Analysis And Simulation For The Flow Around The Composite Cylinder At High Re Number Based On FLUENT Software

The birth of numerical simulation software can be said to be a breakthrough in the development of the field of scientific research. Software has become the direct bridge between the theory and experiment, theories guide experiments and experiments improve the theories, a lot of complex problems can be solved by means of numerical simulation software.As a new way of pipeline hydraulic transportation methods, the main structure was composite cylinder. This article was combined with National Natural Science Foundation of China-"Hydraulic characteristics of pipeline gap spiral (51109115)" and "Energy of pipeline trains (51179116)". This article takes the silt flow when composite cylinder was still in the pipeline, based on numerical simulation methods with the theoretical analysis and experimental research to interpret, the characteristics of the flow around the pipe carriage at high Reynolds numbers were studied. Main results are as follows:1. The situation of single composite cylinder(1) To analyze the force conditions of pipe carriage, it has improved the pipe carriage was forced by pressure force and shearing force. The larger the diameter ratio was, the greater the pressure force was, the easier the pipe carriage started.(2) The pipe was divided into upstream, the gap and the downstream, and the upstream was divided into unaffected area and the affected area. The distribution of velocity in the unaffected area complied with Prandtl exponential distribution, the distribution in section1-1in the affected area can be considered similar to Prandtl exponential distribution, the effect of the stand-bar was larger in section2-2, the velocity was zero in the stand-bar area in section3-3,and the velocity gradient was larger.(3) Axial velocity was distributed symmetrically along any central axis of the stand-bar, and increased firstly and then decreased from cylinder wall to pipe wall, the maximum occurred at4mm away from the pipe wall. The larger the diameter ratio was, the greater axial velocity and velocity gradient were, and the more badly-distributed axial velocity was. The maximum moved to the cylinder wall.(4) The radial velocity in the front section presented cyclic distribution, and increased firstly and then decreased from cylinder wall to pipe wall. The maximum appeared away from the cylinder wall with the increase of the diameter ratio, the radial velocity was negative and well-distributed in the middle section, the radial velocity was positive and well-distributed in the back section, except for the stand-bar area. (5) Tangential velocity was too small that can be negligible when compared to the axial velocity and radial velocity.(6) Through comparing the axial velocity and radial velocity in simulation results and experimental results, it has improved that Using FLUENT to simulate the kinetic characteristic of the silt flow was feasible.(7) It was concluded that the local resistance coefficient of the front section and diameter ratio were exponential relationship, so as the back section. And there existed a critical value of the diameter ratio, the critical value was0.75. When k>kε, the local resistance coefficient of the front section was larger, When k<kε,the back section was larger.(8) There appeared trailing vortex in the downstream, and the downstream was divided into three parts, the velocity decreased firstly then increased and finally plunged in section1-1, and the velocity gradient was great. Velocity in the area between central region and gap region was very small and decreased firstly then increased and finally plunged too in section2-2. It was well-distributed in section3-3, and the distribution tended to pipe water distribution.2. The situation of two composite cylinders(1) To analyze the force conditions of the two pipe carriages, it was concluded that the critical space was between40cm-50cm.(2) Under the same space, there was a critical surface-the outer wall of the pipe carriage, the flow velocity between two pipe carriages was small while the pipe flow velocity was large inside the critical surface, the flow velocity between two pipe carriages was large while the pipe flow velocity was small outside the critical surface.(3) The larger the space was, the more well the velocity between two pipe carriages distributed, and the distribution was closer to the ring. The velocity of the center flow decreased firstly then increased with the space increasing.