| Straight outlet passage and siphon outlet passage are commonly used in vertical axial-flow pumping system.The outlet passage guides the flow from the outlet of the pump guide vane to the outlet pool to better divert and spread smoothly.The outlet passage is a key component of the low-head pumping system,which has a conductive effect on the efficiency of the pumping system.Therefore,it is very important to analyze and evaluate the hydraulic performance of the straight outlet passage and siphon outlet passage accurately,so that it is important to choose the proper form of the pumping system outlet passage.For this reason,this paper uses a combination of numerical simulation and model test,takes the vertical axial-flow pumping system as the research object,and studies the hydraulic characteristics of the straight outlet passage and siphon outlet passage that are matched with the vertical axial-flow pumping system.Especially the identification of the internal vortex structure of the outlet passage.The study of internal instantaneous flow has further engineering significance in further reducing the hydraulic loss of the outlet passage and improving the efficiency of the pumping systemThe CFD software was used to simulate the three-dimensional steady of the vertical axial-flow pumping system.The internal flow characteristics of the straight outlet passage and siphon outlet passage of the vertical axial-flow pumping system under different flow conditions are compared and analyzed by physical model test.At low flow rate,the flow inside the straight outlet passage is obviously spiral,and there is a large area of low-pressure area in the inlet center of the outlet passage.The energy dissipation is large.The vortex is in the form of a whole piece and a cluster,and the large area is concentrated in the inlet circular pipe section and the structural change diffusion section,which causes poor import flow.Under the design condition,the flow state is relatively smooth,the inlet energy dissipation is the smallest,and the vortex is distributed in the passage.At high flow rate,a certain range of outflow occurs below the flow path,and the inlet energy dissipation and vortex distribution are approximately the same as those under design flow conditions.At low flow rate,the siphon outlet passage has a spiral rise in the ascending section,and there is obvious cross-flow at the top and bottom of the hump section.The central turbulent energy value of the inlet section is higher than that of the straight outlet passage.The sorghum kinetic energy region is biased toward the top of the passage,and the vortex is distributed in the form of a sheet at the inlet of the passage and the bottom of the hump.Under the design condition and at high flow rate,the overall flow state is smooth,and there is a small-scale low-pressure zone at the bottom of the hump.Most of the vortex groups are distributed in the strip inlet,the bottom of the hump section and the lower wall of the runner outlet.At high flow rate,the turbulent kinetic energy distribution of the inlet of the passage is relatively uneven.The cross-sectional area of the siphon outlet passage varies greatly,and the horizontal projection length section at 1/4 is uniform,and the pressure and velocity distribution of the siphon outlet passage are relatively uniform.At the horizontal projection length section of 1/2,the low velocity area at the bottom of the siphon outlet channel does not appear.At the 3/4 horizontal projection length section,the flow velocity of the siphon outlet passage is higher,but the area of the low pressure zone is relatively small.At the outlet of the flow channel,a small range of low-speed high-pressure zones occurs due to local de-flow at the bottom of the siphon-type water outlet channel,and the export conditions are poor.The overall hydraulic loss of the siphon outlet passage is greater than that of the straight outlet passageThe instantaneous flow field of the straight outlet passage structure was measured by PIV.Three kinds of intermediate piers with the same starting position and different lengths were installed inside the straight outlet passage.The calculation results of the three schemes under the design conditions are obtained.The numerical simulation of the outlet passage of the pumping system without a loop(no pier)is carried out.Based on the basic theory of PPE,an attempt was made to construct a comprehensive evaluation model of the outlet passage of the pumping system From the perspective of hydraulic performance,structure,and construction,a comprehensive performance evaluation software of the outlet passage of the low-head pumping system based on entropy projection pursuit was attempted.Under different flow rates,the overall trend of the streamline diagram obtained from the PIV test of the straight outlet flow section is the same as that of the CFD.The addition of the middle pier improves the stress conditions of the outlet passage Under the design condition,the longer the length of the middle pier,the greater the friction loss,and the length of the middle pier has no obvious influence on the flow distribution of the straight outlet passage.The average value of the RMS amplitude of the pulsation amplitude of the straight outflow passage test section without the pier is higher than that of the pier.When the average value of the square root is higher than that of the pier,the root mean square of the pressure pulsation amplitude of each straight monitoring point of the straight outlet passage with and without the pier is reduced with the increase of the flow ratio.When the same flow ratio,the root mean square of the pressure pulsation amplitude of each monitoring point increases with the increase of the rotational speed,and the smaller the flow ratio,the larger the root mean square of the pressure pulsation amplitude increases with the increase of the rotational speed.Under the condition of acyclic quantity,the longitudinal velocity distribution of the two types of outlet passages exhibits the same regularity.The water flow is clearly divided into upper and lower layers at the horizontal projection length of 1/2.The bottom of the flow channel forms two symmetrical vortices that rotate outward from the center,and the top water flows back inward to form two secondary vortices that rotate toward the center of the flow passage.There is a distinct vortex zone at the exit of the descending section of the siphon outlet passage,and there is a large range of de-flow... |
PDF Full Text Request