Numerical simulation and verification of hydraulic characteristics of internal flow field in spiral flow generator

Abstract: Low-pressure straight pipeline was usually used to transport sediment-laden flow in the traditional field irrigation. Sediment deposition often triggered pipe blockage and affected normal run of the fluid-conveying pipeline. In order to effectively solve the problem of pipe blockage caused by sediment deposition during a long-distance inter-field water transfer process of the low-pressure straight pipeline, this paper designed a kind of spiral flow generating device: A hydro-spiral generator. Compared with the traditional spiral flow generating device, the guide vanes were fixed on the exterior surface of the barrel which always maintained concentric with the fluid-conveying pipeline. The hydro-spiral generator works by producing reverse resistance and vertical lift on the fluid under the action of the guide vanes, and forming a stable velocity circulation and a spiral flow of uniform vortex strength within the pipeline. The supports made it more flexible to arrange the hydro-spiral generator at any position and greatly enhanced the intensity and scope of continuous generating spiral, which was significant in improving irrigation efficiency of sediment-laden flow in the field irrigation. In order to rationally design structural parameters of the hydro-spiral generator, a geometrical model of the hydro-spiral generator with different guide vane lengths was established by using Auto CAD (computer aided design) software. Based on RNG k-ε turbulent model and PISO algorithm, hydraulic characteristics such as the axial velocity, the radial velocity, the circumferential velocity, the pressure and the vorticity magnitude inside the hydro-spiral generator having different guide vane lengths were investigated numerically with three-dimensional unsteady calculation by using the commercial Fluent 12.0 software. At the same time, the spiral generating efficiency was deduced to further analyze the effects of the guide vane length on spiral generating capability. The hydraulic characteristics of internal flow field were studied by using model tests inside the hydro-spiral generators with guide vane lengths of 0.025, 0.050, 0.075, and 0.100 m respectively. The barrel was 0.1 m long with an outside diameter of 0.05 m, and structure parameters of the guide vane were 0.01 m for height and 30° for placement angle. The seven-port point gauge, pressure sensors and standard dynamic pressure collection box were used to measure flow velocity and pressure distributions at the typical sections, and the simulated values were compared with the experimental values. The results showed that the simulated values of internal flow field in the hydro-spiral generator were in good agreement with the experimental values , and the maximum relative errors of the flow velocity field and the pressure field did not exceed 6.4% and 1.3% respectively, which further indicated that it was feasible for solving hydraulic characteristics of internal flow field inside the hydro-spiral generator using the commercial Fluent 12.0 software. As the length of the guide vane increased, the affected areas of the axial velocity gradually decreased, while the affected areas of the radial velocity, the circumferential velocity and the vorticity magnitude gradually increased at the downstream flow field of the hydro-spiral generator. With the increase of guide vane length, the energy losses caused by the hydro-spiral generator showed an increasing trend. There was an obvious low pressure zone at the downstream flow field of the hydro-spiral generator, and then the pressure again rose along the downstream direction of the fluid-conveying pipeline. The vorticity magnitude of the hydro-spiral generator was mainly distributed in the near-wall areas of the barrel near the entrance to the cyclical slit flow, the near-wall areas of the guide vanes and the downstream flow field of the hydro-spiral generator. As the increase of guide vane length, the spiral generating efficiency of the hydro-spiral generator gradually increased. The study of this paper not only provides references for further designation and optimization of the hydro-spiral generator, but also improves comprehensive theoretical basis for further perfecting the theories of long-distance solid transportation and the technologies of spiral flow solid transportation.