| The bulb tubular pump device is widely used in low-lift pumping stations such as crossbasin water transfer,urban drainage and water diversion irrigation due to its characteristics of large flow,low head,high efficiency,small footprint and straight flow path.In recent years,with the start of the second phase project of the East Route of the South-to-South Water Diversion Project,the demand for high-performance bulb tubular pump devices has become more and more urgent,and with the increase of impeller diameter and unit power,its operation stability has also higher requirement.At present,there are relatively few hydraulic models of high-performance bulb tubular pumps available in China,and there is a certain gap with the international leading level,and there is a lack of clear understanding of the internal hydraulic characteristics of tubular pumps.Therefore,it is of great significance to carry out the optimal design of the bulb tubular pump and its internal flow characteristics for the application and safe and stable operation of the bulb tubular pump.This paper is based on a combination of numerical calculations,model tests,and pressure fluctuation measurements,using theories of entropy production,machine learning,and dynamic mode decomposition,the main influencing parameters and internal pressure pulsation characteristics of the bulb tubular pump are systematically studied,and on this basis,the device is optimized.The thesis mainly includes the following research contents and innovative achievements:1.Through the method of model test,the difference of the hydraulic performance of the front-mounted and rear-mounted tubular pump devices is compared,and the reason for the difference of hydraulic performance is clarified by combining the numerical calculation results.The results show that the rear-mounted scheme has better hydraulic performance,the head and efficiency are generally higher than the front-mounted scheme.The efficiency at the highest efficiency point differs by about one percentage point,and the pressure pulsation intensity in the impeller area is smaller than the rear-mounted scheme.When the bulb body is on the water inlet side,the inflow state of the impeller inlet is poor,and the support of the bulb body and the impeller have a strong interference effect,which not only leads to a decrease in the working efficiency of the impeller,but also increases the pressure pulsation intensity in the impeller area.In addition to impeller efficiency,the main reason for the difference in hydraulic performance between front-mounted and rear-mounted schemes is the hydraulic loss in the outlet part.When the bulb body is located on the water outlet side,it plays a certain rectification effect,which is beneficial to reducing the water circulation at the inlet of the water outlet channel and reducing the hydraulic loss inside the water outlet channel.2.For the more widely used bulb rear-mounted tubular pump device,the pressure pulsation characteristics at the impeller inlet(JP1),impeller area(P1～P3),guide vane area(GP1～GP3)and guide vane outlet(CP1)under different flow conditions were studied by pressure pulsation test.At the same time,the pressure fluctuation of the measuring point in the impeller area of the bulb rear-mounted tubular pump device was studied under different cavitation conditions.The results show that the blade frequency and multiple of blade frequency are the main frequencies inside the tubular pump.The pressure fluctuation intensity of impeller inlet and each monitoring point in the impeller area is related to the impeller’s working ability,and the fluctuation intensity generally decreases with the increase of the flow rate.Affected by the matching degree of the impeller and the guide vane,the relationship between the pulsation intensity and the flow rate of the guide vane area(GP1～GP3)and the guide vane outlet(CP1)is an upward curve,and there is a minimum value near the design flow rate.From small flow to high flow conditions,the maximum pressure fluctuation points in the channel near the trailing edge of the guide vane are the middle,the back and the working surface in tunnel.Under the design flow conditions,the pressure fluctuation intensity of the monitoring points at the leading edge and the middle of the impeller experienced a trend of first decreasing and then increasing with the decrease of cavitation margin,and the trailing edge of the blade showed a trend of slowly increasing.In addition,the pressure pulsation intensity at each monitoring point increases obviously when the cavitation is serious.Under the condition of small flow rate,the pressure pulsation intensity of the trailing edge of the blade drops sharply near the point of efficiency drop,and generally shows an upward trend.Under the condition of large flow rate,cavitation occurs at the front edge of the blade pressure face,and the pulsation intensity of the leading edge P1 of the impeller tends to decrease as the cavitation margin decreases.3.A method for judging the operating state of the bulb tubular pump device based on the pressure pulsation signal was proposed,and the pressure pulsation signal was classified based on wavelet transform and deep learning.When classifying the state of different flow conditions and cavitation conditions of a bulb tubular pump device,it is far superior to the traditional machine learning classification method that directly classifies pressure pulsation signals.Firstly,the pressure pulsation signal is converted into wavelet time-spectrum as image input,which preserves the main pressure pulsation signal characteristics while reducing noise interference.Finally,image classification is performed on the wavelet time-frequency spectrum by deep learning method to judge the operating status of the unit.This method has a high degree of generalization,in actual engineering,the pressure pulsation sampling position can be reasonably determined according to the device form and classification requirements,so as to improve the accuracy of state classification.4.Based on the unsteady numerical calculation method,the distribution and propagation characteristics of pressure fluctuations in the impeller and guide vane of the tubular pump are studied.The DMD method is used to decouple and identify the unsteady flow field in the middle section of the impeller and guide vane,and decompose the flow field into a linear superposition of the average flow field and the oscillatory flow field.In the rotating coordinate system,the dynamic-static interference frequency is the main frequency of pressure fluctuations inside the impeller and guide vane.Affected by the dynamic-static interference,the pressure fluctuation intensity near the interface between the impeller and guide vane is the largest under different flow conditions.There is a strong potential flow interference between the impeller and the guide vane,which is mainly manifested in the flow field structure of alternating positive and negative pressure distributed at the impeller outlet and guide vane inlet.The flow separation at the back of the guide vane is also related to the blade frequency.In addition,the impeller wake also causes the increase of the high-frequency pulsation amplitude in the guide vane channel,and the pulsation amplitude is distributed in strips.Reasonable distribution of the impeller outlet head and determination of the distance between the impeller and the guide vane without blades are beneficial to reduce the pressure pulsation of the tubular pump.5.A comprehensive optimization system based on numerical calculation,optimized Latin hypercube sampling,machine learning,and multi-island genetic algorithm was established.The optimized design of the main flow components of the bulb tubular pump was carried out,and the optimal range of its main structural parameters was summarized.The multi-working condition optimization effect of the impeller was verified through model tests,the efficiency of the pump section of the optimized model is generally greater than that of the original model,and the efficiency improvement is more obvious in the large flow area,and the high-efficiency area is significantly expanded.The hydraulic performance of the optimized tubular pump device is predicted by numerical calculation method,and the device efficiency is significantly improved.The efficiency of the entire bulb tubular pump device is increased by about 2.7 percentage points at 1.0Qd flow rate,about 2.2 percentage points at 0.8Qd flow rate,and about 0.8 percentage points at 1.2Qd flow rate.The efficiency of the device is significantly improved,and the optimization of the bulb tubular pump device based on this optimization system has achieved good results. |
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