Design method for active cooling structure of anti-deposition and anti-clogging CMC material

Abstract

The invention discloses a design method of an active cooling structure of an anti-deposition and anti-clogging CMC (Carboxyl Methyl Cellulose) material, and the design of an anti-deposition and low-cooling-efficiency attenuation air film cooling hole structure is based on key geometric characteristics of an expanded air film hole of a CMC material component and on the basis of traditional fluid-solid coupling heat transfer simulation calculation. The method comprises the following steps: simulating the trajectory of sand and dust particles in a fluid by combining a dispersed phase model, introducing a particle deposition probability model through a user-defined function, and carrying out integrated design of a CMC material air film cooling structure under a dust-containing working condition, so as to form a deposition-resistant cooling-efficiency low-attenuation air film cooling structure scheme of a ceramic-based composite material component. And the cooling effect before and after particle deposition is analyzed and evaluated. Therefore, by simulating and analyzing the influence of the anti-deposition air film holes on the particle deposition rate on the wall surface, an evaluation method for air film cooling effect attenuation after particle deposition is formed, the air film cooling effect attenuation caused by particle deposition can be remarkably reduced, and the air film comprehensive cooling effect of a CMC material component under the long-term dust-containing service condition is improved.

Description

Technical Field

[0001] The invention relates to the technical field of engineering thermal physics, and in particular to a design method for an active cooling structure of a CMC material that resists deposition and clogging. 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, higher thermodynamic cycle parameters (gas temperature exceeding 2200K), longer component life and reliability (life exceeding 6000 hours) and other design requirements have brought outstanding challenges to the development of new generation aircraft engines, especially high-temperature components represented by turbine blades. The existing turbine blade design capabilities based on high-temperature alloys have reached their limits. The application of composite materials represented by ceramic matrix composites (Ceramic Catrix Composites, referred to as CMC) provides the most possible and promising solution.

[0003] CMC materials have become a key solution to improve the heat resistance of hot-end components of aircraft engines, but their heat resistance limit is still lower than the gas temperature of high-performance aircraft engines above 2200K. In particular, the temperature resistance of SiC fiber-reinforced CMC materials currently produced in China is about 1623K, which is still behind that of foreign countries. Therefore, efficient cooling technology is still needed to ensure the safe service of CMC high-temperature components. At present, the cooling structure design of high-temperature components such as CMC turbine blades mostly adopts the idea of ​​replacing the metal blade cooling structure solution, using full air film coverage on the leading edge and pressure surface of the blade, and using slits and spoiler cooling structures on the trailing edge. However, for CMC blades, on the one hand, their operating temperature is higher than that of traditional high-temperature alloys, which is close to or exceeds the melting point of typical sand and dust particles. When serving in a dusty environment, the deposition rate of sand and dust particles increases with the temperature index, and the deposition amount will be significantly higher than that of metal-based blades; on the other hand, CMC materials are heterogeneous structures composed of matrix and toughening fibers, and their molding process is complex. In addition, ceramic-based materials are difficult to process in traditional ways, resulting in a relatively rough surface of CMC components, and sand and dust particles are more likely to deposit on the rough wall. Therefore, it is necessary to design and analyze the anti-deposition blocking, low-attenuation and high-efficiency active cooling structure suitable for CMC turbine blades based on the structure and process characteristics of braided CMC materials.

[0004] For CMC materials, due to the difference in thermal properties between the internal fibers and the matrix, as well as the anisotropy of the fibers themselves, the overall thermal conductivity of CMC materials presents obvious anisotropy. Its internal fiber weaving structure and pore structure and other characteristics will also have a significant impact on the heat transfer process of the cooling structure. Therefore, on the surface of CMC materials, there will be a discrete temperature distribution that changes with the weaving structure, which in turn affects the morphology of particles after deposition. Therefore, the designability of the microstructure of the material can be fully utilized, combined with the characteristics of the efficient cooling structure, to carry out the design of the CMC material's anti-deposition blocking, low-attenuation, and efficient active cooling structure. Summary of the invention

[0005] The present invention provides a design method for active cooling structure of CMC materials that resists deposition and clogging, aiming at the risk of particle deposition and clogging of turbine blade cooling structures made of high-temperature ceramic-based composite materials under dusty service conditions, as well as the cooling efficiency attenuation caused by particle deposition. Based on the adjustment of the shape of the air film holes, the particle deposition characteristics and cooling efficiency anti-attenuation effect of the high-efficiency air film cooling structure are explored, which can significantly improve the coverage effect of the cooling air film outflow, reduce the particle deposition rate near the air film holes, and reduce the comprehensive cooling efficiency attenuation of the air film cooling structure after particle deposition.

[0006] The embodiment of the present invention provides a method for designing an active cooling structure of a CMC material that resists deposition and clogging, comprising the following steps:

[0007] Step 1: Taking advantage of the designability of the structural fiber of the braided CMC material preform, combined with the outflow characteristics and structural features of the expanded air film hole, the integrated design of the expanded air film hole and the material preform structure is carried out, and the anti-deposition air film cooling structure model of the CMC material component and its fluid-solid coupling simulation model are constructed to calculate the material wall temperature distribution and the comprehensive cooling effect of the air film;

[0008] Step 2: For the anti-deposition air film cooling structure model of the CMC material component and its fluid-solid coupling simulation model in step 1, a particle dispersed phase model is introduced to calculate the motion trajectory of dust particles in the flow field. At the same time, a particle deposition probability criterion model is introduced to obtain the wall particle deposition distribution under the simulation results of the anti-deposition air film hole;

[0009] Step 3: According to the wall particle deposition distribution under the simulation result of the anti-deposition air film hole obtained in step 2, when the thickness of the deposition layer is greater than the preset threshold, the volume grid of the deposition layer is reconstructed by moving the grid or extracting the thickness to remodel, and the wall temperature distribution including the influence of the deposition layer on the flow heat transfer and the comprehensive cooling effect of the air film after the particle deposition are calculated; when the thickness of the deposition layer is less than or equal to the preset threshold, the method of assigning thermal resistance to the deposition layer according to the thickness is used to calculate the wall temperature distribution including only the thermal resistance of the deposition layer and the comprehensive cooling effect of the air film after the particle deposition;

[0010] Step 4: Compare the comprehensive cooling effect of the air film after particle deposition calculated in step 3 with the material wall temperature distribution and the comprehensive cooling effect of the air film calculated by the fluid-solid coupling simulation model without particle deposition in step 1 to obtain the cooling effect attenuation, and evaluate the anti-deposition and low attenuation performance of the new air film hole based on the cooling effect attenuation.

[0011] Optionally, in an embodiment of the present invention, step one specifically includes:

[0012] Taking advantage of the designability of the structural fibers of the woven CMC material preform and combining the outflow characteristics and structural features of the expandable air film hole, the fiber bundles are wound back to weave the reserved space in the hole area. At the same time, the number of local fibers is adjusted according to the hole characteristics, and the expandable air film hole and the material preform structure are integrated to form an expandable hole cooling structure. On both sides of the solid domain model of the air film hole structure, the high-temperature mainstream domain and the low-temperature secondary domain are respectively constructed and connected through the air film hole to form the anti-deposition air film cooling structure model of the CMC material component and its fluid-solid coupling simulation model, and the material wall temperature distribution and the comprehensive cooling effect of the air film are calculated.

[0013] Optionally, in an embodiment of the present invention, step 2 specifically includes:

[0014] For the anti-deposition air film cooling structure model of CMC material components and its fluid-solid coupling simulation model in step one, particle deposition calculation is introduced. The numerical simulation of particle deposition on the structure surface includes two aspects: the calculation of particle motion trajectory and the calculation of particle deposition on the structure surface. The particle trajectory is calculated by the Euler-Lagrangian method. The particles are regarded as discrete phases, and the control equation is established by the Lagrangian method. The gas phase is solved by the Euler method. The dispersed phase model simulates the interaction between the two phases, gives the motion trajectory of the particles in the flow field, and describes the landing point of the microparticles. After reaching the near wall surface, the particles will collide with the wall surface under the action of aerodynamic force, and then splash, rebound, spread and adhere. Through the rebound adhesion model based on particle viscosity calculation, the ratio of the critical viscosity of a single particle to the viscosity value when it hits the wall is calculated as the deposition probability to determine whether the particles are deposited. The undeposited particles continue to move according to the rebound velocity calculated by the collision momentum equation, and the deposited particles have their velocity assigned to zero, so that they are consolidated on the wall surface, thereby obtaining the wall particle deposition distribution under the simulation results of the anti-deposition air film hole.

[0015] Optionally, in an embodiment of the present invention, step three specifically includes:

[0016] According to the wall particle deposition distribution under the simulation results of the anti-deposition air film hole obtained in step 2, the wall temperature distribution and comprehensive cooling effect considering the influence of the deposition layer on heat transfer are calculated. Considering the calculation speed and accuracy comprehensively, a preset threshold is set for the maximum thickness of the deposition layer. The wall temperature and cooling effect after particle deposition are calculated in two schemes. When the deposition layer thickness is greater than the preset threshold and will have a significant impact on the flow, the volume grid of the deposition layer is reconstructed by moving the grid or extracting the deposition layer thickness to remodel. After the grid properties of the deposition layer area are reassigned according to the physical properties of the deposition, the iterative calculation is re-performed to obtain the wall temperature distribution and the comprehensive cooling effect of the air film including the influence of the deposition layer on the flow heat transfer. When the deposition layer thickness is less than or equal to the preset threshold, the influence of the deposition on the flow is ignored, and the expression is used to assign the thermal resistance variable to the deposition layer according to the thickness to calculate the wall temperature distribution including only the thermal resistance of the deposition layer wall and the comprehensive cooling effect of the air film after particle deposition.

[0017] Optionally, in an embodiment of the present invention, step 4 specifically includes:

[0018] The comprehensive cooling effect is compared with the comprehensive cooling effect calculated by the fluid-solid coupling simulation model that does not include particle deposition in step one, focusing on the comprehensive cooling effect on the downstream center line of the air film hole outflow and the surface average comprehensive cooling effect of the area near the air film hole. It is compared with the cooling effect value before deposition to obtain the percentage value of the cooling effect attenuation in the characteristic area. The anti-deposition and low attenuation performance of the new air film hole is evaluated based on the cooling effect attenuation.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention avoids the convolution of particles by the vortex at the outlet of the traditional circular air film hole, improves the anti-deposition effect downstream of the air film hole, can significantly reduce the cooling efficiency attenuation after particle deposition, and improves the comprehensive cooling effect of the air film of CMC material components after long-term service under the condition of particle deposition.

[0021] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0023] Figure 1 A flow chart of a method for designing an active cooling structure of a CMC material that resists deposition and clogging according to an embodiment of the present invention;

[0024] Figure 2 This is a schematic diagram of the expansion type air film hole structure of an embodiment of the present invention;

[0025] Figure 3 This is a schematic diagram of a 2.5-dimensional braided CMC material expanded air film cooling flat plate model according to an embodiment of the present invention;

[0026] Figure 4 It is a computational domain model of a 2.5-dimensional braided CMC material flat plate according to an embodiment of the present invention;

[0027] Figure 5 This is a schematic diagram of a circular air film hole structure according to an embodiment of the present invention;

[0028] Figure 6 This is a schematic diagram of a 2.5-dimensional woven CMC material circular air film hole cooling flat plate model according to an embodiment of the present invention;

[0029] Figure 7 Comparison of film cooling effects of circular holes and expanded holes in 2.5D braided CMC materials according to an embodiment of the present invention;

[0030] Figure 8 Comparison of the deposition thickness of circular holes and expanded holes of the 2.5-dimensional woven CMC material according to the embodiment of the present invention;

[0031] Fig. 9 Comparison of the outflow streamlines of the circular hole and the expanded hole air film of the 2.5-dimensional woven CMC material of the embodiment of the present invention;

[0032] Fig.10 Comparison of velocity distribution at the exit of the circular hole and the expansion hole of the 2.5-dimensional braided CMC material of the embodiment of the present invention;

[0033] Fig.11 Comparison of the vortex structures near the circular holes and the expansion holes of the 2.5-dimensional braided CMC material according to the embodiment of the present invention. DETAILED DESCRIPTION

[0034] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0035] Figure 1 The present invention is a flowchart of a method for designing an active cooling structure of a CMC material that resists deposition and clogging according to an embodiment of the present invention.

[0036] like Figure 1 As shown, the active cooling structure design method of the anti-deposition clogging CMC material includes the following steps:

[0037] Step 1: Taking advantage of the designability of the structural fiber of the braided CMC material preform, combined with the outflow characteristics and structural features of the expanded air film hole, the integrated design of the expanded air film hole and the material preform structure is carried out, and the anti-deposition air film cooling structure model of the CMC material component and its fluid-solid coupling simulation model are constructed to calculate the material wall temperature distribution and the comprehensive cooling effect of the air film;

[0038] Step 2: For the anti-deposition air film cooling structure model of the CMC material component and its fluid-solid coupling simulation model in step 1, a particle dispersed phase model is introduced to calculate the motion trajectory of dust particles in the flow field. At the same time, a particle deposition probability criterion model is introduced to obtain the wall particle deposition distribution under the simulation results of the anti-deposition air film hole;

[0039] Step 3: According to the wall particle deposition distribution under the simulation result of the anti-deposition air film hole obtained in step 2, when the thickness of the deposition layer is greater than the preset threshold, the volume grid of the deposition layer is reconstructed by moving the grid or extracting the thickness to remodel, and the wall temperature distribution including the influence of the deposition layer on the flow heat transfer and the comprehensive cooling effect of the air film after the particle deposition are calculated; when the thickness of the deposition layer is less than or equal to the preset threshold, the method of assigning thermal resistance to the deposition layer according to the thickness is used to calculate the wall temperature distribution including only the thermal resistance of the deposition layer and the comprehensive cooling effect of the air film after the particle deposition;

[0040] Step 4: Compare the comprehensive cooling effect of the air film after particle deposition calculated in step 3 with the material wall temperature distribution and the comprehensive cooling effect of the air film calculated by the fluid-solid coupling simulation model without particle deposition in step 1 to obtain the cooling effect attenuation, and evaluate the anti-deposition and low attenuation performance of the new air film hole based on the cooling effect attenuation.

[0041] Optionally, in an embodiment of the present invention, step one specifically includes:

[0042] Taking advantage of the designability of the structural fibers of the woven CMC material preform and combining the outflow characteristics and structural features of the expandable air film hole, the fiber bundles are wound back to weave the reserved space in the hole area. At the same time, the number of local fibers is adjusted according to the hole characteristics, and the expandable air film hole and the material preform structure are integrated to form an expandable hole cooling structure. On both sides of the solid domain model of the air film hole structure, the high-temperature mainstream domain and the low-temperature secondary domain are respectively constructed and connected through the air film hole to form the anti-deposition air film cooling structure model of the CMC material component and its fluid-solid coupling simulation model, and the material wall temperature distribution and the comprehensive cooling effect of the air film are calculated.

[0043] Optionally, in an embodiment of the present invention, step 2 specifically includes:

[0044] For the anti-deposition air film cooling structure model of CMC material components and its fluid-solid coupling simulation model in step one, particle deposition calculation is introduced. The numerical simulation of particle deposition on the structure surface includes two aspects: the calculation of particle motion trajectory and the calculation of particle deposition on the structure surface. The particle trajectory is calculated by the Euler-Lagrangian method. The particles are regarded as discrete phases, and the control equation is established by the Lagrangian method. The gas phase is solved by the Euler method. The dispersed phase model simulates the interaction between the two phases, gives the motion trajectory of the particles in the flow field, and describes the landing point of the microparticles. After reaching the near wall surface, the particles will collide with the wall surface under the action of aerodynamic force, and then splash, rebound, spread and adhere. Through the rebound adhesion model based on particle viscosity calculation, the ratio of the critical viscosity of a single particle to the viscosity value when it hits the wall is calculated as the deposition probability to determine whether the particles are deposited. The undeposited particles continue to move according to the rebound velocity calculated by the collision momentum equation, and the deposited particles have their velocity assigned to zero, so that they are consolidated on the wall surface, thereby obtaining the wall particle deposition distribution under the simulation results of the anti-deposition air film hole.

[0045] Optionally, in an embodiment of the present invention, step three specifically includes:

[0046] According to the wall particle deposition distribution under the simulation results of the anti-deposition air film hole obtained in step 2, the wall temperature distribution and comprehensive cooling effect considering the influence of the deposition layer on heat transfer are calculated. Considering the calculation speed and accuracy comprehensively, a preset threshold is set for the maximum thickness of the deposition layer. The wall temperature and cooling effect after particle deposition are calculated in two schemes. When the deposition layer thickness is greater than the preset threshold and will have a significant impact on the flow, the volume grid of the deposition layer is reconstructed by moving the grid or extracting the deposition layer thickness to remodel. After the grid properties of the deposition layer area are reassigned according to the physical properties of the deposition, the iterative calculation is re-performed to obtain the wall temperature distribution and the comprehensive cooling effect of the air film including the influence of the deposition layer on the flow heat transfer. When the deposition layer thickness is less than or equal to the preset threshold, the influence of the deposition on the flow is ignored, and the expression is used to assign the thermal resistance variable to the deposition layer according to the thickness to calculate the wall temperature distribution including only the thermal resistance of the deposition layer wall and the comprehensive cooling effect of the air film after particle deposition.

[0047] Optionally, in an embodiment of the present invention, step 4 specifically includes:

[0048] The comprehensive cooling effect is compared with the comprehensive cooling effect calculated by the fluid-solid coupling simulation model that does not include particle deposition in step one, focusing on the comprehensive cooling effect on the downstream center line of the air film hole outflow and the surface average comprehensive cooling effect of the area near the air film hole. It is compared with the cooling effect value before deposition to obtain the percentage value of the cooling effect attenuation in the characteristic area. The anti-deposition and low attenuation performance of the new air film hole is evaluated based on the cooling effect attenuation.

[0049] The present invention will be further described below with reference to Examples and Comparative Examples.

[0050] Example:

[0051] Figure 2 A schematic diagram of an anti-deposition low-attenuation expansion type air film pore structure according to an embodiment of the present invention is given. Figure 2 A schematic diagram of a 2.5D woven CMC material anti-deposition low-attenuation expanded film cooling flat plate model is given. The overall size of the plate is 50*6.68*3.45mm, the fiber bundle cross-section is hexagonal, the warp yarn spacing is 0.35mm, and the weft yarn spacing is 0.35mm. Figure 3 The calculation domain model of the flat plate film cooling involved in the calculation simulation is given. The calculation domain is divided into three parts: the geometric size of the mainstream gas domain is 90 mm above the flat plate. In order to improve the particle collision efficiency in the simulation, a 45° turn is set in front of the flat plate by the mainstream channel; the size of the secondary cooling gas domain is 50*6.68*5.6 mm, and the size of the flat plate solid domain is as follows: Figure 3 as shown in .

[0052] 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 backwards as a whole for a certain distance based on the previous layer. This distance should meet the angle requirements of the air film hole, including but not limited to the moving distance and air film hole angle in this article. Then, at the position of the air film hole, the weft yarn is wound back to reserve space for the forward-leaning expansion air film hole. On this basis, the uppermost warp yarn downstream of the air film hole is removed to reserve a larger air film hole operation space, and the 0.75mm vertical direction behind the forward-leaning expansion air film hole is cut to form a new forward-leaning expansion air film hole.

[0053] The numerical study part utilized the non-isothermal flow and coupled heat transfer model in FLUENT software, and introduced the DPM dispersed phase model and particle deposition UDF function to calculate the particle trajectory and deposition criteria. The thermophysical parameters of the flat solid domain were introduced from the microscopic scale weaving 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. The anisotropic thermal conductivity matrix was used in the setting to characterize the change of the thermal conductivity of the fiber bundle part with the direction of the fiber bundle.

[0054] The mainstream inlet boundary in the calculation is: inlet temperature is 1300-2400K, mainstream flow velocity is 60m / s. The secondary flow inlet boundary is: inlet temperature is 790K, blowing ratio is 0.5. The secondary flow enters the secondary flow channel from the secondary flow inlet, and then enters the mainstream channel through the air film hole. After mixing with the mainstream, it flows out from the pressure outlet boundary, and the absolute pressure of the outlet is 101325Pa; the particles are released from the mainstream inlet, and the particle properties are set as: melting point 1478K, diameter 1-40μm, density 1980kg / m 3The two sides of the computational domain are periodic boundaries; the other boundaries are adiabatic boundary conditions.

[0055] In this study, FLUENT software was used to mesh the computational model. Polyhedral meshing was performed on the woven CMC flat plate, and surface meshing was used to encrypt the interface between the fiber and the matrix. Boundary layer encrypted meshes were constructed in the fluid domain near the gas side wall.

[0056] Comparative Example:

[0057] At the same time, in order to compare the deposition characteristics and cooling effect attenuation differences between the 2.5-dimensional woven CMC material anti-deposition low-attenuation expansion air film hole of the present invention and the traditional circular air film cooling hole, the same simulation method was used in the comparative example to simulate the particle deposition and cooling effect of the circular air film hole cooling structure of the 2.5-dimensional woven CMC material. Figure 4 Same as in. Figure 5 A schematic diagram of a circular film cooling hole structure of a comparative example of the present invention is given, and the hole diameter is 0.8 mm. Figure 6 A schematic diagram of a 2.5D woven structure CMC material circular air film hole cooling plate model is given. To calculate the deposition characteristics between the air film holes, two complete air film holes are included. The overall size of the plate is 50*6.68*3.45mm, where the fiber bundle cross section is hexagonal, the warp spacing is 0.35mm, and the weft spacing is 0.35mm. At the same time, the anisotropic thermal conductivity setting, DPM particle setting, mesh division, and boundary condition setting involved in the simulation calculation in the comparative example are the same as those in the embodiment.

[0058] Figure 7 A comparison of the distribution cloud diagrams of the comprehensive cooling efficiency of the air film covering the wall surface when there is no particle deposition in the embodiment (anti-deposition low-attenuation air film hole) and the comparative example (circular air film hole) is given. It can be seen from the figure that compared with the circular air film hole, the air film coverage effect of the anti-deposition low-attenuation air film hole in the downstream is significantly improved, including the value of the air film cooling efficiency is still in the high air film cooling efficiency area range. In the range of 0-10D downstream of the air film hole, the average comprehensive cooling efficiencies of the circular air film hole and the anti-deposition low-attenuation air film hole are 0.15 and 0.24 respectively.

[0059] Figure 8 A comparison of the deposition thickness distribution cloud diagram on the wall in the embodiment and the comparative example is given. It can be seen from the figure that compared with the circular air film hole, the deposition thickness of the anti-deposition low attenuation air film hole in the downstream is significantly lower, including the value of the air film cooling efficiency is still in the high air film cooling efficiency area. In the range of 0-10D downstream of the air film hole, the average deposition thickness of the circular air film hole and the anti-deposition low attenuation air film hole are 0.516mm and 0.335mm respectively.

[0060] Fig. 9The cold air flow diagrams of two 2.5-dimensional braided CMC material air film cooling structures in the embodiment and the comparative example are compared. It can be seen from the figure that compared with the circular air film holes, the air film coverage effect of the 2.5-dimensional braided CMC material expansion hole in the downstream is significantly improved.

[0061] Fig.10 A comparison of the velocity distribution at the outlets of the circular hole and the expansion hole of the 2.5D woven CMC material is given. It can be seen from the figure that the flow velocity at the outlet of the circular air film hole is high, and it is sucked toward the wall on both sides of the high-speed area; the flow velocity at the outlet of the expansion hole is lower, and the outflow is close to the wall, and is more evenly distributed in the span direction.

[0062] Fig.11 The isosurfaces of Q Criterion = 0.1 near the outlets of the two air film cooling structures in the embodiment and the comparative example are given to show the vortex structure. It can be seen from the figure that due to the high flow velocity at the outlet of the circular air film hole, the vortex intensity is large, the vortex lasts longer, and the particles with small particle size collide with the wall surface under the entrainment of the vortex, resulting in a higher local deposition amount at the end of the vortex; while the outlet flow velocity of the anti-deposition low-attenuation air film hole is lower, the air film covers a wider range, the vortex system intensity on both sides of the air film hole outlet is low, and the geometric scale is smaller, so that the particles will not collide with the wall surface in a concentrated manner, thereby reducing the deposition rate.

[0063] On the one hand, since the outflow velocity of the expansion type film hole is lower, the jet is dispersed in the spanwise direction and has good wall adhesion, the mixing vortex of the cooling airflow and the mainstream combustion gas is weaker, making it difficult for sand and dust particles with smaller particle sizes to collide with the wall due to the suction effect of the vortex, thereby reducing the collision rate of particles downstream of the film hole and thus reducing the deposition rate; on the other hand, the cooling airflow of the expansion type film hole has a larger coverage area on the downstream wall, so that the wall maintains a lower temperature in a larger range. Since the deposition probability of particles colliding with the wall is positively correlated with the temperature, the particle deposition amount of the expansion type film hole is lower than that of the circular film hole in the cooling airflow coverage area downstream of the film hole.

[0064] In summary, the present invention establishes a design method for anti-deposition low-attenuation air film holes based on woven structure ceramic matrix composites (CMC), which can greatly improve the comprehensive cooling efficiency of the air film of woven structure CMC material components, reduce the deposition rate of particles on the wall surface, and reduce the attenuation of the air film cooling effect after long-term service in a particle deposition environment.

[0065] According to the method for designing an active cooling structure of CMC materials that resists deposition and clogging proposed in an embodiment of the present invention, based on the key geometric features of the expansion-type air film holes of CMC material components, on the basis of traditional fluid-solid coupling heat transfer simulation calculations, the trajectory of dust particles in the fluid is simulated in combination with the dispersed phase model, and the probability model of particle deposition is introduced through user-defined functions. The integrated design of the air film cooling structure of CMC materials under dusty conditions is carried out, forming a low-attenuation air film cooling structure scheme for anti-deposition cooling efficiency of ceramic-based composite components, and analyzing and evaluating its cooling effect before and after particle deposition. Therefore, by simulating and analyzing the influence of anti-deposition air film holes on the particle deposition rate on the wall surface, an evaluation method for the attenuation of air film cooling efficiency after particle deposition is formed, which can significantly reduce the attenuation of air film cooling efficiency caused by particle deposition and improve the comprehensive air film cooling efficiency of CMC material components under long-term dusty service conditions.

[0066] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or N embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0067] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "N" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0068] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, fragment or portion of code comprising one or N executable instructions for implementing the steps of a custom logical function or process, and the scope of the preferred embodiments of the present invention includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in reverse order depending on the functions involved, which should be understood by technicians in the technical field to which the embodiments of the present invention belong.

Claims

1. A method for designing an active cooling structure of a CMC material that resists deposition and clogging, characterized in that: The following steps are involved: Step 1: Taking advantage of the designability of the structural fiber of the braided CMC material preform, combined with the outflow characteristics and structural features of the expanded air film hole, the integrated design of the expanded air film hole and the material preform structure is carried out, and the anti-deposition air film cooling structure model of the CMC material component and its fluid-solid coupling simulation model are constructed to calculate the material wall temperature distribution and the comprehensive cooling effect of the air film; Step 2: For the anti-deposition air film cooling structure model of the CMC material component and its fluid-solid coupling simulation model in step 1, a particle dispersed phase model is introduced to calculate the motion trajectory of dust particles in the flow field. At the same time, a particle deposition probability criterion model is introduced to obtain the wall particle deposition distribution under the simulation results of the anti-deposition air film hole; Step 3: According to the wall particle deposition distribution under the simulation result of the anti-deposition air film hole obtained in step 2, when the thickness of the deposition layer is greater than the preset threshold, the volume grid of the deposition layer is reconstructed by moving the grid or extracting the thickness to remodel, and the wall temperature distribution including the influence of the deposition layer on the flow heat transfer and the comprehensive cooling effect of the air film after the particle deposition are calculated; when the thickness of the deposition layer is less than or equal to the preset threshold, the method of assigning thermal resistance to the deposition layer according to the thickness is used to calculate the wall temperature distribution including only the thermal resistance of the deposition layer and the comprehensive cooling effect of the air film after the particle deposition; Step 4: Compare the comprehensive cooling effect of the air film after particle deposition calculated in step 3 with the material wall temperature distribution and the comprehensive cooling effect of the air film calculated by the fluid-solid coupling simulation model without particle deposition in step 1 to obtain the cooling effect attenuation, and evaluate the anti-deposition and low attenuation performance of the new air film hole based on the cooling effect attenuation.

2. The method according to claim 1, characterized in that Step 1 specifically includes: Taking advantage of the designability of the structural fibers of the woven CMC material preform and combining the outflow characteristics and structural features of the expandable air film hole, the fiber bundles are wound back to weave the reserved space in the hole area. At the same time, the number of local fibers is adjusted according to the hole characteristics, and the expandable air film hole and the material preform structure are integrated to form an expandable hole cooling structure. On both sides of the solid domain model of the air film hole structure, the high-temperature mainstream domain and the low-temperature secondary domain are respectively constructed and connected through the air film hole to form the anti-deposition air film cooling structure model of the CMC material component and its fluid-solid coupling simulation model, and the material wall temperature distribution and the comprehensive cooling effect of the air film are calculated.

3. The method according to claim 1, characterized in that Step 2 specifically includes: For the anti-deposition air film cooling structure model of CMC material components and its fluid-solid coupling simulation model in step one, particle deposition calculation is introduced. The numerical simulation of particle deposition on the structure surface includes two aspects: the calculation of particle motion trajectory and the calculation of particle deposition on the structure surface. The particle trajectory is calculated by the Euler-Lagrangian method. The particles are regarded as discrete phases, and the control equation is established by the Lagrangian method. The gas phase is solved by the Euler method. The dispersed phase model simulates the interaction between the two phases, gives the motion trajectory of the particles in the flow field, and describes the landing point of the microparticles. After reaching the near wall surface, the particles will collide with the wall surface under the action of aerodynamic force, and then splash, rebound, spread and adhere. Through the rebound adhesion model based on particle viscosity calculation, the ratio of the critical viscosity of a single particle to the viscosity value when it hits the wall is calculated as the deposition probability to determine whether the particles are deposited. The undeposited particles continue to move according to the rebound velocity calculated by the collision momentum equation, and the deposited particles have their velocity assigned to zero, so that they are consolidated on the wall surface, thereby obtaining the wall particle deposition distribution under the simulation results of the anti-deposition air film hole.

4. The method according to claim 1, characterized in that: Step three specifically includes: According to the wall particle deposition distribution under the simulation results of the anti-deposition air film hole obtained in step 2, the wall temperature distribution and comprehensive cooling effect considering the influence of the deposition layer on heat transfer are calculated. Considering the calculation speed and accuracy comprehensively, a preset threshold is set for the maximum thickness of the deposition layer. The wall temperature and cooling effect after particle deposition are calculated in two schemes. When the deposition layer thickness is greater than the preset threshold and will have a significant impact on the flow, the volume grid of the deposition layer is reconstructed by moving the grid or extracting the deposition layer thickness to remodel. After the grid properties of the deposition layer area are reassigned according to the physical properties of the deposition, the iterative calculation is re-performed to obtain the wall temperature distribution and the comprehensive cooling effect of the air film including the influence of the deposition layer on the flow heat transfer. When the deposition layer thickness is less than or equal to the preset threshold, the influence of the deposition on the flow is ignored, and the expression is used to assign the thermal resistance variable to the deposition layer according to the thickness to calculate the wall temperature distribution including only the thermal resistance of the deposition layer wall and the comprehensive cooling effect of the air film after particle deposition.

5. The method according to claim 1, characterized in that Step 4 specifically includes: The comprehensive cooling effect is compared with the comprehensive cooling effect calculated by the fluid-solid coupling simulation model that does not include particle deposition in step one, focusing on the comprehensive cooling effect on the downstream center line of the air film hole outflow and the surface average comprehensive cooling effect of the area near the air film hole. It is compared with the cooling effect value before deposition to obtain the percentage value of the cooling effect attenuation in the characteristic area. The anti-deposition and low attenuation performance of the new air film hole is evaluated based on the cooling effect attenuation.

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