Flow Simulation And V3V Measurement Of Vertical Axial Pump Straight Pipe Outlet Flow Chanel

The outlet channel is the connecting channel connecting the outlet of the pump guide vane with the outlet pool,its role is to make the water flow better divert and diffuse during the process from the pump guide vane outlet to the pool,and maximize the recovery of kinetic energy without separation or vortex.For large low-lift pumping stations,the hydraulic loss of the outlet flow channel accounts for a large proportion of the total head of the pump.Poor design can lead to large flow loss in the flow path inside the flow channel and low pump performance,affecting the overall efficiency of the pumping station.The research method of combining numerical simulation and model experiment is used to study the flow law of the straight pipe outlet flow channel.Through numerical simulation,20 typical sections were taken from 5 parts of the outlet channel for flow analysis(guide vane outlet diffusion section,in the outlet elbow,the inlet of the outlet channel straight pipe section,the outlet of the outlet channel diffusion section,and the outlet of the outlet channel).The results show that:The flow velocity distribution in the diffuser section of the guide vane outlet becomes more uniform as the flow rate increases,and the flow line becomes smoother.There are vortices in each working condition in the outlet bend,the larger the flow,the greater the number of vortices.Velocity distribution is uneven under various conditions at the inlet of the straight pipe diffusion section,and obvious high-speed and low-speed zones appear under large-flow conditions,and the number of vortices increases with the increase of flow.The vortex at the outlet of the straight tube diffusion section still exists but its intensity has been reduced,and the velocity distribution is relatively uniform.The area of the high-speed area at the outlet of the flow channel is significantly reduced,the flow velocity is evenly distributed,the intensity of the vortex is reduced,and the intensity of the vortex is significantly reduced,under small flow conditions,there is no vortex at the outlet of the runner,and the flow line is smooth.The loss in the diffuser section of the guide vane accounted for only 5%under non-operating working conditions,but the loss ratio in this section reached 18%under design working conditions.The proportion of hydraulic loss caused by elbows decreases with the increase of flow,from 52%to 15%,showing a straight downward trend.The loss of straight pipe sections is the opposite.As the flow rate increases,the proportion of losses in straight pipe sections increases,especially in high-flow conditions,up to 35%.The flow field at the inlet of the straight pipe section of the outlet channel was measured by the V3V volume three-dimensional flow field measurement technology.The results show that,in the small flow condition,the high-speed area is located on the right side of the flow channel,and two vortices are distributed in the flow channel.Under the design condition,the high-speed area is located on the upper right side,and two vortices are distributed in the flow channel.The high-speed area is at the top under high flow conditions,and there are 4 vortices in the flow channel.Compared the experimental results with the numerical simulation results,the results are basically the same.Seven types of outlet channels with different diffusion angles and two different diffusion lengths were compared and analyzed from five aspects:the performance of the pump device,the hydraulic loss of the outlet channel,the velocity distribution of the typical section,the vorticity and the kinetic energy recovery rate.It is comprehensively concluded that the hydraulic characteristics of the straight-sided outlet channel with a unilateral diffusion angle of 6°-9° are best;and it is recommended that the diffusion length can be appropriately increased during the design of the straight-pipe outlet channel.The plane diffusion angle and the diffusion length have a great influence on the flow pattern and hydraulic performance of the flow channel,and are the key parameters in the hydraulic design of the straight pipe flow channel.