| Oxidation ditch process is widely applied in the field of wastewater treatment in China.It is because that the oxidation ditch process has a good effect on the removal of nitrogen and phosphorus,and it has a strong ability to withstand impact loads,in addition,its effluent quality is stable.But at the same time,the oxidation ditch has complex hydraulic characteristics.Applying the computational fluid dynamics simulation software to the simulation of oxidation ditch can obtain the hydraulic characteristics in the oxidation ditch quickly and accurately,and can study the effects of changes in hydraulic characteristics on the efficiency and stable operation of the oxidation ditch,which has a certain guiding significance for the adjustment of the equipment,the design and optimization of the oxidation ditch.The paper used Fluent software to establish the oxidation ditch process models and simulated the hydraulic characteristics of the oxidation ditch.The main conclusions are as follows:(1)A gas-liquid two-phase flow model for the oxidation ditch process was established.For the turbulence model,RNG k-? model was selected,and the VOF model was used as the multiphase flow model,the moving reference frame(MRF)model was chose to simulate the rotating area of the disk aerator.The longitudinal velocities of 25 measuring lines at 5 sections in the straight road of the oxidation ditch and the longitudinal,horizontal,vertical velocities of 10 measuring lines at 2 sections in the curves of the oxidation ditch model were extracted to compare with the measured values.The results show that the simulated values of the longitudinal and vertical velocities are in good agreement with the measured values.Although there are some deviations between the simulated values and the measured values of the horizontal velocities at the curves,the simulated values can roughly reflect the change rules of the horizontal velocities along the height,the simulation results have a certain degree of reliability;The RNG k-? model,VOF model,and the moving reference frame model can be applied to the numerical simulation of gas-liquid two-phase flow in oxidation ditch.(2)A gas-liquid two-phase flow model for the oxidation ditch process was established.The effects of four different immersion ratios on the flow field structure,vertical velocity distribution,and the air volume fraction distribution in the oxidation ditch were studied.The optimal immersion ratio of disk aerator ranges from 1/2 to 1/3.(3)Due to the phenomenon of sludge deposition is likely to occur at the bottom of an oxidation ditch with a rectangular section,in this study,the rectangular section of the oxidation ditch was optimized and three sections of "U-shaped","U1-shaped" and "U2-shaped" were designed.Oxidation ditch with different sections were simulated and compared with the flow field structure,gas phase distribution and energy transfer.It was determined that the optimal section of oxidation ditch was "U2-shaped" section.(4)Under the premise of satisfying the oxygen demand for the biochemical reaction in the oxidation ditch,the influence of three different opening methods of the disk aerator on the distribution of velocity and the air volume fraction was studied,and compared with other working conditions,the working condition 3 was the optimal opening method. |
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