Analysis of pollutant diffusion characteristics with intersection angle of 45° in environmental open channel

In order to analyze the transport and diffusion rules of pollutants in the 45° environmental open channel confluence area, the concentration distribution characteristics of pollutants under different velocities of main channel and pollutant mass flow rates of branch channel are studied using the standard k–ε turbulence model and component transport model based on ANSYS Fluent software. The results show that the pollutant have different three-dimensional characteristics. In the vertical distribution, the gradient of pollutant concentration changes the most in the middle layer of water, and the vertical mixing rate is faster in the bottom layer than the surface layer. In terms of horizontal distribution, the concentration gradient of the cross section decreases continuously from the upstream to the downstream. For the longitudinal distribution, pollutants flowing into main stream from tributaries spread along the tributaries, with the highest concentration near the tributaries. Variations of main channel flow velocity have a significant impact on the pollutant diffusion. As the flow velocity increases, the horizontal diffusion range of pollutants gradually decreases, while the longitudinal diffusion distance becomes longer. When the flow velocity is small, pollutants exhibit a block-shaped distribution. Conversely, at the high flow velocities, pollutants are observed to form narrow and elongated bands. With an increase in mass flow rate of pollutants, the lateral and vertical diffusion distances of pollutants increase further and the diffusion area increases. Reducing the mass flow rate of pollutants during discharge can effectively decrease the pollution range of downstream water bodies.