Stratoplane three-dimensional transient thermodynamic analysis method and system

Abstract

The application discloses a stratosphere airship three-dimensional transient thermodynamic analysis method and system, wherein the method steps comprise: obtaining an analysis result by analyzing the stratosphere airship hovering thermal environment; constructing an airship three-dimensional transient thermodynamic internal and external coupling heat transfer model based on the analysis result; and completing thermal analysis of the airship by using the airship three-dimensional transient thermodynamic internal and external coupling heat transfer model. The application establishes the airship three-dimensional transient thermodynamic internal and external coupling heat transfer model, the model couples the airship internal gas flow, the skin surface heat exchange and the external gas flow, and can analyze the day and night change characteristics of the airship temperature. Meanwhile, the problems that the current airship thermodynamic model uses the empirical formula to process the skin internal and external convection heat exchange, ignores the local flow heat exchange characteristics and the influence factors are not considered comprehensively are overcome. In addition, the UDF is used to supplement the simulation calculation of the infrared long-wave radiation part and correct the solar radiation model, so that the simulation calculation is more consistent with the actual situation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flow heat exchange analysis, in particular to a stratosphere airship three-dimensional transient thermodynamic analysis method and system. BACKGROUND

[0002] The stratosphere generally refers to the atmospheric space from the top of the troposphere to about 50 km from the ground. At the bottom of the stratosphere, the atmospheric temperature does not change with height, and the diurnal temperature difference is very small; while in the stratosphere above 20 km from the ground, the atmospheric temperature increases with the increase of height. The stratospheric meteorological conditions are relatively stable, and the atmospheric convection is mainly horizontal flow, which is suitable for long-time fixed-point flight of aircraft. With the development of space technology, the unique space resources of the stratosphere have attracted more and more attention from countries, and have broad application prospects.

[0003] Due to the thinness of the stratospheric air, the airship volume is generally very large, and its thermal characteristics are greatly affected by external environmental heat sources and heat exchange methods during the airship hovering flight, and show obvious diurnal variation. The stratospheric airship is therefore called a thermal aircraft. The thermodynamic modeling of the stratospheric airship plays a crucial role in the safe and stable operation of the airship. At present, different stratospheric airship hovering environmental thermodynamic models have been established. According to the different degrees of model simplification, they can be divided into two categories: node model and dimension model. The node model regards different components of the airship as different heat exchange nodes and considers the heat transfer between the nodes. Specifically, it includes single-node model, two-node model and multi-node model. The zero-node model simplifies the airship as a whole single node, the two-node model divides the airship skin into upper and lower parts, and the multi-node model divides the airship into more typical parts, such as considering the solar cell on the skin as a node and considering its heat dissipation. Compared with the node model, the dimension model discards the node heat transfer and considers the actual heat exchange of the airship. Specifically, the one-dimensional model describes the radial steady-state one-way heat transfer of the airship; the two-dimensional model regards the airship as a two-dimensional infinite long cylinder and considers the influence of external flow wind speed; the three-dimensional model completely considers the three-dimensional heat exchange between the airship skin and the surrounding environment.

[0004] However, in the current stratospheric hovering airship thermodynamic modeling technology and analysis method, the main deficiencies include: (1) the node model simplifies the airship into multiple nodes, only considers node heat transfer, and does not consider the influence of internal and external gas flow on airship heat exchange; (2) the dimension model considers the internal and external convection heat transfer of the airship based on the node model, but the convection heat transfer characteristics of the skin wall surface are calculated by empirical formula, without considering the actual flow heat exchange characteristics of the inside and outside, especially the local temperature characteristics of the internal lifting gas; (3) the study of the transient thermal characteristics of the airship needs to investigate the diurnal variation of the airship skin temperature and the internal lifting gas temperature with time, and the current analysis of the three-dimensional temperature field of the airship skin is a steady-state model, without considering the transient characteristics with time. SUMMARY

[0005] To solve the technical problems in the above background, the present application analyzes the thermal environment of the stratospheric airship, and clarifies the internal and external coupling heat transfer mechanism of the airship. On this basis, a three-dimensional transient thermodynamic internal and external coupling heat transfer model of the airship is established. The model couples the internal gas flow of the airship, the skin surface heat transfer and the external gas flow, and overcomes the problem that the current thermodynamic model of the airship uses empirical formula to process the internal and external convective heat transfer of the skin, which ignores the local flow heat transfer characteristics and the simulation consideration of incomplete influencing factors.

[0006] To achieve the above purpose, the present application provides a three-dimensional transient thermodynamic analysis method of a stratospheric airship, comprising the following steps:

[0007] Analyzing the thermal environment of the stratospheric airship to obtain an analysis result;

[0008] Based on the analysis result, a three-dimensional transient thermodynamic internal and external coupling heat transfer model of the airship is constructed;

[0009] The thermal analysis of the airship is completed by using the three-dimensional transient thermodynamic internal and external coupling heat transfer model of the airship.

[0010] Preferably, the analysis result includes external radiation, skin radiation and convective heat transfer; wherein the external radiation includes direct solar radiation, diffuse solar radiation, reflected solar radiation and infrared long-wave radiation; the skin radiation includes radiation heat transfer between the outer surface of the skin and the external atmosphere, radiation heat transfer between different positions of the outer surface of the skin, radiation heat transfer between different positions of the inner surface of the skin, and radiation heat transfer between the inner surface of the skin and the internal filling gas; the convective heat transfer includes mixed convective heat transfer between the outer surface of the skin and the external atmosphere and natural convective heat transfer between the inner surface of the skin and the internal filling gas.

[0011] Preferably, the three-dimensional transient thermodynamic internal and external coupling heat transfer model of the airship is a combined model, including an external radiation heat source model, a skin surface radiation model and an airship internal and external convective model.

[0012] Preferably, the external radiation heat source model includes a solar radiation heat load model and a long-wave radiation heat load model; the solar radiation heat load model is used to calculate the load of the direct solar radiation, the diffuse solar radiation and the reflected solar radiation; the long-wave radiation heat load model is used to calculate the load of the infrared long-wave radiation.

[0013] Preferably, UDF is used to simulate and calculate the infrared long-wave radiation and the reflected solar radiation; the specific steps include: calculating the heat load of the reflected solar radiation and the infrared long-wave radiation, and adding them to the skin of the airship model in the form of body heat source to participate in the coupling calculation.

[0014] Preferably, the skin surface radiation model specifically adopts a discrete coordinate radiation model, solves a radiation transfer equation of a limited number of discrete solid angles, and converts the radiation transfer equation into a transport equation of radiation intensity under spatial coordinates; then, the radiation transfer equation in a vector direction is regarded as a field equation for solving.

[0015] Preferably, the internal and external convection model of the airship is based on a flow control equation considering near-wall viscous action, adopts a Reynolds average method, and solves to obtain dynamic characteristics and convection heat transfer characteristics of flow.

[0016] Preferably, when calculating internal and external convection heat transfer of the airship, the skin is regarded as an interface of internal gas and external gas, and is processed accordingly; specific steps include: when calculating internal and external convection of the airship, the skin is processed as a fixed no-slip wall; when calculating heat transfer of the airship, the skin is processed as a heat transfer boundary of internal and external gas, and wall heat fluxes of inner and outer surfaces thereof are calculated respectively.

[0017] The application also provides a stratospheric airship three-dimensional transient thermodynamic analysis system, which is used to realize the above method and includes an analysis module, a construction module and a result generation module.

[0018] The analysis module is used to obtain an analysis result by analyzing a stratospheric airship stationary thermal environment.

[0019] The construction module is used to construct a three-dimensional transient thermodynamic internal and external coupling heat transfer model of the airship based on the analysis result.

[0020] The result generation module is used to complete thermal analysis of the airship by using the three-dimensional transient thermodynamic internal and external coupling heat transfer model of the airship.

[0021] Compared with the prior art, the application has the following beneficial effects:

[0022] 1. A three-dimensional transient thermodynamic internal and external coupling heat transfer model of the airship is established, the model couples and processes airship internal gas flow, skin surface heat transfer and external gas flow, and can analyze diurnal variation characteristics of airship temperature.

[0023] 2. The problem that local flow heat transfer characteristics are ignored and influencing factors are not considered comprehensively due to use of an empirical formula in processing skin internal and external convection heat transfer in a current airship thermodynamic model is overcome.

[0024] 3. Simulation calculation of an infrared long-wave radiation part is realized by using a UDF, so that a solar radiation model is more consistent with actual conditions.

[0025] 4. The UDF is used to modify the ground and cloud layer reflection radiation part in the solar radiation model, the influence of different terrains and different weather on the thermal characteristics of the airship is comprehensively considered, and the application range of the airship thermodynamic model is expanded. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the present application, the drawings used in the embodiments will be briefly introduced as follows. Obviously, the drawings described in the following embodiments are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0027] Figure 1 The method flowchart of the embodiment of the present application is shown in the figure.

[0028] Figure 2 The three-dimensional transient thermodynamic internal and external coupled heat transfer model of the airship of the embodiment of the present application is shown in the figure.

[0029] Figure 3 The flowchart of data processing using UDF of the embodiment of the present application is shown in the figure.

[0030] Figure 4 The variation of the average temperature of the airship filling gas in 24 hours of the embodiment of the present application is shown in the figure. Figure 4 a is under different terrain conditions; Figure 4 b is under different weather conditions;

[0031] Figure 5 The three views of the 12h airship skin temperature distribution under the condition of grassland terrain and sunny day of the embodiment of the present application are shown in the figure.

[0032] Figure 6 The system structure diagram of the embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0034] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0035] Embodiment one

[0036] As Figure 1As shown, it is a method flow diagram of the embodiment of the present application, and the steps include:

[0037] S1. Obtain an analysis result by analyzing the stratosphere airship stationary heat environment.

[0038] In the embodiment, the analysis result mainly includes the main heat sources and heat exchange affecting the thermodynamic characteristics of the airship outer skin and internal filling gas, which are finely divided into three categories, including external radiation, skin radiation, and convective heat exchange. The external radiation is composed of direct solar radiation, diffuse solar radiation, reflected solar radiation (ground and cloud reflection radiation), and infrared long-wave radiation (ground and atmospheric long-wave radiation). The skin radiation can be divided into four parts, including the radiation heat exchange between the skin outer surface and the external atmosphere, the radiation heat exchange between different positions of the skin outer surface, the radiation heat exchange between different positions of the skin inner surface, and the radiation heat exchange between the skin inner surface and the internal filling gas. The convective heat exchange is composed of two parts, including the mixed convective heat exchange between the skin outer surface and the external atmosphere, and the natural convective heat exchange between the skin inner surface and the internal filling gas.

[0039] S2. Construct a three-dimensional transient thermodynamic internal and external coupling heat transfer model of the airship based on the analysis result.

[0040] After the internal and external coupling heat transfer mechanism of the airship is clarified through the above analysis result, it can be known that the external heat environment factors and internal heat exchange factors of the airship are coupled through the skin. Then, according to the heat transfer mechanism of the airship, a three-dimensional transient thermodynamic model of the airship is established, which is an internal and external coupling heat transfer model considering convective heat exchange.

[0041] As shown in the figure, Figure 2 The three-dimensional transient thermodynamic internal and external coupling heat transfer model of the airship is a combined model composed of an external radiation heat source model, a skin surface radiation model, and an airship internal and external convection model, which correspond to the three categories of parameters in the above analysis result.

[0042] The external radiation heat source model includes a solar radiation heat load model and a long-wave radiation heat load model. The solar radiation heat load model is used to calculate the heat load of solar radiation, and the long-wave radiation heat load model is used to calculate the load of infrared long-wave radiation.

[0043] The solar radiation specifically includes direct solar radiation, diffuse solar radiation, and reflected solar radiation (ground and cloud reflection radiation). Since the solar radiation varies with different positions on the earth, time, and date, to calculate the solar radiation, the spatial position of the sun and the relative position of the sun and the surface of the illuminated object need to be determined. The solar altitude angle (solar altitude) α is the angle between the day-earth line and the horizontal plane, and the solar azimuth angle (solar azimuth) Φ is the angle between the projection of the day-earth line on the horizontal plane and the local meridian (due south direction). It can be calculated by the following formula:

[0044] sinαsinLsin0(1)

[0045]

[0046] Where L is the local latitude, H is the solar hour angle, and δ is the declination angle.

[0047] For the incident solar radiation and the surface it illuminates, there are three controlling angles: the surface solar azimuth γ, which is the angle between the projection of the Earth-Sun line onto the Earth's horizontal plane and the projection of the surface normal onto the Earth's horizontal plane; the angle of incidence θ, which is the angle between the Earth-Sun line and the surface normal; and the tilt angle Σ, which is the angle between the surface of the object and the Earth's horizontal plane. There are also conversion relationships between these three:

[0048] cosθ=cosαcosγsin+·sinαcos∑ (3)

[0049] For the horizontal plane, we have cosθ H =sinα; for the vertical plane, then cosθ V =cosαcosγ.

[0050] After determining the sun's spatial position and the orientation of the illuminated surface, the first step is to calculate the direct solar radiation heat flux (irradiance). Referring to the ASHRAE manual, the direct solar radiation under clear weather conditions is:

[0051]

[0052] In the formula, EDN is the direct radiative heat flux, A is the apparent solar irradiance when the atmospheric mass is zero, and B is the atmospheric extinction coefficient.

[0053] The calculation of diffuse radiative heat flux in the solar model is divided into diffusion on the vertical surface and diffusion on other surfaces. The diffuse heat flux of the sun on the vertical surface is:

[0054] E d =CYE DN (5)

[0055] Where C is a constant, Y is the ratio of diffuse radiation from the vertical surface to diffuse radiation from the horizontal surface, and is a function of the incident angle, as shown in the following formula:

[0056]

[0057] The diffuse solar radiation on other surfaces is as follows:

[0058]

[0059] The reflected solar radiation is:

[0060]

[0061] In the formula, ρ g Let be the reflectivity of the ground cloud layer. The total diffuse radiation on a given surface is the sum of Ed and Er.

[0062] For a given surface, the total solar radiation is calculated as follows:

[0063] E t =E DN cosθ+E d +E r (9)

[0064] In addition to the solar radiation (shortwave radiation) mentioned above, for airships in flight, the external thermal environment also includes longwave radiation from the Earth's surface and the surrounding atmosphere. For ground-based longwave radiation, the Earth can generally be considered as a gray body, and its radiation intensity mainly depends on the gray body's temperature and emissivity. The formula for calculating the intensity of ground-based longwave radiation can be written as:

[0065]

[0066] Where, ε Earth This is the ground emissivity, and σ is the Stefan-Boltzmann constant, which is 5.67 × 10⁻⁶. -8 W / (m 2 ·K 4 ), T E rath is the surface temperature, τ a The long-wavelength radiation transmittance of the Earth's surface is calculated by the following formula:

[0067]

[0068] Where, p a p0 is the atmospheric pressure around the airship and p0 is the atmospheric pressure at the Earth's surface.

[0069]

[0070] Among them, T a It is the ambient temperature around the airship, ε sky The equivalent emissivity of the sky can be calculated using the following formula:

[0071]

[0072] Where, p w The partial pressure of water vapor in the atmosphere, in kPa, is calculated as follows:

[0073]

[0074] Rh is the relative humidity, which can be calculated by the following formula:

[0075]

[0076] The ground long-wave radiation intensity I Earth and the atmospheric long-wave radiation intensity I sky Then, the amount of long-wave radiation absorbed by the surface skin unit i of the airship per unit time can be calculated by the following formula:

[0077]

[0078]

[0079] wherein ε skin，i is the infrared emissivity of the outer surface unit i of the skin, A skin，i is the area of the surface unit i of the airship.

[0080] The ground and atmospheric long-wave radiation is not considered in the solar radiation model provided by Fluent, and although the ground and cloud layer reflection radiation is calculated, it cannot be directly reflected in the calculation results (i.e. the reflection radiation amount of the object surface under the solar radiation is zero). Therefore, the user-defined function (UDF) is used to correct the ground and cloud layer reflection radiation and supplement the ground and atmospheric long-wave radiation. The specific operation idea is to calculate the ground and cloud layer reflection radiation and the ground and atmospheric long-wave radiation by the above-mentioned formula respectively, and add them to the skin of the airship model in the form of body heat source to participate in the coupling calculation. The data processing flow is shown in Figure 3 .

[0081] The skin surface radiation model is used to calculate the radiation heat exchange between the outer surface of the skin and the external atmosphere, the radiation heat exchange between different positions of the outer surface of the skin, the radiation heat exchange between different positions of the inner surface of the skin, and the radiation heat exchange between the inner surface of the skin and the internal filling gas.

[0082] The skin surface radiation model specifically adopts the discrete coordinate (DO) radiation model to solve the radiation transfer equation (RTE) of a limited number of discrete solid angles, each angle being related to the vector direction s in the global Cartesian coordinate system (x, y, z). The DO radiation model converts the RTE into a transport equation of radiation intensity under the spatial coordinates (x, y, z). The DO radiation model regards the RTE in the direction s as a field equation to be solved.

[0083] When calculating gray body radiation, an opaque wall is considered as a gray body. The radiant energy incident on an opaque wall can be reflected back to the surrounding medium and absorbed by the wall. The reflected radiation can be diffuse reflection and specular reflection, depending on the diffuse reflection fraction f d . Let q in be the radiant energy incident on the opaque wall, the general physical quantities of the opaque wall are calculated as follows:

[0084] Wall surface radiation

[0085] Diffuse reflection energy-f d (1-ε w )q in

[0086] Specular reflection energy-(1-f d )(1-ε w )q in

[0087] Wall surface absorbed radiation-ω w q in

[0088] where n is the refractive index of the adjacent medium, ε w is the wall emissivity, σ is the Stefan-Boltzmann constant, and T w is the wall temperature. The wall absorption is assumed to be equal to the emissivity. For a purely diffuse wall, f d is equal to 1, and there is no specular reflection energy. Similarly, for a purely specular reflection wall, f d is equal to 0, and there is no diffuse reflection energy. When the diffuse reflection coefficient is between 0 and 1, there is both partial diffuse reflection energy and partial specular reflection energy.

[0089] During the operation of the airship, there is forced convective heat transfer between the outer surface of the skin and the surrounding atmosphere, and natural convective heat transfer between the inner surface of the skin and the gas filled in the capsule. Convective heat transfer is related to gas flow, and the heat transfer amount and other thermodynamic properties need to be solved according to the conservation equation of gas flow and heat transfer (i.e., the constructed internal and external convective model of the floating vehicle).

[0090] The internal and external convective model of the floating vehicle is specifically based on the flow control equation (Navier-Stokes equation) considering the near-wall viscous effect, adopts the Reynolds average (RANS) method, and solves to obtain the dynamic characteristics (pressure, shear force, etc.) and convective heat transfer characteristics (temperature, heat flow, etc.) of the flow. The RANS method specifically uses the RNG k-ε turbulence model.

[0091] For natural convection of the air inside the airship, the Boussinesq model is used to simplify the fluid density in the governing equations. It converges faster than solving the fluid density as a function of temperature. Except for the buoyancy term in the momentum equation, the model treats the density as a constant value in the rest of the governing equations. Specifically, the gravity term in the momentum equation is treated as:

[0092] (ρ-ρ0)g≈-ρ0β(T-T0)g (18)

[0093] where ρ is the fluid density, T is the flow temperature, ρ0 is the reference density of the fluid, T0 is the ambient temperature, β is the thermal expansion coefficient (β = 1 / T m , T m is the qualitative temperature), and g is the gravitational acceleration. When the actual density variation is small (i.e., β(T-T0) « 1), the approximation is more accurate.

[0094] In calculating the internal and external convective heat transfer of the airship, the skin needs to be handled specifically as the interface between the internal and external air. For internal and external convection, the skin can be treated as a fixed no-slip wall. For heat transfer, the skin as a heat transfer boundary between internal and external air, its inner and outer surfaces need to consider the wall heat flow respectively, and there is also a solid film heat conduction process inside the skin. Specifically, there is the following heat transfer process: external air - skin outer surface - skin inside - skin inner surface - internal air. In order to handle the thermal boundary conditions of the skin, the skin is treated as the interface between the internal and external flow fields, and the coupled heat transfer method is used to solve the heat transfer between the skin and the internal and external air.

[0095] When using the coupled heat transfer boundary, the skin wall needs to be pre-processed as a double-sided wall, that is, each side of the wall has a fluid domain. When solving the energy equation, the heat transfer between the flow and the wall is calculated directly according to the solution in the adjacent fluid grid on both sides of the wall. In addition, for the heat conduction process inside the skin, the skin is treated as a thin wall, and the thin wall heat conduction is solved. The wall surface adjacent to the internal and external flow field grid is treated as a wall surface. When solving the heat conduction inside the skin, the heat conduction resistance of the wall is calculated by the one-dimensional steady-state heat conduction equation, and by setting the heat conduction coefficient and thickness of the wall, the heat resistance of the wall can be obtained as Δx / k, k is the heat conduction coefficient, and Δx is the thickness of the skin.

[0096] S3. Using the three-dimensional transient thermodynamic internal and external coupled heat transfer model of the airship, the thermal analysis of the airship is completed.

[0097] Finally, using the three-dimensional transient thermodynamic model of the airship constructed by the above steps, the three-dimensional transient thermodynamic analysis of the stratospheric airship is completed.

[0098] Example Two​

[0099] In this embodiment, a typical aerostat shape is selected as an example to evaluate the characteristics of the aerostat across the day and night, and to explore the influence of different terrain and weather conditions on the thermodynamic characteristics of the aerostat. The selected aerostat shape is a typical axisymmetric rotating body, with a length of 250 m and a width of 75 m. The specific geometric parameters are shown in Table 1.

[0100] Table 1

[0101]

[0102] The time is June 21, and the specific calculation state parameter table is shown in Table 2. The reflectivity and ground emissivity in the table take into account the influence of terrain and weather.

[0103] Table 2

[0104]

[0105]

[0106] Figure 4 (a) The average temperature of the filling gas inside the airship in 24 hours under different terrain conditions, i.e. experimental numbers 1-4 in the above Table 3, Figure 4 (b) The average temperature of the filling gas inside the airship in 24 hours under different weather conditions, i.e. experimental numbers 3, 5, and 6 in the above Table 3. Taking experimental number 4 (i.e. grassland sunny conditions) in the above Table 3 as an example, the three view images of the airship skin temperature distribution at a certain time predicted by the model are shown in Figure 5 .

[0107] Example Three

[0108] As shown in Figure 6 , the system structure diagram of this embodiment includes an analysis module, a construction module, and a result generation module. The analysis module is used to obtain analysis results by analyzing the stratospheric airship hovering thermal environment. The construction module is used to construct a three-dimensional transient thermodynamic internal and external coupling heat transfer model of the airship based on the analysis results. The result generation module is used to complete the thermal analysis of the airship by using the three-dimensional transient thermodynamic internal and external coupling heat transfer model of the airship.

[0109] The analysis results include external radiation, skin radiation and convection heat exchange; the external radiation includes direct solar radiation, diffuse solar radiation, reflected solar radiation and infrared long-wave radiation; the skin radiation includes radiation heat exchange between the outer surface of the skin and the external atmosphere, radiation heat exchange between different positions of the outer surface of the skin, radiation heat exchange between different positions of the inner surface of the skin, and radiation heat exchange between the inner surface of the skin and the internal filling gas; the convection heat exchange includes mixed convection heat exchange between the outer surface of the skin and the external atmosphere and natural convection heat exchange between the inner surface of the skin and the internal filling gas.

[0110] The above-described embodiments are only descriptions of the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A method for analyzing the three-dimensional transient thermodynamics of a stratospheric airship, characterized by the following steps: include: The analytical results were obtained by analyzing the thermal environment of a stratospheric airship in its stationary position. Based on the analysis results, a three-dimensional transient thermodynamic internal and external coupled heat transfer model of the airship is constructed. The three-dimensional transient thermodynamic internal and external coupled heat transfer model of the airship is a combined model, including: an external radiation heat source model, a skin surface radiation model, and an internal and external convection model of the airship; UDF is used to simulate and calculate the infrared long-wave radiation and reflected solar radiation; the specific steps include: calculating the heat load of the reflected solar radiation and the infrared long-wave radiation, and adding it to the skin of the airship model in the form of a volume heat source to participate in the coupled calculation; The thermal analysis of the airship was completed using the aforementioned three-dimensional transient thermodynamic coupled internal and external heat transfer model.

2. The analytical method for the three-dimensional transient thermodynamics of stratospheric airships according to claim 1, characterized in that, The analysis results include: external radiation, skin radiation, and convective heat transfer; wherein, the external radiation includes: direct solar radiation, diffuse solar radiation, reflected solar radiation, and infrared long-wave radiation; skin radiation includes: radiative heat transfer between the outer surface of the skin and the external atmosphere, radiative heat transfer between different locations on the outer surface of the skin, radiative heat transfer between different locations on the inner surface of the skin, and radiative heat transfer between the inner surface of the skin and the internal filling gas; convective heat transfer includes: mixed convective heat transfer between the outer surface of the skin and the external atmosphere, and natural convective heat transfer between the inner surface of the skin and the internal filling gas.

3. The analytical method for the three-dimensional transient thermodynamics of stratospheric airships according to claim 2, characterized in that, The external radiation heat source model includes: a solar radiation heat load model and a long-wave radiation heat load model; the solar radiation heat load model is used to calculate the load of the direct solar radiation, the diffuse solar radiation and the reflected solar radiation; the long-wave radiation heat load model is used to calculate the load of the infrared long-wave radiation.

4. The analytical method for the three-dimensional transient thermodynamics of stratospheric airships according to claim 1, characterized in that, The radiation model of the skin surface specifically adopts a discrete coordinate radiation model, which solves the radiation transfer equation for a finite number of discrete solid angles, and then transforms the radiation transfer equation into a transport equation for radiation intensity in spatial coordinates; subsequently, the radiation transfer equation in the vector direction is treated as a field equation and solved.

5. The analytical method for the three-dimensional transient thermodynamics of stratospheric airships according to claim 1, characterized in that, The internal and external convection model of the airship is based on the flow control equations that take into account the viscosity near the wall. The Reynolds-averaged method is used to solve for the dynamic characteristics of the flow and the convective heat transfer characteristics.

6. The analytical method for the three-dimensional transient thermodynamics of stratospheric airships according to claim 5, characterized in that, When calculating the internal and external convective heat transfer of an airship, the skin is treated as the interface between the internal and external gases and is specifically handled. The specific steps include: when calculating the internal and external convection of the airship, the skin is treated as a fixed, non-slip wall surface; when calculating the heat transfer of the airship, the skin is treated as the heat transfer boundary between the internal and external gases, and the wall heat flux of its inner and outer surfaces is calculated separately.

7. A system for analyzing the three-dimensional transient thermodynamics of a stratospheric airship, said system being used to implement the method described in any one of claims 1-6, characterized in that, include: Analysis module, construction module, and results generation module; The analysis module is used to obtain analysis results by analyzing the thermal environment of a stratospheric airship in mid-air; The construction module is used to construct a three-dimensional transient thermodynamic internal and external coupled heat transfer model of the airship based on the analysis results; The result generation module is used to perform thermal analysis of the airship by utilizing the three-dimensional transient thermodynamic internal and external coupled heat transfer model of the airship.

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