Model Test On Vertical Axial Flow Pump Device And Internal Flow Characteristic Analysis On Inlet Conduit And Outlet Conduit

China's territory is vast,but the distribution of water resources in space and time are not balanced.Among all the water conservancy projects,the construction of pumping station project is a very important measure for inter-basin water diversion and rational allocation of water resources.It is also very necessary for the supplying of the demand of agricultural,industrial,urban domestic water demand,also for improving the ecological environment.In pumping station engineering,low-lift vertical axial flow pump device due to its mature technology,convenient installation and maintenance has been widely used.In low lift pump system,however,the hydraulic loss of inlet conduit and outlet conduit in pump device occupies a larger proportion in total losses.When fluid enters pump and leaves pump,the fluid would change its direction of 90 degree for two times.Therefore,the unstable flow,such as flow separation,vortex would easily appear in the passage,and it could bring negative influence on the operation of the pump unit.Therefore,in this thesis,a vertical axial flow pump unit equipped with elbow-shaped inlet conduit and straight outlet conduit was researched by whole passage simulation under different working conditions,and combined with pump model test,the internal flow characteristics of inlet conduit and outlet conduit were studied.The research work and innovation points are as follows:?1?The numerical simulation and experimental research on inlet passage and outlet passage of the vertical axial flow pump units were summarized.?2?The model experiment on the vertical axial-flow pump unit was conducted on the high precision test bench.The experiment includes the energy characteristic test,cavitation test,runaway speed test,and the passage hydraulic loss test of different blade angles?-6°,-4°,-2°,0°,+2°?.The experiment results show that with the increase of blade angle,the efficiency curve and lift curve of the pump unit move toward high flow rate direction.The highest efficiency point of the pump unit appears under 0 degree blade angle.Furthermore,under all the blade angle,the efficiency of pump unit are lower than 80.5%.Moreover,the cavitation performance of the pump unit is quite good,and the possibility of damaging runaway is relatively low.The results could provide operation instruction for the same type of vertical axial-flow pump device.?3?The three-dimensional calculation model was established.Then,the whole flow passage simulation was conducted on the model under different conditions at blade angle of 0degree,and the lift and efficiency value of the simulation were compared with the test results.The results show that under the part load condition,the head from the simulation is lower than test,and under the designed condition,the error of hydraulic characteristic of numerical value and experimental value is minimum,the efficiency error is 1.51%.Under 0.8Q_d and 1.2Q_d conditions,the efficiency is 4.16%and 3.75%.The efficiency under different blade angles were also calculated.The results show that the numerical simulation are up to the basic calculation accuracy requirements.?4?Based on the full flow passage simulation,the internal flow characteristics of the inlet conduit under the different conditions was analyzed from several aspects,through pressure and streamline distribution on the middle section,streamline distribution analysis basic flow regime inside the inlet port.Two different vortex identification technology,the Q criterion and?₂criterion was used for the vortex indentification.The distribution of the vorticity on the cross section in the bending tapered section of the cross section by the two criterions is pretty obvious.It is found that the?₂ criterion could recognize more vortex structure near the wall.?5?Based on the full flow passage simulation,the internal flow characteristics of the outlet conduit under different conditions was analyzed from several aspects.Combining with the turbulent kinetic energy,streamline distribution and pressure distribution,the dynamic characteristics of unsteady flow inside the outlet conduit was researched.Then,the Q criterion and?₂ criterion were used to analyze the vortex structure in the outlet conduit,the results show that the vortex gathers at the entrance of the outlet conduit,as the fluid flows,vortex cloud dissipation gradually;comparing the vortex bold distribution under different Q value at the same time under the partload condition,and the results show that when the Q value is small,vortex bold occupies a great position in the outlet conduit,with the increase of Q value,location of vortex bold distribution reduces.Based on the eigenvalue method and the vorticity method,the vortex core was extracted from the outlet conduit under different working conditions in an unsteady rotation cycle.The results show that the strength of vortex core reduces gradually as the fluid flows from the entrance of the outlet conduit;the number of vortex under designed condition is the least for both the two methods,and the vortex core number is the most under partload condition;under the designed conditions,there is no vortex core at the middle part.?6?The pressure monitoring points were set in the inlet conduit,the interface of inlet conduit and the impeller,impeller and guide vane,as well as the outlet conduit to research the pressure fluctuation characteristic of the pump unit.There are some conclusions:the pressure pulsation in inlet conduit are greatly influenced by the impeller prewhirl,and its time domain graph in each cycle shows like sinusoid distribution,and there are three peaks and three troughs;the pressure fluctuation of the points closer to the impeller is more intense.The pressure fluctuation amplitude is smallest under the partload condition;in the outlet conduit,the strength of the pressure pulsation is lower than the inlet conduit,and the influence of the impeller rotation on the pressure fluctuation is quite small.?7?Changing the blade numbers in the guide vane,the relative position of guide vane and impeller,and the initial position of the division pier,and then the numerical calculation under different conditions was conducted on these schemes.Their influence on the outlet conduit internal characteristics was analyzed through various aspects,such as pressure distribution,velocity distribution and hydraulic losses.It could be found from the results that when the guide vane blade number was 5 pieces,and the relative position of the guide vane and the impeller was 8 mm,the internal characteristics of the outlet conduit is the best.The division pier could increase the hydraulic loss of the outlet conduit,but it could also make the flow pattern better.