A Simulation Method for Infrared Radiation Characteristics of Aircraft Skin-Pyroblast Full Flow Field Coupling

Abstract

This invention discloses a method for simulating the infrared radiation characteristics of an aircraft skin-exhaust plume coupled with the entire flow field. The method includes: drawing the fuselage and external flow field regions to establish a full flow field model of the aircraft skin-exhaust plume; obtaining aircraft flight parameters and engine parameters; setting flow field boundary conditions based on these parameters; performing flow field simulation to calculate the heat flux density on the aircraft skin surface and the temperature distribution of the exhaust gas; using the heat flux density on the aircraft skin surface as a second type of boundary condition to perform solid heat conduction simulation and calculate the temperature distribution on the aircraft skin surface; establishing infrared emissivity models for both the aircraft skin surface and the exhaust plume; and combining the obtained exhaust gas temperature distribution, aircraft skin surface temperature distribution, and infrared emissivity models to calculate the infrared radiation characteristics of the aircraft skin surface and the exhaust plume. Using this invention improves the accuracy and precision of simulating the infrared radiation characteristics of aircraft.

Description

Technical Field

[0001] This invention relates to the field of infrared radiation characteristic simulation technology, and in particular to a method for simulating infrared radiation characteristics of aircraft skin-exhaust flame full flow field coupling. Background Technology

[0002] With the development of modern aviation technology, accurate simulation of aircraft infrared radiation characteristics has become increasingly important. The infrared radiation of an aircraft during flight is affected by various factors, including engine exhaust plumes, surface temperature distribution, and atmospheric conditions. Accurate simulation and prediction of aircraft infrared radiation characteristics are crucial for the detection and interception of stealth aircraft.

[0003] Studies on the infrared radiation characteristics of aircraft are mainly conducted through numerical simulation methods. In related technologies, due to significant differences between the infrared radiation model of the aircraft fuselage and the gas infrared radiation model of the engine exhaust, the aircraft fuselage and engine exhaust are typically studied separately.

[0004] For example, Chinese patent document CN101976275A models the aircraft skin, engine nozzle, and aircraft plume, and analyzes the influence of the atmospheric environment on the aircraft's infrared radiation; Chinese patent document CN109658496A establishes a three-dimensional model of the aircraft skin, obtains the aircraft skin temperature field data, and generates a three-dimensional temperature model to simulate the aircraft's infrared texture image.

[0005] Some of the methods mentioned above only analyzed one of the aircraft fuselage and the exhaust plume, or although they analyzed both the fuselage and the exhaust plume, they treated the aircraft fuselage and the exhaust plume as two independent parts in the flow field calculation, ignoring the heating effect of the exhaust plume on the fuselage and the influence of the flow field on the fuselage surface on the shape and temperature distribution of the exhaust plume. Summary of the Invention

[0006] This invention provides a simulation method for infrared radiation characteristics of aircraft skin-exhaust flame full flow field coupling, which is beneficial to improving the accuracy and precision of aircraft infrared radiation characteristics simulation.

[0007] A method for simulating the infrared radiation characteristics of aircraft skin-exhaust plume full-field coupling includes the following steps:

[0008] (1) Draw the fuselage and external flow field regions, and establish a full flow field model of the aircraft skin-tail flame;

[0009] (2) Obtain aircraft flight parameters and engine parameters, set flow field boundary conditions based on aircraft flight parameters and engine parameters, perform flow field simulation based on the full flow field model, and calculate the heat flux density on the aircraft skin surface and the temperature distribution of the exhaust gas.

[0010] (3) Using the heat flux density on the aircraft skin surface as the second type of boundary condition, perform solid heat conduction simulation and calculate the temperature distribution on the aircraft skin surface.

[0011] (4) Establish infrared emissivity models for the aircraft skin surface and the exhaust plume, respectively;

[0012] (5) Combine the exhaust gas temperature distribution obtained in step (2), the aircraft skin surface temperature distribution obtained in step (3), and the infrared emissivity model obtained in step (4) to calculate the infrared radiation characteristics of the aircraft skin surface and exhaust.

[0013] Further, in step (1), the fuselage area is drawn according to the actual aircraft size; at the same time, a cylindrical or cuboid external flow field area is drawn, with a length more than ten times the length of the actual aircraft; finally, the flow field calculation domain is obtained by performing Boolean difference operation between the external flow field area and the fuselage area, thereby establishing the full flow field model of the aircraft skin-tail flame.

[0014] Furthermore, in step (2), the aircraft flight parameters include flight speed, atmospheric pressure and temperature at the corresponding flight altitude; the aircraft engine parameters include the speed, temperature and pressure of the gas ejected from the engine nozzle.

[0015] The flow field boundary conditions are set based on the aircraft flight parameters and engine parameters, specifically as follows:

[0016] The inlet of the external flow field is set as a velocity inlet, with the corresponding flow velocity set to the aircraft's flight speed, and the temperature and pressure set according to the atmospheric parameters at the aircraft's flight altitude; the engine nozzle is set as an internal velocity inlet, with the corresponding flow velocity set to the gas flow velocity at the engine nozzle, and the temperature and pressure set to the temperature and pressure at the engine nozzle.

[0017] Fluid simulation was performed to calculate the heat flux density on the aircraft skin surface and the temperature distribution of the exhaust gases. The specific process is as follows:

[0018] (2-1) The aircraft fuselage is meshed using an unstructured meshing method, and the mesh is refined at locations with large curvature gradients on the fuselage surface and at the engine nozzles.

[0019] (2-2) Based on the set boundary conditions, CFD fluid simulation was performed using FLUENT software; the flow field simulation was conducted by solving the three-dimensional Navier-Stokes equations:

[0020]

[0021] Where ρ is the fluid density, u is the velocity vector, t is time, p is the fluid pressure, μ is the dynamic viscosity coefficient, and f is the external volume force;

[0022] (2-3) Post-process the simulation results data to obtain the heat flux density on the fuselage skin surface and the temperature distribution of the exhaust gas.

[0023] Furthermore, the specific process of step (3) is as follows:

[0024] (3-1) Use a separate aircraft model to establish a heat conduction simulation model, and mesh the heat conduction simulation model;

[0025] (3-2) Using the heat flux density on the fuselage skin surface calculated in step (2) as the second type of boundary condition, the heat conduction equation is solved using the finite element method. The heat conduction equation is:

[0026]

[0027] Where u = u(t,x,y,z) represents temperature, which is a function of time and coordinates; k is the thermal diffusivity of the fuselage material; and x, y, and z are coordinates.

[0028] When setting the second type of boundary conditions, in addition to the heat flux density on the fuselage skin surface, the radiative heat dissipation from the fuselage skin surface also needs to be considered; the formula for calculating radiative heat dissipation is:

[0029] Q=εσ(T 4 -T env 4 )

[0030] Where Q is the radiative heat dissipation per unit area of ​​the fuselage skin per unit time, ε is the emissivity of the aircraft skin material, σ is the Boltzmann constant, and T is the surface temperature of the corresponding aircraft skin region. env This refers to the atmospheric temperature.

[0031] Furthermore, the specific process of step (4) is as follows:

[0032] (4-1) Determine the type of aircraft skin material and the composition of exhaust gases by consulting official technical documents;

[0033] (4-2) Find the infrared spectral emissivity of the corresponding aircraft skin material and the spectral absorption coefficient of the corresponding gas component; the spectral absorption coefficient of the gas is calculated from the spectral transmittance of the gas layer, and the relationship between the two is as follows:

[0034] A = 1 - T

[0035] Where A is the spectral absorption coefficient of the gas, and T is the spectral transmittance of the gas layer; the gas layer transmittance is obtained by searching in the publicly available spectral parameter database HITEMP.

[0036] Furthermore, the specific process of step (5) is as follows:

[0037] (5-1) Calculate the spectral radiant exitance M of the aircraft skin surface based on the temperature distribution obtained in step (3). λ :

[0038]

[0039] In the formula, λ is the wavelength; c1 is the first radiation constant; c2 is the second radiation constant; and T is the surface temperature of the aircraft skin area.

[0040] (5-2) Calculate the infrared radiance L of the aircraft skin surface:

[0041]

[0042] Where ε0 is the emissivity of the aircraft surface material obtained in step (4), that is, the ratio of the amplitude of surface radiation to that of blackbody radiation at the same temperature; M λ λ represents the spectral radiative exitance of the fuselage surface; λ is the wavelength.

[0043] (5-3) Calculate the infrared radiation amplitude of the exhaust plume based on the temperature distribution of the exhaust gas obtained in step (2) and the infrared emissivity model of the exhaust plume established in step (4), specifically including:

[0044] The tail flame is divided into several gas layers. When calculating, the infrared radiation absorption and emission of each gas layer need to be considered from bottom to top. The absorption of infrared radiation by the gas layer is directly calculated using the spectral infrared radiation transmittance obtained from the HITEMP database in step (4). The calculation method for the infrared radiation amplitude of the gas layer is the same as the calculation method for the infrared radiation amplitude of the skin surface in (5-1) and (5-2).

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] This invention proposes a method that can calculate the flow fields of the aircraft skin and the exhaust plume together. By combining the simulation of the aircraft skin and the exhaust plume, the interaction between the fuselage flow field and the exhaust plume flow field is taken into account, which can effectively simulate the overall flow field of the fuselage during flight and greatly improve the simulation accuracy of the infrared radiation characteristics of aerial targets. Attached Figure Description

[0047] Figure 1 This is a flowchart of a simulation method for infrared radiation characteristics of aircraft skin-exhaust flame full flow field coupling according to an embodiment of the present invention;

[0048] Figure 2 This is the result of unstructured mesh generation during fluid simulation in an embodiment of the present invention;

[0049] Figure 3The engine exhaust temperature distribution and fuselage skin surface temperature distribution obtained through simulation in this embodiment of the invention;

[0050] Figure 4 The above are simulation results of the fuselage infrared radiation obtained from the simulation of an embodiment of the present invention. Detailed Implementation

[0051] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not constitute any limitation thereof.

[0052] like Figure 1 As shown, a simulation method for infrared radiation characteristics of aircraft skin-exhaust plume full-field coupling includes the following steps:

[0053] (1) Draw the fuselage and external flow field regions, and establish a full flow field model of the aircraft skin-tail flame;

[0054] (2) Obtain aircraft flight parameters and engine parameters, set flow field boundary conditions based on aircraft flight parameters and engine parameters, perform flow field simulation based on the full flow field model, and calculate the heat flux density on the aircraft skin surface and the temperature distribution of the exhaust gas.

[0055] (3) Using the heat flux density on the aircraft skin surface as the second type of boundary condition, perform solid heat conduction simulation and calculate the temperature distribution on the aircraft skin surface.

[0056] (4) Establish infrared emissivity models for the aircraft skin surface and the exhaust plume, respectively;

[0057] (5) Combine the exhaust gas temperature distribution obtained in step (2), the aircraft skin surface temperature distribution obtained in step (3), and the infrared emissivity model obtained in step (4) to calculate the infrared radiation characteristics of the aircraft skin surface and exhaust.

[0058] The method of the present invention will be further analyzed below using the Boeing 777-300ER aircraft as an example.

[0059] First, a full flow field model of the aircraft skin-exhaust plume is established: The model is created according to the actual dimensions of the Boeing 777-300ER aircraft, and a cylindrical external flow field region with a length ten times the fuselage length and a diameter five times the fuselage width is drawn. Boolean difference operations are used to obtain the fluid computational domain, such as... Figure 2 As shown.

[0060] Next, fluid simulation was performed using FLUENT software. Boundary conditions needed to be given according to the aircraft flight parameters and engine operating parameters during the fluid simulation. The core parameters of the Boeing 777-300ER aircraft and its GE90 engine used in the simulation are shown in Table 1.

[0061] Table 1 Boundary Condition Setting Parameters

[0062]

[0063] After setting the boundary conditions according to the parameters, fluid simulation was performed to obtain data on the heat flux density distribution on the fuselage skin surface and the temperature distribution of the exhaust gas, such as... Figure 3 (a)

[0064] Next, the heat flux density distribution data of the fuselage skin surface obtained from the simulation is exported and used as the second type of boundary condition for the solid-state heat conduction simulation of the fuselage. The simulation is performed using the finite element method, and solid-domain meshing is required before the simulation. Heat conduction simulation calculations are relatively easy and usually do not require non-mechanical meshing techniques; conventional triangular or quadrilateral meshes can be used. The emissivity of the fuselage skin surface is 0.85. After setting the boundary conditions, the heat conduction simulation is performed to obtain the aircraft skin temperature distribution data, such as... Figure 3 (b)

[0065] After obtaining the temperature distribution data of the aircraft skin and exhaust plume, a corresponding infrared emissivity model needs to be established. The emissivity of the aircraft skin material remains essentially constant across different infrared bands and can be set as a constant of 0.85; the gas composition of the exhaust plume can be obtained from the parameters of the GE90 engine, with the core data shown in Table 2.

[0066] Table 2. Components and proportions of exhaust gases

[0067]

[0068] The wavelength range was selected as 3–5 μm, and the gas layer thickness was set to 40 cm. The spectral transmittance of the gas layer was obtained from the HITEMP database to obtain the infrared emissivity model of the exhaust flame.

[0069] Finally, combining the simulation data of temperature distribution on the skin surface and the exhaust plume with the corresponding infrared emissivity model, the spectral radiative exitance and spectral radiative intensity were calculated sequentially to obtain the infrared radiation characteristics of the aircraft skin surface and exhaust plume. The final calculated complete distribution of infrared radiation intensity of the aircraft skin and exhaust plume within 3–5 μm is shown below. Figure 4 As shown.

[0070] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for simulating the infrared radiation characteristics of aircraft skin-exhaust plume full-field coupling, characterized in that, Includes the following steps: (1) Draw the fuselage and external flow field regions, and establish a full flow field model of the aircraft skin-tail flame; (2) Obtain aircraft flight parameters and engine parameters, set flow field boundary conditions based on aircraft flight parameters and engine parameters, perform flow field simulation based on the full flow field model, and calculate the heat flux density on the aircraft skin surface and the temperature distribution of the exhaust gas; the specific process is as follows: (2-1) The aircraft fuselage is meshed using an unstructured mesh generation method, and the mesh is refined at locations with large curvature gradients on the fuselage surface and at the engine nozzles. (2-2) Based on the set boundary conditions, CFD fluid simulation was performed using FLUENT software; the flow field simulation was conducted by solving the three-dimensional Navier-Stokes equations: Where ρ is the fluid density, u is the velocity vector, t is time, p is the fluid pressure, μ is the dynamic viscosity coefficient, and f is the external volume force; (2-3) Post-process the simulation results data to obtain the heat flux density on the aircraft skin surface and the temperature distribution of the exhaust gas. (3) Using the heat flux density on the aircraft skin surface as the second type of boundary condition, solid heat conduction simulation is performed to calculate the temperature distribution on the aircraft skin surface; the specific process is as follows: (3-1) Use a separate aircraft model to establish a heat conduction simulation model, and mesh the heat conduction simulation model; (3-2) Using the heat flux density on the aircraft skin surface calculated in step (2) as the second type of boundary condition, the heat conduction equation is solved using the finite element method. The heat conduction equation is: Where u = u(t,x,y,z) represents temperature, which is a function of time and coordinates; k is the thermal diffusivity of the fuselage material; and x, y, and z are coordinates. When setting the second type of boundary conditions, in addition to the heat flux density of the aircraft skin surface, the radiative heat dissipation of the fuselage skin surface also needs to be considered; the formula for calculating radiative heat dissipation is: Q=εσ(T 4 -T env 4 ) Where Q is the radiative heat dissipation per unit area of ​​the fuselage skin per unit time, ε is the emissivity of the aircraft skin material, σ is the Boltzmann constant, and T is the surface temperature of the corresponding aircraft skin region. env Atmospheric temperature; (4) Establish infrared emissivity models for the aircraft skin surface and the exhaust plume, respectively; (5) Combine the exhaust gas temperature distribution obtained in step (2), the aircraft skin surface temperature distribution obtained in step (3), and the infrared emissivity model obtained in step (4) to calculate the infrared radiation characteristics of the aircraft skin surface and exhaust.

2. The simulation method for infrared radiation characteristics of aircraft skin-exhaust plume full-field coupling according to claim 1, characterized in that, In step (1), the fuselage area is drawn according to the actual aircraft size; at the same time, the external flow field area in the shape of a cylinder or cuboid is drawn, with a length more than ten times the length of the actual aircraft; finally, the flow field calculation domain is obtained by performing Boolean difference operation between the external flow field area and the fuselage area, thereby establishing the full flow field model of the aircraft skin-tail flame.

3. The simulation method for infrared radiation characteristics of aircraft skin-exhaust flame full-field coupling according to claim 1, characterized in that, In step (2), the aircraft flight parameters include flight speed, atmospheric pressure and temperature at the corresponding flight altitude; the aircraft engine parameters include the speed, temperature and pressure of the gas ejected from the engine nozzle.

4. The simulation method for infrared radiation characteristics of aircraft skin-exhaust plume full-field coupling according to claim 1, characterized in that, In step (2), the flow field boundary conditions are set according to the aircraft flight parameters and engine parameters, specifically as follows: The inlet of the external flow field is set as a velocity inlet, with the corresponding flow velocity set to the aircraft's flight speed, and the temperature and pressure set according to the atmospheric parameters at the aircraft's flight altitude; the engine nozzle is set as an internal velocity inlet, with the corresponding flow velocity set to the gas flow velocity at the engine nozzle, and the temperature and pressure set to the temperature and pressure at the engine nozzle.

5. The simulation method for infrared radiation characteristics of aircraft skin-exhaust plume full-field coupling according to claim 1, characterized in that, The specific process of step (4) is as follows: (4-1) Determine the type of aircraft skin material and the composition of exhaust gases by consulting technical documents; (4-2) Find the infrared spectral emissivity of the corresponding aircraft skin material and the spectral absorption coefficient of the corresponding gas component; the spectral absorption coefficient of the gas is calculated from the spectral transmittance of the gas layer, and the relationship between the two is as follows: A = 1 - T Where A is the absorption coefficient of the gas spectral line, and T is the transmittance of the gas layer spectral line; the transmittance of the gas layer spectral line is obtained by searching in the publicly available spectral parameter database HITEMP.

6. The simulation method for infrared radiation characteristics of aircraft skin-exhaust plume full-field coupling according to claim 1, characterized in that, The specific process of step (5) is as follows: (5-1) Calculate the spectral radiant exitance M of the aircraft skin surface based on the temperature distribution obtained in step (3). λ : In the formula, λ is the wavelength; c1 is the first radiation constant; c2 is the second radiation constant; and T is the surface temperature of the aircraft skin area. (5-2) Calculate the infrared radiance L of the aircraft skin surface: Where ε0 is the emissivity of the aircraft surface material obtained in step (4), that is, the ratio of the radiance of surface radiation to that of blackbody radiation at the same temperature; M λ λ represents the spectral radiative exitance of the fuselage surface; λ is the wavelength. (5-3) Calculate the infrared radiation amplitude of the exhaust plume based on the temperature distribution of the exhaust gas obtained in step (2) and the infrared emissivity model of the exhaust plume established in step (4), specifically including: The tail flame is divided into several gas layers. When calculating, the infrared radiation absorption and emission of each gas layer need to be considered from bottom to top. The absorption of infrared radiation by the gas layer is directly calculated using the spectral infrared radiation transmittance obtained from the HITEMP database in step (4). The calculation method for the infrared radiation radiance generated by the gas layer is the same as the calculation method for the infrared radiation radiance of the skin surface in (5-1) and (5-2).

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