Design method for a fan-shaped to ablation slit type film cooling structure for braided CMC material

Abstract

This invention discloses a design method for a fan-shaped, constricted slit type film cooling structure for braided CMC material. The invention involves creating a preliminary space within the CMC material structure by shifting the warp threads of each layer to the right by a distance d over the warp threads of the upper layer in a vertically aligned 2.5D braided CMC material structure, while simultaneously curving and connecting the braided weft threads and folding them back. A fusible core is then filled into this preliminary space to form a forward-sloping fan-shaped film hole. A single warp thread located downstream of the forward-sloping fan-shaped film hole and close to the upper wall surface is removed to obtain a structural space. A slit is formed in the vertical upper wall surface from which the warp thread was removed, and the fan-shaped cross section of the forward-sloping fan-shaped film hole is connected to the formed slit by a UG wire weave surface command to form a fan-shaped, constricted slit type film cooling hole. This invention avoids damage to the strength of the CMC material member due to direct perforation, provides a solution in which the braided structure and efficient film holes cooperate, significantly improves the blow-out coating effect of the cooling film, and improves the overall film cooling efficiency of the CMC material member.

Description

Technical Field

[0001] The present invention belongs to the field of thermophysical engineering technology, and particularly relates to a design method for a sector-constricted slit type film cooling structure of a woven CMC material.

Background Art

[0002] In the future, the demand for highly intrusion-resistant and stealthy air combat power must be supported by the core power of high-performance aeroengines. However, design requirements such as higher thermodynamic cycle parameters (gas temperature exceeding 2200K), longer component life and reliability (life exceeding 6000 hours), etc. pose significant challenges to the research and manufacture of new-generation aeroengines, especially high-temperature components represented by turbine blades. The design ability of conventional turbine blades based on superalloys is approaching its limit, and the application of composite materials represented by ceramic matrix composites (abbreviated as CMC) provides the most promising and future-oriented solution.

[0003] While CMC materials offer an important solution for improving the heat resistance of high-temperature end components in aircraft engines, their heat resistance limit remains lower than the gas temperatures of high-performance aircraft engines (over 2200K). In particular, the heat resistance of SiC fiber-reinforced CMC materials currently produced in China is approximately 1623K, which is still significantly lower than that of other countries. Therefore, efficient cooling technology is still needed to ensure the safe operation of high-temperature components made of CMC materials. Currently, the design of cooling structures for high-temperature components such as CMC turbine blades often adopts alternative concepts to metal blade cooling structure designs, employing full-surface film coating on the leading edge and pressure surface of the blade, and cooling structures such as slots and pin fins on the trailing edge. However, for CMC blades, the full-surface film coating cooling structure generates excessive cooling air consumption, further reducing the amount of cooling air available in the future. On the other hand, because CMC materials have a heterogeneous structure composed of matrix and reinforcing fibers, the full-surface film cooling structure destroys the continuous fiber reinforcement structure over a large area, further seriously affecting the strength of the CMC blade. Therefore, it is necessary to develop efficient cooling structure designs and analyses applicable to CMC turbine blades, taking into account the structure and process characteristics of braided CMC materials.

[0004] Regarding CMC materials, the difference in thermal properties between the internal fibers and the matrix, as well as the anisotropy of the fibers themselves, results in a clearly anisotropic heat transfer coefficient for the entire CMC material. Furthermore, features such as the internal fiber weave structure and pore structure significantly influence the heat transfer and mass transfer processes of the cooling structure. Next, the preform braided structure and composite process of CMC materials offer design possibilities, influencing the anisotropic heat conduction and heat transfer / mass transfer processes within the material. Therefore, by fully utilizing the design possibilities of the material's micro-structure and combining it with efficient cooling structure features, it is possible to develop an integrated design of CMC material structure and blade cooling function. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] This invention addresses the need for efficient cooling technology for high-temperature components of aircraft engines, such as turbine blades. Considering the relatively good gas isolation and cooling effect of film cooling, and combining the special characteristics of the CMC material braiding process and the pores present in the material, this invention explores the effectiveness of implementing an efficient film cooling structure by combining the preform braiding process with a fusible core, including adjustments to fiber misalignment, braiding folds, and local fiber count. Furthermore, it aims to achieve higher heat resistance of CMC material turbine blades under conditions of relatively low cooling air usage. This invention provides a design method for a fan-shaped-restricted slit type film cooling structure for braided CMC material, which avoids damage to the strength of the CMC material component due to direct perforation, significantly improves the blow-out coating effect of the cooling film, and improves the overall film cooling efficiency of the CMC material component. [Means for solving the problem]

[0006] To achieve the above objective, the present invention employs the following technical solutions. The design method for a fan-shaped tore slit type film cooling structure for braided CMC material is as follows: Step 1 involves creating a reserve space within the CMC material structure by shifting the warp threads of each layer to the right by a distance d over the warp threads of the upper layer in order to misalign the vertically aligned 2.5D braided CMC material structure, while simultaneously curving and connecting the braided weft threads and folding them back. Step 2 involves filling the preliminary space in Step 1 with a fusible core to form a forward-sloping fan-shaped film hole, Step 3 involves obtaining a structural space by removing one warp thread downstream of the forward-sloping fan-shaped film hole, based on the forward-sloping fan-shaped film hole formed in Step 2, and the warp thread that is close to the upper wall surface. Step 4 includes forming a slit in the vertical upper wall surface from which the warp threads have been removed, based on the structural space obtained in Step 3, and connecting the fan-shaped cross section of the forward-sloping fan-shaped film hole to the formed slit using the UG wire weaving surface, thereby forming a fan-shaped-restricted slit-type film cooling hole.

[0007] Preferably, the inclination angle of the fan-shaped-aperture slit-type film cooling holes is determined by the travel distance d of each layer in step 1, and the larger d is, the smaller the inclination angle.

[0008] Preferably, in step 2, the expansion angle of the forward-tilting fan-shaped film hole is limited by the size of the reserve space in step 1, and the expansion angle is between 0 and 12 degrees.

[0009] Preferably, in step 4, the angle of the transition segment from the fan-shaped cross section to the slit is determined by both the forward tilt angle of the forward-tilting fan-shaped film hole in step 2 and the structural space obtained in step 3, and this angle is an increase of 3 to 5 degrees above the expansion angle of the forward-tilting fan-shaped film hole. [Effects of the Invention]

[0010] Compared to conventional technology, the present invention has the following beneficial effects. This invention avoids damage to the strength of CMC material members caused by direct perforation, forms a solution in which a braided structure and efficient film holes cooperate, significantly improves the blow-out coating effect of the cooling film, and improves the overall film cooling efficiency of the CMC material member. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of a fan-shaped aperture slit type film hole structure. [Figure 2] (1) is a schematic diagram of a sector-type slit film cooling plate model of a 2.5-dimensional braided CMC material, and (2) is a partial enlargement of (1), where a is the removed warp thread. [Figure 3] This is a computational domain model for calculating the film cooling efficiency of a 2.5-dimensional braided CMC material plate. [Figure 4] This is a schematic diagram of the structure of a circular film hole. [Figure 5] This is a schematic diagram of a circular film-perforated cooling plate model of a 2.5-dimensional braided CMC material. [Figure 6]This study compares the film cooling effects of circular holes and fan-shaped / restricted slit-type holes in a 2.5-dimensional braided CMC material. [Figure 7] This is a comparison of film blowout streamlines for circular holes and fan-shaped-aperture slit-type holes in a 2.5-dimensional braided CMC material. [Modes for carrying out the invention]

[0012] The present invention will be further described below in reference to examples and comparative examples.

[0013] (Examples) This invention describes a fan-shaped, narrowed slit-type film cooling hole based on a core preparation method in a braided ceramic matrix composite (CMC) material, and the effect of implementing film cooling using a film cooling plate of a 2.5-dimensional braided CMC material as an example.

[0014] Figure 1 shows a schematic diagram of a fan-shaped-restricted slit type film cooling hole structure according to an embodiment of the present invention. Figure 2 shows a schematic diagram of a fan-shaped-restricted slit type film cooling plate model of a 2.5-dimensional braided structure CMC material, with overall plate dimensions of 50*3.34*3.45 mm, where the cross-section of the fiber bundle is hexagonal, the warp pitch is 0.35 mm, and the weft pitch is 0.35 mm. Figure 3 shows a calculation domain model for flat plate film cooling related to computational simulation, where the calculation domain is divided into three parts, the geometric dimensions of the primary flow gas domain are 50*3.34*10 mm, the dimensions of the secondary flow cooling air domain are 50*3.34*5.6 mm, and the dimensions of the flat plate solid domain are as shown in Figure 2.

[0015] In the modeling process, first, operations are performed on the general 2.5D braided warp threads. The bottom layer of warp threads is fixed, and the upper layer of warp threads is each moved backward by a certain distance as a whole on the previous layer. This distance should be adjusted according to the angle requirements of the film holes, including but not limited to the moving distance and film hole angle in this specification. Subsequently, at the film hole location, the weft thread is folded back to prepare the space for the forward-tilted fan-shaped film hole. Then, the top layer of warp threads downstream of the film hole is removed to prepare a larger film hole operation space, and a 0.75 mm location in the vertical direction behind the forward-tilted fan-shaped film hole is cut to form a new forward-tilted fan-shaped film hole. Furthermore, the upper layer of warp threads is extracted to construct a slit, and the new forward-tilted fan-shaped film hole and the slit are used to form the final fan-shaped - throttle slit type film cooling hole through UG wire weaving surface operation.

[0016] The numerical research part utilizes the non-isothermal flow and conjugate heat transfer model in COMSOL software. Here, the thermophysical property parameters of the flat plate solid region are introduced and set from the braided structure of microscopic dimensions. That is, an isotropic heat transfer rate is set for the matrix part, and an anisotropic heat transfer rate is set for the fiber bundle part. Also, when setting, the curvilinear coordinate system in COMSOL software is adopted to characterize the change of the anisotropic heat transfer rate of the fiber bundle part according to the fiber bundle direction.

[0017] The boundary of the primary flow inlet in the calculation is at an inlet temperature of 325.72 K and a primary flow velocity of 30 m / s. The boundary of the secondary flow inlet is at an inlet temperature of 293.15 K and a blowing ratio of 0.5. The secondary flow enters the secondary flow passage from the secondary flow inlet, further enters the primary flow passage through the film, mixes with the primary flow, and then flows out from the outlet. As the boundary condition of the pressure outlet, the absolute pressure at the outlet is 101325 Pa, and other boundaries are adiabatic boundary conditions. [[ID=IO]]

[0018] In the research, mesh division is performed on the computational model using COMSOL software. Free tetrahedral mesh division is carried out on the woven CMC flat part, the type of mesh unit is tetrahedron, and mesh refinement is adopted at the boundary between the fiber and the matrix. The air flow region part is generated by adopting the method of solid region wall mesh sweep, and a boundary layer refined mesh is constructed in the fluid region near the gas side wall.

[0019] (Comparative Example) In addition, in order to compare the difference in cooling effects between the fan-shaped - throttle slit type film holes of the 2.5D woven CMC material of the present invention and the conventional circular film cooling holes, in the comparative example, the same simulation method is adopted to perform a simulation analysis of the cooling effect on the circular film hole cooling structure of the 2.5D woven CMC material. FIG. 4 shows a schematic diagram of the circular film cooling hole structure of the comparative example of the present invention, and the hole diameter is 0.8 mm. FIG. 5 shows a schematic diagram of the circular film hole cooling flat plate model of the CMC material with a 2.5D woven structure. The overall dimensions of the flat plate are 50 * 3.34 * 3.45 mm. Here, the cross-section of the fiber bundle is hexagonal, the warp pitch is 0.35 mm, and the weft pitch is 0.35 mm. The calculation region model and dimensions of the circular film hole cooling flat plate are the same as those in FIG. 3. Also, the settings of the anisotropic heat transfer rate, mesh division, and boundary conditions related to the simulation calculation in the comparative example are all the same as those in the example.

[0020] FIG. 6 shows a comparison of scatter plots of the overall cooling efficiency of the film-covered wall surface in the example (fan-shaped - throttle slit type film hole) and the comparative example (circular film hole). As can be seen from the figure, compared with the circular film hole, the fan-shaped - throttle slit type hole of the 2.5D woven CMC material has a significantly improved film covering effect downstream, and the numerical value of the film cooling efficiency is in the high film cooling efficiency region range. Within the range of 0 - 10D downstream of the film hole, the average overall cooling efficiencies of the circular film hole and the fan-shaped - throttle slit type film hole are 0.53 and 0.23 respectively.

[0021] Figure 7 shows a comparison of the streamlines of the film cooling structures of two types of 2.5-dimensional braided CMC materials in the examples and comparative examples. As can be seen from the figure, the film coating effect downstream of the fan-shaped-aperture slit type holes in the 2.5-dimensional braided CMC material is significantly improved compared to the circular film holes.

[0022] As described above, the fan-shaped-restricted slit-type film cooling holes based on the core preparation method in the braided ceramic matrix composite material (CMC) constructed in the present invention can significantly improve the overall film cooling efficiency of the braided CMC material member without destroying the reinforcing fiber bundles.

[0023] The above are merely preferred embodiments of the present invention, and it should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for designing a fan-shaped torrent-type film cooling structure for braided CMC material, Step 1 involves creating a reserve space within the CMC material structure by shifting the warp threads of each layer to the right by a distance d over the warp threads of the upper layer in order to offset the vertically aligned 2.5D braided CMC material structure, while simultaneously curving and connecting the braided weft threads and folding them back. Step 2 involves filling the preliminary space in Step 1 with a fusible core to form a forward-sloping fan-shaped film hole, Step 3 involves removing one warp thread located downstream of the forward-sloping fan-shaped film hole, which is close to the upper wall surface, to obtain a structural space. A method for designing a fan-shaped, constricted slit type film cooling structure for a braided CMC material, comprising: step 3, based on the structural space obtained, a slit is formed in the vertical upper wall surface from which the warp threads have been removed, and the fan-shaped cross section of the forward-sloping fan-shaped film hole is connected to the formed slit by the UG wire weaving surface, thereby forming a fan-shaped, constricted slit type film cooling hole.

2. The method for designing a fan-shaped tore slit type film cooling structure for a braided CMC material according to claim 1, characterized in that in step 2, the expansion angle of the forward-tilting fan-shaped film hole is limited by the size of the preliminary space in step 1 and is between 0 and 12 degrees.

3. The inclination angle of the fan-shaped-restricted slit-type film cooling holes is determined by the distance d traveled by the warp threads of each layer in step 1, and the larger d is, the smaller the inclination angle, characterized in that, the design method for a fan-shaped-restricted slit-type film cooling structure for a braided CMC material according to claim 1.

4. The method for designing a fan-shaped to slit type film cooling structure for braided CMC material according to claim 1, characterized in that in step 4, the angle of the transition segment from the fan-shaped cross section to the slit is determined by both the forward tilt angle of the forward-tilting fan-shaped film hole in step 2 and the structural space obtained in step 3, and the angle of the transition segment is an increase of 3 to 5 degrees above the expansion angle of the forward-tilting fan-shaped film hole.

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