Abstract:
Gill-piece separation device, which consists of gill-pieces and gill-duct, is a kind of new-type device with advantages of simple structure, low cost and fast water-sediment separation velocity. This device is found wide applications in sediment pretreatment at water works or the treatment of irrigation water. With the development of computer technology and computational fluid dynamics, solid-liquid two-phase flow field simulated by numerical model have been widely used. This paper adopts multiphase flow model that is Eulerian model and Mixture model provided by Fluent software to study water-sediment two-phase flow field in the gill-piece separation device under hydrostatic condition. At the same time, in order to check the reliability of numerical simulation, the test data of PIV technique are used to evaluate the simulation results. This paper shows velocity vector distribution and velocity nephogram of part of the sections using Eulerian model, mixture model and PIV test results under the condition of S=10kg/m3. It is shown that velocity vector distribution obtained by Eulerian simulation and Mixture simulation are the same as those from the PIV test. The flow is dominated by sediment flow settlement in the section of Z=0.035m along width direction and the section of X=0.005m along length direction. The sediment particles slide downward along the short sides of the gill-pieces at an inclination angle of α. When they reach the long side of the gill-pieces, they surge to sediment channel along with particles at inclination angle of β. The flow is dominated by upward movement of clear water in the section of Z=0.005m along width direction and the section of X=0.095m along length direction. The clear water flow upward along the short side of gill-piece at inclination angle of α. When they reach the long side of the gill-piece, they move upward to enter the water channel at an inclination angle of β. But velocity nephogram of different sections is different between simulation results and PIV test results at the same time point. The maximum relative errors of calculation results by Eulerian model and Mixture model from PIV test result are 9.09% and 36.36%, respectively. So Eulerian model is more accurate and reliable, and is used to simulate water-sediment two-phase flow in the gill-piece separation device. And than the distribution characteristics of sediment and velocity in gill-piece separation device is analyzed using Eulerian model calculation results. Average sediment concentration and velocity distribution, which is on the upper surface and the lower surface of the gill-piece, is relevant with gill-piece location and time. The characteristic of sediment distribution is different along different height direction of the gill-piece separation device. The faster water-sediment separation is, when closer to top of gill-piece separation device, the easier it is to get water. The variation of average sediment velocity with time in sediment channel is consistent with average water velocity in the water channel. And average sediment velocity is generally larger than average water velocity.