| Many rivers which lie in the North China and northwest China have the characteristics of high sediment concentration and the sediment particle diameter is very small. It is very difficult to remove the fine sand whose diameter are smaller than 0.03mm and quality occupies 40% of the total quality. The turbid water hydraulic separation device is able to separate sediment (consists of fine sand and clay grain) and extract clear water from turbid water of high sediment concentration. It only relies on the water self-contained energy under dynamic conditions. In the process of separation, no any chemical is needed and no external energy is provided. So it is known as the green environmental protection device. The device can be applied in the running water factory to pretreat the turbid water, and also provide good source of water for the advanced water conservation technology such as spray and drip irrigation. In order to find out the water-sediment separation mechanism under dynamics conditions and make optimization for the structure of the device as well as provide principle basis for the application, experiment studies and numerical simulations as well as theoretical analysis are used to research the rule of weak swirling turbulent flow field and the water-sediment separation mechanism and the scaling rules of the device.The contents of experimental research consist of four sections. The first part is experiment studies for clean water flow field under different incoming discharge which is conducted by Particle Image Velocity(PIV). The results of tests have revealed the flow characteristics in the device. Secondly, the uniform orthogonal designs method with the projection pursuit regression(PPR) method to deal with the measured data, and single factor experiments have both been utilized to find out the main factors influencing on the water-sediment separation efficiency of the device. The third part is experiment studies about observing the sediment flocculation and testing the sediment concentration of the overflowing water at different time in the device with different incoming discharges and sediment concentrations. The results have promulgated the influence of silt hydrodynamic flocculation or the formation of interface between clean water and turbid water due to silt flocculation under high sediment concentration on the separation efficiency of the device. The last section is to study the sediment volume fraction distribution rule in the device. The test points were arranged at different positions of the device, and then the sediment concentration of each one was measured. The results of the tests can be used to verify the multiphase flow numerical simulation results.The numerical simulation research mainly includes the clean water turbulent flow field simulation and the water sediment multiphase flow field calculations. Numerical simulations were conducted for the single-phase (clear water) flow field in the device by applying the RNG k-εmodel and the Reynolds-stress model with the different schemes of grid division. According to the computational results, the characteristics of radial, tangential and axial velocity and Reynolds-stress are analyzed in detail, and the calculation results are contrasted with the experimental data by PIV. The results show that both models can accurately predict the flow field, with a comprehensive consideration of simulation precision and time consumption, we can simulate the flow field of the device by applying RNG k-εmodel, which is less time consuming than the Reynolds-stress model.Nowadays, in the solid-liquid two phase flow theory, there are two methods to describe the solid particle movement. They are Euler-Euler and Euler-Lagrangian method, respectively. After the two methods and their corresponding computational models have been compared with each other in detail, the Eulerian model-Algebraic Slip Mixture Model was selected for simulating the two-phase (water &sediment) flow field in the device. The flow field characteristics of the device are predicted by means of computational fluid dynamics technology under different operating conditions including different inlet sediment concentration, different inlet discharges as well as uniform graded sediment and non-uniform graded sediment. The results have revealed the characteristic and the distribution rules of three-dimensional velocity, dynamical pressure, intensity, sediment concentration as well as the different grain diameter sediment and the simulation results are in good agreement with the experimental data. The results show that it is reasonable and accurate to use the Mixture model for the water& sediment two-phase flow field of the device.Combining with the experiment and simulation results, the mechanism for that the sediment is separated from the turbid water with high sediment concentration is clarified from the different views such as considering the separation forces acting on the different particle size sediment, the flow field characteristics of the device and the particular structure of the device, which can provide instructions for making optimization in the structure or operation conditions.Finally, considering synchronously the drag force, gravity force, adjunctive mass force, pressure gradient force, Basset force, lift force, Magnus force, Saffman force, and neglecting the interation between particles at the low inlet sediment concentration, the movement differential equations for the sediment was established. In order to apply the model experiment conclusions on the prototype device and instruct its design, Combing with the three-dimensional time average control equations for the water and sediment movement equations, the scaling rules is derived to according to dimensional analysis method of similarity theory and Equation analytic method.
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