| Turbine blade is the component with the highest temperature,the most severe load changes and the most complex stress,which make it an important component that affects the overall performance and span life of aero-engines.However,the design of traditional turbine blade still starts from designing and manufacturing prototypes with one-dimensional empirical formulas,which usually go through several cycles of designing and manufacturing samples based on one-dimensional empirical formulas,finding problems through experiments,modifying the design and remanufacturing samples,and re-testing samples to find problems.Most of the one-dimensional empirical formulas obtained from simplified experimental conditions.For example,the empirical formulas of heat transfer in the ribbed channel are obtained through experiments under the assumption of isothermal boundary condition,and the channel shape simplified to rectangle,triangle or trapezoid.Obviously,this low design starting point,which is far from the real channel shape and turbine operating conditions,seriously drags down the development and design speed of the aero-engines.To meet rapidly improving aero-engine performance requirements of army and improve the design speed and accuracy of air-cooled structure of turbine components,the design based on the one-dimensional empirical formula has been moved to a quasithree-dimensional design that is closer to the real geometry and operating conditions.This research group has formulated the modular design of cooling structure of turbine components,and the cooling structures are dividing into four parts:leading edge,blade middle portion,trailing edge and end-wall.It is expected that through the experimental research of the four cooling modules,the scientific problems exposed in engine design will be condensed,the mathematical model and numerical strategy will be verified,and the module design will be improved and optimized under real operating environment of the cascade provided by the engineering application department.This dissertation mainly involves two cooling modules:internal cooling of blade middle portion and film cooling of turbine end-wall.Although internal cooling of blade middle portion and film cooling of turbine endwall are not new research topics,there are still many unsolved problems existing in the process of various experimental and numerical studies.For example,most of the previous ribbed channel designs came from a simplified geometric model and a given experimental condition of constant temperature/heat flux.However,the research on the cooling effect of the real geometric model under the real turbine operating conditions is still lacking.Another example:Most of the previous research on enhanced cooling technology focused on cooling efficiency and resistance characteristics.But while setting ribs to improve the internal cooling effect,the reduction of channel resistance loss and coolant consumption,and the multi-objective design of minimizing temperature gradient still need to focus on.In this dissertation,experiment and numerical simulations are used to study the heat transfer and flow characteristics of the ribbed channels,and the core purpose is to analyze the effect of geometry simplification and boundary simplification on the results.Then,this work selects a multi-objective optimization method to optimize the important geometric parameters in the cooling structure,and finally obtains an excellent cooling design scheme.The main work and conclusions of this dissertation are as follow:(1)The effect of the divergent/convergent cross-sectional shape of the ribbed channel on the flow and heat transfer characteristics is studied.The infrared thermography method is used to measure the heat transfer coefficient on the ribbed wall of the convergent channel,and the measured data are selected to verify various numerical turbulence models.Finally,numerical simulations with the reliable turbulence model are carried out to compare and analyze the flow and heat transfer characteristics of divergent/convergent/straight channels.The numerical results show that,under the low Re number condition,the convergent cross-sectional shape can significantly affect the distribution of the secondary flow in the channel,and cause the heat transfer distribution of the convergent channel to be different from the other two channels.(2)The effects of real channel shape and real turbine operating boundary conditions on the channel performance are analyzed.Firstly,the numerical simulations find that the heat transfer coefficient distributions on the channel ribbed walls obtained by the coupled wall boundary condition are far away from the results of the simplified constant temperature/heat flux conditions.Then,the differences in the heat transfer distribution of the real ribbed channel and the simplified square channel are also obvious.Finally,in the real channel,the blade rotation significantly improve the heat transfer coefficient on the trailing surface at the joint region between the inlet pass and bend region.With the increase of rotation number,the heat transfer coefficient of the joint region increases by more than 100%.(3)The multi-objective optimization algorithm is selected to optimize the heat transfer and flow characteristics of the semi-attached ribbed channel.The results show that the heat transfer coefficient of the optimized model is increased by 9%,and the friction factor is reduced by 7%.And,it can be seen that the optimal model greatly improves the heat transfer coefficient of the middle area of the channel wall by sacrificing a small part of the heat transfer coefficient of the channel right sidewall.(4)The multi-objective optimization algorithm is used to optimize the arrangement of the discrete film cooling holes on a high-pressure turbine end-wall.The results show that,compared with the original film hole arrangement,the area-averaged overall cooling effectiveness of the end-wall of the optimal model is increased by about 8.7%-9.5%,the total pressure loss is reduced by about 4.8%-6.1%.Meanwhile,it can be found that the spacing of the adjacent film holes near the pressure side has a great influence on the area-averaged overall cooling effectiveness of the end-wall,while the compound angle of the film holes near the leading edge has a great influence on the total pressure loss of the turbine cascade.(5)The construction and operation of two optimization platforms(Ansys Workbench and Isight)are completed innovatively,and the application of the above two optimization platforms in the design of turbine cooling structures is realized. |
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