Numerical Simulation Of Flow In A Mixed-flow Pump With Guide Vanes Under Variable Working Conditions And Robust Optimization Design

As a kind of pump type which combines the advantages of centrifugal pump and axial flow pump,mixed flow pump has the advantages of large range of head and wide range of high efficiency and so on.It has a good application prospect.However,for its blade design,a set of mature and perfect design guidelines have not yet been formed.And in the existing optimization design of the mixed flow pump,the most important is the deterministic single-point optimization,and the second is the multi-points optimization.All of them do not consider the influence of uncertain factors such as random fluctuation of the working conditions,making the traditional results are optimal only under a certain discrete operating point.When the working conditions change randomly,the performance of pumps will deteriorate rapidly,which will not meet the requirements of stability and energy saving.Therefore,based on the shortcomings,it is of great significance to establish a new optimization mathematical model and carry out the optimization design of mixed-flow pump,which takes the uncertain factors into account,so as to get closer to the actual robust optimal solution.In this paper,a guide vane mixed-flow pump with a specific speed of 520.17 in a pump enterprise in Shanghai is taken as the research object,and a new robust optimization method is carried out for it.The main research work and conclusions are as follows:1.Numerical simulation of flow field in the original guide vane mixed-flow pump under variable conditions.Firstly,according to the structural parameters of the designed mixed-flow pump,a three-dimensional modeling,structural mesh generation and grid independence test were carried out.Secondly,based on the CFD calculation and the experimental data,the comparison and selection of three turbulence models were completed.Finally,based on the above established numerical simulation method,the flow field characteristics of the pump in the condition of 0.8Q_N,1.0Q_N,1.2Q_N and 1.4Q_N were compared and analyzed.The results show that when the pump runs off the best operating point,the change of the working condition parameters will aggravate the bad flow in the pump,cause the unsteady flow of the fluid in the pump and the greater energy loss.Besides,it will also reduce the performance of the pump and meanwhile show the extreme instability.2.The establishment and experimental verification of robust optimization mathematical model.Firstly,on the basis of the introduction of the concept of robust optimization and robustness,a new method of robustness evaluation was proposed and its definition was mathematically described.Secondly,a robust optimization mathematical model was established for uncertain stochastic fluctuations of working conditions in a certain interval.In order to infinitely approximate the robust optimization index,the optimization problem was decomposed into the robust and the optimal sub optimization problems in the modeling process.Meanwhile,the uncertainty analysis was also carried out.Finally,based on the mathematical model of the robust optimization,the shape of the 791 airfoil was optimized,and the numerical simulation and the PIV experiment of the water tunnel were,respectively,carried out to verify the optimization results.The results show that the numerical simulation results are in good agreement with the experimental results.Then,it can be concluded that the optimization results are correct,and the robust optimization mathematical model is also reasonable and reliable.3.The establishment of surrogate model between optimization objectives and optimization variables in the robust optimization design of mixed-flow pump's impeller.Firstly,based on the two element design theory of blade,three parameters in a dimensionless four polynomial polynomial were selected as the optimization variables to indirectly control the shape of the blade.Secondly,the above established robust optimization mathematical model was applied to the optimization design of the mixed-flow pump's impeller,and the objectives was determined.Then,combining the uniform test design method,CFD calculation and uncertainty analysis,three kinds of surrogate model between the objectives and the variables were constructed.Based on the evaluation criteria of the model prediction effect,the prediction ability of these three models was compared.The results show that the RSM proxy model has better prediction accuracy and can be used as the fitness evaluation function in the following optimization operation.4.The multi-objective genetic algorithm calculation in the robust optimization design of mixed-flow pump's impeller.Firstly,based on the introduction of multi-objective optimization and multi-objective genetic algorithm,the concrete flow chart of robust optimization was constructed.Secondly,the RSM proxy model with multi-objective genetic algorithm was combined,and the robust-optimal solution in the feasible solution space was found based on the MATLAB platform.Finally,the performance of the mixed flow pump before and after the optimization was compared.The results show that the robust optimization mathematical model constructed in this paper also has good optimization results for mixed-flow pumps running in uncertain environments.Besides,it can simultaneously improve the optimality and stability of the hydraulic performance and the internal flow field of the pump during variable operation conditions.Meanwhile,the degree of influence that is affected by the change of the working conditions is also reduced.