Investigation Of CMC's Thermal Conduction Mechanism And Its Application In Thermal Analysis For Turbine Vane

The fiber reinforced composites,such as the CMC(Ceramic Matrix Composite)material,have been widely applied in the hot components of turbine engine,for that it has good thermal resistance,excellent structure properties and low density.Several typical fiber reinforced composites were adopted in the present study,to investigate the relationship between the micro-structure and the macroscopic thermal properties.The estimation models of effective thermal conductivities were developed,and the method to introduce the anisotropic thermal conductivity to CMC turbine vane's thermal analysis was also established.At the same time,studies were performed about the film cooling effect over a flat plate with anisotropic thermal conductivity,and its application on the CMC turbine vane.Firstly,the thermal analysis of long fiber reinforced composites was carried on based on the RVE(Representative Volume Element)model,using the Monte Carlo simulation and the probabilistic analysis.The effective thermal conductivity,the heat flux field and the thermal gradient field were simulated,which were used as the multi-criteria for the minimal RVE size.The distribution characteristics of the internal heat flux field and thermal gradient field were obtained,and the estimation accuracy of the effective thermal conductivity was improved.The results showed that,the RVE model depending only on the effective thermal conductivity,could lead to errors in the simulation of heat flux and thermal gradient fields of the composites.In this thesis,the minimal non-dimensional size of RVE in the thermal analysis of fiber reinforced composites was found to be 80.At the same time,the 2.5D braided fiber reinforced composite was applied in the study.The RVE model with periodic boundary and the whole-size model based on vane's actual thickness were built to study the effect of composite's thickness on the estimation accuracy of the effective thermal conductivity.The validation experiment was also carried out to verify the estimation method of the effective thermal conductivity.The results showed that,in the thermal analysis of thin-walled structure,such as the turbine vane,the RVE model would lead to large deviation in the estimation of effective thermal conductivity,for that the periodic hypothesis could not be satisfied.The relative error between the numerical data based on the RVE model and the experimental data reached 10.93%,and it was only 3.53% between the numerical data based on the whole-size model and the experimental data.Then the numerical and experimental studies of film cooling over a flat plate with anisotropic thermal conductivity were performed.The internal heat transfer mechanism was explored,and the effects of anisotropic thermal conductivity and its variations on the film cooling effect were obtained under different blowing ratios.It was found that,the effects of anisotropic thermal conductivities are complex.When the inclined angles between the principle direction of thermal conductivity and the calculate coordinate changed,the average value and the standard deviation of the cooling efficiency were both changed significantly.The average cooling efficiency was affected non-monotonically by the inclined angles on the flow direction ? and the span-wise angles ?.For the film cooling over a flat plate with single row holes,when the blowing ratio was 0.5,the angle ? and ? should be 35° and 60° respectively,in order to produce the highest average cooling efficiency focusing on the 0-10D(D was the diameter of the film cooling hole)downstream region.If the blowing ratio changed,the influences of the inclined angles on the cooling effect were also different.For example,when the blowing ratio changed to 1.5,the angle ? and ? also changed to 60° and 0° respectively in order to obtain the highest average cooling efficiency on the 0-10 D downstream region.After obtaining the estimation model of effective thermal conductivity,the method of thermal analysis and the film cooling effect for typical fiber reinforced composites,the thermal analysis method for the CMC turbine vane was developed innovatively,which was based on the whole-size estimation model of effective thermal conductivity considering the anisotropic thermal conductivity's variation due to the vane's complex profile.At the same time,the experiments were performed to study the cooling effects of two CMC turbine vanes with different cooling configurations.The distribution characteristics of the cooling efficiency were analyzed,and the accuracy of the thermal analysis model and the estimation method in this thesis was further verified.The results showed that,for the average cooling efficiency at the leading edge,the pressure surface and suction surface,the relative errors between the numerical data and experimental data were 8.48%,7.75% and 2.11% respectively.