| Raising the initial temperature of gas turbine can give a boost to the output power and overall thermal efficiency.It is required that the blades being protected due to the harsh working environment.Commen internal cooling is a combination of ribbed serpentine channel,pin fin and leading edge impingment.Matrix is a special cooling scheme which produces stronger heat transfer,larger pressure penalty and better strength than conventional structures.Previous research on matrix lack detailed heat transfer measurement and influence patterns of various geomatric factors.The fall behind also includes optimization and performance evaluation under near-real applications and comparison with other cooling schemes.his dissertation carried out a research.Through wind tunnel test and CFD,heat transfer,flow field and mechanism of heat transfer enhancement is analyzed in detail,besides,geometric factors are included and optimization is carried out.Flow and heat transfer under different conditions are calculated,the effect of bleed and sidewall slots is investigated.A comparision is made between matrix and pin fin for the trailing edge,by using hybrid structure of matrix and pin fin the cooling performance can be improved significantly.This work produces large amount of performance data on matrix,provides methods for cooling prediction and direction for optimization.Following conclusions are made:1.A wind tunnel system is built based on the theory of ransient thermal-chromic liquid crystal technique.A special rig is designed for the calibration of liquid crystal to obtain the hue-temperature relationship.The uncertainties of measurement are presented.Through test work on smooth channel and typical ribbed channel the methods liquid crystal is verified.It proves that transient liquid crystal is an ideal method to measure convective heat transfer coefficient.2.Pressure drop and heat transfer distribution is measured for typical matrix channel under different Reynolds numbers.Various RANS methods are evaluated to select a best turbulence model.With large eddy simulation,detailed flow field and heat transfer mechanism of matrix channel are analysed.Also,the connection between flow and heat transfer distribution is revealed.The results incidate that large scale longitudinal vortx created by the sidewall turning is the main reason of the heat transfer augmentation.3.Geometric analysis is carried out in terms of rib angle,blockage ratio and sub-channel concerntration.With responses surface method,combined effect of various factors is studied,the purpose is to persue how to optimize the arrangement of cooling scheme in a fixed cooling space.With regression,multi-termquadratic mathametical expressions are established for the performance prediction.It proves that rib angle is the most important factor and that sparse matrics have better thermal performance but dense matrics provide better cooling uniformity.4.The effect of bleed extraction on the performance of matrix is investigated.The cooling capacity is evalutated with coolant reduction.By orthogonal analysis the influence of various arrangements of bleed holes are evaluated.Hole size,position and concerntration are included and their effect on the cooling capacity and heat transfer distribution is studied.It proves that the spanwise location of bleed is the most important.Heat transfer near holes is greatly enhanced and the thermal performance can be improved by 6%~7%.5.The effect of different outflow schemes is studied.Various geometries of sidewall slots are compared.Slots’ position,size and angle of attack are included.The research aims at finding a way of maintaining or even improving the cooling and thermal performance of the channel under the condition of reduced coolant.The effect of topside outflow is evaluated.The reaults showed that the outflow location affects performance the most and thermal performance can be improved at comparable cooling strength.6.Matrix has potential to be applied in the trailing edge cooling of turbine blade as an alternative to pin fin array for its better structural strength.This work made a comprehensive comparison between dense and sparse matrics,and circular and square pin fins through wind tunnel test and numerical simulations.Specifically,an innovative hybrid structure composed of matrix and pin fin is proposed which has much better thermal performance than the single matrix or pin fin array.As for the hybrid,effect of pin arrangement is studied.Besides,a conjugate heat transfer calculation is carried out to compare the performance of various structures in terms of temperature decrease and distribution.It is indicated that hybrid strcutrure yields 26%~38% higher thermal performance than pure pin fin array.Average solid temperature can have a further 100 K reduction with pin fin array being replaced by hybrids. |
