Investigation On Flow Mechanism And Optimal Design Methods Of An Axial Turbine Exhaust Volute

Gas turbine engine is widely used in the field of transportation and modern industry.As one of the most important component in the exhaust system,the exhaust volute's aerodynamic performance has a great influence on the work efficiency of turbine and the performance of downstream components indirectly.Hence,it is pretty important for saving energy and reducing emissions to explore the optimal design method which can decrease the flow loss in the exhaust volute.In this article,a non-axisymmetric exhaust volute that had been used in engineering practice was chosen as a research target.Meanwhile,its inner flow characteristics and main source of flow losses were revealed through numerical simulation.In order to reduce the flow losses in the exhaust volute,some different kinds of profile optimal design methods were researched,and an integrated optimal platform was established to further improve the aerodynamic performance.The main research work of this article contains several different parts as follows:(1)The flow characteristics of original exhaust volute were numerically researched.In this part,the geometry of the exhaust volute was introduced,and the mesh topology of it was created.After that,the effectiveness of the numerical methods was checked.By analyzing the inner flow mechanisms,the main source of flow losses was revealed.The results show that the aerodynamic performance of original exhaust volute is pretty bad,and its flow losses mainly come from the low-speed flow in the mixing area,the swirling flow in the exhaust hood,the mixing action among the flow in the exhaust passage and the flow separation in the diffusing structure.(2)Different kinds of optimal design methods were explored.By analyzing the geometric structure and flow field of the exhaust volute,it was validated that the research target had the space to optimize,and three different optimal ways were designed to get the exhaust volute a better performance.The results of numerical simulation show that twist line design,spiral line design and inner separated layer design can all improve the aerodynamic performance of the exhaust volute.The total pressure loss coefficient is decreased,and the static pressure recovery coefficient is raised.Relatively speaking,the effectiveness of the spiral line design is the most apparent,but it also increases the radial size of exhaust hood.So,under the condition of strictly limited dimensions,inner separated layer design can be an effective way of reducing the flow loss in the exhaust hood,as well as being benefit to the turbine work.(3)An integrated optimal system was established.In order to give a further and detailed optimization to the exhaust volute,a platform was built which was based on the integrated function of Isight.In the optimal system,the total pressure loss coefficient was treated as the optimal target.The numerical result shows that the performance of optimal exhaust volute is improved,it can get a much more uniform outlet flow field,with the area of low-speed and high-speed flow being relatively reduced and secondary flow being much weaken.(4)The analysis about the interaction between turbine and exhaust volute was given.The flow field of the exhaust volute with last stage turbine was calculated,and Fourier analysis was carried out based on the results of full channel unsteady calculation.Finally,the mechanism of interaction between two components was stated.It shows that the influence from the non-axisymmetric back pressure distribution imposed by the exhaust volute on the turbine blades is much stronger than that of the interaction between the rotor and stator.