| Gas turbine is closely related to the national energy industry and aviation industry.In order to improve its performance,the bearing temperature of turbine blades should be increased.How to reasonably conduct the blade heat transfer calculation is one of the key problems in the design work of gas turbine.Advanced cooling structure can take maximum extent use of cooling air.In the precondition of gas turbine thermal efficiency and power output,composite cooling structure collocated by many heat transfer components,distributes cooling air to the required protection part,and integrates various cooling technologies to generate the relatively global optimum cooling effect.With the development of computer science and fluid dynamics simulation technology,many organizations invest in human and material resources to the modeling and numerical simulation of composite cooling structures.In order to reflect the working fluid flow parameters distribution in turbine blade cooling passages,and to to guide cooling structure design,this thesis studys from the one-dimensional flow principle,and develops a network algorithm which is suitable to calculate the cooling flow path.The solving part compused in this thesis covers a lot of flow resistance and heat transfer characteristics of the heat exchanger element calculations,temperature and pressure solving process alternately.Combing with the pre-treatment procedure for constructing pipeline network model,this thesis proposes a unique solution.By taking use of U-shape ribbed channel heat transfer test in reference literature,verificaition for the feasibility of pipeling network program has been conducted.The acquired average parameters for each segment have the same trend with test results.Based on this,the outflow field calculation procedure has been invoked in.Blade wall surface is divided into horizontal and vertical units.Through each unit's interface the contaction of internal and external flow field is established,and the coupling algorithm is made up.This thesis selects C3 X blade heat transfer test to verify coupling algorithm's validity.The validation has showed that blade temperature and heat transfer coefficient both have substantially uniform distribution trends with test measured value,and the emergence region of maximum temperature in line with expectations.In comparison with commercial software CFX simulation results,it can be seen that the pipeline network coupling procedure can reliably obtain the cooling effect of air-cooled blade,and the position need thermal protection can be accurately estimated.However,the computation time and the computer hardware resources consumption are much less than CFX.The parametric modeling principle is introduced to compile a program for the geometry updating of complex cooling structure.Combining with the rapid estimation feature of pipeline network coupling method for cooling structure heat transfer,the data transfer of parametric modeling and pre/post processing module is uniformlly allocated,thus to build the HIT3D-Coolnet design platform which can be deployed in scheme design and concrete structure design.On the basis of C3 X airfoil,the composite cooling structure of impingement hole-double wall-film hole is designed.To explore which kind of framework is appropriate to this composite cooling,in this thesis the scheme design in the computing platform based on pipeline network coupling is used to several cooling schemes of different intake and outflow modes.The network coupling program has calculated the internal flow field,temperature field of these schemes.Through the comparison of blade wall temperature distribution contours and temperature values,it get known that the second kind of double wall cooling scheme has lowest average temperature and its cooling effect is relatively good,so set it as the primary scheme.The cooling effect of surface wall position corresponding to suction side double-wall narrow channel is very significant.Especially in the nearby of film hole outlets,the lowest temperature of whole blade wall appears in.Detailed three-dimensional simulation results by CFX show that,the diffusion flow of impact jet forms flattened oval swirls in narrow cavity.High rotation cooling air orbiting makes the heat of cavity inner wall taken away quickly.The adherent stream around cavity wall is returned to the swirl core zone by entrainment,where arises dramatic heat exchange.While behind suction side film holes,vortex structures are also been developed.The heat absorbed from cavity wall passes to the upstream through winding,and it is brought to blade outside by orifice outflow,so that the cavity maintains relatively lower temperature.However,this scheme still exists issues of gas intrusion,high local temperature and relatively greater temperature gradient in rear segment of pressure surface.So according to the analysis of temperature field and inner flow field,a few improvement measures are taken to refine the scheme design.Retrofit design makes up the deficiencies of the primary scheme,plays the cooling performance of double-walled composite structure on both blade sides.Pressure side film holes smoothly effuse out the cooling airflow,make the film protection extended to rear area of this side,significantly reducing the local temperature of blade tail.To explore the application of pipeline network coupling algorithm in engineering,a certain type of high pressure rotor blade with internal composite cooling structure is selected to do simulation calculation.The modified structure based on prototype has increased the lower elbow's radius,and added in through holes between the rear channels.By parametric modeling methods,the blade cavity is reconstructed by the adjustable and fast updating geometric modeling module in HIT3D-Coolnet design platform.The rib height and inclination angle of the ribbed channel,the impingement hole diameter and impinging distance of impingement cooling,film cooling aperture,etc,set as characteristic parameters of the heat exchange components to control the accurate construction of internal air cooling structure.Compared with the prototype of high pressure rotor blade,elbow's improvement has made the local high temperature of rear blade root significantly weakened.Combining with through holes,the high temperature area of blade rear part has constricted backward.Through holes bring the horizontal supplemental airflow to trailing edge channel,which effuses via the tail slits,enhances the local heat transfer effect of slot outlet.The design platform based on pipeline network coupling method provides the interface to connect iSiGHT-FD,the latter calls all modules on this platform to build an automatic optimization process.For the high pressure rotor blade composite internal cooling structure,the MIGA optimization algorithm is applied to search the parameters combination in the multi dimension design space,thus to optimize the details of cooling structure.After optimization,the average blade wall temperature is decreased significantly.CFX simulation confirms the improvement effect.Design ideas and computational analysis methods in this thesis have guidance significance for advanced new air-cooled turbine blade design and development. |
PDF Full Text Request