Engine ceramic matrix composite material guide vane structure optimization method

Abstract

An engine ceramic matrix composite material guide vane structure optimization method comprises the following steps that a guide vane initial structure, a guide vane service condition and constraint conditions under the service condition are provided, a finite element model is established to calculate the temperature and stress distribution of the guide vane under the service condition, and when the stress distribution under the service condition does not meet the strength constraint condition, a finite element model is established; and the cooling condition, the wall body thickness and the leading edge radius of the guide vane are iteratively optimized in sequence until the optimized structure meets the strength constraint condition of the guide vane in finite element simulation calculation. According to the method, mechanism optimization of the ceramic matrix composite guide vane can be effectively achieved, mutual interference of different design factors in the structure optimization process is avoided, the design efficiency is improved, and repeated work is reduced.

Description

Technical Field

[0001] This invention belongs to the field of aero-engines, specifically relating to a method for optimizing the structure of a ceramic matrix composite guide vane in an engine. Background Technology

[0002] With the continuous development of aero-engine technology, the total inlet temperature of engines is gradually approaching the service limit of traditional high-temperature alloy materials. Traditional nickel-based high-temperature alloys and other materials are no longer sufficient to meet the requirements of aero-engines for improving thrust-to-weight ratio and reducing fuel consumption. Therefore, ceramic matrix composites, which have better advantages in high temperature resistance, corrosion resistance, high specific strength, and high specific stiffness, are beginning to be widely used in the manufacture of aero-engine inlet materials. Among them, turbine guide vanes have complex structures, constrained by multiple key indicators such as aerodynamics, heat transfer, and strength, involving complex processes. Due to the difference in thermal conductivity, the leading edge region of the guide vane is prone to excessive thermal stress due to the temperature difference between the inner and outer walls, affecting the service life of the guide vane. Furthermore, due to the limitations of the manufacturing process of ceramic matrix composites themselves, the design optimization of the guide vane structure cannot be applied to the optimization process of traditional metal parts, resulting in a long design optimization cycle and high cost for ceramic matrix composite guide vanes. Therefore, providing a method for optimizing the structure of engine ceramic matrix composite guide vanes has high practical value for reducing engine design costs and shortening the design cycle. Summary of the Invention

[0003] The purpose of this invention is to provide a method for optimizing the structure of engine ceramic matrix composite guide vanes, thereby improving the optimization efficiency of the leading edge structure of composite guide vanes.

[0004] According to an embodiment of the present invention, a method for optimizing the structure of an engine ceramic composite guide vane is provided. The method includes the following steps: providing an initial guide vane structure, the initial guide vane structure including guide vane wall thickness t, leading edge radius R, and cooling condition C; providing guide vane service conditions and constraints under service conditions, the constraints under service conditions including temperature constraints, strength constraints, and aerodynamic performance constraints; establishing a finite element model of the initial guide vane structure and calculating the temperature distribution and stress distribution under the service conditions; when the stress distribution under the service conditions does not meet the strength constraints, adjusting the initial guide vane structure according to the following method: within the allowable range of the temperature constraints, using the finite element model to adjust the cooling condition C to reduce the temperature difference between the inner and outer sides of the leading edge wall, performing iterative calculations until the stress distribution meets the strength constraints or reaches the boundary of the temperature constraints, obtaining a first optimized guide vane structure; when the first optimized guide vane structure does not meet the strength constraints, maintaining the cooling condition C and using the finite element model to adjust part or all of the guide vane wall thickness t in the region, performing iterative calculations until the stress distribution meets the strength constraints or the leading edge wall thickness t meets the strength constraints. When the maximum stress reaches its minimum value, the second optimized guide vane structure is obtained. If the second optimized guide vane structure does not meet the strength constraint condition, the guide vane wall thickness t is maintained, and the leading edge radius R is adjusted using the finite element model within the aerodynamic constraint condition, and iterative calculations are performed until the stress distribution meets the strength constraint condition or the maximum stress of the leading edge wall reaches its minimum value, thus obtaining the third optimized guide vane structure. If the third optimized guide vane structure does not meet the strength constraint condition, the third optimized guide vane structure is used as the initial guide vane structure for re-iteration. When any one of the first, second, or third optimized guide vane structures meets the strength constraint condition, the iteration stops.

[0005] The above method can effectively improve the optimization efficiency of the leading edge structure of ceramic matrix composite guide vanes, avoid mutual interference between the aerodynamic performance, temperature, strength and other constraints of the guide vane when optimizing and adjusting the guide vane structure, make the structural optimization process have a clear direction and purpose, reduce repetitive work, and at the same time ensure that the optimized structure is manufacturable.

[0006] Furthermore, in some embodiments, the cooling condition C includes coating conditions, film cooling conditions, and impingement cooling conditions. By applying a coating to the outer surface of the guide vane leading edge and increasing the number, area, or angle of the film cooling holes, the temperature on the outer side of the leading edge can be reduced. Increasing the temperature of the impingement cooling airflow can raise the temperature on the inner surface of the leading edge, thereby reducing the temperature difference between the inner and outer sides of the leading edge wall.

[0007] Furthermore, in some embodiments, the method for adjusting the guide vane wall thickness t includes increasing or decreasing the number of ceramic fiber lay-up layers.

[0008] Furthermore, in some embodiments, the method for adjusting the guide vane wall thickness t further includes providing a filler in the ceramic fiber layup.

[0009] Furthermore, in some embodiments, the number of ceramic fiber layups increases by no more than 3 layers and decreases by no more than 6 layers.

[0010] Furthermore, in some embodiments, the adjustment of the leading edge radius R has geometric limits, which are -2% to 20%.

[0011] Furthermore, in some embodiments, the finite element model has at least three layers of elements in the thickness direction.

[0012] Furthermore, in some embodiments, the first principal direction of the unit is consistent with the fiber extension direction of the ceramic fiber layup.

[0013] Furthermore, in some embodiments, the strength constraints include circumferential stress constraints, interlayer stress constraints, and interlayer shear stress constraints. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of a ceramic matrix composite guide vane structure in one embodiment;

[0015] Figure 2 for Figure 1 Schematic diagram of the AA section structure;

[0016] Figure 3 This is a schematic diagram of the leading edge portion of the initial structure of the guide vane in one embodiment;

[0017] Figure 4 A schematic diagram showing the optimized leading edge structure of the guide vane;

[0018] Figure 5 This is a schematic diagram of a method for optimizing the structure of a ceramic matrix composite guide vane in one embodiment.

[0019] The purpose of the above-described drawings is to provide a detailed description of the present invention so that those skilled in the art can understand the technical concept of the invention, and is not intended to limit the invention. For the sake of brevity, the above-described drawings only schematically depict the structures related to the technical features of the present invention, and do not depict the complete structure and all details strictly according to actual scale. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0021] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment herein. The phrase appearing in various places in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive, independent, or alternative embodiments. Those skilled in the art will understand that the embodiments herein can be combined with other embodiments without causing structural conflicts.

[0022] In this description, unless otherwise expressly specified and limited, the technical terms "installation," "connection," "joining," etc., should be interpreted broadly, referring to movable connections, fixed connections, or integration. Those skilled in the art can understand the specific meaning of these terms in the embodiments of this application based on the specific circumstances.

[0023] In this description, terms such as "upper," "lower," "left," "right," "lateral," "longitudinal," "height," "length," and "width," which indicate orientation or positional relationships, are intended to accurately describe the embodiments and simplify the description, rather than limiting the parts or structures involved to have a specific orientation, or to be installed or operated in a specific orientation, and should not be construed as limiting the embodiments in this document.

[0024] In this description, terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating relative importance or limiting the number, specific order, or primary / secondary relationship of the described technical features. In this description, "multiple" means at least two.

[0025] As the thrust and efficiency requirements of civil aero engines continue to increase, the total inlet temperature of engines is also rising, with turbine inlet gas temperatures reaching 1978K under high-temperature takeoff conditions. Currently, for turbine stator components, the service temperature and performance of traditional high-temperature alloy materials are nearing their limits under conventional cooling and thermal barrier coating technologies, making it difficult to meet the design requirements of next-generation advanced aero engines. Compared to traditional high-temperature alloys, ceramic matrix composites (CMCs) offer advantages such as high temperature resistance, corrosion resistance, high specific strength, and high specific stiffness. Applying CMC materials to turbine stator components, such as turbine guide vanes, based on these advantages can improve aero engine performance in multiple ways, including reducing cooling gas consumption, increasing turbine temperature, and reducing NOx emissions, thereby meeting the needs of next-generation advanced aero engines.

[0026] Turbine guide vane design needs to meet multiple requirements, including aerodynamics, heat transfer, and strength. For example, the blade shape must meet certain aerodynamic efficiency requirements, the heat transfer design must prevent the blade from overheating, and the stress at all points on the blade must be below the strength limit. Generally, iterative optimization of the structural dimensions is required to meet these requirements. In one embodiment, the CMC guide vane structure is as follows: Figure 1As shown, the guide vane includes upper and lower end plates 1, with the blade body 2 between the plate plates 1, and a cavity 3 inside the blade body 2. For the guide vane as a whole, the area containing the arc-shaped structure such as the leading edge 4 is prone to thermal stress causing the material to bear stress exceeding the allowable range. Specifically, as... Figure 2 As shown, the internal and external temperature difference will cause tensile circumferential stress 6 to form on the cold end (inner) wall and compressive circumferential stress 7 on the hot end (outer) wall, while tensile stress and shear stress will also form in the thickness direction. From an aerodynamic perspective, when the outer radius R of the leading edge 4 changes, the aerodynamic shape of the blade changes, causing changes in the aerodynamic pressure and velocity distribution on the blade surface, which in turn changes the blade strength load boundary and heat transfer boundary. From a strength perspective, the guide vane wall thickness t and radius R affect the blade stiffness and stress concentration factor, which in turn affect the stress caused by mechanical load. From a heat transfer perspective, when the wall thickness t and radius R change, the thermal resistance of the CMC guide vane changes, causing the internal and external temperature difference ΔT and the internal temperature gradient to change accordingly. The internal and external temperature difference ΔT and the temperature gradient affect the thermal stress. Overall, changes in the structural parameters t and R directly affect the blade stiffness, and indirectly affect the blade strength by changing the heat transfer and aerodynamic boundaries. The interrelationships of these parameters (t, R, ΔT) are complex. Modifying one parameter often inevitably affects other parameters, making it difficult to directly determine the optimal parameter combination.

[0027] To address the aforementioned issues, embodiments of the present invention provide an iterative optimization design method that, by combining finite element simulation calculations, can obtain guide vane structure dimensions that simultaneously meet aerodynamic, heat transfer, and strength requirements.

[0028] In a preferred embodiment, the process of structurally optimizing the engine CMC guide vane is as follows: Figure 5 As shown, it includes the following steps:

[0029] First, based on the engine aerodynamic performance requirements (aerodynamic performance constraints), material processing requirements (strength constraints and the processability limitations of CMC materials), and heat transfer design requirements (temperature constraints), determine as follows: Figure 1 The initial structure of the CMC guide vane shown has a leading edge 4 with a radius R, and the wall surrounding the cavity 3, except for the trailing edge 5, has a uniform thickness t. The guide vane has cooling conditions C. Specifically, in a preferred embodiment, cooling conditions C include coating conditions, film cooling conditions, and impact cooling conditions on the outer surface of the CMC guide vane.

[0030] Next, a finite element model of the guide vane is established, and the model is meshed with a mesh size of 0.1mm-3mm, with at least three layers of elements in the thickness direction. In a preferred embodiment, the material parameters used in the finite element model are anisotropic parameters, and a material element coordinate system is established for all elements. Considering the anisotropy of ceramic matrix composites, the first principal direction of the element is aligned with the extension direction of the fibers in the CMC fiber layup when establishing the finite element model. Based on the aerodynamic shape of the guide vane and the turbine inlet and outlet boundary conditions, the aerodynamic pressure P and the corresponding airflow velocity v borne by the aerodynamic shape are calculated using computational fluid dynamics and other methods. The overall temperature distribution T of the guide vane is calculated in conjunction with the cooling condition C. Displacement constraints are set according to the actual installation of the CMC guide vane, and pressure boundaries (aerodynamic pressure P) and temperature distribution T are applied to calculate the stress distribution state of the overall CMC guide vane structure.

[0031] Based on the element coordinate system, the circumferential stress, interlaminar stress, and interlaminar shear stress in the stress results are extracted, and it is determined whether they meet the strength constraints. Specifically, it is determined whether the stress at any position on the leading edge 4 of the CMC guide vane exceeds the allowable stress of the material. If the CMC guide vane meets the strength constraints, no structural optimization is required.

[0032] If the CMC guide vane does not meet the strength constraints under the initial structure, the structure shall be optimized as follows:

[0033] The first step is to reduce the temperature difference between the inner and outer sides of the leading edge 4 in the finite element model (i.e., change the cooling condition C) within the temperature constraint range of the CMC guide vane. In engineering practice, reducing the temperature difference is achieved by: setting a thermal barrier coating on the outer side of the leading edge 4, increasing the number or area of ​​film cooling holes, optimizing the angle of the film cooling holes, and / or increasing the temperature of the impinging cooling airflow in the cavity 3 or reducing the cooling airflow rate. Iterative calculations are performed in the finite element model until the stress distribution meets the strength constraint conditions by reducing the temperature difference, or until the CMC guide vane structure corresponding to the minimum temperature difference achievable through the above modifications is reached. This structure is then used as the first optimized structure for the guide vane.

[0034] The second step involves retaining the cooling condition C determined by the first optimized guide vane structure and reducing the wall thickness t while keeping the outer radius R of the leading edge 4 unchanged. The modification of thickness t should satisfy the process boundary conditions, namely, the minimum requirements for wall thickness in the formability of the CMC guide vane and the basic requirements for structural strength under aerodynamic loads. In different regions surrounding the cavity 3, the modification of wall thickness t may be the same or different. In some regions, the thickness can be reduced by decreasing the CMC fiber layup, while in others, it can be increased by increasing the CMC fiber layup or by adding fillers between the layups. In a preferred embodiment, the adjustment range for the number of CMC fiber layups is that the number of layers reduced does not exceed 6, and the number of layers added does not exceed 3. The finite element model is used to iteratively calculate different wall thicknesses t until the stress distribution satisfies the strength constraint conditions, or until the thickness t where the maximum stress within the leading edge 4 reaches its minimum value is obtained. The corresponding CMC guide vane structure is then taken as the second optimized guide vane structure.

[0035] Third, if the second optimized structure of the guide vane still does not meet the strength constraint conditions, retain the thickness t determined by the second optimized structure, and adjust the outer radius R of the leading edge 4 based on the second optimized structure. Since the outer radius R of the leading edge 4 is related to aerodynamic efficiency, in the preferred embodiment, the adjustment range of the radius R of the leading edge 4 has a geometric limit, which is -2% to 20%, that is, the adjusted radius R of the leading edge 4 is 98% to 120% of the original value. The finite element model is used to iteratively calculate the CMC guide vane structural components with different R values ​​until the stress distribution meets the strength constraint conditions, or the radius R in which the maximum stress within the leading edge 4 reaches the minimum value is obtained, and the corresponding CMC guide vane structure is taken as the third optimized structure of the guide vane.

[0036] Finally, finite element simulation is performed based on the third optimized structure of the guide vane. If the strength constraints are met, the structural optimization is complete. However, if the third optimized structure of the guide vane still does not meet the strength constraints, this third optimized structure is used as the initial structure of the guide vane, and the process returns to the first step to repeat the structural optimization iteration until the cooling conditions C, wall thickness t, and leading edge radius R that meet the strength constraints are obtained.

[0037] In a preferred embodiment, the initial local structure of region 4 of the CMC guide vane leading edge is as follows: Figure 4As shown, the outer radius R of the leading edge 4 is 5mm, the wall thickness of the cavity 3 is 3mm on all sides, the cooling condition C is no air film pores, and four rows of impact cooling holes are set on the inner surface of the cavity 3. The leading edge 4 is formed by laying 10 layers of CMC fiber layup 8. A finite element model was established and simulation calculations were performed under service conditions. It was found that the circumferential stress on the inner surface reached 3 times the allowable value, the interlayer tensile stress reached 2 times the allowable value, and the interlayer shear stress reached 2 times the allowable value. This initial structure does not meet the strength constraint conditions of the guide vane.

[0038] The structure of the guide vane was optimized using the engine ceramic matrix composite material structure optimization method described in the previous embodiment. In the first round of optimization, the cooling condition C was iteratively optimized, resulting in the scheme with the minimum temperature difference between the inner and outer sides of the leading edge 4: a single exhaust film hole was provided at the leading edge 4 to reduce the outer temperature, and the number of impact cooling holes on the inner surface of the cavity 3 was reduced to two rows to increase the inner temperature. This structure was used as the first optimized guide vane structure. Simulation calculations using a finite element model showed that under service conditions, the circumferential stress on the inner surface was twice the allowable material value, the interlaminar tensile stress was 1.5 times the allowable material value, and the interlaminar shear stress was 1.5 times the allowable material value. Therefore, the first optimized guide vane structure did not meet the strength constraint conditions.

[0039] Next, a second round of optimization was conducted, adjusting the wall thickness t. During the adjustment process, based on the cooling condition C determined by the first optimized structure of the guide vane, the wall thickness was iteratively optimized. The wall thickness of the leading edge 4 (3mm) and radius R (5mm) remained unchanged, while the wall thickness of other areas around the cavity 3 was reduced to 2.5mm. At this point, the maximum stress of the leading edge 4 reached its minimum value, and this structure was used as the second optimized structure of the guide vane. Simulation calculations using a finite element model showed that the circumferential stress on the inner surface under service conditions was 1.2 times the allowable value of the material, the interlaminar tensile stress was basically the same as the allowable value of the material, and the interlaminar shear stress was the same as the allowable value of the material during icing. The second optimized structure of the guide vane still did not meet the strength constraint conditions.

[0040] Subsequently, a third round of optimization was conducted, adjusting the outer radius R of the leading edge 4 within geometric limits. Based on the wall thickness obtained from the second optimized structure of the guide vane, the outer radius R of the leading edge 4 was iteratively optimized. By using the filler 9 between the CMC fiber layers in the leading edge 4 region, the outer radius R of the leading edge 4 was increased to 5.2 mm. At this point, the maximum stress of the leading edge 4 reached its minimum value. Figure 4 As shown, this structure is used as the third optimized structure of the guide vane. Using a finite element model, calculations show that under service conditions, the circumferential stress on the inner surface, the interlaminar tensile stress, and the interlaminar shear stress all do not exceed the allowable values ​​of the material. Therefore, the third optimized structure of the guide vane satisfies the strength constraints, and this structure is used as the optimized structure of the CMC guide vane.

[0041] The purpose of the above embodiments is to provide a further detailed description of the present invention in conjunction with the accompanying drawings, so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, optimization or equivalent substitution of the method steps involved, as well as combination of implementation methods in different embodiments without causing structural and principle conflicts, all fall within the protection scope of the present invention.

Claims

1. A method for optimizing the structure of a ceramic matrix composite guide vane for an engine, characterized in that, Includes the following steps: The initial structure of the guide vane is provided, which includes the guide vane wall thickness t, leading edge radius R, and cooling conditions C; the service conditions of the guide vane and the constraints under the service conditions are provided, which include temperature constraints, strength constraints, and aerodynamic performance constraints. A finite element model of the initial structure of the guide vane was established, and the temperature and stress distribution under the service conditions were calculated. If the stress distribution under the service conditions does not meet the strength constraint conditions, the initial structure of the guide vane shall be adjusted according to the following method: Within the allowable range of the temperature constraint conditions, the cooling condition C is adjusted using the finite element model to reduce the temperature difference between the inner and outer sides of the leading edge wall. Iterative calculations are performed until the stress distribution satisfies the strength constraint conditions or reaches the boundary of the temperature constraint conditions, thus obtaining the first optimized structure of the guide vane. When the first optimized structure of the guide vane does not meet the strength constraint condition, the cooling condition C is maintained and the thickness t of the guide vane wall in part or all of the region is adjusted using the finite element model for iterative calculation until the stress distribution meets the strength constraint condition or the maximum stress of the leading edge wall reaches the minimum value, thus obtaining the second optimized structure of the guide vane. When the second optimized structure of the guide vane does not meet the strength constraint condition, the guide vane wall thickness t is maintained and the leading edge radius R is adjusted using the finite element model within the aerodynamic constraint condition and iterative calculation is performed until the stress distribution meets the strength constraint condition or the maximum stress of the leading edge wall reaches the minimum value, thus obtaining the third optimized structure of the guide vane. When the third optimized structure of the guide vane does not meet the strength constraint condition, the third optimized structure of the guide vane is used as the initial structure of the guide vane for re-iteration. The iteration stops when any one of the first optimized guide vane structure, the second optimized guide vane structure, or the third optimized guide vane structure satisfies the strength constraint condition.

2. The method for optimizing the structure of engine ceramic matrix composite guide vanes according to claim 1, characterized in that, The cooling condition C includes coating conditions, film cooling conditions, and impact cooling conditions.

3. The method for optimizing the structure of engine ceramic matrix composite guide vanes according to claim 1 or 2, characterized in that, The method for adjusting the thickness t of the guide vane wall includes increasing or decreasing the number of ceramic fiber lay-up layers.

4. The method for optimizing the structure of engine ceramic matrix composite guide vanes according to claim 3, characterized in that, The method for adjusting the thickness t of the guide vane wall also includes setting a filler in the ceramic fiber layup.

5. The method for optimizing the structure of engine ceramic matrix composite guide vanes according to claim 3, characterized in that, The number of ceramic fiber lay-ups can be increased by no more than 3 layers and decreased by no more than 6 layers.

6. The method for optimizing the structure of engine ceramic matrix composite guide vanes according to claim 1 or 2, characterized in that, The leading edge radius R is adjusted with geometric limits of -2% to 20%.

7. The method for optimizing the structure of engine ceramic matrix composite guide vanes according to claim 1 or 2, characterized in that, The finite element model has at least three layers of elements in the thickness direction.

8. The method for optimizing the structure of engine ceramic matrix composite guide vanes according to claim 7, characterized in that, The first principal direction of the unit is consistent with the fiber extension direction of the ceramic fiber layup.

9. The method for optimizing the structure of engine ceramic matrix composite guide vanes according to claim 1 or 2, characterized in that, The strength constraints include circumferential stress constraints, interlayer stress constraints, and interlayer shear stress constraints.

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