Research On Conjugate Heat Transfer Simulation And Turbine Vane Cooling Structure Optimization With Bem

Aircraft engine technology has become an important indicator for measuringthe science and technology level and comprehensive national strength. So manystates begin to carry out the aircraft engine's high-tech research. With thedevelopment of aviation industry, the engine is made a higher demand. It needs tohave a higher thrust-weight ratio, a greater output power per unit volume, a lowerfuel consumption and a better reliability. Increasing turbine inlet gas temperature isan effective way to improve engine performance. However, turbine inlettemperature increased much faster than the blade material heat resistance rate ofdevelopment. So the efficient cooling technology and thermal protection measuresmust be adopted for ensuring turbine safety and reliability work. The accurateprediction of the turbines thermal environment can effectively guide the researcherto design turbine blade cooling structure, to improve cooling efficiency and extendthe working life of turbine. The purpose this study is to set up a numericalsimulation platform of air-cooled turbine conjugate heat transfer calculation withindependent intellectual property rights. The numerical simulation platform is basedon the fluid solver of Propulsion Theory and Technology Institute of HarbinInstitute of Technology. In addition, this paper researches detailedly the effect ofturbulence models, turbulence characteristics conditions of cooling channelentrance and heat transfer coefficient experimental criteria on the conjugate heattransfer results. Using the Boundary Element Method (BEM)/Finite DifferenceMethod (FDM) conjugate heat transfer solver, this paper sets up the full conjugateoptimization design system for air-cooled turbine vane cooling structure.Firstly, the BEM theory was study deep and then the controlling equations of2D and 3D BEM solving the potential function were deduced detailedly. The paperset up the BEM mathematical model for the solution of the solid regional heatconduction problem and compiled the 2D and 3D boundary element programs. Theprogram verification work was finished with the analytical and numerical solutions.The results showed that the BEM is that no volumetric grid is required inside thesolid, so it saves the numerical simulation pre-processing time and computation time. At the same time, the analytical and discrete combination characteristics makethe BEM get the accurate results and higher accuracy. The research results of BEMadaptation of the grid showed that the BEM has little dependence on the gridquality.The BEM was applied to the conjugate heat transfer analysis of gas turbinevane and a numerical simulation platform of air-cooled turbine conjugate heattransfer calculation was set up. The conjugate heat transfer numerical simulationplatform was employed to simulate the two different typical flow characteristicsexperimental conditions of NASA-MarkII turbine guide vane. The calculationresults showed that three-dimensional conjugate heat transfer solver can simulateaccurately different flow characteristics of turbine vane. The temperaturedistribution results showed that within flow boundary layer of turbine blade surfacethe temperature gradient is great and heat transfer course is severe. The complicatedflow characteristics make the 3D conjugate heat transfer solver which adopted theB-L algebraic model has a little error for the calculation of turbine vane heattransfer characteristics.Secondly, computational fluid dynamics software Fluent and CFX wereemployed to simulate the same experimental turbine vane with the conjugate heattransfer method. The paper finished the grid adaptation research of conjugate heattransfer calculation and cooling channel inlet turbulence characteristics conditionsresearch. In addition, the paper researched the effect of turbulence models on theflow, heat transfer and thermal stress characteristics for the turbine vane with theflow separation characteristics. The results showed that the flow characteristicsresult has little dependence on the flow boundary layer grid and has lower demandfor the grid quality. However, the grid quality has some effect on heat transfercharacteristics results. The main factors are the flow boundary layer thickness andthe grid refinement along flow direction. For internal flow of turbine blade coolingchannels or cooling holes, the turbulence intensity at the inlets is totally dependenton the upstream history of the flow. So the inlet turbulence characteristics have agreat effect on the flow development and conjugate heat transfer results of air-cooled turbine vane. CFX provides the K- -SST- - turbulence model whichconsiders the transition flow characteristics. The results showed that K- -SST- - turbulence models can exactly simulate the laminar flow and transition flow status and can predict accurately flow and heat transfer characteristics of turbinevane. But k- -SST- - turbulence model overestimates the turbulence kineticenergy of blade local region and makes the heat transfer coefficient higher. It causesthat local region temperature is higher. The 3D conjugate heat transfer solveradopted the B-L algebraic model. The calculation results of B-L algebra turbulencemodel showed that B-L model can simulate accurately turbine vane thermalenvironment without flow separation or with small flow separation. The results ofB-L model are more accurate than K- -SST- - turbulence model besides it hasa little temperature error in the suction side transition region. Simultaneously,turbine blade thermal stress results showed that the temperature distribution resulthas a great effect on the prediction of turbine blade thermal stress and life cycle,which can guide effectively the researcher to design the cooling structure of turbineblade.In addition, heat transfer coefficient experimental criteria were applied to theconjugate heat transfer calculation of air-cooled turbine vane. Heat transfercoefficient experimental criteria consider the correction coefficient which based onthe different geometry and work conditions of air-cooled turbine vane inner-coolingchannels. The paper analyzed the effect of different heat transfer coefficientexperimental criteria on conjugate heat transfer calculation results. At the same time,the paper also analyzed the prediction ability of the different turbulence models forturbine flow and heat transfer course when the air-cooled turbine vane inner-cooling channels adopted and not adopted the heat transfer coefficient experimentalcriteria. The results showed that the conjugate heat transfer calculation of turbineblade cooling channels or cooling holes which adopted the heat transfer coefficientexperimental criteria can get the accurate turbine flow field and temperature fielddistribution. This method avoids the solution process of turbine vane coolingchannels and makes the different turbulence models simulate single the turbinecascade main flow region. Thus this method avoids the accumulative error of multi-zone flow field calculation and saves the calculation time.Finally, using conjugate heat transfer solver, this paper set up the fullconjugate optimization design system for air-cooled turbine vane cooling structure.The analysis involved the optimization of location, size and coolant mass flow often internal cooling passages of NASA-MarkII air-cooled turbine vane. The optimization objectives included the maximum temperature, the averagetemperature and coolant mass flow. In order to meet the optimal solution, multi-objective function was transformed into a single objective function through a formof weighted sum of particular criteria. Owe to the BEM which was employed tosolve the solid region heat transfer problem, the full conjugate optimizationcalculation time was saved. In the optimization process the BEM avoided therepeated generation and calculation work of solid region grid. At the same time, itavoided the Interpolation error between solid region grid and fluid region grid andimproved the optimize efficiency and solution accuracy. The optimization resultsshowed that the full conjugate optimization calculation decreased the maximumtemperature and saved the coolant mass flow. The average temperature increased,but the amplitude was very small. In addition, optimization calculation decreasedthe effect of entrance on cooling channels heat transfer and reduced radialtemperature gradient of turbine blade.