| Over 70 percent of coalmine exploitation in China is underground mining.However,with the increasing of mining depth,hydrogeological conditions are more complex,the safety construction of mines and safe mining of mines are affected seriously by aquifer in underground mine and mine inflow induced by uncertain water source.To strength the mining drainage capacity,code for design of mine of coal industry clearly define there are three sets of drainage system of pump including work,spare and overhaul for the construction of large-water mines.Radial diffuser multistage pump is gradually become the mine drainage equipment with the longest single machine running time and the largest power consumption in the process of discharge and handle of mine water due to the characteristics of high lift and large flow.The main overflow part of the radial diffuser multistage pump is connected by overflow parts of two or more centrifugal pumps in series connection.The structure of flow channel is complex.And the fluid in pumps goes through the process of radial-axial-radial alternative change.The operating efficiency of radial diffuser multistage pump is lower than that of single-stage centrifugal pump and about 10%lower than that of foreign centrifugal pump.Therefore,it has important practical significance and considerable actual economic benefits to carry out the research on hydraulic performance optimization of radial diffuser multistage pump for the problem of low efficiency and high energy-consumption of radial diffuser multistage pump in operation.In this paper,the radial diffuser multistage pump is researched by combining of theoretical analysis,numerical simulation and experimental study.The steady flow and unsteady flow of radial diffuser multistage pump under different flow rate are calculated.The flow structure,generation mechanism and flow law of unstable flow phenomenon in pumps are explored.Entropy production and flow loss in different flow rate are studied by entropy production theory.The original experimental data of unsteady pressure fluctuation in pump are obtained and the analysis of time domain and frequency domain is carried out by the performance test and unsteady pressure fluctuation test.The accuracy and scientificity of the solving strategy of numerical simulation fot the calculation of steady and unsteady is verified.A mathematical model for the optimization of hydraulic performance of radial diffuser multistage pump based on neural network and genetic algorithm is proposed.The optimal combination of the key geometric parameters of overflow parts is discussed.The energy-saving reform and hydraulic performance improvement of radial diffuser multistage pump which provide useful reference for that of the same type or similar pump products are realized.The specific contents of this paper are as follows:(1)The research on internal steady flow characteristic of radial diffuser multistage pumpAccording to the structural characteristic of overflow parts of radial diffuser multistage pump,the governing equations of computational domain of fluid flow and internal fluid flow for MD500-57×3 radial diffuser multistage pump are built by analyzing the characteristics of fluid flow in pump.The solution theory of numerical simulation,mesh generation and optimization and solution strategy of numerical simulation are further determined which lays a foundation to study the structure of internal fluid and flow mechanism of radial diffuser multistage pump deeply.Then,the flow characteristics and rules of flow field in pump are explored after analyzing the flow characteristics of flow field in pump by ANSYS FLUENT software.Research suggests that:? The scientific of solution strategy of numerical simulation and the accuracy of calculation results are verified by comparing the simulation results with the experimental results.?Study on the external characteristics of impellers and radial diffusers at different flow rates indicates that the efficiency of the first stage impeller is the lowest,and the flow loss in the radial radial diffusers at all levels is larger.?The unstable flow phenomena such as secondary flow,reflux of impeller inlet and outlet,whirlpool,jet-wake and interference between dynamic and static components are the key reasons for the flow loss of the pump and the low efficiency of the whole pump.At the same time,the region of unstable flow in the pump is predicted.(2)The research on unsteady pressure fluctuation characteristics of radial diffuser multistage pumpTaking the steady calculation results as the initial value of unsteady calculation,the numerical calculation of unsteady pressure fluctuation characteristics of the flow field for MD500-57*3 three-stage radial diffuser multi-stage pump under different flow conditions were carried out.The unsteady characteristics of the internal flow field in different flow conditions is revealed by analyzing the time-domain and frequency-domain characteristics of the fluid pressure fluctuation in each overcurrent component.It lays a foundation for the following research on internal flow loss of radial diffuser multistage pump.Research suggests that:? The pressure fluctuation period of impellers at different flow rates is the same as the number of impeller blades at all levels through the analysis of the time domain characteristics of pressure fluctuation of impellers and guide vanes.The amplitude of pressure fluctuation coefficient increases gradually and the asymmetric distribution of pressure fluctuation coefficient is also obvious gradually from the impeller inlet to the impeller outlet.The pressure fluctuation of the internal monitoring points of the guide vanes at all levels is mainly affected by the rotation of the impeller at the same stage.?The analysis of frequency domain characteristics of pressure fluctuation in impellers and guide vanes shows that the main frequency of pressure fluctuation coefficients at each monitoring point in impellers is blade frequency of impellers at all levels.From the inlet to outlet of the first impeller,the low frequency signal decreases gradually until disappears,and the high frequency signal increases continuously,while the frequency of pressure fluctuation coefficients in the second and last impellers increases some low frequency signals with the pump stage.With the increase of the number,the low-frequency signal increases gradually,and the pressure fluctuation of the internal monitoring points of the guide vanes at all levels is mainly affected by the rotation of the impeller at the same stage.? Through analyzing the frequency-domain characteristics of pressure fluctuation at the inlet and outlet of impellers under different flow rates,the pressure fluctuation source at the inlet of first stage impeller is mainly the rotation of the first stage impeller,and the pressure fluctuation sources at the inlet of the secondary and last stage impellers are affected by multiple pressure fluctuation sources;The pressure fluctuation source at the outlet of impellers at all levels is mainly the interference of dynamic and static components,which is hardly affected by other pressure fluctuation sources.?The specific frequency range of the broadband fluctuation caused by the unstable flow vortices is revealed according to the study on the relationship between the separated vortices and the fluid pressure fluctuation in the flow passages of impellers,,which indicates that the broadband fluctuation caused by unstable vortices is usually smaller than the blade frequency.(3)The research on entropy production analysis and flow loss of radial diffuser multistage pumpAccording to the computing results of steady and unsteady for MD500-57×3 radial diffuser multistage pump,the position and size of total entropy production and various entropy productions in overflow parts of radial diffuser multistage pump under different flow rate are analyzed by entropy production theory.The generation mechanism and change rules of entropy production in pumps are explored by the combining the feature of static pressure distribution,velocity distribution and streamline distribution of fluid field in the pump at the corresponding position.The size of hydraulic loss of whole flow passage in pump is obtained.The results show that:?The total entropy production of the whole pump unit is the smallest,and the entropy production value of the first impeller,second impeller and last impeller is almost the same at rated flow conditions.The sum of the three accounts for about 77.04%of the total entropy production of the whole pump unit.? With the increasing of pump flow rate,the viscous entropy production caused by viscous dissipation decreases gradually,while the turbulent entropy production caused by turbulent dissipation decreases firstly and then increases.?With the increasing of pump flow rate,the viscous entropy production caused by viscous dissipation in guide vanes at different flow rates increases gradually,and the turbulent entropy production caused by turbulent dissipation also increases gradually.(4)The research on the experiments of hydraulic performance and unsteady pressure fluctuation? The curve of external characteristic of the flow rate-lift and flow-efficiency are obtained by the experiments of hydraulic performance of radial diffuser multistage pump.It shows that the efficiency curve of pumps has a significant downward trend when the pump's flow rate is less than 360m3/h(0.72 times of design conditions).By comparing the steady calculation results with the hydraulic performance test results,the scientificity of the numerical simulation strategy and the accuracy of the calculation results are verified.?By comparing the calculated results of the unsteady value at the outlet of the first stage impeller with the experimental results in time domain and frequency domain,it is shown that the calculation results of the unsteady value are in consisent with the experimental results,and the accuracy and scientificity of the simulated results of the unsteady value are verified.?The time-domain characteristic of lift pulsation is analyzed.The results show that there are no obvious periodic change rules for lift with periodic rotation of impellers under different flow rates,but the quantity of head pulsation of the test pump is larger at low flow rates(the maximum quantity of pulsation is 2.1m).The maximum of the head pulsation for first stage impeller lags behind with the increasing of pumps flow rate in time domain,while the minimum lags ahead with the increasing of pump flow rate of in time domain.?The degree of inhomogeneity of static pressure distribution at outlet of impellers decreases firstly and then increases with the increasing of flow rates by analyzing the static pressure distribution at outlet of impellers.The non-uniformity of static pressure distribution is the lowest near the rated flow rate,and the non-uniformity of static pressure increases obviously under the conditions of small flow rate and large flow rate.?The time domain analysis of pressure fluctuation at the outlet of impellers shows that the pressure fluctuation at the outlet of impellers at all levels is mainly determined by the rotation of impellers and the number of impeller blades.The frequency domain analysis of pressure fluctuation at the outlet of impellers at all levels shows that the maximum value of pressure fluctuation at the outlet of impellers under different flow rates occurs at the axial frequency,and the attenuation of high frequency amplitude of pressure fluctuation is fast.(5)Construction of the design system of the optimization of hydraulic performance based on neural network and genetic algorithmBased on the velocity coefficient method and expert experience,the range of the key geometric parameters of the overflow components is determined.The input layer is the key geometric parameters of overflow parts and output layer is the lift,efficiency and total entropy production for research objects,the corresponding model is established by using genetic algorithm which fitness value is the error of neural network.A BP neural network with 13 neurons in the input layer,10 neurons in the hidden layer and 3 neurons in the output layer was constructed.The prediction model of hydraulic performance of radial diffuser multistage pump based on genetic algorithm and neural network is proposed.The orthogonal experimental schemes for test factors are determined by using the method of orthogonal experimental design and are solved by the calculating method of numerical simulation.After obtaining the space of training samples,the neural network is trained and tested.The index of hydraulic performance of radial diffuser multistage pump is optimized globally for the range of the key geometric parameters of overflow parts.Then,the optimal combination scheme of key geometric parameters of flow passage components is acquired.The test results show that the head increases by 2.4m and the efficiency increases by 3.34%under the design conditions,and the range of high efficiency zone is widened.At the same time,the feasibility and scientific of the optimization design method of hydraulic performance proposed in this paper are also indicated. |
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