| The design of elbow-shaped inlet pipe of the inline pump is more complicated,which usually results in serious flow distortions and causes serious hydraulic loss,and reduce the performance of the inline pump.Therefore,the study of the influence of flow distortion on the performance of vertical inline pump provides a theoretical basis for the forward design and shows a great academic significance.Aiming at the problem of the flow distortion of the inline pump,the design parameters of the inline pump are analyzed and studied,and the components of the inline pump are optimized,which is beneficial to improve the working stability and has good engineering value and economic value.This study was supported by the National Natural Science Foundation of China(Grant No.51976079),the China Postdoctoral Science Foundation(Grant No.2019M661745)and the Jiangsu Province Industry-University-Research Cooperation Project(Grant No.BY2019059).In this study,a vertical inline pump with the specific speed of 132 was selected for research.The difference between the SST turbulence model and the DES turbulence model in simulating the inlet flow distortion of the pipe pump is explored,and the advantages of the DES method in simulating the flow distortion of the inline pump are revealed.Finally,the curved inlet pipe and the impeller of the original inline pump are parameterized,and the influence of different decision variables on the performance and internal flow stability of the pipeline pump is studied through correlation analysis.The combination optimization design of the inlet pipe and impeller of the pipeline pump is carried out based on multi-objective particle swarm optimization algorithm and artificial neural network.The main contents and achievements of this paper are as follows:(1)Summarized the current situation of flow distortion,internal flow analysis method based on DES turbulence model and optimization theories,expounded some existing problems;A multi-function test rig of the inline pump was built to test the variation law of external characteristics under different working conditions of the inline pump,and the dimensionless treatment on the test results was adopted.It was found that the characteristic test results showed as good agreement with the computational results.(2)The internal flow of the model pump with different inlet pipe schemes is numerically simulated,and the degree of reflux and velocity inhomogeneity of the straight pipe and the curved pipe under part-load conditions were compared,it can be found that the velocity distribution of the straight pipe under different working conditions is more uniform.Under the small flow conditions,the backflow zone in the curved pipe is larger,the channel blockage is more serious,and the flow distortion is greater.It can be concluded that the reflux in the straight pipe is mainly caused by the overflow of the rotating fluid in the impeller,while the backflow in the inline pump is mainly caused by the elbow inlet pipe.(3)Through the distribution of vortex mass,axial velocity curve of impeller and velocity streamline distribution of inlet channel in the inline pump based on Q criterion,it can be found that the calculation results based on DES model can capture more details of flow field and the calculation results are more accurate under the same grid number;(4)Under different working conditions,the flow distortion in the inlet channel of the inline pump is found in different degrees,and the inlet flow of the impeller of the inline pump is very uneven.Under the part-load condition,the flow distortion of the inlet section of the impeller is mainly reflux,the flow distortion in the inlet pipe is mainly the reflux on the upper side of the second bend,and the flow separation phenomenon in a small range also appears on the lower side of the first bend,but the strength and influence area of the reflux vortex are much larger than the separation vortex;under the nominal condition and the overload conditions,the flow distortion of the inlet flow of the pipeline pump is mainly the flow separation caused by the secondary flow.(5)On the one hand,the inlet flow distortion of the inline pump leads to the deterioration of the flow state of the upper and lower sides of the second bend and the lower side of the first bend,thus affecting the performance of the pump;on the other hand,the inlet flow distortion makes the bottom flow channel of the inlet pipe not fully utilized,so the geometric design of the inlet pipe needs to be optimized and improved.(6)Based on the entropy production theory of the second law of thermodynamics,the internal flow losses of the inline pump under different working conditions is qualitatively analyzed.It is found that the hydraulic losses of the inline pump is mainly related to the entropy production caused by turbulent flow,but the direct energy dissipation caused by viscous force is small,which can be ignored for the performance.Under the design flow rate,the internal energy dissipation of the inlet bend is the smallest,and the energy dissipation in the inlet bend under the small flow rate is larger.The energy dissipation inside the inlet bend is 17.1 times higher than the design flow under 0.6 times design flow condition.the internal energy dissipation distribution is not symmetrical,and the positions of the high dissipation areas are all concentrated on the side close to the interlaced tongue.the interior of these high dissipation areas generally has the effect of obvious vortex or reflux,which leads to the increase of flow loss.(7)Using the Latin Hypercube sampling method,300 sets of samples of decision variables were generated,and the performance parameters and internal flow parameters corresponding to these 300 sets of decision variables were obtained by using the automatic numerical analysis script.The influence of design variables on the flow and performance parameters was studied by correlation analysis.It showed that the performance is mainly related to the blade placement angle and the blade number,while the stability of the internal flow is mainly related to the external shape and blade shape of the inlet bend.Increasing the transverse length of the inlet bend and decreasing the curvature of each bend have positive effects on the stability of the internal flow.For the blade shape,it is necessary to select the appropriate placement angle and blade number according to the required design requirements to balance the pump performance and stability;(8)According to the correlation conclusions,the dimensionality of decision variables is reduced,and the inline pump is optimized by combining artificial neural network and multi-objective particle swarm optimization.the optimization process shows that for different designs,the efficiency under large flow rate remained stable when the performance of the inline pump under small flow rate and design flow rate is not too prominent;the optimized pipeline pump design has a significant performance improvement relative to the original model,and the efficiency improvement under 0.5 times design and design conditions has reached 9.65% and 7.95%. |
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