Design method for woven CMC fan-shaped-converging slot shaped film cooling structure

Abstract

A design method for a woven CMC fan-shaped-converging slot shaped film cooling structure. The design method comprises: for 2.5D woven CMC structures, which are orderly arranged one above another, by means of staggering, moving a warp yarn of each layer to the right by a distance d on the basis of a warp yarn of a previous layer, and bending, connecting and hooking back woven weft yarns to form reserved spaces in the CMC structures; filling the reserved spaces with ablatable cores to construct forward-tilting fan-shaped film holes; removing one warp yarn that is located downstream of the forward-tilting fan-shaped film holes and is close to an upper wall surface to obtain a construction space; and forming, according to the construction space, a slot in the vertical upper wall surface from which the warp yarn is removed, and connecting the fan-shaped cross sections of the forward-tilting fan-shaped film holes to the constructed slot by means of UG straight grains to form a fan-shaped-converging slot shaped film cooling hole.

Description

A design method for a fan-shaped and convergent seam film cooling structure made of woven CMC materials Technical Field

[0001] The invention belongs to the technical field of engineering thermophysics, and in particular relates to a design method for a fan-shaped and convergent seam type air film cooling structure made of a braided CMC material. Background Art

[0002] The future demand for ultra-strong penetration and high-stealth aircraft combat capabilities is inseparable from the core power support of high-performance aircraft engines. However, design requirements such as higher thermodynamic cycle parameters (gas temperature exceeding 2200K), longer component life and reliability (life exceeding 6000 hours) have brought significant challenges to the development of new-generation aircraft engines, especially high-temperature components represented by turbine blades. The existing design capabilities of turbine blades based on high-temperature alloys have reached their limits. The application of composite materials represented by ceramic matrix composites (CMC) provides the most possible and promising solution.

[0003] CMC materials have become a key solution for improving the temperature resistance of hot-end components in aircraft engines, but their thermal limit remains below the 2200K+ combustion temperatures of high-performance aircraft engines. In particular, the temperature resistance of currently produced domestically produced SiC fiber-reinforced CMC materials is approximately 1623K, which lags behind that of foreign materials. Therefore, efficient cooling technologies are still needed to ensure the safe service life of CMC high-temperature components. Currently, cooling structures for high-temperature components such as CMC turbine blades mostly rely on replacing metal blade cooling structures, employing full film coverage on the leading edge and pressure side of the blades and slits and spoilers on the trailing edge. However, for CMC blades, full film coverage cooling structures consume excessive cooling air, further reducing the amount of available cooling air in the future. Furthermore, CMC materials are a heterogeneous structure composed of a matrix and reinforced fibers. Full film cooling structures can significantly damage the continuous fiber reinforcement structure, severely compromising the strength of CMC blades. Therefore, it is necessary to design and analyze efficient cooling structures suitable for CMC turbine blades, taking into account the structural and processing characteristics of braided CMC materials.

[0004] For CMC materials, due to the differences in thermal properties between the internal fibers and the matrix, as well as the anisotropy of the fibers themselves, the overall thermal conductivity of the CMC material exhibits obvious anisotropic characteristics. Its internal fiber weaving structure and pore structure and other characteristics will also have a significant impact on the heat and mass transfer process of the cooling structure. Secondly, the preform weaving structure and composite process of the CMC material are designable and affect the anisotropic thermal conductivity and heat and mass transfer process within the material. Therefore, the designability of the material's microstructure can be fully utilized, combined with the characteristics of the efficient cooling structure, to carry out the integrated design of the CMC material structure and blade cooling function. Technical issues

[0005] This invention addresses the need for efficient cooling technology for high-temperature aeroengine components such as turbine blades. Taking into account the superior gas barrier and cooling effects of film cooling, and combining the specificities of CMC weaving processes and the porosity of the material, this invention explores the implementation of efficient film cooling structures through preform weaving processes such as fiber staggering, weaving loops, and adjusting the local fiber count, combined with ablative cores. This approach allows for higher temperature-bearing capabilities of CMC turbine blades while using less cooling air. This invention provides a design method for a fan-shaped, convergent-slit film cooling structure in woven CMC materials. This design avoids the damage to the strength of CMC components caused by direct drilling, significantly improves the outflow coverage of the cooling film, and enhances the overall film cooling efficiency of CMC components. Technical Solutions

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A design method for a braided CMC material fan-shaped and convergent seam type air film cooling structure includes the following steps:

[0008] Step 1: For a 2.5D woven CMC material structure that is neatly arranged up and down, the warp yarns of each layer are shifted to the right by a distance d based on the warp yarns of the previous layer by staggering. At the same time, a reserved space is formed in the CMC material structure by bending and hooking the weft yarns.

[0009] Step 2: Fill the reserved space in step 1 with an ablative core to form a forward-inclined fan-shaped air film hole;

[0010] Step 3: Based on the forward-inclined fan-shaped air film hole constructed in step 2, a warp yarn is removed downstream of the forward-inclined fan-shaped air film hole and close to the upper wall to obtain a construction space;

[0011] Step 4: Based on the construction space obtained in step 3, a slit is constructed on the vertical upper wall surface where the warp yarn is removed, and the fan-shaped cross section of the forward-inclined fan-shaped film hole is connected to the constructed slit through UG straight lines to form a fan-shaped-convergent slit type film cooling hole.

[0012] Preferably, the inclination angle of the fan-shaped-convergent slit-type film cooling hole is determined by the moving distance d of each layer in step 1. The larger d is, the smaller the inclination angle is.

[0013] Preferably, in step 2, the expansion angle of the forward-inclined fan-shaped air film hole is limited by the size of the reserved space in step 1, and the expansion angle is between 0 degrees and 12 degrees.

[0014] Preferably, in step four, the angle of the transition section from the fan-shaped section to the slit is determined by the forward inclination angle of the forward-inclined fan-shaped air film hole in step two and the construction space obtained in step three. This angle is increased by 3 to 5 degrees based on the expansion angle of the forward-inclined fan-shaped air film hole. Beneficial effects

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention avoids the damage to the strength of CMC material components caused by direct punching, forms a synergistic cooperation scheme of the woven structure and the high-efficiency air film holes, can significantly improve the outflow coverage effect of the cooling air film, and enhance the comprehensive cooling effect of the air film of the CMC material components. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram of the fan-shaped-convergent slit-type air film hole structure;

[0018] Figure 2 (1) is a schematic diagram of a 2.5D braided CMC material fan-convergent seam type air film cooling flat plate model;

[0019] Figure 2 (2) is a partial enlarged schematic diagram of Figure 2 (1), where ① is the removed warp;

[0020] Figure 3 is the calculation domain model of the cooling effect of the flat air film of 2.5D woven CMC material;

[0021] Figure 4 is a schematic diagram of a circular air film hole structure;

[0022] Figure 5 is a schematic diagram of a 2.5D woven CMC material circular air film hole cooling plate model;

[0023] Figure 6 shows the comparison of film cooling effects between circular holes and fan-shaped-convergent slit-shaped holes in 2.5D braided CMC materials;

[0024] Figure 7 is a comparison of the outflow streamlines of the circular hole and fan-shaped-convergent slit-shaped hole air film of 2.5D woven CMC material. Best Mode for Carrying Out the Invention

[0025] The present invention will be further described below with reference to Examples and Comparative Examples. Example

[0026] The present invention takes a 2.5-dimensional woven structure CMC material film cooling flat plate as an example to illustrate a fan-shaped and convergent seam type film cooling hole based on a woven structure ceramic matrix composite (CMC) material core reservation method, and its film cooling implementation effect.

[0027] Figure 1 shows a schematic diagram of the fan-shaped and convergent seam-type film cooling hole structure of an embodiment of the present invention. Figure 2 shows a schematic diagram of a 2.5-dimensional woven structure CMC material fan-shaped and convergent seam-type film cooling flat plate model. The overall size of the flat plate is 50*3.34*3.45mm, wherein the fiber bundle cross-section is hexagonal, the warp spacing is 0.35mm, and the weft spacing is 0.35mm. Figure 3 shows the flat plate film cooling calculation domain model involved in the calculation simulation. The calculation domain is divided into three parts: the main flow gas domain has a geometric size of 50*3.34*10mm; the secondary flow cold air domain has a size of 50*3.34*5.6mm, and the size of the flat plate solid domain is shown in Figure 2.

[0028] During the modeling process, the conventional 2.5D woven warp yarns are first operated, the warp yarns of the bottom layer are fixed, and the upper warp yarns are moved backward a certain distance as a whole based on the previous layer. This distance should match the angle requirements of the film hole, including but not limited to the moving distance and the angle of the film hole in this article. Then, at the position of the film hole, the weft yarn is wound back to reserve space for the forward-leaning fan-shaped film hole. On this basis, the warp yarns of the uppermost layer downstream of the film hole are removed to reserve a larger operating space for the film hole, and a new forward-leaning fan-shaped film hole is cut at 0.75mm in the vertical direction behind the forward-leaning fan-shaped film hole to form a new forward-leaning fan-shaped film hole. After extracting the upper layer of the warp yarn, a slit is constructed, and the new forward-leaning fan-shaped film hole and the slit are combined through the ug straight grain operation to form the final fan-shaped-convergent seam-type film cooling hole.

[0029] The numerical research part utilized the non-isothermal flow and conjugate heat transfer models in the COMSOL software, in which the thermophysical properties of the flat solid domain were introduced and set from the micro-scale woven structure, that is, the isotropic thermal conductivity was set for the matrix part, and the anisotropic thermal conductivity was set for the fiber bundle part. At the same time, the curvilinear coordinate system in the COMSOL software was used in the setting to characterize the change of the anisotropic thermal conductivity of the fiber bundle part with the direction of the fiber bundle.

[0030] The calculations used the following boundary conditions for the mainstream inlet: an inlet temperature of 325.72 K and a mainstream velocity of 30 m / s; the following boundary conditions for the secondary inlet: an inlet temperature of 293.15 K and a blowing ratio of 0.5. The secondary flow enters the secondary channel through the secondary inlet, then enters the mainstream channel through the air film holes. After mixing with the mainstream, it exits through the outlet. This is the pressure outlet boundary condition, with an absolute pressure of 101325 Pa at the outlet. All other boundaries are adiabatic.

[0031] COMSOL software was used to mesh the computational model. A free tetrahedral mesh was used for the woven CMC flat plate, with tetrahedral elements and mesh refinement at the fiber-matrix interface. The air flow domain was generated using a solid-domain wall sweeping method, while a boundary layer mesh was constructed in the fluid domain near the gas-side wall.

[0032] Comparative Example:

[0033] At the same time, in order to compare the difference in cooling effect between the fan-shaped-convergent seam-type air film holes of the 2.5-dimensional woven CMC material of the present invention and the traditional circular air film cooling holes, the same simulation method was used in the comparative example to simulate and analyze the cooling effect of the circular air film hole cooling structure of the 2.5-dimensional woven CMC material. Figure 4 shows a schematic diagram of the circular air film cooling hole structure of the comparative example of the present invention, with a pore diameter of 0.8mm. Figure 5 shows a schematic diagram of the circular air film hole cooling flat plate model of the 2.5-dimensional woven structure CMC material, with an overall flat plate size of 50*3.34*3.45mm, wherein the fiber bundle cross-section is hexagonal, the warp yarn spacing is 0.35mm, and the weft yarn spacing is 0.35mm. The calculation domain model and size of the circular air film hole cooling flat plate are the same as those in Figure 3. At the same time, the anisotropic thermal conductivity setting, mesh division, and boundary condition setting involved in the simulation calculation in the comparative example are the same as those in the embodiment.

[0034] Figure 6 compares the distribution of comprehensive cooling efficiency for the air film-covered wall surface in the example (sector-shaped, converging slit-type film holes) and the comparative example (circular film holes). The figure shows that compared with circular film holes, the sector-shaped, converging slit-type film holes in the 2.5D woven CMC material significantly improve film coverage downstream, with film cooling efficiency remaining in the high-efficiency range. Within the 0-10D range downstream of the film holes, the average comprehensive cooling efficiencies for the circular and sector-shaped, converging slit-type film holes are 0.53 and 0.23, respectively.

[0035] FIG7 shows a streamline comparison of the two 2.5-dimensional woven CMC material film cooling structures in the embodiment and the comparative example. It can be seen from the figure that compared with the circular film holes, the fan-shaped and convergent slit-type air holes of the 2.5-dimensional woven CMC material have significantly improved air film coverage in the downstream.

[0036] In summary, the fan-shaped and convergent seam-type film cooling holes established in the present invention based on the core reservation method of the woven structure ceramic matrix composite (CMC) material can greatly improve the comprehensive cooling efficiency of the air film of the woven structure CMC material components without destroying the toughening fiber bundles.

[0037] 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 principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A design method for a fan-shaped and convergent seam type air film cooling structure of a braided CMC material, characterized in that: The following steps are involved: Step 1: The 2.5D woven CMC material structure is neatly arranged up and down, and the warp yarns of each layer are moved to the right by a distance d based on the warp yarns of the previous layer by dislocation. At the same time, a reserved space is formed in the CMC material structure by bending and hooking the weft yarns; Step 2: Fill the reserved space in step 1 with an ablative core to form a forward-inclined fan-shaped air film hole; Step 3: remove a warp yarn at the downstream of the forward-inclined fan-shaped air film hole and close to the upper wall surface to obtain a construction space; Step 4: According to the construction space obtained in step 3, a slit is constructed on the vertical upper wall surface where the warp yarn is removed, and the fan-shaped section of the forward-inclined fan-shaped air film hole is connected with the constructed slit through UG straight lines to form a fan-shaped-convergent slit-type air film cooling hole.

2. The design method of a braided CMC material fan-convergent seam type air film cooling structure according to claim 1, characterized in that: In the step 2, the expansion angle of the forward-inclined fan-shaped air film hole is limited by the size of the reserved space in the step 1, and is between 0 degrees and 12 degrees.

3. The design method of a braided CMC material fan-convergent seam type air film cooling structure according to claim 1, characterized in that: The inclination angle of the fan-shaped-convergent seam-type air film cooling hole is determined by the moving distance d of each layer of warp yarn in step 1. The larger d is, the smaller the inclination angle is.

4. The design method of a braided CMC material fan-convergent seam type air film cooling structure according to claim 1, characterized in that: In the step 4, the transition section angle from the fan-shaped section to the slit is determined by the forward tilting angle of the forward tilting fan-shaped air film hole in step 2 and the construction space obtained in step 3. The transition section angle is increased by 3 to 5 degrees based on the expansion angle of the forward tilting fan-shaped air film hole.

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