Thermal analysis method of ceramic matrix composite turbine blades considering micro-weaving structure and fiber bundle orientation variation

Abstract

The present invention discloses a thermal analysis method for a ceramic matrix composite turbine blade that takes into account the microscopic weaving structure and the change in the direction of the fiber bundle, including the following steps: obtaining the geometric characteristics of the fiber bundle of the weaving structure inside the ceramic matrix composite; establishing a microscopic model of the warp yarn, weft yarn and ceramic matrix composite matrix of the weaving structure; constructing a woven structure ceramic matrix composite blade model with a microstructure period width in the blade height direction; assigning an anisotropic thermal conductivity matrix that changes accordingly according to the change of the blade profile; performing meshing; carrying out finite element calculation of the temperature field; obtaining the temperature field calculation results of the woven structure ceramic matrix composite turbine blade model, comparing and analyzing the calculation results of the thermal analysis method based on the equivalent thermal conductivity homogenization, and extracting and analyzing the fluctuation characteristics of the temperature field of the woven structure ceramic matrix composite turbine blade. The present invention can make up for the defect of the homogenization thermal analysis method in simulating the distortion of the temperature field fluctuation information.

Description

Technical Field

[0001] The invention belongs to the technical field of engineering thermophysics, and in particular relates to a thermal analysis method for a turbine blade of a ceramic matrix composite material taking into account microscopic weaving structure and changes in fiber bundle direction. Background Art

[0002] At present, high thrust-to-weight ratio aircraft engines have higher and higher requirements for the heat resistance of hot end components such as turbine blades, while the increasingly complex cooling structure and limited cooling air volume have brought huge challenges to the thermal protection of turbine blades. Therefore, high temperature resistant materials represented by ceramic matrix composites (Ceramic Matrix Composite, CMC) toughened by woven structure fibers have received more and more attention and application.

[0003] The US government-led "Intergrated High Performance Turbine Engine Technology (IHPTET)" and "Ultra Efficient Energy Technology (UEET)" programs, the Japanese government-led "Research and Development of Environmentally Compatible Propulsion System for Next Generation Supersonic Transport (ESPR)" program, and the Russian government-led "National Technology Foundation 2007-2011" program all have special funds for the research and development of CMC hot end components. The Leap-X engine designed and manufactured by CFM and installed on the COMAC C919 also uses CMC materials for its core hot end components such as the first-stage outer ring of the high-pressure turbine, the guide vanes of the low-pressure turbine, and the tail cone, which makes the engine more effective in reducing noise and improving propulsion efficiency.

[0004] Braided CMC materials are fiber bundles interwoven in space to form a fiber-reinforced body, which is then compounded with a matrix material. Due to the anisotropy of the internal toughening fibers themselves and the differences in thermal conductivity between the fibers and the matrix, the overall thermal conductivity of the material often exhibits anisotropy. At the same time, since the geometric scale of the fiber bundle is close to that of thin-walled hot end components such as turbine blades, the periodic variation characteristics of the braided structure will inevitably affect the distribution characteristics of the temperature field of the turbine blades. Therefore, it is necessary to establish a thermal analysis model for braided CMC turbine blades.

[0005] At present, most thermal analysis of composite parts adopts the homogenization thermal analysis method based on anisotropic equivalent thermal conductivity, that is, the characteristics of the braided structure of the toughened fiber of CMC material are not considered, the calculation model is simplified to a homogenous model, and the macro equivalent thermal conductivity in three different coordinate directions under the global coordinate system is set during the calculation to complete the calculation of the temperature field. For example, Zhao Hongli et al. (Zhao Hongli. Finite element analysis of temperature field of carbon / carbon braided composite materials [D]. Jinan: Shandong Institute of Light Industry, 2012) and Chen Longmiao (Chen Longmiao. Study on thermal properties of composite barrels [D]. Nanjing: Nanjing University of Science and Technology, 2005) respectively used this method to conduct numerical simulation research on the temperature field of rocket engine tail nozzles and composite gun barrels made of carbon / carbon braided composite materials. Nita et al. (Nita K, Okita Y, Nakamata C. Experimental and numerical study on application of a CMC nozzle for high temperature gas turbine. Mechanical Properties and Performance of Engineering Ceramics and Composites VII, 2013, 315-324.) conducted experimental and numerical simulation studies on CMC turbine blades. First, a high-temperature gas cascade test was carried out on the blades, and the temperature of the blade wall was measured with an infrared thermal imager. Then, in the numerical simulation, the test results were used as boundary conditions, and the anisotropic physical properties of the CMC material were set using the overall homogenization method. The thermal stress of the CMC turbine blade was analyzed in detail. Xu Rui et al. (Xu Rui. Calculation method of thermal conductivity of unidirectional fiber reinforced ceramic matrix composite materials [D]. Nanjing: Nanjing University of Aeronautics and Astronautics, 2013) studied the influence of anisotropy and dispersion of thermal conductivity on the temperature field distribution of Mark II turbine blades. The overall homogenization thermal analysis method was also used in the study, that is, the macroscopic equivalent thermal conductivity of the turbine blade in three directions was given, and the law of change of thermal conductivity in the high temperature area of ​​the blade was obtained.Based on the above research, Zecan Tu et al. (Z.Tu, JKMao, H.Jiang, et al. Numerical method for the thermal analysis of a ceramic matrix composite turbine vane considering the spatial distribution of the anisotropic thermal conductivity, Applied Thermal Engineering, 2017, 127: 436-452.) further considered the spatial variation of anisotropic thermal conductivity with the blade profile and established a more accurate thermal analysis method for CMC material turbine blades.

[0006] However, the above thermal analysis method cannot reflect the influence of the internal braiding structure of the material on the temperature field of the turbine blade because the micro-braiding structure characteristics are homogenized. According to the research of Zhao Xiao et al. (Zhao Xiao. Study on film cooling of composite materials considering the interference between film holes and braiding structure [D]. Nanjing: Nanjing University of Aeronautics and Astronautics, 2017: 9-120.), the overall homogenization calculation method cannot obtain the temperature information of CMC caused by fiber braiding structure. The modeling method based on full-size micro-braiding structure can restore the temperature field of CMC more accurately, grasp the heat transfer mechanism inside the hot end components of CMC, and help to establish a refined thermal analysis method for the hot end components of CMC.

[0007] Therefore, it is necessary to establish a thermal analysis model of CMC turbine blades based on the micro-woven structure on the basis of obtaining the microstructural characteristics of the material, so as to make up for the defect of the homogenized thermal analysis method in simulating the distortion of temperature field fluctuation information and improve the accuracy of temperature field estimation of woven structure CMC turbine blades. Summary of the invention

[0008] The purpose of the present invention is to provide a thermal analysis method for ceramic matrix composite turbine blades taking into account the micro-weaving structure and the changes in the direction of the fiber bundle. The problem in the prior art is that the micro-weaving structure is characterized in a homogenized manner, which makes it impossible for this method to obtain the temperature field fluctuation characteristics caused by the weaving structure and cannot meet the needs of high-precision thermal analysis of woven structure CMC turbine blades.

[0009] To achieve the above object, the technical solution adopted by the present invention is:

[0010] A thermal analysis method for a ceramic matrix composite turbine blade taking into account microscopic weaving structure and fiber bundle direction changes comprises the following steps:

[0011] Step 1, obtaining the geometric characteristics of the fiber bundles of the internal woven structure of the ceramic matrix composite material based on a scanning electron microscope;

[0012] Step 2: Based on the geometric features obtained in step 1 and the actual thickness of the ceramic matrix composite turbine blade, a microscopic model of the warp yarn, the weft yarn and the ceramic matrix composite matrix of the woven structure is established;

[0013] Step 3, according to the geometric periodic characteristics of the braided structure, a braided structure ceramic matrix composite blade model with a microstructure period width in the blade height direction is constructed;

[0014] Step 4: for the woven structure ceramic matrix composite turbine blade model constructed in step 3, assign an anisotropic thermal conductivity matrix that changes accordingly according to the change of the blade profile;

[0015] Step 5, meshing the woven structure ceramic matrix composite turbine blade model constructed in step 3;

[0016] Step six, performing finite element calculation of the temperature field of the woven structure ceramic matrix composite turbine blade model;

[0017] Step seven, obtain the temperature field calculation results of the woven structure ceramic matrix composite turbine blade model, compare and analyze them with the calculation results based on the equivalent thermal conductivity homogenization thermal analysis method, and extract and analyze the fluctuation characteristics of the temperature field of the woven structure ceramic matrix composite turbine blade.

[0018] In the step 1, the geometric features include cross-sectional size features and fiber bundle spacing.

[0019] In the step three, in the woven structure ceramic matrix composite material blade model, the direction of the warp yarn changes along the blade profile, and the weft yarn is woven around the warp yarn.

[0020] In step three, the warp yarn section is firstly swept along the characteristic line of the blade profile to establish the warp yarn features at different thickness positions, and then the weft yarn section is interlaced and woven around the warp yarn in the blade height direction, and the spacing between the warp yarn and the weft yarn is the fiber bundle spacing.

[0021] In the step 4, the anisotropic thermal conductivity matrix of the warp and weft yarns changes with the space of the blade surface through the curvilinear coordinates in the mathematical module of the Comsol-Multiphysics software. Local curvilinear coordinates that change with the geometric surface are set for the warp and weft yarns inside the blade respectively, and then the anisotropic thermal conductivity in three directions of the local area is assigned based on the curvilinear coordinates to characterize the spatial variation characteristics of the anisotropic thermal conductivity matrix.

[0022] In the step five, local mesh encryption is performed in the fiber bundle dense area and the area where the fiber bundle and the matrix meet.

[0023] In the step six, the third type of convective heat transfer boundary conditions are applied to the inner and outer surfaces of the woven structure ceramic matrix composite turbine blade model respectively, and the periodic boundary conditions are applied to the upper and lower periodic structure surfaces, and then the finite element calculation of the temperature field is carried out.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention can establish a thermal analysis model of a CMC turbine blade based on the microscopic woven structure of the material, and carry out temperature field prediction based on the model, thereby compensating for the defect of the homogenized thermal analysis method in distorting the temperature field fluctuation information and improving the accuracy of temperature field prediction of the woven structure CMC turbine blade. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a turbine blade model of CMC material based on micro-woven structure;

[0027] Figure 2 This is a schematic diagram of the local calculation coordinate system distribution;

[0028] Figure 3 is the heat transfer coefficient distribution of the blade outer surface;

[0029] Figure 4 is a homogenized blade model based on equivalent thermal conductivity;

[0030] Figure 5 is the temperature distribution of the blade. (a) is a uniform blade; (b) is a braided blade; (c) is the outer surface of a uniform blade; (d) is the outer surface of a braided blade;

[0031] Figure 6 This is a comparison diagram of temperature distribution on the characteristic lines of the two models: the woven structure blade and the homogenized blade. DETAILED DESCRIPTION

[0032] The present invention is aimed at the demand for thermal analysis methods of turbine blades made of woven CMC materials. Considering that the current thermal analysis of CMC turbine blades often uses a homogenization method based on anisotropic equivalent thermal conductivity, this method can better obtain the regular characteristics of the temperature field distribution of CMC turbine blades. However, since the micro-woven structure is characterized by homogenization, this method cannot obtain the temperature field fluctuation characteristics caused by the woven structure, and cannot meet the demand for high-precision thermal analysis of woven CMC turbine blades. Therefore, the present invention proposes a thermal analysis method for ceramic-based composite turbine blades that takes into account the micro-woven structure and changes in the direction of the fiber bundle, including the following steps:

[0033] Step 1: obtaining the geometric characteristics of the fiber bundles of the woven structure inside the ceramic matrix composite material based on a scanning electron microscope; wherein the geometric characteristics include cross-sectional size characteristics and fiber bundle spacing;

[0034] Step 2: Based on the geometric features obtained in step 1 and the actual thickness of the ceramic matrix composite turbine blade, a microscopic model of the warp yarn, the weft yarn and the ceramic matrix composite matrix of the woven structure is established;

[0035] Step three, according to the geometric periodic characteristics of the weaving structure, a woven structure ceramic matrix composite material blade model with a microstructure period width in the blade height direction is constructed; wherein, in the woven structure ceramic matrix composite material blade model, the warp yarn direction changes along the blade profile, and the weft yarn is woven around the warp yarn. First, the warp yarn cross section is swept along the characteristic line of the blade profile to establish the warp yarn characteristics at different thickness positions, and then the weft yarn cross section is interlaced and woven around the warp yarn in the blade height direction, and the spacing between the warp yarn and the weft yarn is the fiber bundle spacing;

[0036] Step 4: for the woven structure ceramic matrix composite turbine blade model constructed in step 3, assign an anisotropic thermal conductivity matrix that changes accordingly according to the change of the blade profile; wherein, the anisotropic thermal conductivity matrix of the warp and weft yarns changes with the space of the blade profile, which is realized by the curvilinear coordinates in the mathematical module of the Comsol-Multiphysics software, and the local curvilinear coordinates that change with the geometric surface are set for the warp and weft yarns inside the blade respectively, and then the anisotropic thermal conductivity in three directions of the local area is assigned based on the curvilinear coordinates to characterize the spatial variation characteristics of the anisotropic thermal conductivity matrix;

[0037] Step 5, meshing the woven structure ceramic matrix composite turbine blade model constructed in step 3; wherein the mesh is locally encrypted in the fiber bundle dense area and the area where the fiber bundle and the matrix meet;

[0038] Step 6: Apply the third type of convective heat transfer boundary conditions to the inner and outer surfaces of the woven structure ceramic matrix composite turbine blade model, and apply periodic boundary conditions to the upper and lower periodic structure surfaces, and then carry out finite element calculation of the temperature field;

[0039] Step seven, obtain the temperature field calculation results of the woven structure ceramic matrix composite turbine blade model, compare and analyze them with the calculation results based on the equivalent thermal conductivity homogenization thermal analysis method, and extract and analyze the fluctuation characteristics of the temperature field of the woven structure ceramic matrix composite turbine blade.

[0040] The present invention is further described below in conjunction with embodiments and comparative examples.

[0041] Example

[0042] This embodiment takes the C3X blade as an example. The blade is made of a 2.5D braided composite material. The size of a single period of the braided structure is length × width × height = 10 × 4.8 × 3.3 mm. The width of the material fiber bundle is 1.6 mm and the thickness is 0.2 mm. The spacing of the weft yarns in the length direction is 2 mm, the spacing of the warp yarns in the thickness direction is 0.6 mm, and the braiding angle is 34°. Figure 1 The braided structure turbine blade shown has an axial chord length of 78 mm, a circumferential chord length of 145 mm, and a braided structure with a period length of 10 mm in the blade height direction (Y). The blade consists of an annular blade body and straight ribs. Straight ribs 1 and 2 divide the interior of the blade into three internal cooling channels. The thickness of the ribs and blades is 3.3 mm.

[0043] For the above-mentioned braided CMC turbine blade model, the mesh division adopts the free tetrahedron mesh in Comsol-Multiphysics, with the maximum unit of the selected mesh being 0.8mm, the minimum unit being 0.1mm, the maximum growth rate being 1.45, and the curvature factor being 0.5. The mesh is refined in the area where the curvature of the braided structure changes greatly to avoid local torsion and inversion of the surface unit of the mesh. The mesh volume of the braided structure blade is finally 10106385.

[0044] The woven structure blade contains 2696 different entity domains. In addition to the isotropic matrix, the woven yarn has obvious anisotropic characteristics, and the warp and weft yarns are distributed differently in the blade, resulting in the anisotropic thermal conductivity direction coordinate system of the warp and weft yarns being deflected in space from the calculation coordinate system. It is necessary to perform spatial transformation on the main direction of the thermal conductivity of the warp and weft yarns to set the thermal conductivity. This embodiment uses the curvilinear coordinates in the Comsol-Multiphysics mathematical module to set local coordinate systems that change with spatial distribution for the warp and weft yarns inside the blade, such as Figure 2 For warp and weft yarns, it is only necessary to give the thermal conductivity in three directions in their local coordinate system.

[0045] Then, the third type of boundary conditions are applied to the blade surface for calculation. The experimental results of working condition 4521 in reference (LDHylton, MSMihelc, ERTurner, et al.Analytical and Experimental Evaluation of the Heat Transfer Distribution Over the Surfaces of Turbine Vane [R]. America: National Aeronautics and Space Administration NASA Lewis Research Center, 1983: 1-225.) are used to select the experimental data of the outer surface of the blade under this working condition as the outer contour heat transfer coefficient of the braided structure CMC turbine blade, such as Figure 3 As shown. The figure shows the distribution of heat transfer coefficient on the suction surface and pressure surface respectively, where the horizontal axis is the ratio of the distance from the point on the suction surface (or pressure surface) to the leading edge to the entire arc length of the suction surface (or pressure surface), and the vertical axis is the size of the heat transfer coefficient. According to the previous section, when solving the spatial distribution of the uniform blade thermal conductivity in the calculation coordinate system, the expressions of the suction surface and the pressure surface are fitted, and the points corresponding to the experimental data on the outer contour line are obtained by solving the curve integral, and the points are assigned values. For areas where no experimental data are given, the heat transfer coefficients at the front and rear ends of the area are used for linear interpolation, and finally the distribution of the heat transfer coefficient on the entire outer contour of the blade is obtained. The above work is completed in Matlab, and the equation file of the outer contour heat transfer coefficient is obtained and can be called through the Comsol link with Matlb module and used as the external heat transfer boundary condition. The temperature of the outer contour is the mainstream inlet temperature, which is 818K.

[0046] The blade is constructed based on the blade profile of the C3X blade. The cooling channel in the blade is divided into three cooling channels by fins, which are respectively recorded as cooling channel 1, cooling channel 2 and cooling channel 3. The specific values ​​of the wall heat transfer coefficient and the corresponding gas temperature are summarized in Table 1:

[0047] Table 1 Boundary conditions for heat transfer in the cooling channel of the braided blade

[0048]

[0049] Comparative Example

[0050] In order to compare and analyze the difference between the thermal analysis model established in the present invention and the thermal analysis model based on the equivalent thermal conductivity homogenization, the following is also established: Figure 4The homogenized blade model shown in the figure uses the numerical method of the literature (Z.Tu, JKMao, H.Jiang, et al.Numerical method for the thermal analysis of a ceramic matrix composite turbine vane considering the spatial distribution of the anisotropic thermal conductivity, Applied Thermal Engineering, 2017, 127: 436-452.) to obtain the homogenized temperature field of the woven structure CMC material turbine blade.

[0051] Figure 5 The temperature distribution diagram of the homogenized blade and the braided blade is given. It can be seen from the figure that the overall temperature of the braided blade is significantly higher than that of the homogenized blade, and the temperature field distribution on the surface of the homogenized blade is relatively uniform. From the temperature distribution on the outer surface of the blade, it can be further seen that the surface temperature of the braided blade has obvious temperature fluctuation characteristics, and the temperature is alternately distributed with the braided structure. The maximum and minimum temperatures appear at the same position on the outer surface of the blade, but the temperature is far apart. The maximum temperature of the braided blade surface is 42.683K higher than that of the homogenized blade surface, and the minimum temperature of the two is also 72.631K different, which is a significant difference.

[0052] Figure 6 The temperature distribution of the uniform blade and the braided structure blade on the characteristic lines along the blade height direction at the leading edge, suction surface, pressure surface and trailing edge of the blade is given. The two ends of the characteristic line pass through the base area, and the middle passes through the braided area. From the figure, it can be more clearly found that the temperature of the braided structure blade is higher than that of the uniform blade. The temperature of the uniform blade in the blade height direction is basically unchanged, while the temperature on the characteristic line of the braided structure blade is high at both ends and low in the middle, and the temperature fluctuates significantly. Further analysis of the data on the characteristic line shows that the difference between the average temperature on the characteristic line of the uniform blade and the average temperature on the characteristic line of the braided structure blade is as small as 38.7K, and the maximum average temperature difference is as high as 93.3K. The maximum temperature change of the braided structure blade on the characteristic line is close to 35K, and the maximum amplitude of the temperature fluctuation on the characteristic line is also more than 18K, which has significant non-uniformity and drastic temperature fluctuation.

[0053] Therefore, compared with the comparative example, the embodiment can more accurately obtain the temperature field fluctuation information of the turbine blade caused by the material weaving structure, and further improve the simulation accuracy of the turbine blade of the woven structure CMC material.

[0054] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A thermal analysis method for ceramic matrix composite turbine blades taking into account the microscopic weaving structure and fiber bundle direction changes, characterized in that: The following steps are involved: Step 1, obtaining the geometric characteristics of the fiber bundles of the internal woven structure of the ceramic matrix composite material based on a scanning electron microscope; Step 2: Based on the geometric features obtained in step 1 and the actual thickness of the ceramic matrix composite turbine blade, a microscopic model of the warp yarn, the weft yarn and the ceramic matrix composite matrix of the woven structure is established; Step 3, according to the geometric periodic characteristics of the braided structure, a braided structure ceramic matrix composite blade model with a microstructure period width in the blade height direction is constructed; Step 4: for the woven structure ceramic matrix composite turbine blade model constructed in step 3, assign an anisotropic thermal conductivity matrix that changes accordingly according to the change of the blade profile; Step 5, meshing the woven structure ceramic matrix composite turbine blade model constructed in step 3; Step six, performing finite element calculation of the temperature field of the woven structure ceramic matrix composite turbine blade model; Step 7, obtaining the temperature field calculation results of the woven structure ceramic matrix composite turbine blade model, comparing and analyzing the calculation results based on the equivalent thermal conductivity homogenization thermal analysis method, and extracting and analyzing the fluctuation characteristics of the temperature field of the woven structure ceramic matrix composite turbine blade; In the step 3, the warp yarn section is firstly swept along the characteristic line of the blade profile to establish the warp yarn features at different thickness positions, and then the weft yarn section is interlaced and woven around the warp yarn in the blade height direction, and the spacing between the warp yarn and the weft yarn is the fiber bundle spacing; In the step 4, the anisotropic thermal conductivity matrix of the warp and weft yarns changes with the space of the blade surface through the curvilinear coordinates in the mathematical module of the Comsol-Multiphysics software. Local curvilinear coordinates that change with the geometric surface are set for the warp and weft yarns inside the blade respectively, and then the anisotropic thermal conductivity in three directions of the local area is assigned based on the curvilinear coordinates to characterize the spatial variation characteristics of the anisotropic thermal conductivity matrix.

2. The thermal analysis method of ceramic matrix composite turbine blades considering microscopic weaving structure and fiber bundle direction changes according to claim 1 is characterized by: In the step 1, the geometric features include cross-sectional size features and fiber bundle spacing.

3. The thermal analysis method of ceramic matrix composite turbine blades considering microscopic weaving structure and fiber bundle direction changes according to claim 1 is characterized in that: In the step three, in the woven structure ceramic matrix composite material blade model, the direction of the warp yarn changes along the blade profile, and the weft yarn is woven around the warp yarn.

4. The thermal analysis method of ceramic matrix composite turbine blades considering microscopic weaving structure and fiber bundle direction changes according to claim 1 is characterized in that: In the step five, local mesh encryption is performed in the fiber bundle dense area and the area where the fiber bundle and the matrix meet.

5. The thermal analysis method of ceramic matrix composite turbine blades considering microscopic weaving structure and fiber bundle direction changes according to claim 1 is characterized in that: In the step six, the third type of convective heat transfer boundary conditions are applied to the inner and outer surfaces of the woven structure ceramic matrix composite turbine blade model respectively, and the periodic boundary conditions are applied to the upper and lower periodic structure surfaces, and then the finite element calculation of the temperature field is carried out.

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