Numerical Study On Complex Flow In The Inlet And Outlet Of Ultra-Supercritical Steam Turbines

The development of ultra-supercritical steam turbine has high demands on internal flow and stability.The import and export flow of turbine is very complex,which has great influence on the performance and safety of the turbine.High-pressure inlet chamber is an important component,which receives the high-temperature and high-pressure steam from the boiler.The flow direction of steam is transferred from radial flow to axial flow and then the steam is discharged to promote impeller work.the internal flow conditions and the capacity of circumferential uniformity seriously affects the inlet conditions of the blades as well as the workability.Low-pressure last stage exhaust system is to guide the steam which is discharged from the low-pressure last-stage blade to the condensing device.The length of last-stage blade is longer,and the exhaust chamber has a large volume capacity,when in alternating conditions it is easy to produce vibration and aerodynamic noise and other issues,seriously affecting the operation of the unit stability and security.Therefore,in this paper,high-pressure inlet chamber and low-pressure last-stage exhaust system are selected as the research object,and the complex flow is analyzed by numerical simulation.This research has important value in engineering application.In this paper,the internal flow characteristics of high pressure inlet chamber are analyzed by numerical calculation,and the influence of key geometric parameters on the performance of the high pressure inlet chamber is analyzed.In order to improve the aerodynamic performance of the chamber,the aerodynamic optimization of the chamber structure was carried out by using the optimization algorithm based on the Kriging model.Secondly,the unsteady numerical calculation is used to simulate the low-pressure last-stage exhaust system under special operating conditions.Combined with the flow field and the aerodynamic parameters obtained by setting the calculated monitoring points,spectral analysis is carried out to determine the rotation instability and then to get the characteristics of the relevant frequency and distribution.The relationship between eigen frequency and circumferential mode is further studied by using the dynamic mode decomposition method.The content of this paper is as follows:1.The numerical simulation is used to calculate the internal flow of the high pressure inlet chamber of the ultra-supercritical steam turbine,and the geometrical parameters which seriously affect the flow performance are found on the basis of obtaining the overall aerodynamic performance and internal flow characteristics.Geometric parameters on the aerodynamic performance of the chamber were compared.2.A simple and accurate optimization method is proposed,and an aerodynamic optimization platform is built in MATLAB.Combining the influence of the geometrical parameters on the chamber performance,the improved chamber structure is proposed.The chamber structure is optimized according to the corresponding objective function.The optimized chamber flow performance is compared with the prototype,to verify the effectiveness of its optimization.3.Unsteady numerical study is used to the low-pressure last stage exhaust system of the steam turbine in the special working conditions,the whole performance and the flow field characteristics are obtained,and the frequency spectrum is obtained according to the monitoring point data.The unsteady flow field is analyzed,the source of the disturbance and the structure of the flow field are analyzed.The unsteady flow field is used to analyze the flow instability structure of the flow field and obtain the information of the characteristic frequency and the circumferential propagation velocity.4.The DMD method is used to decompose the unsteady flow field information and to obtain the characteristic flow field corresponding to the disturbance frequency,further verify the relationship between the disturbance frequency and the flow field structure,and verify the DMD method for the analysis of flow rotation instability feasibility.