A pipe hydrocyclone is easy to disassemble in agricultural machinery. Spiral flow can be generated to drive the movement of impurities in the pipe, thereby effectively reducing the accumulation of impurities. Different structural parameters can form differences in the annular gap space of hydrocyclones. The structure of the annular gap space can also dominate the flow field distribution and swirl efficiency. Therefore, this article aims to explore the annular gap spiral flow formed by the hydrocyclones with different structural parameters using physical model experiments. The research results show that the structural parameters of hydrocyclone were dominated by the magnitude and dispersion of axial, radial and circumferential flow rates, where the most contribution was the radial and circumferential flow rates. There was no change in the overall distribution pattern of the annular gap flow field. Furthermore, there was the roughly same variation trend of axial average velocity and standard deviation along the water flow direction under different structural parameters. Both showed a gradually decreasing trend along the way. However there was a relatively small amplitude of the decrease in the axial average velocity along the way. The standard deviation of the cross-section gradually decreased in the constant diameter of the hydrocyclone, as the length increased, whereas, the axial average velocity increased. However, there were relatively small changes in the standard deviation and axial average velocity. Both axial average flow velocity and standard deviation increased in the constant length of the hydrocyclone, as the diameter increased, whereas, there was a relatively large variation in their amplitude. The radial average velocity and standard deviation showed a "V" shaped trend of decreasing first and then increasing along the flow under different structural parameters. The radial average velocity and flow velocity fluctuation of each section gradually increased in the constant diameter of hydrocyclone, as the length increased, but the increase was relatively small. The radial average velocity decreased in the constant length of hydrocyclone, as the diameter increased, but the flow velocity fluctuation of each section increased gradually. The circumferential average velocity and standard deviation of different structural parameters showed a gradually increasing trend along the water flow, but their growth rate in the first half of the annular gap was relatively small. The circumferential average velocity and flow velocity fluctuation showed a gradually increasing trend in the constant diameter of hydrocyclone, as the length increased, but the increased amplitude of both was relatively small. The circumferential average velocity and flow velocity fluctuation showed a gradually increasing trend in the constant length of hydrocyclone, as the diameter increased. Both energy consumption and rotation efficiency increased significantly, as the length or diameter of hydrocyclone increased. In addition, there was a higher increase rate with the diameter than that with the length. This experiment demonstrated that the hydrocyclone with a structural parameter of 70 mm×100 mm presented the highest starting efficiency. The optimal structural parameter of hydrocyclone was in the size of 70 mm×100 mm. This finding can provide a strong theoretical basis and reference for the selection and structural optimization of the hydrocyclone.

A diversion port is often constructed on the side of the main channel for drainage. The water flow can be diverted from the channel into the field for irrigation. A curved water flow is usually formed when the water flows from the channel into the diversion port. In addition, the sudden contraction of the diversion port section can cause a drastic variation in the flow state of the water in the diversion area, thus forming outstanding high-speed and low-speed zones. This uniform distribution of flow velocity can have a great impact on the diversion flow rate and sediment distribution. The water distribution of side pipes can often experience a state of free pressure, due to the variation in the flow rate and pipe diameter. This study aims to investigate the influence of free-pressure side pipes on the hydraulic characteristics of the channel diversion zone. A series of physical model experiments were conducted to determine the three-dimensional flow velocity, turbulence intensity, diversion width, and diversion ratio of the channel diversion zone under different filling degrees. The experimental results indicate that there was no variation in the distribution of three-dimensional flow velocity and turbulence intensity at the channel separation zone under different filling degrees. But the free-pressure pipe flow posed a great influence on the magnitude of the three-dimensional flow velocity and turbulence intensity. Furthermore, the longitudinal, transverse, and vertical flow velocities all shared a gradually increasing trend from the bottom of the canal to the water surface. The longitudinal average flow velocity gradually decreased from the upstream to the downstream of the water outlet. While the transverse and vertical average flow velocities first increased and then decreased. The longitudinal, transverse, and vertical turbulence intensity first increased and then decreased. The turbulence intensity was higher in the area directly at the pipeline inlet. There were relatively high horizontal and vertical flow velocities at the diversion port. Therefore, the diversion flow of the pipe increased correspondingly. However, the vertical flow velocity decreased at the diversion port. The sediment carrying capacity of the water flow was reduced near the diversion port. At the same time, the water flow was prone to form a circulation in this area, leading to settling and accumulating the sediment in the diversion area. There was an increase in the longitudinal average flow velocity and turbulence intensity, as well as the vertical average flow velocity, of each section of the channel, as the filling degree increased. While the increase was found in the transverse average flow velocity and turbulence intensity, as well as the vertical turbulence intensity. There was an increase in the diversion width of free pressure pipe flow, with the increase of filling degree. In the rectangular diversion ports, the diversion width gradually increased from the water surface downwards. By contrast, there was a more complex variation in the diversion width of free-pressure pipes along the water depth direction. The water dividing width was required to formulate the free-pressure pipe flow rather than the original formula. Once the filling degree was less than 0.5, the dividing width gradually decreased from the water surface downwards. When the filling degree was greater than 0.5, the dividing width first increased and then decreased from the water surface downwards. When the flow rate of the main channel was constant, the diversion ratio increased with the increase of filling degree; When the filling degree was constant, the diversion ratio decreased, as the flow rate of the main channel increased. Therefore, the water depth in the main channel was improved the pipeline diversion and flow at the constant inflow in the actual water supply. The finding can provide the technical support to design and maintain the canal water diversion in fields.