| Pump as turbine(PAT)is simple in structure and easy to maintain.It is widely used in residual pressure energy recovery in process industry.Because such a turbine is designed according to the pump working condition,its operation efficiency is generally low.Turbine impeller is the core component of PAT to convert energy,which plays a decisive role in improving the performance of PAT.Therefore,it is of practical significance to carry out the research on the optimization of PAT blade.In view of the main problems faced by PAT blade optimization at present,such as many optimization parameters,strong coupling between parameters,nonlinear relationship between optimization parameters and objective function,by learning from the solution of nonlinear problems and absorbing the advantages of machine learning,a high dimensional hybrid model combining support vector machine(SVM)and high dimensional representation(HDMR)method was proposed to be applied to PAT blade optimization,and the surrogate model optimization of PAT cylindrical blade,double curved blade,twisted blade and double curved twisted blade was completed respectively.A relatively complete optimization,verification,and analysis system of PAT SVM-HDMR surrogate model was constructed.Therefore,the main research contents of this dissertation are as follows:1.The PAT with specific speed of 48 was selected as the research object,according to the specific geometry of cylindrical blade profile,five blade profile control variables were separated after parameterization with Bézier curve.According to the optimization system of PAT SVM-HDMR surrogate model,through the algorithm learning of 120 cylindrical blade PAT hydraulic models,the three-time optimization of cylindrical blade PAT was completed.The results show that the numerical simulation efficiency of PAT is increased by 5.49% and the test efficiency is increased by 5.1%.Through the analysis of the spatial and surface velocity streamline diagram of PAT in each optimization stage,it is found that the improvement of PAT efficiency is mainly due to the disappearance of flow disorder area at the blade outlet.By analyzing the cloud diagram of each term of kinetic energy equation on the selected surface of PAT in each optimization stage,it is found that with the optimization of the blade profile,the transport intensity of the internal energy of the PAT is weakened and the dissipated energy is reduced,indicating the improvement of the energy conversion capacity of the PAT after optimization.2.The cylindrical blade PAT after three optimization was taken as the research object,through the flow analysis of the separation vortex zone at the blade inlet of cylindrical blade PAT,the double curved blade was introduced to solve the separation phenomenon at the blade inlet.After the machine learning of 37 hydraulic models of double curved blade PAT,the optimization of double curved blade profile is completed.The results show that at the design operating point,the efficiency of PAT is increased by 4.96% by blade modification,and the efficiency is increased by 2.05%by blade optimization again.By analyzing the spatial and surface velocity streamline diagram of the PAT at each stage of blade modification and optimization,it is found that the improvement of the efficiency of the PAT is mainly due to the disappearance of the separation vortex zone at the blade inlet,and the improvement of the efficiency of the PAT is mainly due to the disappearance of the cross disorder of the velocity streamline in the first passage of the impeller and the improvement of the uneven velocity distribution at the blade outlet.By analyzing the distribution of vorticity intensity and vortex structure before and after blade modification and optimization,it is found that with the progress of blade modification and optimization,the high intensity region of the overall vorticity intensity distribution in the impeller dwindles and the intensity decreases;The strength and area of vortex structure in the impeller blade area are reduced and shrunk to a certain extent,while the tailrace vortex is gradually enhanced.3.The PAT with specific speed of 93 was selected as the research object,according to the drawing principle of twisted blade,the plane blade profile of twisted blade was redrawn with the blade wrap angle as the independent variable,so as to meet the conditions of rapid blade modeling,combined with the surrogate model optimization system of two-dimensional blade profile,and taking 105 twisted blade PAT hydraulic models as training samples,the surrogate model optimization of twisted blade was completed.The results show that at the optimal operating point,the numerical simulation efficiency of PAT is increased by 3.51% and the test efficiency is increased by 3.4%.By analyzing the surface streamline diagram of the PAT at each stage of optimization,it is found that the improvement of the efficiency of the PAT is mainly due to the improvement of the liquid flow uniformity and order at the blade outlet.By analyzing the 2-norm numerical distribution cloud diagram of the vorticity dynamic equation on the selected surface of the PAT in each stage of optimization,it is found that with the progress of optimization,the distribution intensity is weakened and the distribution area is reduced,indicating that the velocity gradient distribution intensity of the internal flow field of the impeller is weakened,the energy consumption is decreasing,and the energy conversion efficiency of the impeller is increasing.4.Based on the modification idea of double curved blade and the drawing principle of twisted blade,the double curved twisted blade was introduced.After the algorithm learning of 52 PAT hydraulic models,the surrogate model optimization of double curved twisted blade was completed.The results show that at the design operating point,the efficiency of PAT is increased by 0.4% by blade modification,and the efficiency of PAT is increased by 0.65% by blade optimization.By analyzing the velocity streamline diagram of the selected surface of the PAT,it is found that after modification and optimization,the improvement of the liquid flow uniformity at the blade outlet will improve the efficiency of the PAT to a certain extent.At the same time,the formation and expansion of the vortex zone at the blade inlet offset some of the improvement of the performance of the PAT.By analyzing the distribution cloud diagram of turbulent kinetic energy related terms on the selected surface of PAT in each stage of modification and optimization,it is found that the distribution areas of turbulent viscosity,turbulent dissipation rate and turbulent kinetic energy are very different before and after blade modification,but the distribution intensity area has not been significantly reduced.5.Taking the results of each stage of cylindrical blade PAT optimization as an example,the unity of fluid kinetic energy equation,vorticity intensity distribution characteristics of flow field,determination and distribution of vorticity,vorticity dynamic equation and turbulent kinetic energy transport equation were studied and analyzed from the dissipation term of fluid kinetic energy equation,enstrophy equation and turbulent time average kinetic energy equation. |
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