| The operating efficiency of turbomachinery mainly depends on the flow loss caused by complicated flows in the blade passages,such as separation,leakage,and secondary flow.In recent years,the formation mechanism of loss and the corresponding flow control has been a hot issue in this field.Benefit from the development of modern testing and numerical technology,it is not difficult to obtain the refined flow structure in the impeller,but how to evaluate the flow loss and its distribution law accurately has become the key to the design and optimization of turbomachinery.Supported by the national key research and development program,a flow loss calculation method based on entropy generation theory was established in this study,and a multi-parameter and multi-objective optimizer was also constructed.Then the numerical optimizations and experiments are carried out on the shape of airfoils and fan blades.The main work is as follows:1.According to the assumptions of turbulent kinetic energy transport and eddy-viscosity,a direct calculation model and analysis method for entropy generation under turbulent flow are constructed and then verified by three typical flows.Based on the numerical calculation of the entropy,a calculation method of airfoil drag using entropy generation integral was developed,and the feasibility and accuracy are verified through theoretical analysis and numerical examples.The results show that the entropy generation mid-field integration method depends less on the mesh quality than the near-field and the wake far-field integration method.The spurious drag is also decomposed,which is beneficial to the calculation accuracy of the airfoil drag force.The results show that turbulent dissipation is primarily responsible for flow losses of the flow state in a high Reynolds number,and the turbulent dissipation loss reaches 90% when the airfoil stalls.2.The entropy generation loss model for turbomachinery was improved and successfully applied to flow loss analysis of low-pressure fan impeller and high-pressure compressor rotor under different working conditions.Different from process metrics such as total pressure loss coefficient,the entropy generation loss model can not only accurately quantify the loss in any region by integrating the entropy generation,but also effectively locate the high loss area in the three-dimensional flow field by calculating the local entropy generation ratio.It is shown that the flow loss in a low-pressure fan is dominated by the corner separation and the leakage flow;the loss at the blade tip region reaches 56.5%under the near-stall condition.However,the high loss in a transonic compressor under near-choke conditions is mainly caused by corner separations,and the flow loss at the blade root accounts for 29.5% of the total.As the flow rate decreases,the flow loss at the blade tip increases significantly to 40.7% under near-stall conditions.3.An aerodynamic optimization platform for the fan blade was built by coupling parameterized modeling,rapid mesh generation,and a parallel genetic algorithm.Taking the minimum entropy generation as the optimization object,the effects of shape parameters on airfoil lift-drag,shock wave position,and cascade performance was explored.The entropy generation is successfully applied in the multi-variable,large-space,three-dimensional optimization of a low-pressure axial fan,and the factors dominant the flow loss of the fan was also concluded.The total pressure of the two optimized fans with low-entropy generation increased by 42.6% and 61.7%,respectively.The corresponding improvement of their total pressure efficiency is increased by 3.9% and 3.0%.Based on entropy generation theory,in-depth aerodynamic optimization and experimental research on blade profiles were carried out in the present dissertation.The flow loss distribution characteristics and the dominant factor were accurately obtained,which provides internal references for turbomachinery in flow loss reduction and performance improvement. |
PDF Full Text Request