Active ablative multi-gradient thermal protection structure and design method thereof

Abstract

The application discloses an active ablative multi-gradient heat protection and insulation structure and a design method thereof. The structure comprises, from outside to inside, an active ablative layer, a heat protection layer and an insulation layer. The heat protection layer reinforcing body is formed by alternately laying fiber cloth and quartz fiber web tires, and the outermost layer is the fiber cloth. Each layer is connected into an integral fiber preform by needling. The design method is based on a one-dimensional transient heat conduction model and a pyrolysis reaction kinetics equation to calculate the ablation recession and carbonization depth. The thickness of the active ablative layer is greater than the ablation recession, the thickness of the heat protection layer is greater than 1.5 times the carbonization depth, and the back temperature meets the requirements as the criterion. The thickness of each layer is iteratively optimized to the minimum value. The structure consumes aerodynamic heat through active ablation under the condition of medium and low heat flow, reduces the surface temperature, and reduces the carbonization depth. The back plate temperature can be reduced by 20% to 30% compared with the conventional heat protection structure, and the ablation thickness is controllable and the structure is lightweight.

Description

Technical Field

[0001] This application belongs to the field of heat insulation materials technology, specifically relating to an active ablation multi-gradient heat insulation structure and its design method. Background Technology

[0002] When hypersonic vehicles fly at speeds exceeding Mach 5 for extended periods within the atmosphere, their surfaces are subjected to severe aerodynamic heating. Therefore, external thermal protection systems are essential to prevent structural failure due to overheating. These systems often utilize fiber-reinforced resin-based composite materials, employing ablation and insulation mechanisms to impede heat transfer to the interior. Composite materials made from quartz fiber and phenolic resin are currently the most widely used heat-resistant material system.

[0003] One existing form of thermal protection uses a single-density heat shield layer, such as quartz fiber cloth obliquely wound and impregnated with phenolic resin, where both ablation resistance and thermal insulation are performed by the same material. This type of structure has a relatively high overall density, limited thermal insulation efficiency, and results in a significant increase in weight added to the aircraft. To reduce the overall density, a gradient heat shield layer composed of two-density materials has been developed, typically molded using a molding process. The outer layer provides ablation resistance, while the inner layer provides thermal insulation. However, the phenolic resin used in this molding process still has a high thermal conductivity after curing, resulting in insufficient improvement in overall thermal conductivity and unsatisfactory thermal insulation efficiency. To further reduce thermal conductivity, some solutions use a fiber preform and low-density phenolic resin composite cured via resin transfer molding, which improves thermal insulation capabilities to some extent.

[0004] Patent document CN111331941A discloses an integrated density gradient thermal protection material and its preparation method, wherein the outer layer uses a material with a density of 0.5–2.0 g / cm³. 3 High-density fiber woven fabrics (2.5D braided or coarse-fiber fabrics) are used to enhance resistance to ablation and erosion. Under high heat flux environments, these high-density fiber reinforcement layers do exhibit good ablation resistance. However, under medium or low heat flux environments, the outer layer ablation is minimal, even approaching zero, while the resin inside the material undergoes primarily carbonization. The resulting carbonized layer has high thermal conductivity and alters the surface heat exchange characteristics, maintaining a high surface temperature. This drives the carbonization reaction to continue extending inward, forming a deeper carbonized layer, ultimately leading to a significant decline in the overall thermal insulation efficiency of the thermal protection system. Furthermore, conventional design schemes use carbonization depth as a reference to determine the thickness of the ablation-resistant layer to ensure internal structural safety. This often results in a thicker high-density fiber layer on the surface, further increasing structural weight and manufacturing costs.

[0005] In summary, under low to medium heat flux conditions, the existing thermal protection structure's surface ablation-resistant layer is dominated by carbonization reaction due to insufficient ablation. The carbonization layer continues to advance inward, severely weakening the overall thermal insulation efficiency. Furthermore, the thickened ablation-resistant layer to avoid excessive carbonization leads to a significant increase in weight and cost. Summary of the Invention

[0006] To address the problems of deep carbonization of the surface ablation-resistant layer, low thermal insulation efficiency, and high manufacturing cost under low heat flux conditions in existing technologies, this application provides an active ablation multi-gradient thermal insulation structure and design method. By adding a low-density active ablation layer on the outside to ablate and consume peak heat flux, the carbonization depth of the thermal insulation layer is reduced, thereby improving the overall thermal insulation efficiency and reducing the structural weight.

[0007] To achieve the above technical objectives, this application specifically employs the following technical solution: In one aspect of this application, an active ablation multi-gradient heat insulation structure is provided, the active ablation multi-gradient heat insulation structure comprising, from the outside to the inside, sequentially composited: The active ablation layer is reinforced by multiple layers of first quartz fiber mesh. The heat-resistant layer comprises alternating layers of fiber cloth and a second quartz fiber mesh as reinforcement, and the outermost layer of the heat-resistant layer is the fiber cloth; The insulation layer is reinforced with multiple layers of second quartz fiber mesh; The active ablation layer, the heat-resistant layer, and the heat-insulating layer are stacked and then connected by a needle punching process to form an integral fiber preform. The integral fiber preform is then composited with a low-density hybrid phenolic resin and cured.

[0008] In one embodiment, the areal density of the first quartz fiber mesh is 100-200 g / m². 2 .

[0009] In one embodiment, the fiber cloth is a quartz fiber cloth or a high-silica fiber cloth, or a mixture of quartz fiber cloth and high-silica fiber cloth.

[0010] In one embodiment, the areal density of the fiber cloth is 200-280 g / m². 2 .

[0011] In one embodiment, the volume ratio of the fiber cloth to the second quartz fiber mesh in the heat-insulating layer is 50-70:30-50.

[0012] In one embodiment, the areal density of the second quartz fiber mesh in the insulation layer is 60-200 g / m². 2 .

[0013] In one embodiment, the needle punching process employs a double-needle plate alternating layer-by-layer needle punching method, with the needle punching thread passing through at least the alternating layers of quartz fiber mesh-fiber cloth-quartz fiber mesh, and the inner layer needle punching density being 20-30 needles / cm. 2 The surface needle density is 30-40 needles / cm. 2 .

[0014] In one implementation, at 500-1200 kW / m 2 Under medium to low heat flux conditions, the active ablation layer consumes peak heat flux through active ablation, so that the fiber cloth of the heat protection layer avoids ablation by peak heat flux.

[0015] In one embodiment, an ablation stop surface can be formed on the surface of the fiber cloth of the heat-insulating layer; the thickness of the active ablation layer is such that after the active ablation layer is ablated, the temperature on the outer side of the heat-insulating layer drops significantly, and the ablation rate of the fiber cloth is reduced to less than 0.01 mm / s.

[0016] In another aspect of this application, a design method for the aforementioned active ablation multi-gradient heat insulation structure is provided, comprising the following steps: Step 1: Establish a one-dimensional transient heat transfer model, input the aircraft parameters, and calculate the back temperature, ablation retreat, and carbonization depth of the aircraft throughout the entire heat transfer process. Step 2: Establish design criteria. When calculated based on 1.3 times the heat flux coefficient, the thickness of the active ablation layer is greater than the ablation retreat amount, the thickness of the heat protection layer is greater than 1.5 times the carbonization depth, and the back temperature meets the preset back temperature design requirements. Step 3: Adjust the thickness of the active ablation layer, the heat protection layer, and the heat insulation layer. Repeat Step 1 and Step 2, iterating repeatedly until the minimum thickness of the active ablation layer, the heat protection layer, and the heat insulation layer still satisfies the design criterion of Step 2, thus obtaining the design values ​​for the thickness of the active ablation layer, the heat protection layer, and the heat insulation layer.

[0017] In one implementation, the one-dimensional transient heat conduction model established in step 1 is a simplified one-dimensional transient heat conduction model along the thickness direction, wherein the simplified one-dimensional transient heat conduction model is as follows:

[0018] in, For material density, The specific heat capacity at constant pressure of the material. The thermal conductivity of the material. To prevent the coordinates of the insulation structure in the thickness direction, For temperature, For time, This represents the enthalpy of the surface pyrolysis gas.

[0019] In one implementation, the heat flow heating boundary condition of the one-dimensional transient heat conduction model is:

[0020] in, The cold wall heat flux density of the aircraft as a function of flight time. This represents the enthalpy of the wall gas as a function of the aircraft over flight time. The enthalpy of recovery of the airflow as the aircraft changes over time. To prevent the surface emissivity of the insulation material, This is the Stephan-Boltzmann constant. To prevent the surface temperature of the insulation structure from rising.

[0021] In one implementation, in the one-dimensional transient heat conduction model, except for the outer surface of the active ablation multi-gradient heat insulation structure where heat exchange occurs, all other surfaces are calculated as ideal insulating walls: .

[0022] In one embodiment, the calculation of the ablation retreat and the carbonization depth in step 1 uses a first-order Arrhenius model to describe the pyrolysis reaction rate of the material:

[0023] in, The density of the resin, Pre-exponential factor, For activation energy, is the gas constant.

[0024] In one embodiment, the surface ablation interface retreat rate of the actively ablated layer is dominated by resin pyrolysis, and the ablation retreat amount... The calculation method is as follows: .

[0025] In one embodiment, the carbonization reaction of the heat-resistant layer depends on the efficiency of resin conversion into a carbon layer, and the carbonization depth. The calculation method is as follows:

[0026]

[0027] in, The density of the carbonized layer, This is the efficiency coefficient for the conversion of resin into a carbon layer.

[0028] In one embodiment, the carbonization layer density Take 0.6 times the density of the heat-insulating layer.

[0029] In one implementation, the specific process of iterative iteration in step 3 is as follows: while keeping the total thickness unchanged, adjust the thickness distribution of the active ablation layer, the heat protection layer and the heat insulation layer, and repeatedly execute the heat conduction calculation in step 1 and the design criterion judgment in step 2 until the thickness of each layer is minimized and still meets the design criterion.

[0030] The beneficial effects of this application are as follows: 1. By setting an active ablation layer composed of a low-density quartz fiber mesh on the outside of the heat insulation layer, active ablation occurs under medium and low heat flow conditions and aerodynamic heat is consumed, effectively reducing the surface temperature. This allows the outermost fiber cloth of the heat insulation layer to avoid direct ablation by the peak heat flow, slowing down the rate of carbonization reaction spreading inward, thereby reducing the depth of the carbonization layer, maintaining the original low thermal conductivity characteristics of the material, and improving the overall heat insulation efficiency.

[0031] 2. After the active ablation layer is completely ablated, the surface temperature of the exposed heat-insulating fiber cloth drops significantly. The fiber cloth's own ablation resistance reduces the ablation rate to a micro-ablation or near-zero ablation state, naturally forming an ablation cutoff surface, blocking the risk of ablation spreading to the heat insulation layer, and achieving designable and controllable ablation thickness.

[0032] 3. The lower surface density of the mesh layer facilitates needle penetration and the formation of dense needle lines during the needle punching process. The increased needle punching density significantly enhances the interlayer bonding strength between the active ablation layer and the heat-insulating layer, reducing the risk of pneumatic peeling or interlayer delamination. Traditional pure fiber fabric surface layers are difficult to achieve the same bonding effect through needle punching.

[0033] 4. The insulation layer uses a low-area-density mesh as reinforcement and is combined with a low-density hybrid phenolic resin. The resin has a low thermal conductivity, and together with the porous structure of the mesh, it further enhances the insulation capacity and reduces the overall back temperature of the structure.

[0034] 5. Compared with single-density or simple gradient heat insulation structures using winding or molding, the backplate temperature can be reduced by 20% to 30% under medium and low heat flux conditions, and the overall thickness of the heat insulation structure can be reduced, achieving the goals of lightweighting and low cost.

[0035] 6. A rapid calculation method based on a one-dimensional transient heat conduction model and pyrolysis reaction kinetic equations can accurately predict ablation retreat and carbonization depth. By iteratively optimizing the thickness of the active ablation layer, heat protection layer, and heat insulation layer, the minimum thickness of each layer is obtained under the premise of satisfying the back temperature and ablation margin constraints, providing a highly efficient parameter design method for heat protection and insulation structures. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the active ablation multi-gradient heat insulation structure according to an embodiment of this application; In the figure: 1-Active ablation layer, 2-Heatproof layer, 3-Heat insulation layer, 4-Needle-punched line, 5-First quartz fiber mesh, 6-Fiber cloth, 7-Second quartz fiber mesh. Detailed Implementation

[0037] The technical solution of this application will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are only some embodiments of this application, not all embodiments, and are only used to illustrate this application, and should not be regarded as limiting the scope of this application. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] To address the problems of high overall density, high manufacturing cost, and low overall thermal insulation efficiency in existing heat-resistant structures, and to further improve overall thermal insulation efficiency while reducing the weight and cost of the entire heat-resistant layer, this application provides an active ablation multi-gradient heat-resistant structure and its design method. An active ablation layer composed of low-density materials is added to the outside of a high-density heat-resistant layer or an anti-ablation layer. Under medium and low heat flux conditions, a large amount of heat is consumed through ablation of the active ablation layer, which can reduce the surface temperature and further reduce the back temperature of the heat-resistant structure.

[0039] This application proposes a multi-gradient heat insulation structure consisting of an "active ablation layer + heat protection layer + heat insulation layer," which addresses the problem of high surface temperature and deep carbonization layer affecting overall heat insulation efficiency in traditional heat insulation structures when facing medium and low heat flux conditions. The designable active ablation layer actively dissipates surface heat, reduces temperature, and improves overall heat insulation efficiency. Based on the "active ablation layer + heat protection layer + heat insulation layer," a rapid ablation and heat conduction calculation model is proposed, and a design method for the thickness of the active ablation layer and heat protection layer is provided to optimize the thickness of each layer and achieve highly efficient heat insulation.

[0040] In one specific implementation, refer to Figure 1 As shown, an active ablation multi-gradient heat insulation structure is provided. This structure comprises, from the outside to the inside, an active ablation layer 1, a heat insulation layer 2, and a heat insulation layer 3, sequentially laminated. The active ablation layer 1, the heat insulation layer 2, and the heat insulation layer 3 are stacked and then connected by a needle-punching process to form an integral fiber preform. The integral fiber preform is then laminated with a low-density hybrid phenolic resin and cured.

[0041] Specifically, the active ablation layer 1 is reinforced by multiple layers of first quartz fiber mesh 5, the areal density of which is 100-200 g / m². 2The heat-insulating layer 2 comprises alternating layers of fiber cloth 6 and a second quartz fiber mesh 7 as reinforcement, with the fiber cloth 6 being the outermost layer of the heat-insulating layer 2. The fiber cloth 6 is quartz fiber cloth or high-silica fiber cloth, or a mixture of quartz fiber cloth and high-silica fiber cloth. The areal density of the fiber cloth 6 is 200-280 g / m³. 2 The volume ratio of the fiber cloth 6 to the second quartz fiber mesh 7 in the heat-insulating layer 2 is 50-70:30-50. The heat-insulating layer 3 is reinforced with multiple layers of the second quartz fiber mesh 7, and the areal density of the second quartz fiber mesh 7 in the heat-insulating layer 3 is 60-200 g / m². 2 .

[0042] The active ablation layer 1, heat-resistant layer 2, and heat-insulating layer 3 are stacked in order from the outside to the inside. The stacked active ablation layer 1, heat-resistant layer 2, and heat-insulating layer 3 are interconnected by a needle punching process to form an integral fiber preform.

[0043] The needle-punching process employs an alternating double-needle plate layer-by-layer needle-punching method, with the needle-punching thread 4 passing through alternating layers of quartz fiber mesh, fiber cloth, and quartz fiber mesh. Specifically, a single needle-punching thread 4 penetrates at least one complete laminated unit consisting of an upper mesh layer, a middle fiber cloth layer, and a lower mesh layer along the thickness direction. When the needle penetrates, the barbs drag some fibers from each layer downwards, forming interlayer locked fiber bundles upon withdrawal. Both the upper and lower interfaces of the fiber cloth are anchored by the needle-punched fibers, eliminating the reliance on resin-cured interface bonding between layers. The inner layer needle-punching density is 20-30 needles / cm². 2 The surface needle density is 30-40 needles / cm. 2 After forming the integral fiber preform, the integral fiber preform is placed in a mold and compounded with low-density hybrid phenolic resin by pressure injection. After the air bubbles are removed, it is placed in an oven for heating and curing. After curing, it is cooled and demolded to obtain an active ablation multi-gradient heat insulation structure.

[0044] For 500-1200kW / m 2 Under medium to low heat flux conditions, the active ablation layer 1 consumes the peak heat flux through active ablation, so that the fiber cloth 6 of the heat protection layer 2 avoids the direct ablation effect of the peak heat flux.

[0045] The surface of the fiber cloth 6 of the heat-insulating layer 2 can form an ablation stop surface. The thickness of the active ablation layer 1 is such that after the active ablation layer 1 completes ablation, the temperature on the outside of the heat-insulating layer 2 drops significantly. At this time, the ablation rate of the fiber cloth 6 is reduced to less than 0.01 mm / s, so that the fiber cloth 6 is in a micro-ablation or near-zero ablation state, forming an ablation stop surface to reduce the risk of further ablation.

[0046] The advantages of the aforementioned heat-insulating structure are mainly achieved through the design of a reasonable active ablation layer and the thickness of the heat-insulating layer. In another specific embodiment, a design calculation method for the aforementioned heat-insulating structure is proposed, and the specific implementation steps are as follows: Step 1: Establish a one-dimensional simplified transient heat conduction model along the thickness direction, with the thickness direction coordinate set as y. The one-dimensional simplified transient heat conduction model is as follows:

[0047] in, For material density, The specific heat capacity at constant pressure of the material. The thermal conductivity of the material. For temperature, For time, This represents the enthalpy of the surface pyrolysis gas.

[0048] The boundary conditions employ heat flow heating, considering heat convection, heat radiation, and heat conduction into the structure:

[0049] in, The cold wall heat flux density of the aircraft as a function of flight time. This represents the enthalpy of the wall gas as a function of the aircraft over flight time. The enthalpy of recovery of airflow for an aircraft as it flies over time. To prevent the surface emissivity of the insulation material, Let be the Stephan-Boltzmann constant, taken as 5.67 × 10⁻⁶. -8 W / m 2 K 4 , To prevent the surface temperature of the insulation structure from rising.

[0050] Except for the outer surface of the heat-insulating structure where heat exchange occurs, all other surfaces are calculated as ideal insulating walls, i.e.: .

[0051] The pyrolysis reaction rate equation of the material is described by a first-order Arrhenius model:

[0052] in, The density of the resin, Pre-exponential factor, For activation energy, is the gas constant. and Obtained through experimental testing.

[0053] The active ablation layer has a low density and low fiber content. The surface ablation interface retreat rate is dominated by resin pyrolysis, and the ablation retreat amount... The calculation method is directly related to the pyrolysis rate: .

[0054] After the active ablation layer undergoes pyrolysis, the carbonization reaction of the heat-resistant layer depends on the efficiency of resin conversion into a carbon layer. Assuming the residual carbon layer density remains stable after pyrolysis and secondary reactions are negligible, the carbonization layer density... rate of change and carbonization depth The calculation method is as follows:

[0055]

[0056] in, This is the efficiency coefficient for the conversion of resin into a carbon layer. Take 0.6 times the density of the heat-insulating layer.

[0057] The back temperature and ablation migration during the entire heat transfer process of the aircraft are calculated using the above formulas. and carbonization depth .

[0058] Step 2: Establish design criteria for heat insulation structures Based on the back temperature and ablation migration calculated in step 1 and carbonization depth Design criteria were established for the thickness of each layer: the active ablation layer, the heat shield layer, and the insulation layer. When calculating based on a heat flux coefficient of 1.3, the thickness of the active ablation layer needs to be greater than the ablation retreat amount calculated in step 1. The thickness of the heat-insulating layer needs to be greater than 1.5 times the carbonization layer depth calculated in step 1. The back temperature needs to meet the pre-set design requirements.

[0059] Step 3: Adjust the thickness of the active ablation layer, the heat protection layer, and the insulation layer. Repeat the heat conduction calculation in Step 1 and the design criterion judgment in Step 2. Iterate repeatedly until the minimum thickness of the active ablation layer, the heat protection layer, and the insulation layer can still meet the design criterion established in Step 2. Then the iteration ends and the design values ​​of the thickness of the active ablation layer, the heat protection layer, and the insulation layer are obtained.

[0060] In some embodiments, the iterative process specifically involves: while keeping the total thickness of the active ablation multi-gradient heat insulation structure constant, adjusting the thickness distribution of the active ablation layer, the heat insulation layer, and the heat insulation layer, and repeatedly executing the heat conduction calculation in step 1 and the design criterion judgment in step 2 until the design criterion is still satisfied when the thickness of each layer is minimized.

[0061] Example 1 Based on the thermal environment conditions of a certain aircraft, the technology of this application is used for the design of a heat insulation structure. The highest heat flux peak of the aircraft's thermal environment is 1.2MW, lasting approximately 400 seconds, which is classified as a medium heat flux environment.

[0062] Input heat flow based on the aircraft's thermal environment conditions , wall enthalpy enthalpy of gas recovery Based on parameters such as ablation and heat transfer, a simplified calculation model is used to perform ablation and heat transfer calculations. In this embodiment, the initial thickness of the active ablation layer of the heat insulation structure is set to 1 mm, the initial thickness of the heat insulation layer is set to 4 mm, the initial thickness of the heat insulation layer is set to 7 mm, and the initial total thickness of the heat insulation structure is 12 mm.

[0063] Through iterative calculations, the final determined active ablation layer thickness was 0.8 mm, the heat-resistant layer thickness was 3.2 mm, the heat insulation layer thickness was 6 mm, and the total thickness of the heat-resistant and heat-insulating structure was optimized to 10 mm. The calculated ablation regression of this heat-resistant and heat-insulating structure was 0.6 mm, the carbonization depth was 2 mm, and the back temperature rise was 65℃, which meets the design requirements.

[0064] In this embodiment, the total thickness of the heat insulation structure is 10mm. The prefabricated body is designed with a thickness ratio of 1.2:1 to the cured body thickness, resulting in a total prefabricated body thickness of 12mm. The active ablation layer uses a 1mm thick quartz fiber mesh base layer with a density of 0.6g / cm³. 3 The heat-insulating layer adopts a 4mm thick two-layer fabric-one-layer mesh structure, namely a laminated structure of two layers of quartz fiber cloth + one layer of quartz fiber mesh; the heat insulation layer adopts a 7mm thick quartz fiber mesh layer. After the three-layer structure is made into a preform through needle punching, the fiber preform is placed in a mold with inner and outer molds, the mold cavity thickness is controlled at 10mm, and after the mold is closed, low-density hybrid phenolic resin (LP-50 phenolic resin, Beijing Fiberglass Institute Composite Materials Co., Ltd.) is injected under pressure. After the air bubbles are removed, it is placed in an oven for curing and molding. After the curing process is completed, it is cooled and demolded to obtain the 10mm thick heat-insulating structure described in this embodiment.

[0065] Example 2 Based on the thermal environment conditions of a certain aircraft, the technology of this invention is used to design a heat insulation structure. The highest heat flux peak of the aircraft's thermal environment is 0.6MW, lasting approximately 600 seconds, which is classified as a low heat flux environment.

[0066] Input heat flow based on the aircraft's thermal environment conditions , wall enthalpy enthalpy of gas recovery Based on parameters such as ablation and heat transfer, a simplified calculation model is used to perform ablation and heat transfer calculations. In this embodiment, the initial thickness of the active ablation layer of the heat insulation structure is set to 1 mm, the initial thickness of the heat insulation layer is set to 4 mm, the initial thickness of the heat insulation layer is set to 7 mm, and the initial total thickness of the heat insulation structure is 12 mm.

[0067] Through iterative calculations, the final determined active ablation layer thickness was 0.4 mm, the heat-resistant layer thickness was 2.6 mm, the heat insulation layer thickness was 5 mm, and the total thickness of the heat-resistant and heat-insulating structure was optimized to 8 mm. The calculated ablation regression of this heat-resistant and heat-insulating structure was 0.32 mm, the carbonization depth was 1.7 mm, and the back temperature rise was 78 °C, which meets the design requirements.

[0068] In this embodiment, the total thickness of the heat insulation structure is 8mm. The prefabricated body is designed with a thickness ratio of 1.1:1 to the cured body thickness, resulting in a total thickness of 8.5-9.0mm. The active ablation layer uses a 0.5mm thick quartz fiber mesh base layer with a density of 0.4g / cm³. 3 The heat-insulating layer adopts a 2.9mm thick fabric-mesh structure, namely a layer of quartz fiber cloth + a layer of quartz fiber mesh; the heat insulation layer adopts a 5.5mm thick quartz fiber mesh layer. After the three-layer structure is made into a preform by needle punching, the fiber preform is placed in a mold with inner and outer molds, the mold cavity thickness is controlled at 8mm, and after the mold is closed, low-density hybrid phenolic resin (SL-1241 phenolic resin, Shandong Non-metallic Materials Research Institute) is injected under pressure. After the air bubbles are removed, it is placed in an oven for curing and molding. After the curing process is completed, it is cooled and demolded to obtain the 8mm thick heat-insulating structure described in this embodiment.

[0069] Compared with Example 2, Example 1 has a higher thermal environment due to its heat insulation structure design. In order to cope with the higher heat flow environment and improve the ablation resistance, the quartz fiber mesh used in the active ablation layer of Example 1 has a higher density. The heat insulation layer also adopts a combination of two layers of fiber cloth + one layer of quartz fiber mesh as a unit, which increases the proportion of fiber cloth.

[0070] Although the embodiments of this application have been described above in conjunction with the accompanying drawings, this application is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of this application, and these are all within the scope of protection of this application.

Claims

1. An active ablation multi-gradient heat insulation structure, characterized in that, The active ablation multi-gradient heat insulation structure comprises, from the outside to the inside, the following components: The active ablation layer consists of multiple layers of first quartz fiber mesh as reinforcement, with the areal density of the first quartz fiber mesh being 100-200 g / m². 2 ; The heat-insulating layer comprises alternating layers of fiber cloth and a second quartz fiber mesh as reinforcement, with the outermost layer being the fiber cloth, the areal density of which is 200-280 g / m³. 2 The areal density of the second quartz fiber mesh is 60-200 g / m². 2 ; The insulation layer is reinforced with multiple layers of second quartz fiber mesh; The active ablation layer, the heat-resistant layer, and the heat-insulating layer are stacked and then connected by a needle punching process to form an integral fiber preform. The integral fiber preform is then composited with a low-density hybrid phenolic resin and cured.

2. The active ablation multi-gradient heat insulation structure according to claim 1, characterized in that, The volume ratio of the fiber cloth to the second quartz fiber mesh in the heat-insulating layer is 50-70:30-50.

3. A design method for an active ablation multi-gradient heat insulation structure based on any one of claims 1 to 2, characterized in that, Includes the following steps: Step 1: Establish a one-dimensional transient heat transfer model, input the aircraft parameters, and calculate the back temperature, ablation retreat, and carbonization depth of the aircraft throughout the entire heat transfer process. Step 2: Establish design criteria. When calculated based on 1.3 times the heat flux coefficient, the thickness of the active ablation layer is greater than the ablation retreat amount, the thickness of the heat protection layer is greater than 1.5 times the carbonization depth, and the back temperature meets the preset back temperature design requirements. Step 3: Adjust the thickness of the active ablation layer, the heat protection layer, and the heat insulation layer. Repeat Step 1 and Step 2, iterating repeatedly until the minimum thickness of the active ablation layer, the heat protection layer, and the heat insulation layer still satisfies the design criterion of Step 2, thus obtaining the design values ​​for the thickness of the active ablation layer, the heat protection layer, and the heat insulation layer.

4. The design method according to claim 3, characterized in that, The one-dimensional transient heat conduction model established in step 1 is a simplified one-dimensional transient heat conduction model along the thickness direction. The simplified one-dimensional transient heat conduction model is as follows: in, For material density, The specific heat capacity at constant pressure of the material. The thermal conductivity of the material. To prevent the coordinates of the insulation structure in the thickness direction, For temperature, For time, This represents the enthalpy of the surface pyrolysis gas.

5. The design method according to claim 4, characterized in that, The heat flow heating boundary condition for the one-dimensional transient heat conduction model is: in, The cold wall heat flux density of the aircraft as a function of flight time. This represents the enthalpy of the wall gas as a function of the aircraft over flight time. The enthalpy of recovery of the airflow as the aircraft changes over time. To prevent the surface emissivity of the insulation material, This is the Stephan-Boltzmann constant. To prevent the surface temperature of the insulation structure from rising.

6. The design method according to claim 4, characterized in that, In the one-dimensional transient heat conduction model, except for the outer surface of the active ablation multi-gradient heat insulation structure where heat exchange occurs, all other surfaces are calculated as ideal insulation walls: 。 7. The design method according to claim 3, characterized in that, In step 1, the ablation retreat and carbonization depth are calculated using a first-order Arrhenius model to describe the pyrolysis reaction rate of the material. in, The density of the resin, Pre-exponential factor, For activation energy, is the gas constant.

8. The design method according to claim 7, characterized in that, The surface ablation interface retreat rate of the active ablation layer is dominated by resin pyrolysis, and the ablation retreat amount... The calculation method is as follows: 。 9. The design method according to claim 7, characterized in that, The carbonization reaction of the heat-resistant layer depends on the efficiency of resin conversion into a carbon layer, and the carbonization depth... The calculation method is as follows: in, The density of the carbonized layer, This is the efficiency coefficient for the conversion of resin into a carbon layer.

10. The design method according to claim 9, characterized in that, The carbonized layer density Take 0.6 times the density of the heat-insulating layer.

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