| China is a country with a serious shortage of water resources, and agriculture consumes a large amount of water. Developing the water-saving agricultural irrigation energetically is an important measure to promote sustainable utilization of water resources, ensure national food security and accelerate transformation of economic development mode. Sprinkler irrigation is a kind of efficient water-saving irrigation technique, while sprinkler irrigation pump is the core equipment of sprinkler irrigation system and the key equipment for water-saving. Therefore, to develop the efficient and reliable low-specific-speed multistage self-priming spray irrigation pump not only meets the urgent demand of the market, but also conforms the national strategy of energy conservation and emission reduction. This study is financially supported by the National Science & Technology Support Plan of China (No.2011BAF14B01), Natural Science Foundation of China (51279069) and Jiangsu Provincial Project for Innovative Graduate (No. CXLX12-0642).Based on theoretical analysis, numerical calculation and model test, the self-priming mechanism, energy loss and rotor-stator interference phenomenon of the low-specific-speed multistage self-priming spray irrigation pump have been studied systematically. The main research work and creative achievements are as follows:1. Based on the single-stage self-priming centrifugal pump, a kind of self-priming device of multistage self-priming pump with high self-priming performance and external characteristic was proposed. Based on the positive and inverse diffuser, the backflow device was creatively designed and composed of gas-liquid separation chamber, outer shell, self-priming cover plate and gas-liquid mixture chamber. The high-pressure water of the final-stage pump chamber was sent to the first-stage pump chamber through the backwater device, and the gas-water mix repeatedly in the self-priming process. When the self-priming was completed, backflow valve in the self-priming cover plate was automatically shut off under huge pressure difference, which effectively improved the efficiency of self-priming pump.2. Based on the multi-objective fuzzy optimization design, the multi-objective optimization model with the maximum head of off dead point and minimum value of maximum shaft power was determined. Combined with design experience and technological needs, relevant constraints were established and solved through nonlinear extremum. Finally, the hydraulic optimization design of flow components was completed with the optimum solution. By doing the external experiments of multistage self-priming spray irrigation pump, it’s concluded that the head of off dead point and maximum shaft power meet the demand, which provides a new reference for the optimization design of the pump.3. Combined with the orthogonal test, grey correlation analysis and priming test, the study on shortening the priming time of multistage self-priming pump has been done. The outlet width of impeller blade b2, the radial clearance between the impeller and diffuser δ, the area of backflow hole S and the series of multistage pump is were selected as the test factors. Three levels were selected and nine schemes were designed according to the L9 (43) orthogonal test. Based on the orthogonal test, the arrange order of test factors influencing the priming time were accurately obtained through the grey correlation analysis. Finally, the optimal combination of influencing factors was obtained based on the orthogonal test and grey correlation analysis. Moreover, the priming time of 5 m height through the optimal priming pump is 40 s by doing the priming test, which proves the priming performance of the optimal priming pump is much better than the national standard’s requirement of Tp≤100 s.4. Adopting ANSYS CFX software, the gas-liquid two-phase flow numerical calculation was conducted both to simulate the self-priming process of the single-stage self-priming pump and the multistage self-priming pump (4 stages). Meanwhile we installed transparent plastic tube at the exit of the multistage self-priming pump, observed the gas-liquid overflow phenomenon of the multistage self-priming pump with photographic technology, and compared the result with the numerical calculation. The self-priming process of the self-priming pump is divided into three stages:the air suction stage due to the impeller rotating role drainage in the initial self-priming stage, the air suction stage due to the gas-water mixing and the gas-water separation role exhaust in the middle self-priming stage, the air suction stage due to the exhaust by reason of water flow from the import into the pump chamber in the last self-priming stage. Among them, the initial self-priming stage and the last self-priming stage accounts for a smaller percentage of time, but they have a faster self-priming speed. The middle self-priming stage is the accented phase of the self-priming process which determines the length of the whole self-priming time. Observing the gas-liquid overflow phenomenon of the multistage self-priming pump with photographic technology, it finds that the experimental results are quite close to numerical calculations in the whole initial self-priming stage and middle self-priming stage. They not only have the same change rule basically, but also have less-than 0.1m discrepancy.5. For a typical low specific speed multistage centrifugal pump, a series of research about the setting method of numeric calculation has been done. In the meantime, the influence law of roughness on the pump performance was analyzed emphatically. The results show that the roughness of the low specific speed centrifugal pump has enormous influence on the numerical results:With the increase of roughness, pump’s head and efficiency decrease, while the influence of roughness on efficiency is greater than the impact on the head. With the increase of roughness, the disk friction loss power of the pump and the hydraulic power are increasing, while the influence of roughness on disc friction loss power is greater than the influence on hydraulic power. With the increase of the roughness, the hydraulic efficiency, the volume efficiency, and the mechanical efficiency of pump decrease constantly. Roughness generates the overall efficiency of low specific speed multistage centrifugal pump greatly decreasing mainly by reducing the efficiency of hydraulic and mechanical efficiency. With the increase of flow quantity, the influence of roughness on pump’s and efficiency increases, but the influence on the pump’s power basically remains unchanged. In addition, the roughness has more significant inhibitory effect on the efficiency of the pump under high speed.6. A loss model method based on numerical calculation was established, considering various types of losses which included the hydraulic loss at inlet section, outlet section, impeller, guide vane and pump chamber, the disk friction loss, the ring leakage loss and the interstage leakage loss. All the various losses were calculated to obtain the interactional and proportional relationships between the various types of losses:regardless of the interstage leakage and the volume leakage, with the increase of flow rate, the hydraulic power loss of pump decreases first and then increases, and it comes to a minimum at a proper flow condition.(usually the rated flow conditions). And the disk friction loss power of the pump has a downward trend with the increase of the flow, but its decline is very slow. After taking the interstage leakage into consideration, the disk friction loss power and hydraulic loss power of the pump both increases. Actually, the increased hydraulic losses power is the power transformed from the disk friction losses. After taking the front ring volume leakage into consideration, because of the increase of the actual impeller through flow, the hydraulic loss power of the pump moves to the big flow direction, and the disk friction loss power reduces. Also, the increased amount of volume leakage also leads to the decrease of interstage leakage which further reduces the disk friction loss power.7. Using the unsteady numerical calculation, this paper studied the changing law and internal influence factors of pressure pulsation wave’s amplitude, frequency and phase in the impeller, the diffuser and the pump chamber of low specific speed multistage priming pump. It shows that there are mainly four factors influencing the pressure pulsation intensity of any point inside the pump:the distance between the arbitrary point and the pulse source, the pressure gradient at the arbitrary point, the flow field’s instability at the arbitrary point (turbulent kinetic energy) and the relative position of the arbitrary point and the pulse source. Among them, the pressure pulsation intensity of arbitrary point has a positive correlation with pressure gradient and turbulent kinetic energy, and a negatively correlation with distance. While, the relative position of arbitrary point and pulsating source affects the strength of the negative correlation. That means when the arbitrary point is in the downstream of pulse source, the negatively correlation influence of distance on pulse intensity is weak, but the impact is rather strong when the point is in the upstream of pulse source. There are mainly two factors influencing the pressure pulsation frequency of any point inside the pump:the number of pulse source and the rotating speed of the impeller. Thereinto, the basic frequency of arbitrary point’s pressure pulsation coefficient in impeller is diffuser’s frequency, while the basic frequency of arbitrary point’s pressure pulsation coefficient in diffuser and pump chamber is impeller’s frequency. In addition, some low frequency signals may be instead of frequency signal when the pressure pulsation intensity of the arbitrary point is extremely weak. There are mainly two factors influencing the pressure pulsation phase of any point inside the pump:the distance between the arbitrary point and the pulse source and the location of the arbitrary point.8. Based on the numerical calculation method, it obtained the velocity field in the rotor-stator interaction area (r/R=1.005) between the impeller and the positive diffuser, found that the velocity distribution in the rotor-stator interaction area between the impeller and the positive diffuser has very obvious unsteady characteristic which is influenced by the combined effect of both impeller’s outlet side and diffuser’s inlet side. Furthermore, the velocity distribution forward spread to the next level diffuser, reverse spread to the previous level impeller and lateral spread to the pump chamber. The tests of vibration and external noise test on the multistage priming pump were done, and found that the change rule of main frequency and amplitude of main frequency on the vibration, noise and pressure pulsation is almost the same, which shows they have strong correlation. |
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