| The inlet and outlet pipelines have a greater impact on the performance of the low-lift pump system,especially in axial-flow pumps and mixed-flow pumps with higher rotational speeds.The forebay of the pumping station ensures that the water flow gradually spreads and smoothly enters the reception basin,providing a good inflow condition for the reception basin.In the terrain conditions are limited cannot be arranged in the forward inlet flow forebay,often using lateral inlet flow forebay.The flow in the forebay of the lateral inlet pumping station is generally oblique with the axis direction of the inlet flow forebay.It is easy to form a return flow or whirlpool after the water enters the reception basin.With the development of the flow,the safe and stable operation of the unit must be harmed after entering the impeller.The pressure pulsation is the fluctuation of the pressure acting on the affected object over time,the greater pressure pulsation will cause the pump vibration noise,make the leaves crack,reduce pump efficiency.In this paper,the impeller speed is 2200r/min,and the deflectorplate device can be simulated lateral inlet flow at the inlet section of the inlet conduit.By adjusting the deflector plate angle,the bias condition is provided for the inflow into the reception basin.The CFX software is used to simulate the whole of the pump system.The difference between the external characteristics of the numerical simulation and the model test and the change of the external characteristics with the variation of the drift angle are analyzed.The changes of the three-dimensional flow field and the flow change of the characteristic section in the inlet conduit,the impeller,the guide vane,the elbow and the outlet conduit are analyzedwith thedifferent drift angle,and the variation of hydraulic loss of each component with drift angleis drawn.Based on the method of physical model test,the change of the energy in the time domain and the frequency domain and the frequency band of the pressure fluctuation monitoring point in the outlet section of inlet and outlet conduit and outlet conduit with the working conditions and drift angleis analyzed.Through the above research and analysis of the data obtained the following conclusions:(1)The flow rate of the inlet conduit is better at 0° drift angle,the efficiency of the pump is the highest,and the maximum efficiency point is reduced with the increase of the drift angle.Due to the guiding effect of the deflector plate,the flow of the inlet conduit is disturbed and the hydraulic loss is increasing at 20°,50°,80°drift angle,the uniformity of the outflow velocity of the inlet conduit increases first and then decreases with the increase of the drift angle.(2)The three-dimensional flow field in impeller and guide vane is less affected by drift angle change.In the small flow condition,there is unstable flow in the vicinity of the impeller hub and the guide vane.Under the different drift angle,the static pressure distribution of the blade pressure surface is basically the same,and the pressure from the hub to the rim gradually increases,the high pressure of the blade area near the rim has been reduced,and thepressure surface close to the hub has been increased.(3)Under the different drift angle,the small flow condition,the flow of the elbow and outlet conduit are spiral;under the design condition,the flow of the outlet conduit is smooth and there is a separation of flow in small range of the area near the wall,but there is still some spiral motion in the flow.Under the high flow condition,there is no obvious separation flow area,and the difference of the three-dimensional flow field is quietly small under different drift angle.(4)Theoutlet pressure pulsation monitoring point time domain waveform of the inlet flow conduit has obvious periodicity,the waveform ofthe outlet conduit is disturbed.The frequency of the main channel is reduced first and then increased with the increase of the flow when the frequency of the inlet conduit is 4 times,and there is a significant peak at the frequency and its harmonics;the flow spectrum of the outlet conduit is more disturbed,the frequency of its impact is small,the overall pressure amplitude of each monitoring point is decreasing with the flow increases,large flow conditions(1.2Qbep)is the smallest,which there is a certain relationship as a large flow conditions under the outletconduit flow is relatively smooth.(5)The use of wavelet packet decomposition reconstruction signal,the small flow conditions,the inlet conduit monitoring point reconstruction signal,the node(4,0)the largest proportion,as the flow increases,the proportion of nodes(4,0)decreases first and then increases,and the design conditions are the smallest,corresponding to the design conditions of the flow smoothly.As the outlet conduit relative disorder,to node(4,0)corresponding to the low-frequency signal-based.The wavelet packet energy spectrum is used to solve the energy change of each node.Under different drift angle,the energy change of the inlet conduit is affected by the drift angle,and the outlet conduit is less affected by the drift angle.The energy of the inlet conduit is the largest in the frequency band,and the energy of the monitoring channel is mainly concentrated in 0?31.25Hz,corresponding to the low frequency and large scale vortex in the flow. |
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