Anisotropic thermal analysis method for CMC material turbine blades based on Fluent UDF

Abstract

The present invention discloses a CMC material turbine blade anisotropic thermal analysis method based on Fluent UDF. The method realizes the setting of the direction of the anisotropic thermal conductivity of the CMC blade changing with the blade shape based on the Fluent UDF function. A calculation method for the spatial distribution of the anisotropic thermal conductivity of the CMC blade is developed, which can better introduce the anisotropic thermal conductivity characteristics of the CMC blade solid domain in the turbine blade flow heat transfer analysis, thereby meeting the functional requirements of the anisotropic CMC turbine blade thermal analysis method.

Description

Technical Field

[0001] The invention belongs to the technical field of engineering thermophysics, and in particular relates to an anisotropic thermal analysis method for a CMC material turbine blade based on Fluent UDF. Background Art

[0002] With the continuous development of aircraft engine technology, the performance indicators of engines are constantly improving, resulting in higher and higher requirements for materials in aircraft engines. In particular, the improvement of engine thrust-to-weight ratio has made the temperature of turbine inlet gas higher and higher. The combustion chamber temperature of modern aircraft engines is as high as 2200K, which is far beyond the heat resistance limit of metal turbine blades. Therefore, ceramic matrix composites (Ceramic Matrix Composite, referred to as CMC materials) with good high temperature resistance and mechanical properties have become one of the most promising research directions.

[0003] CMC material adds fiber reinforcement phase to the ceramic matrix, which greatly improves its strength and toughness on the basis of its original low density and high temperature resistance. However, due to the characteristics of the material's heterogeneous structure, its macroscopic thermal conductivity shows obvious anisotropy characteristics, and depending on the weaving method, the direction of the material's thermal conductivity will also change with the change of the blade shape. This brings technical difficulties to how to consider and introduce the changes in the thermal conductivity anisotropy characteristics of CMC materials with the blade surface when conducting flow heat transfer analysis of CMC turbine blades. Therefore, it is necessary to establish a flow heat transfer analysis method suitable for CMC turbine blades based on the thermal conductivity anisotropy characteristics of CMC material turbine blades. Summary of the invention

[0004] The present invention provides a solution to the problem that the material property setting is difficult and the accuracy is insufficient when the flow heat transfer simulation calculation of the woven CMC material turbine blade is performed because the thermal conductivity of the woven CMC material is anisotropic and the direction of the thermal conductivity changes with the blade shape. A method for setting the material property of the material with anisotropic thermal conductivity and changing with the blade shape is implemented by Fluent UDF.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for anisotropic thermal analysis of a CMC material turbine blade based on Fluent UDF includes the following steps:

[0007] Step 1: Construct a CMC turbine blade model, and set the absolute coordinate system of the CMC turbine blade model in the Fluent environment as the main coordinate system; set the outer surface normal direction of the CMC turbine blade as the X-axis, and the blade height direction as the Z-axis to obtain the coordinate system as the calculation coordinate system; according to the three-dimensional coordinate point data of the three outer lines of the CMC turbine blade, take the two three-dimensional coordinate point data closest to the calculated three-dimensional coordinate point, calculate the slope of the line connecting the two three-dimensional coordinate points, and then use the arctan method to obtain the deflection angle of each three-dimensional coordinate point in the three outer lines relative to the main coordinate system;

[0008] Step 2: Calculate the basis vectors of each three-dimensional coordinate point of the outer mold line in three directions in the calculation coordinate system using the deflection angle obtained in step 1, and define the conversion relationship between the thermal conductivity matrix of each three-dimensional coordinate point of the outer mold line in the calculation coordinate system and the thermal conductivity matrix in the principal coordinate system;

[0009] Step 3: According to the macroscopic equivalent anisotropic thermal conductivity condition of CMC material in the given calculation coordinate system, the thermal conductivity matrix of each coordinate point of the CMC turbine blade profile in the principal coordinate system is obtained through the conversion relationship in step 2;

[0010] Step 4: Calculate the distance between each grid unit of the CMC turbine blade model and all three-dimensional coordinate points of the three outer lines, assign the thermal conductivity matrix of the three-dimensional coordinate point of the outer line closest to the grid unit to the grid unit, and complete the setting of the anisotropic thermal conductivity of the blade changing with the blade shape.

[0011] Preferably, in step 1, the three-dimensional coordinate point data of each outer mold line is obtained by taking three-dimensional coordinate points equidistantly on the outer mold line of the CMC turbine blade, and the three-dimensional coordinate point data of each outer mold line is stored separately in a txt file, and the three-dimensional coordinate points taken for each outer mold line should be no less than 200, and repeated selection between three-dimensional coordinate points is prohibited.

[0012] Preferably, in step 1, the slope of the line connecting two three-dimensional coordinate points is calculated and then the arctan method is used to obtain the deflection angle of each three-dimensional coordinate point in the three outer mold lines relative to the main coordinate system. The thermal conductivity matrix of the three-dimensional coordinate point of each outer mold line in the main coordinate system and the relationship matrix between the calculation coordinate system and the main coordinate thermal conductivity matrix are determined by the deflection angle in step 1.

[0013] Preferably, the conversion formula between the thermal conductivity matrix in the calculated coordinate system and the thermal conductivity matrix in the principal coordinate system in step 2 is:

[0014] B=P -1 AP

[0015] Where B is the thermal conductivity matrix in the principal coordinate system, A is the thermal conductivity matrix in the computational coordinate system, and P is the transition matrix between the principal coordinate system and the computational coordinate system:

[0016] Assuming that the global coordinate system is obtained by rotating the local coordinate system around the X-axis by an angle α, then around the Y-axis by an angle β, and finally around the Z-axis by an angle γ, the transition matrix P is:

[0017]

[0018] The rotation angle γ is the deflection angle calculated in step 1, and the rotation angle α and the rotation angle β are obtained through the deflection angle.

[0019] Preferably, in step 4, the thermal conductivity matrix of each grid cell of the CMC blade model is determined by the distance between the coordinates of the grid cell and the three-dimensional coordinate point of the blade outer profile line: the thermal conductivity matrix in the principal coordinate system stored at the three-dimensional coordinate point of the outer profile line closest to the grid cell is assigned to the grid cell, and this method is used to loop through all grid cells on the CMC turbine blade until the assignment of all grid cells of the blade is completed.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] When performing flow and heat transfer simulation calculations on woven CMC material turbine blades, only the coordinate point data of three blade outer lines need to be provided. In this way, the material properties of the anisotropic thermal conductivity of the woven CMC material turbine blades and the direction of the thermal conductivity changing with the blade shape can be set in Fluent, thereby improving the accuracy of flow and heat transfer simulation calculations. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram showing the angle between the global coordinate system and the calculation coordinate system calculated using the blade profile line;

[0023] Figure 2 CMC blade thermal conductivity changes with blade shape. DETAILED DESCRIPTION

[0024] The principle and use method of the present invention are further explained below with reference to examples.

[0025] Detailed explanation of UDF principle:

[0026] Since the thermal conductivity of the turbine blade made of woven CMC material is anisotropic and the direction of the thermal conductivity varies with the blade shape, the absolute coordinate system of the blade model in the Fluent environment is set as the principal coordinate system, and the coordinate system obtained by setting the three direction vectors of the given equivalent thermal conductivity of the material as the basis is the calculation coordinate system. The conversion formula between the thermal conductivity matrix in the calculation coordinate system and the thermal conductivity matrix in the principal coordinate system is shown in Equation 1.

[0027] B=P -1 AP (1)

[0028] Where B is the matrix of thermal conductivity in the principal coordinate system, and A is the matrix of thermal conductivity in the computational coordinate system. P is the transition matrix between the principal coordinate system and the local computational coordinate system. From the mathematical matrix theory, we know that the value of the P matrix is ​​only related to the angle between the two coordinate system basis vectors. Assuming that the global coordinate system is the local coordinate system rotated around the X-axis by an angle α, then around the Y-axis by an angle β, and finally around the Z-axis by an angle γ (where the angle is positive counterclockwise and negative clockwise), the direction cosine matrix P of the coordinate system rotation is:

[0029]

[0030] Among them, l1, l2, l3 are the cosines of the angles between the x-axis of the principal coordinate system and the x, y, z-axis of the calculation coordinate system, m1, m2, m3 are the cosines of the angles between the y-axis of the principal coordinate system and the x, y, z-axis of the calculation coordinate system, and n1, n2, n3 are the cosines of the angles between the z-axis of the principal coordinate system and the x, y, z-axis of the calculation coordinate system.

[0031] When writing UDF, the present invention uses the three outer line coordinate points used in blade design as input to approximately calculate the deflection angle of the center coordinate point of each grid unit of the blade. During the calculation, the Z-axis coordinates in the outer line coordinate points are removed, and it is assumed that the global coordinates and the calculated coordinates rotate around the Z axis (the Z-axis vector direction is along the blade height direction), and the three-dimensional curve is converted into a two-dimensional curve. After that, the angle between the calculated coordinate system and the main coordinate system of each coordinate point is calculated using the two points closest to the point. The calculation principle is as follows: Figure 1 As shown, assuming Figure 1 The coordinate axis in the lower left corner is the direction of the global coordinate axis vector, where the direction pointing into the plane is assumed to be the Z-axis direction. To calculate the angle of rotation of the computational coordinate system and the global coordinate system around the Z-axis at point 2, you only need to find the slope of the vector direction from point 1 to point 3 and then find arctan. Substitute the calculated deflection angle into the transition matrix P in formula 2.

[0032] Assuming that the basis vector matrix A of the global coordinate system is a unit matrix, the basis vector matrix of the local coordinate system can be calculated by substituting P and A into formula 1. It can be known from mathematical theorem that the thermal conductivity matrix in the local coordinate system and the thermal conductivity matrix in the global coordinate system also satisfy formula 1, and the p values ​​of the two relations are the same, so the thermal conductivity matrix of all points of the blade profile line in the global coordinate system can be obtained by formula 1. In this way, the thermal conductivity matrix of all points of the three profile lines in the global coordinate system can be calculated, and then the difference between the center coordinate point of each blade grid unit and all the coordinate points of the three profile lines is calculated to calculate the distance, and then the global thermal conductivity matrix of each grid unit of the blade is equal to the global thermal conductivity matrix of the coordinate point of the profile line closest to it. In this way, the thermal conductivity matrix of each grid unit can be changed with the change of the blade shape. Figure 2 The cloud diagram of blade thermal conductivity changing with blade shape after adding UDF is shown.

[0033] UDF details:

[0034] The UDF in the present invention uses two macros, ON_DEMAND and ANISOTROPIC_CONDUCTIVITY. Among them, the ON_DEMAND macro needs to be run manually before calculation, and its function is to realize the above-mentioned matrix operation process, while the ANISOTROPIC_CONDUCTIVITY macro runs automatically when the material thermal conductivity data needs to be called during the calculation process of FLUENT, and its function is to assign the thermal conductivity conversion matrix calculated by the ON_DEMAND macro as a material parameter to each grid unit. The C_UDMI macro is used to transfer data between the two macros. Therefore, when using this UDF, 9 memories for storing matrix data need to be created in advance. The specific operation method is described in the subsequent examples.

[0035] In addition to the grid file, this UDF needs to provide 4 files and a command code before use. The 4 files are a .c format file storing the UDF source code and three .txt format files storing the blade profile coordinate point data. The .txt file format storing the blade profile coordinate point data needs to meet the following five requirements:

[0036] 1) The coordinate data stored in the .txt file must be in meters.

[0037] 2). Each line of the txt file can only store one 3D coordinate point, and the x, y, and z coordinate data of a line can only be separated by a "space" or a "tab" symbol. Lines are separated by a carriage return symbol. There are only as many lines as there are coordinate points in the file, and no extra carriage return and line feed characters are allowed at the end of the file.

[0038] 3) Two points with the same coordinates are not allowed.

[0039] 4) Chinese characters are allowed in file names, but uppercase letters are not allowed.

[0040] 5) Each .txt file can store up to 1999 data points, which means that the number of lines in each .txt file is not allowed to exceed 1999.

[0041] To avoid repeated code modification, the value of the thermal conductivity of the blade material in the calculation coordinate system is not given in the program when the UDF source code is written, so it needs to be manually entered in the Fluent console before the program is run. At the same time, the UDF needs to read three .txt files of blade profile coordinate data stored in the computer when it is running. Therefore, before running the UDF, you also need to enter the file addresses and file names of the three files storing the blade profile coordinate point data in the Fluent console.

[0042] UDF usage examples:

[0043] Operation 1: Input the value of thermal conductivity of the braided CMC material in the calculation coordinate system and the file address and file name of the data file storing the blade profile coordinate point data in the console.

[0044] First, declare the make-new-rpvar macro and allocate storage space. The instructions are as follows:

[0045] (define(make-new-rpvar name default type)

[0046] (if(not(rp-var-object name))

[0047] (rp-var-define name default type#f)))

[0048] Then enter the file address and file name of the file storing the blade profile coordinate point data. The command is as follows:

[0049] (make-new-rpvar`myUDF / path1"E: / project / a1.txt"`string)

[0050] (make-new-rpvar`myUDF / path2"E: / project / b1.txt"`string)

[0051] (make-new-rpvar`myUDF / path3"E: / project / c1.txt"`string)

[0052] The part in double quotes is the file address and file name, which can be modified according to the actual file storage location and name.

[0053] Finally, enter the value of the thermal conductivity of the woven CMC material in the calculation coordinate system. The command is as follows

[0054] (make-new-rpvar`myUDF / kk112'real)

[0055] (make-new-rpvar`myUDF / kk2210'real)

[0056] (make-new-rpvar`myUDF / kk3310'real)

[0057] Among them, 2, 10, and 10 are input values, which can be modified according to the material properties during calculation. The first line is the thermal conductivity value in the normal direction of the blade surface, and the third line is the thermal conductivity value of the blade in the direction along the blade height.

[0058] Operation 2: Open up memory space. The above UDF uses two UDF macros. To enable data to be transferred between the two UDF macros, the present invention adds the C_UDMI function to the UDF. This function needs to open up memory space in FLUENT before use. Because the thermal conductivity matrix is ​​a 3*3 matrix, 9 memory spaces for storing data need to be opened in each grid cell.

[0059] Operation 3: Load UDF. This UDF is loaded by compiling UDF. Before loading UDF, you need to put the .c program file of UDF source code into the FLUENT working directory.

[0060] Operation 4: Set the CMC blade model material properties to the loaded UDF.

[0061] Operation 5: Initialize the parameters and run the UDF manually after initialization. Run the program in the ON_DEMAND macro in the UDF first.

[0062] Operation 6: After the UDF runs, you can view the results of the blade thermal conductivity matrix changing with the blade shape in the result cloud chart.

[0063] In summary, the present invention aims at the thermal properties of woven CMC turbine blades and creates a FluentUDF-based anisotropic thermal analysis method for CMC turbine blades. This method only needs to provide the coordinate point data of three blade profile lines when performing flow heat transfer simulation calculations on woven CMC turbine blades. The setting of the material properties that the thermal conductivity of woven CMC turbine blades is anisotropic and the direction of thermal conductivity changes with the blade shape can be realized in the Fluent simulation calculation, thereby improving the accuracy of flow heat transfer simulation calculations.

[0064] 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 method for anisotropic thermal analysis of CMC material turbine blades based on Fluent UDF, characterized in that: The following steps are involved: Step 1: Construct a CMC turbine blade model, and set the absolute coordinate system of the CMC turbine blade model in the Fluent environment as the main coordinate system; set the outer surface normal direction of the CMC turbine blade as the X-axis, and the blade height direction as the Z-axis to obtain the coordinate system as the calculation coordinate system; according to the three-dimensional coordinate point data of the three outer lines of the CMC turbine blade, take the two three-dimensional coordinate point data closest to the calculated three-dimensional coordinate point, calculate the slope of the line connecting the two three-dimensional coordinate points, and then use the arctan method to obtain the deflection angle of each three-dimensional coordinate point in the three outer lines relative to the main coordinate system; Step 2: Calculate the basis vectors of each three-dimensional coordinate point of the outer mold line in three directions in the calculation coordinate system using the deflection angle obtained in step 1, and define the conversion relationship between the thermal conductivity matrix of each three-dimensional coordinate point of the outer mold line in the calculation coordinate system and the thermal conductivity matrix in the principal coordinate system; Step 3: According to the macroscopic equivalent anisotropic thermal conductivity condition of CMC material in the given calculation coordinate system, the thermal conductivity matrix of each coordinate point of the CMC turbine blade profile in the principal coordinate system is obtained through the conversion relationship in step 2; Step 4: Calculate the distance between each grid unit of the CMC turbine blade model and all three-dimensional coordinate points of the three outer lines, assign the thermal conductivity matrix of the three-dimensional coordinate point of the outer line closest to the grid unit to the grid unit, and complete the setting of the anisotropic thermal conductivity of the blade changing with the blade shape.

2. The anisotropic thermal analysis method of CMC material turbine blades based on Fluent UDF according to claim 1 is characterized by: In the step 1, the three-dimensional coordinate point data of each outer mold line is obtained by taking three-dimensional coordinate points at equal intervals on the outer mold line of the CMC turbine blade, and the three-dimensional coordinate point data of each outer mold line is stored separately in a txt file. The three-dimensional coordinate points taken for each outer mold line should be no less than 200, and repeated selection between three-dimensional coordinate points is prohibited.

3. The anisotropic thermal analysis method of CMC material turbine blades based on Fluent UDF according to claim 1 is characterized in that: In the step 1, the slope of the line connecting the two three-dimensional coordinate points is calculated and then the arctan method is used to obtain the deflection angle of each three-dimensional coordinate point in the three outer lines relative to the main coordinate system. The thermal conductivity matrix of each three-dimensional coordinate point of the outer line in the main coordinate system and the relationship matrix between the calculation coordinate system and the main coordinate thermal conductivity matrix are determined by the deflection angle in step 1.

4. The anisotropic thermal analysis method of CMC material turbine blades based on Fluent UDF according to claim 1 is characterized by: The conversion formula between the thermal conductivity matrix in the calculated coordinate system and the thermal conductivity matrix in the principal coordinate system in step 2 is: B=P -1 AP Where B is the thermal conductivity matrix in the principal coordinate system, A is the thermal conductivity matrix in the computational coordinate system, and P is the transition matrix between the principal coordinate system and the computational coordinate system: Assuming that the global coordinate system is obtained by rotating the local coordinate system around the X-axis by an angle α, then around the Y-axis by an angle β, and finally around the Z-axis by an angle γ, the transition matrix P is: The rotation angle γ is the deflection angle calculated in step 1, and the rotation angle α and the rotation angle β are obtained through the deflection angle.

5. The anisotropic thermal analysis method of CMC material turbine blades based on Fluent UDF according to claim 1 is characterized by: In step 4, the thermal conductivity matrix of each grid cell of the CMC blade model is determined by the distance between the coordinates of the grid cell and the three-dimensional coordinate point of the blade outer profile line: the thermal conductivity matrix in the principal coordinate system stored in the three-dimensional coordinate point of the outer profile line closest to the grid cell is assigned to the grid cell, and this method is used to loop through all grid cells on the CMC turbine blade until the assignment of all grid cells of the blade is completed.

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