A thermal analysis method, system and computer device for heat shield

Abstract

The present invention discloses a thermal analysis method, system and computer equipment for a heat shield, which relates to the field of thermal analysis technology, and includes the steps of: constructing an exhaust system model with a heat shield, acquiring the flow field of the exhaust system model, obtaining the temperature field distribution of the cavity wall, and the pressure, temperature and component concentration information of the fluid inside the cavity; calculating the radiation transfer equation by the Monte Carlo method, obtaining the infrared radiation intensity of the surface of the heat shield thermal radiation source term, and obtaining the thermal analysis result by the infrared radiation intensity. The present invention acquires the flow field of the model, obtains the temperature field distribution and fluid information, fully considers the radiation in the exhaust system, understands the radiation distribution in the exhaust system, and plays an important role in the subsequent analysis of the thermal radiation source term. At the same time, the Monte Carlo method is used to obtain the radiation source term of the heat shield. Based on this radiation source term, the temperature distribution of the heat shield can be better analyzed, and the reliability of the components can be improved to protect the engine wall.

Description

Technical Field

[0001] The present invention relates to the field of thermal analysis technology, and in particular to a thermal analysis method, system and computer equipment for a heat insulation screen. Background Art

[0002] With the development of engines, the temperature requirements are gradually increasing. For example, the appearance of afterburner increases the temperature inside the combustion chamber, which causes the temperature of the gas discharged from the downstream nozzle to increase rapidly. The heating condition of the exhaust system wall is very bad, which will cause serious damage to the structure and greatly reduce the service life of the components. Adding a heat shield can improve the temperature distribution in the flow channel inside the nozzle, which is beneficial to improve the temperature resistance and reliability of the nozzle components.

[0003] Flat plate, transverse corrugated, longitudinal corrugated heat shields, and impact / divergent double-layer wall cooling structures have been applied. "Experimental Study on the Comprehensive Cooling Efficiency of Double-wall Heat Shield in Afterburner" uses numerical simulation to study the cooling characteristics of multi-inclined holes in the heat shield of the ramjet combustion chamber; "Simulation of Cooling Characteristics of Corrugated Plate Heat Shield with Non-uniform Cooling Holes" studies the influence of the arrangement of gas mold holes of longitudinal corrugated heat shield on the cooling efficiency; "The Influence of Heat Shield Position on Infrared Characteristics of Vector Nozzle" proposes the net radiation discretization method and compiles a program to study the influence of the heat shield position on the infrared radiation of the nozzle.

[0004] It can be seen that the existing technology uses commercial software for numerical simulation, and most of them use the DO radiation model, which is the most commonly used discrete coordinate method. However, the low-order discrete coordinate method has large calculation errors and may also produce false scattering and ray effects. For geometric shapes and irregular surfaces, details may be lost and accuracy may be reduced. The radiation in the exhaust system is not considered sufficiently, and the radiation distribution in the obtained results is not accurate. Summary of the invention

[0005] The purpose of the present invention is to provide a thermal analysis method, system and computer equipment for heat shields in view of the above-mentioned deficiencies of the prior art, so as to solve the problems that the low-order discrete coordinate method in the prior art has large errors, may also produce false scattering and ray effects, may lose details and reduce accuracy for geometric shapes and irregular surfaces, and does not adequately consider the radiation in the exhaust system, resulting in inaccurate radiation distribution in the obtained results.

[0006] The present invention specifically provides the following technical solution: a thermal analysis method for a heat shield, comprising the following steps:

[0007] The exhaust system model is constructed by arranging a center cone, a flame stabilizer, an outer duct, an inner duct and a heat shield in the cavity of the engine combustion chamber, and arranging a connected nozzle outside the cavity;

[0008] Conducting two-dimensional heat conduction on the internal heat source in the exhaust system model flow field to obtain the temperature field distribution of the heat insulation shield wall in the exhaust system model, and to obtain the pressure, temperature and component concentration information of the fluid inside the cavity;

[0009] Based on the temperature field distribution, as well as the pressure, temperature and component concentration information of the fluid inside the cavity, a radiation transfer factor is obtained by simulating beam tracing using the Monte Carlo method, and the radiation intensity on the surface of the heat shield is obtained through the radiation transfer factor;

[0010] The thermal analysis results of the heat radiation source items of the heat insulation shield are obtained through the radiation intensity analysis.

[0011] Preferably, performing two-dimensional heat conduction on the internal heat source in the flow field of the exhaust system model to obtain the temperature field distribution of the wall surface of the heat insulation screen in the exhaust system model comprises the following steps:

[0012] The sum of the convective heat transfer and the radiative heat transfer introduced into and exported from the gas side and the cold air side of the heat insulation screen is regarded as the internal heat source;

[0013] Substitute the internal heat source into the two-dimensional heat conduction equation, and obtain the temperature field distribution on the heat insulation screen through iteration of the two-dimensional heat conduction equation; the specific expression is:

[0014]

[0015] in, is the partial derivative, is the thermal conductivity, is the internal heat source, x and y is the coordinate system coordinate, T is the coordinate point ( x,y ) temperature distribution at .

[0016] Preferably, when constructing the exhaust system model, the exhaust system model is divided into unstructured grids, and the grids are encrypted at the center cone, the flame stabilizer, near the wall, and the air film holes of the heat insulation screen.

[0017] Preferably, obtaining the pressure, temperature and component concentration information of the fluid inside the cavity comprises the following steps:

[0018] Set component concentrations for the outer and inner channels in the cavity, and obtain component mass fractions through the component concentrations;

[0019] Set the pressure and temperature for the external flow field at the pressure outlet, and set adiabatic at the center cone.

[0020] Preferably, in the process of obtaining the pressure, temperature and component concentration information of the fluid inside the cavity, the fluid is compressed gas, the inner duct and the outer duct are both given flow inlet boundary conditions, and the flow direction is along the axial direction of the engine exhaust system; the outer duct is the ambient atmosphere, and its components include N2 and O2, and the fuel gas components in the inner duct include N2, O2, CO2, H2O and CO.

[0021] Preferably, the radiation transfer factor is obtained by simulating beam tracing using the Monte Carlo method, and the specific expression is:

[0022]

[0023] Where I is the three-dimensional vector of radiation intensity, s is the path length, is the divergence operator, is the dielectric absorption coefficient, is the surface reflection coefficient.

[0024] Preferably, when the radiation transfer factor is obtained by simulating beam tracing using the Monte Carlo method, the specific expression further includes other auxiliary terms, including the scattering, absorption and reflection characteristics of the radiation, and the wavelength of the radiation.

[0025] Preferably, when the Monte Carlo method is used to simulate beam tracing to obtain the radiation transfer factor, the path of the exit energy beam is simulated, and the radiation intensity of the energy beam is obtained from the spectral radiation brightness at the exit.

[0026] The present invention also provides a thermal analysis system for a heat shield, comprising:

[0027] A model building module, used to build an exhaust system model by setting a center cone, a flame stabilizer, an outer duct, an inner duct and a heat shield in the cavity of the engine combustion chamber, and setting a connected nozzle outside the cavity;

[0028] A flow field acquisition module, used to conduct two-dimensional heat conduction on the internal heat source in the flow field of the exhaust system model, obtain the temperature field distribution of the heat insulation screen wall in the exhaust system model, and obtain the pressure, temperature and component concentration information of the fluid inside the cavity;

[0029] A radiation acquisition module, for obtaining a radiation transfer factor by simulating beam tracing using a Monte Carlo method based on the temperature field distribution and the pressure, temperature and component concentration information of the fluid inside the cavity, and obtaining the radiation intensity of the heat shield surface through the radiation transfer factor;

[0030] The analysis module is used to obtain the thermal analysis results of the heat shield thermal radiation source item through radiation intensity analysis.

[0031] The present invention provides a computer device, comprising a memory and a processor, wherein a program is stored in the memory, and when the program is executed by the processor, the processor executes the steps of a thermal analysis method of a heat insulation screen.

[0032] Compared with the prior art, the present invention has the following significant advantages:

[0033] The present invention constructs an exhaust system model with a heat shield. First, the flow field of the model is acquired to obtain the temperature field distribution and fluid information. The radiation in the exhaust system is fully considered to understand the radiation distribution in the exhaust system, which plays an important role in the subsequent analysis of thermal radiation source terms. At the same time, the Monte Carlo method is used to obtain the radiation source term of the heat shield. Based on this radiation source term, the temperature distribution of the heat shield can be better analyzed, and the reliability of components can be improved to protect the engine wall. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the overall flow chart of the present invention;

[0035] Figure 2 is a schematic diagram of an exhaust system of the present invention;

[0036] Figure 3 It is a schematic diagram of heat conduction of the longitudinally corrugated heat insulation screen of the present invention;

[0037] Figure 4 It is the Monte Carlo obtained RD process diagram of the present invention;

[0038] Figure 5 It is a diagram of the thermal analysis method of the present invention.

[0039] Reference numerals: 1-center cone, 2-flame stabilizer, 3-outer duct, 4-inner duct, 5-heat shield, 6-nozzle, 7-cold air duct, 8-gas duct, 9- Q in , 10- Q out . DETAILED DESCRIPTION

[0040] The following is a clear and complete description of the technical solutions of the embodiments of the present invention in conjunction with the drawings in the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0041] In view of the above problems, the present invention proposes a thermal analysis method for heat shields. The thermal analysis method needs to be carried out in two steps. First, the flow field is acquired to obtain the temperature distribution of the cavity wall, the pressure, temperature, component concentration and other information of the internal fluid. Then, the infrared radiation intensity is acquired by the Monte Carlo method to obtain the radiation source term of the heat shield component required by the present invention.

[0042] The specific heat transfer link of the corrugated longitudinal heat insulation screen is analyzed, and the composition of the heat conduction equation of the heat insulation screen wall is explained in detail and discretized. The convective heat transfer and radiation heat transfer on both sides of the heat insulation screen are obtained, and they are used as the heat source of the heat insulation screen and substituted into the heat conduction equation for iteration. The Monte Carlo method can reverse the possible input distribution from the known output data. For the research background of the present invention, when the aircraft is in operation, its radiation characteristics can be regarded as the countless rays it emits outward. Some of the rays are received by the outside world, and after determining their direction and path process, the rays are discretized along the path, and the radiation transmission equation is obtained to obtain the radiation energy of a ray. For radiation, the Monte Carlo method is used to achieve accurate acquisition of thermal radiation transmission and radiation heat transfer, and the method has high engineering applicability. When the number of rays counted is large enough, the total radiation intensity can be calculated.

[0043] like Figure 1 and Figure 5 As shown, an embodiment of the present application provides a thermal analysis method for a heat shield, comprising the following steps:

[0044] Step S1: construct an exhaust system model by arranging a central cone 1, a flame stabilizer 2, an outer duct 3, an inner duct 4 and a heat shield 5 in the cavity of the engine combustion chamber, and arranging a connected nozzle 6 outside the cavity.

[0045] The flow field is acquired in advance to obtain the flow field information of the research object. First, a physical model of the research object is established. The exhaust system studied in this invention is as follows: Figure 2 .

[0046] Fluent is used for numerical simulation, which is completed through steps such as model cleaning, surface mesh generation, volume mesh generation and processing, boundary condition application, calculation, and post-processing.

[0047] Unstructured grid division: the grid is encrypted near the central cone 1, flame stabilizer 2, wall surface, and air film holes of the heat shield 5, and gradually becomes sparse along the jet downstream and core.

[0048] Step S2: Perform two-dimensional heat conduction on the internal heat source in the exhaust system model flow field to obtain the temperature field distribution of the wall of the heat insulation screen 5 in the exhaust system model, as well as the pressure, temperature and component concentration information of the fluid inside the cavity.

[0049] Specifically:

[0050] like Figure 3 As shown, one side of the longitudinally corrugated heat shield 5 is a high-temperature and high-pressure gas flow, that is, the gas flow is input from the gas channel 8, and the other side is a cooling air flow with a lower temperature. The temperature difference between the two sides is large, and there is also forced convection heat exchange in the internal air film holes, that is, the cooling air flow is input from the cold air channel 7. This causes the heat conduction of the heat shield 5 in the axial direction to be uneven, which can be treated as two-dimensional heat conduction.

[0051] The sum of the convective heat transfer and the radiative heat transfer imported and exported from both sides of the heat insulation screen 5 is regarded as the internal heat source, and the internal heat source is substituted into the two-dimensional heat conduction equation to obtain the temperature field distribution on the heat insulation screen 5; the specific expression is:

[0052]

[0053] in, is the partial derivative, is the thermal conductivity, is the internal heat source, x and y is the coordinate system coordinate, T is the coordinate point m( x,y ) temperature distribution at .

[0054] The air film hole is treated as the third type of boundary condition and is processed as a source term and put into the control equation.

[0055] In actual use, a heat shield 5 is installed in the combustion chamber of the ramjet engine. A gap is left between the heat shield 5 and the wall to form an outer duct 3, and cold air is introduced, thereby realizing efficient thermal protection of the engine. The atmosphere, as a cooling airflow, enters the gas side through the air mold holes on the heat shield 5, and forms an air film on the wall of the heat shield 5 on the gas side. On the one hand, the air film separates the high-temperature gas from the heat shield 5 to avoid direct convection heat exchange between the gas and the wall of the heat shield 5. On the other hand, it also absorbs the radiation heat of the high-temperature gas to the heat shield 5. For the longitudinally corrugated heat shield 5, it increases the fluid disturbance and the heat exchange area, thereby enhancing the convective heat exchange. The cooling advantages of the longitudinally corrugated heat shield 5 make it widely used.

[0056] From the perspective of heat transfer, the basic heat transfer processes involved in the longitudinal corrugated heat shield 5 are mainly: ① radiation heat exchange and convection heat exchange between high-temperature combustion gas and the longitudinal corrugated heat shield 5; ② convection heat exchange between the longitudinal corrugated heat shield 5 and cold air; ③ radiation heat exchange between the longitudinal corrugated heat shield 5 and the inner side of the wall; ④ inside the longitudinal corrugated heat shield 5, heat is transferred in the form of pure heat conduction; ⑤ in the air film holes of the longitudinal corrugated plate, the cold air flowing through the air film holes directly exchanges forced convection with the wall of the air film holes.

[0057] The heat source consists of two parts: 1. The heat transferred from the gas to the heat shield 5 in the form of convection heat transfer and radiation heat transfer. The sum of the two is recorded as Q in 9; 2. The sum of the heat released by the heat shield 5 to the cooling airflow in the outer duct 3 by convection heat transfer, the heat removed by forced convection heat transfer in the air film holes, and the heat released to the wall by radiation heat transfer is recorded as Q out 10.

[0058] Analysis of convection heat transfer process:

[0059] 1. Since the high-temperature and high-pressure gas and the cold air flowing out of the film hole are mixed with each other, it is difficult to determine the qualitative heat transfer temperature of the gas side of the heat insulation screen 5 for convective heat transfer. Therefore, the adiabatic cooling effect is introduced to define the qualitative heat transfer temperature and heat transfer coefficient.

[0060] The convective heat transfer in the presence of film cooling is generally obtained as follows:

[0061]

[0062] In the formula, Q c1 Convection heat transfer on the gas side, h aw is the convective heat transfer coefficient on the gas side, T aw is the adiabatic wall temperature, T w1 is the wall temperature of the corrugated longitudinal heat insulation screen 5 on the gas side.

[0063] Get the adiabatic wall temperature T aw It is also necessary to obtain the cooling efficiency of the air film η , generally calculated using the following formula:

[0064]

[0065] In the formula, T g is the gas temperature, T cg is the temperature of the cooling air flow at the jet outlet.

[0066] The distribution law of heat transfer coefficient under the superposition of multiple rows of porous air films is studied, fitted into a calculation correlation formula, and applied to the wall temperature analysis and calculation program.

[0067] 2. The calculation formula for the convection heat transfer on the cold air side is:

[0068]

[0069] In the formula, Qc2 Convection heat transfer for the cold air side. h c2 is the convective heat transfer coefficient on the cold air side, T ce is the air conditioning temperature, T w2 is the wall temperature of the heat insulation screen 5 on the cold air side.

[0070] The longitudinally corrugated heat shield 5 is a continuously undulating curved surface, and the presence of air film holes enhances its heat exchange effect. The heat transfer law is relatively complex, and the existing experimental correlation formula is difficult to meet the calculation requirements. It is necessary to use the results of numerical simulation to fit into an empirical formula and apply it to the wall temperature analysis and calculation program.

[0071] 3. Heat transfer of the inner wall of the air film hole Q cm for:

[0072]

[0073] In the formula, T c0 and T cg is the inlet and outlet temperature of the air film hole, T w1 is the wall temperature of heat shield 5, h cm is the heat transfer coefficient of the inner wall of the film hole.

[0074] h cm Determined by the Gnielinski formula, it has a higher accuracy and is in the following form:

[0075]

[0076] In the formula, Nu is the Nusselt number, l is the length of the air film hole, Re is the Reynolds number of the cold air flow, Pr is the Planck number of the cold air flow, d is the pipe diameter, f is the Darcy drag coefficient of turbulent flow in the tube, calculated according to the Konakoff formula:

[0077]

[0078] The increase ratio of the Darcy resistance coefficient to the heat transfer coefficient of the inner wall of the air film hole is 1, so the Darcy resistance coefficient is used instead of the heat transfer coefficient of the inner wall of the air film hole. h cm .

[0079] Radiative heat transfer calculation:

[0080] The combustion products of the engine mainly include water vapor, carbon dioxide, carbon monoxide and carbon black particles, etc. It is necessary to consider the absorption, reflection and scattering of radiation by various particles in the gas. Especially for the high-temperature and high-pressure gas side, it is more complicated to calculate its radiation heat flux. The wall surface of the air film hole of the longitudinally corrugated heat shield 5 is usually a cylindrical surface. The heat exchange area and angular coefficient of the cylinder for the entire heat transfer system are small, so the radiation heat exchange in the air film hole is very small, and the radiation heat exchange can be ignored.

[0081] Step S3: Based on the temperature field distribution, as well as the pressure, temperature and component concentration information of the fluid inside the cavity, the Monte Carlo method is used to simulate beam tracing to obtain the radiation transfer factor, and the radiation intensity on the surface of the heat shield 5 is obtained through the radiation transfer factor.

[0082] Specifically: Calculate the radiation transfer equation through the Monte Carlo method to obtain its radiation source term. Write a calculation method for the far-infrared radiation characteristics of the target surface based on the reverse Monte Carlo method. The Monte Carlo method is used to simulate radiation heat transfer, which includes four parts, namely, the absorption, emission and scattering simulation of the internal gas flow medium, and the emission, reflection and absorption simulation of the solid wall of the exhaust system. The radiation transfer equation is obtained using the Monte Carlo method, and its form is as follows:

[0083]

[0084] in, I is the three-dimensional vector of radiation intensity, s is the path length, is the divergence operator, is the dielectric absorption coefficient, is the surface reflection coefficient.

[0085] The above is a basic expression for describing the scattering, reflection and absorption phenomena in three-dimensional infrared transmission. The specific transmission equation in practical applications may also contain other auxiliary terms, such as the wavelength-dependent characteristics of scattering, absorption and reflection, and be appropriately modified and simplified according to the specific problem.

[0086] The present invention adopts the Monte Carlo method to obtain the radiation transfer factor by simulating beam tracing, thereby calculating the radiation source term. Figure 4 shown.

[0087] The definition of radiation transfer factor RD is the fraction of energy radiated by element i absorbed by element j in a heat exchange system. It is assumed that the value of RD remains unchanged within a certain range of operating temperature, pressure and composition of the turbine guide vane. Thus, by obtaining the radiation transfer equation once, the probability of radiation transfer between the medium and the wall grid is obtained, which is then brought into the energy balance equation for iteration to achieve rapid acquisition of the wall temperature field. The Monte Carlo method for obtaining the radiation transfer factor can be divided into the simulation of the emission point position, the simulation of the emission direction, and the simulation of reflection, scattering and absorption. By writing a Monte Carlo program, the divided unstructured tetrahedral grid is used as the medium and wall grid for ray tracing, the above process is simulated to obtain the radiation transfer factor and calculate the radiation source term.

[0088] By selecting the emission point position and determining the emission direction, the initial emission number N0=0 is obtained. After the emission starts, it is determined that N0<10000. If not, the next unit is used to return to the step of selecting the emission point position. When N0<10000, the energy carried by the emitted light is obtained, E0=1.0. The relationship between the absorption distance and the scattering distance is determined, and then the absorption distance and the minimum distance of the grid are determined, or the reflected part is re-tracked when the energy is absorbed by the surface. After the absorption distance and the minimum distance of the grid are determined, E0< ζ When , the radiation transfer factor is updated, and the step of judging whether N0<10000 is repeated in N0+1.

[0089] The density coupling-based algorithm is used, and the standard SST k-ω two-equation model is adopted. The flow equations and turbulence model equations are discretized using the second-order upwind format, and the standard wall function is used near the wall. The fluid is a compressible gas. Both the inner duct 4 and the outer duct 3 are given flow inlet boundary conditions. The flow direction is along the axial direction of the engine exhaust system, and their total temperature and total pressure are set respectively. The outer duct 3 is the ambient atmosphere, and its main components are N2 and O2. The fuel gas in the inner duct 4 includes N2, O2, CO2, H2O and CO. According to the experimental measurement values, the component concentrations are set for the outer duct 3 and the inner duct 4 in the cavity, and the component mass fractions are calculated through the component transport model.

[0090] The radiation adopts the DO model. The external flow field is the pressure outlet and the pressure and temperature are set. The central cone 1 is set to be adiabatic. The temperature of the wall is given according to the experimental measurement value. The cavity wall is set to fluid-solid coupling and the emissivity is set. It can be calculated as a gray body with an emissivity of 0.9.

[0091] The path of the exit energy beam is simulated by the Monte Carlo method, and the radiation intensity of the beam is obtained from the spectral radiation brightness at the exit point.

[0092] Step S4: obtaining the thermal analysis result of the thermal radiation source item of the heat insulation shield 5 through radiation intensity analysis.

[0093] The Monte Carlo algorithm program is obtained by programming and imported into Fluent. According to the temperature field distribution obtained in the flow field acquisition part, as well as the pressure field and component concentration distribution of the internal airflow, combined with the other boundary condition settings in the aforementioned part, the radiation source calculation of the heat shield 5 can be performed.

[0094] In order to solve the problem of autonomous programming of mesh division, the mesh division of CFD simulation process is used as discrete mesh units obtained in radiation transfer process, and the mesh file is imported in a special format as the medium and wall mesh of ray tracing. The mesh can be an unstructured mesh, so it has high applicability.

[0095] Based on the above method, the present invention provides a thermal analysis system for a heat shield, comprising: a model building module, a flow field acquisition module, a radiation acquisition module and an analysis module.

[0096] Among them, the model construction module is used to set the central cone 1, the flame stabilizer 2, the outer duct 3, the inner duct 4 and the heat shield 5 in the cavity of the engine combustion chamber, and set a connected nozzle 6 outside the cavity to construct the exhaust system model; the flow field acquisition module is used to perform two-dimensional heat conduction calculation on the internal heat source in the flow field of the exhaust system model, obtain the temperature field distribution of the wall of the heat shield 5 in the exhaust system model, and obtain the pressure, temperature and component concentration information of the fluid inside the cavity; the radiation acquisition module is used to obtain the radiation transfer factor by simulating beam tracing using the Monte Carlo method based on the temperature field distribution and the pressure, temperature and component concentration information of the fluid inside the cavity, and calculate the radiation intensity on the surface of the heat shield 5 through the radiation transfer factor; the analysis module is used to obtain the thermal analysis results of the thermal radiation source item of the heat shield 5 through radiation intensity analysis.

[0097] The present invention also provides a computer device, including a memory and a processor. The memory stores a program. When the program is executed by the processor, the processor executes the steps of a thermal analysis method for a heat insulation screen.

[0098] According to the disclosed embodiments, a computing device may communicate with one or more external devices (e.g., keyboards, pointing devices, Bluetooth communications, etc.), or with any device (e.g., routers, modems, etc.) that enables a computing device to communicate with one or more other computing devices.

[0099] The above content is a further detailed description of the present invention in combination with a specific preferred embodiment. For technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A thermal analysis method for a heat shield, characterized in that: The steps include: The exhaust system model is constructed by arranging a center cone, a flame stabilizer, an outer duct, an inner duct and a heat shield in the cavity of the engine combustion chamber, and arranging a connected nozzle outside the cavity; Conducting two-dimensional heat conduction on the internal heat source in the exhaust system model flow field to obtain the temperature field distribution of the heat insulation shield wall in the exhaust system model, and obtaining the pressure, temperature and component concentration information of the fluid inside the cavity through the exhaust system model flow field; Based on the temperature field distribution, as well as the pressure, temperature and component concentration information of the fluid inside the cavity, a radiation transfer factor is obtained by simulating beam tracing using the Monte Carlo method, and the radiation intensity on the surface of the heat shield is obtained through the radiation transfer factor; The thermal analysis results of the heat radiation source items of the heat insulation shield are obtained through the radiation intensity analysis.

2. A thermal analysis method for a heat shield as claimed in claim 1, characterized in that: Performing two-dimensional heat conduction on the internal heat source in the flow field of the exhaust system model to obtain the temperature field distribution of the heat insulation shield wall in the exhaust system model includes the following steps: The sum of the convective heat transfer and the radiative heat transfer introduced into and exported from the gas side and the cold air side of the heat insulation screen is regarded as the internal heat source; Substitute the internal heat source into the two-dimensional heat conduction equation, and obtain the temperature field distribution on the heat insulation screen through iteration of the two-dimensional heat conduction equation; the specific expression is: in, is the partial derivative, λ is the thermal conductivity, is the internal heat source, x and y are the coordinates of the coordinate system, and T is the temperature distribution at the coordinate point (x, y).

3. A thermal analysis method for a heat shield as claimed in claim 1, characterized in that: When constructing the exhaust system model, the exhaust system model is divided into unstructured grids, and the grids are encrypted at the center cone, the flame stabilizer, near the wall, and the air film holes of the heat insulation screen.

4. A thermal analysis method for a heat shield as claimed in claim 1, characterized in that: The step of obtaining the pressure, temperature and component concentration information of the fluid inside the cavity comprises the following steps: Set component concentrations for the outer and inner channels in the cavity, and obtain component mass fractions through the component concentrations; Set the pressure and temperature for the external flow at the pressure outlet and set the central cone to be adiabatic.

5. The thermal analysis method of a heat shield according to claim 1, characterized in that: The pressure, temperature and component concentration information of the fluid inside the cavity are obtained, the fluid is compressed gas, the inner duct and the outer duct both have given flow inlet boundary conditions, and the flow direction is along the axial direction of the engine exhaust system; the outer duct is the ambient atmosphere, and its components include N2 and O2, and the fuel gas components in the inner duct include N2, O2, CO2, H2O and CO.

6. A thermal analysis method for a heat shield as claimed in claim 1, characterized in that: The Monte Carlo method is used to simulate beam tracing to obtain the radiation transfer factor, and the specific expression is: Where I is the three-dimensional vector of radiation intensity, s is the path length, is the divergence operator, α is the medium absorption coefficient, and β is the surface reflection coefficient.

7. A thermal analysis method for a heat shield as claimed in claim 1, characterized in that: When the Monte Carlo method is used to simulate beam tracing to obtain the radiation transfer factor, the specific expression also includes other auxiliary terms, including the scattering, absorption and reflection characteristics of the radiation, and the wavelength of the radiation.

8. The thermal analysis method of a heat shield according to claim 1, characterized in that: When the Monte Carlo method is used to simulate beam tracing to obtain the radiation transfer factor, the path of the exit energy beam is simulated, and the radiation intensity of the energy beam is obtained from the spectral radiation brightness at the exit.

9. A thermal analysis system for a heat shield, characterized in that: include: A model building module, used to build an exhaust system model by setting a center cone, a flame stabilizer, an outer duct, an inner duct and a heat shield in the cavity of the engine combustion chamber, and setting a connected nozzle outside the cavity; A flow field acquisition module, used to conduct two-dimensional heat conduction on the internal heat source in the exhaust system model flow field, obtain the temperature field distribution of the heat insulation screen wall in the exhaust system model, and obtain the pressure, temperature and component concentration information of the fluid inside the cavity through the exhaust system model flow field; A radiation acquisition module, for obtaining a radiation transfer factor by simulating beam tracing using a Monte Carlo method based on the temperature field distribution and the pressure, temperature and component concentration information of the fluid inside the cavity, and obtaining the radiation intensity of the heat shield surface through the radiation transfer factor; The analysis module is used to obtain the thermal analysis results of the heat shield thermal radiation source item through radiation intensity analysis.

10. A computer device, characterized in that: The invention comprises a memory and a processor, wherein a program is stored in the memory, and when the program is executed by the processor, the processor executes the steps of the thermal analysis method of a heat insulation shield as claimed in any one of claims 1 to 8.

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