the influence of water flow velocity changes on the river reaeration mechanism and mechanism caused by the spoil aeration device widely used in the ecological restoration of rivers and lakes is not clear.Therefore,it is particularly important to protect the aquatic ecosystem and prevent eutrophication of the water body,to understand the laws of atmospheric-water body reaeration,and to maintain the concentration of dissolved oxygen in the water body.In this paper,a deepcontrolled horizontal thrust aeration device will be designed and developed.Based on this device,the influence of river flow velocity excitation on the water-atmosphere deoxygenation process under artificial disturbance will be researched,the phenomenon of reaeration surge will be found,and the theoretical formula of turbulent reaeration process will be established.(1)Design and develop a deep-controlled horizontal push-flow aeration device.Collect related patents and device performance indicators of aeration aerators and compare them.In response to the shortcomings of the existing aerators,a deepcontrolled horizontal push-flow aeration device designed to improve the connectivity of urban secondary river channels was designed and developed.Compared with other aerators,this device can effectively change the local water flow velocity while improving the dissolved oxygen in the water body.(2)Based on this device,the influence of river flow velocity excitation on the wateratmosphere deoxygenation process was studied,and a phenomenon of reaeration surge was found.This device was used to carry out an in-situ test in the outer ring river of Tianjin to explore the effect of changes in flow velocity on the reaeration process under river turbulence.The reaeration coefficient was calculated using the reaeration equation,and the results were compared with the classic reaeration coefficient formula.It is found that the empirical formulas for river reaeration coefficients,such as the classic Owens formula,underestimate the reaeration coefficient under human disturbance,that is,the river reaeration surges under human disturbance,and the velocity stimulation has a significant effect on the reaeration process.(3)The effect of water turbulence on the reaeration coefficient.The relationship between turbulence and reaeration surge was analyzed using turbulent flow energy as a physical quantity representing water turbulence.The study found that the turbulent flow energy had a significant positive correlation with the river reaeration coefficient.Different from natural flow,the artificial disturbance increased the longitudinal and vertical turbulent flow energy of the water body,accelerated the diffusion of dissolved oxygen in the lower and middle water bodies,increased the reaeration rate,and then a reaeration surge occurred.(4)Deduction of theoretical formula for turbulent reaeration process.Using dimensional analysis and ? theorem,the hydraulic factors related to the reaeration coefficient are reduced and simplified,and a multiple linear regression model is used to estimate the parameters.The formula for reaeration coefficient correction with turbulent flow energy is obtained.The above results show that the turbulent flow energy has a significant effect on the reaeration coefficient,artificial disturbances have changed the reaeration law of natural rivers,and the water velocity excitation has accelerated the reaeration process.Exploring the rule of reaeration between the water body and the atmosphere is helpful to predict the change of dissolved oxygen concentration in the water body and the occurrence of eutrophication in river water bodies such as cyanobacteria outbreaks.At the same time,the research results provide a scientific basis for the reaeration mechanism of aeration equipment based on hydraulic principles,and help the promotion and application of new equipment for urban river ecological restoration.