Infrared radiation characteristic simulation method for aircraft skin-tail flame full flow field coupling

Abstract

The invention discloses an aircraft skin-tail flame full flow field coupled infrared radiation characteristic simulation method, which comprises the following steps of: drawing a fuselage and an external flow field area, and establishing an aircraft skin-tail flame full flow field model; aircraft flight parameters and engine parameters are obtained, flow field boundary conditions are set according to the aircraft flight parameters and the engine parameters, flow field simulation is carried out, and aircraft skin surface heat flux density and tail flame gas temperature distribution are calculated; performing solid heat conduction simulation by taking the heat flux density on the surface of the aircraft skin as a second type of boundary condition, and calculating temperature distribution on the surface of the aircraft skin; respectively establishing infrared emissivity models of the skin surface and the tail flame of the aircraft; and combining the obtained tail flame gas temperature distribution, the aircraft skin surface temperature distribution and the infrared emissivity model to calculate the infrared radiation characteristics of the aircraft skin surface and the tail flame. By utilizing the method, the simulation accuracy and precision of the infrared radiation characteristics of the airplane can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of infrared radiation characteristic simulation, and in particular to an infrared radiation characteristic simulation method of aircraft skin-tail flame full flow field coupling. Background Art

[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 many factors, such as engine tail flame, surface temperature distribution of the aircraft, and atmospheric environment. Accurate simulation and prediction of the infrared radiation characteristics of an aircraft is crucial for the identification and detection of stealth aircraft.

[0003] The study of aircraft infrared radiation characteristics is mainly carried out through numerical simulation methods. In related technologies, due to the large difference between the infrared radiation model of the aircraft fuselage and the infrared radiation model of the gas of the engine tail flame, the aircraft fuselage and the engine tail flame are usually studied separately.

[0004] For example, in the Chinese patent document with publication number CN101976275A, the aircraft skin, engine nozzle, and aircraft plume are modeled separately, and the influence of the atmospheric environment on the aircraft infrared radiation is analyzed; in the Chinese patent document with publication number CN109658496A, a three-dimensional model of the aircraft skin is established, the aircraft skin temperature field data is obtained, and a three-dimensional temperature model is generated to simulate the aircraft infrared texture image.

[0005] Some of the above methods only analyze one of the aircraft fuselage and the tail flame during analysis, or although the fuselage and the tail flame are analyzed at the same time, the aircraft fuselage and the tail flame are regarded as two independent parts during flow field calculation, ignoring the heating effect of the tail flame on the fuselage and the influence of the flow field on the fuselage surface on the tail flame shape and temperature distribution. Summary of the invention

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

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

[0008] (1) Draw the fuselage and external flow field area and establish the 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 the 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 tail flame gas;

[0010] (3) Taking the heat flux density on the aircraft skin surface as the second-class boundary condition, solid heat conduction simulation is performed to calculate the temperature distribution on the aircraft skin surface;

[0011] (4) Establish infrared emissivity models for the aircraft skin surface and tail flame respectively;

[0012] (5) Calculate the infrared radiation characteristics of the aircraft skin surface and the tail flame by combining the tail flame 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).

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

[0014] Furthermore, in step (2), the aircraft flight parameters include the flight speed, the atmospheric pressure and temperature at the corresponding flight altitude; and 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 according to the aircraft flight parameters and engine parameters, specifically:

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

[0017] Perform fluid simulation to calculate the heat flux density on the aircraft skin surface and the temperature distribution of the tail flame gas. The specific process is as follows:

[0018] (2-1) The aircraft fuselage is meshed using an unstructured meshing method, and meshes are encrypted at locations where the curvature gradient of the fuselage surface is large and at the engine nozzles;

[0019] (2-2) According to the set boundary conditions, CFD fluid simulation is performed using FLUENT software; the flow field simulation is performed by solving the three-dimensional NS equations:

[0020]

[0021] Among them, ρ is the fluid density, u is the velocity vector, t is the 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 result data to obtain the heat flux density on the fuselage skin surface and the temperature distribution of the tail flame gas.

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

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

[0025] (3-2) The heat flux density on the fuselage skin surface calculated in step (2) is used as the second-class boundary condition, and the finite element method is used to solve the heat conduction equation, which is:

[0026]

[0027] Among them, u = u (t, x, y, z) represents temperature, which is a function of time and coordinates; k is the thermal diffusion coefficient of the fuselage material; x, y, 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 radiation heat dissipation on the fuselage skin surface also needs to be considered; the radiation heat dissipation calculation formula is:

[0029] Q=εσ(T 4 -T env 4 )

[0030] Where Q is the amount of heat radiated from the fuselage skin surface per unit area per unit time, ε is the emissivity of the aircraft skin material, σ is the Boltzmann constant, T is the surface temperature of the corresponding aircraft skin area, T env is the atmospheric temperature.

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

[0032] (4-1) Determine the aircraft skin material type and tail flame gas composition 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:

[0034] A=1-T

[0035] Wherein, 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 public spectral parameter database HITEMP.

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

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

[0038]

[0039] Where 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 radiation radiance L of the aircraft skin surface:

[0041]

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

[0043] (5-3) calculating the infrared radiation amplitude brightness of the tail flame according to the temperature distribution of the aircraft tail flame gas obtained in step (2) and the infrared emissivity model of the tail flame established in step (4), specifically including:

[0044] The tail flame is divided into several gas layers. The infrared radiation absorption and emission of each gas layer need to be considered from bottom to top during calculation. The infrared radiation absorption of the gas layer is directly calculated using the spectral infrared radiation transmittance obtained by searching the HITEMP database in step (4). The calculation method for the infrared radiation amplitude brightness generated by the gas layer is the same as the calculation method for the infrared radiation amplitude brightness 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] The present invention proposes a method that can calculate the skin and tail flame flow fields together. By combining the simulation of the aircraft skin and the tail flame, the interaction between the fuselage flow field and the tail flame 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. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0048] Figure 2 The unstructured grid division result performed when performing fluid simulation in an embodiment of the present invention;

[0049] Figure 3The engine tail flame temperature distribution and the fuselage skin surface temperature distribution obtained by simulation in an embodiment of the present invention;

[0050] Figure 4 This is a simulation result of the infrared radiation of the fuselage obtained by simulating an embodiment of the present invention. DETAILED DESCRIPTION

[0051] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

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

[0053] (1) Draw the fuselage and external flow field area and establish the 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 the 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 tail flame gas;

[0055] (3) Taking the heat flux density on the aircraft skin surface as the second-class boundary condition, solid heat conduction simulation is performed to calculate the temperature distribution on the aircraft skin surface;

[0056] (4) Establish infrared emissivity models for the aircraft skin surface and tail flame respectively;

[0057] (5) Calculate the infrared radiation characteristics of the aircraft skin surface and the tail flame by combining the tail flame 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).

[0058] The method of the present invention is further analyzed below by taking the Boeing 777-300ER aircraft as an example.

[0059] First, the aircraft skin-tail flame full flow field model is established: the model is built according to the actual Boeing 777-300ER aircraft size, and a cylindrical external flow field area with a length ten times the fuselage length and a diameter five times the fuselage width is drawn. The fluid calculation domain is obtained using Boolean difference operation, such as Figure 2 shown.

[0060] Next, the fluid simulation is performed using FLUENT software. When performing fluid simulation, boundary conditions need to be given according to the aircraft flight parameters and engine operating parameters. The core parameters of the Boeing 777-300ER aircraft and the 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, the fluid simulation is performed to obtain the heat flux density distribution on the fuselage skin surface and the tail flame gas temperature distribution data, such as Figure 3 Middle (a).

[0064] Secondly, the heat flux density distribution data of the fuselage skin surface obtained by simulation is exported as the second type of boundary condition for the fuselage solid heat conduction simulation. The simulation is performed using the finite element algorithm, and solid domain meshing is required before 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 for division. The emissivity of the fuselage skin surface is 0.85. After setting the boundary conditions, a heat conduction simulation is performed to obtain the aircraft skin temperature distribution data, such as Figure 3 Middle (b).

[0065] After obtaining the temperature distribution data of the aircraft skin and tail flame, it is necessary to establish the corresponding infrared emissivity model. The emissivity of the aircraft skin material is basically unchanged in different infrared bands and can be set to a constant of 0.85; the gas composition of the tail flame can be obtained from the GE90 engine parameters, and the core data is shown in Table 2.

[0066] Table 2 Tail flame gas components and their proportions

[0067]

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

[0069] Finally, combining the temperature distribution simulation data of the skin surface and the tail flame with the corresponding infrared emissivity model, the spectral radiation emittance and spectral radiation intensity are calculated in turn to obtain the infrared radiation characteristics of the aircraft skin surface and the tail flame. The final calculated infrared radiation intensity of the aircraft skin and tail flame within 3 to 5 μm is as follows: Figure 4 shown.

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

Claims

1. A method for simulating infrared radiation characteristics of aircraft skin-tail flame full flow field coupling, characterized in that: The following steps are involved: (1) Draw the fuselage and external flow field area and establish the 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 the 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 tail flame gas; (3) Taking the heat flux density on the aircraft skin surface as the second-class boundary condition, solid heat conduction simulation is performed to calculate the temperature distribution on the aircraft skin surface; (4) Establish infrared emissivity models for the aircraft skin surface and tail flame respectively; (5) Calculate the infrared radiation characteristics of the aircraft skin surface and the tail flame by combining the tail flame 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).

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

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

4. The infrared radiation characteristic simulation method of aircraft skin-tail flame full flow field coupling according to claim 1 is characterized in that: In step (2), the flow field boundary conditions are set according to the aircraft flight parameters and engine parameters, specifically: The inlet of the external flow field is set as the velocity inlet, the corresponding flow velocity is set to the aircraft flight speed, and the temperature and pressure are set according to the atmospheric parameters at the aircraft flight altitude; the engine nozzle is set as the internal velocity inlet, the corresponding flow velocity is set to the gas flow velocity at the engine nozzle, and the temperature and pressure are set to the temperature and air pressure of the engine nozzle.

5. The infrared radiation characteristic simulation method of aircraft skin-tail flame full flow field coupling according to claim 1 is characterized in that: In step (2), fluid simulation is performed to calculate the heat flux density on the aircraft skin surface and the temperature distribution of the tail flame gas. The specific process is as follows: (2-1) The aircraft fuselage is meshed using an unstructured meshing method, and meshes are encrypted at locations where the curvature gradient of the fuselage surface is large and at the engine nozzles; (2-2) According to the set boundary conditions, CFD fluid simulation is performed using FLUENT software; the flow field simulation is performed by solving the three-dimensional NS equations: Among them, ρ is the fluid density, u is the velocity vector, t is the 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 result data to obtain the heat flux density on the aircraft skin surface and the temperature distribution of the tail flame gas.

6. The infrared radiation characteristic simulation method of aircraft skin-tail flame full flow field coupling according to claim 1 is characterized in that: The specific process of step (3) is as follows: (3-1) Using a separate aircraft model to establish a heat conduction simulation model, and meshing the heat conduction simulation model; (3-2) The heat flux density on the aircraft skin surface calculated in step (2) is used as the second-class boundary condition, and the finite element method is used to solve the heat conduction equation, which is: Among them, u = u (t, x, y, z) represents temperature, which is a function of time and coordinates; k is the thermal diffusion coefficient of the fuselage material; x, y, z are coordinates.

7. The infrared radiation characteristic simulation method of aircraft skin-tail flame full flow field coupling according to claim 6 is characterized in that: When setting the second type of boundary conditions, in addition to the heat flux density on the aircraft skin surface, the radiation heat dissipation on the fuselage skin surface also needs to be considered; the radiation heat dissipation calculation formula is: Q=εσ(T 4 -T env 4 ) Where Q is the amount of heat radiated from the fuselage skin surface per unit area per unit time, ε is the emissivity of the aircraft skin material, σ is the Boltzmann constant, T is the surface temperature of the corresponding aircraft skin area, T env is the atmospheric temperature.

8. The infrared radiation characteristic simulation method of aircraft skin-tail flame full flow field coupling according to claim 1 is 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 the tail gas 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: A=1-T Wherein, A is the spectral absorption coefficient of the gas, and T is the spectral transmittance of the gas layer; the spectral transmittance of the gas layer is obtained by searching in the public spectral parameter database HITEMP.

9. The infrared radiation characteristic simulation method of aircraft skin-tail flame full flow field coupling according to claim 1 is characterized in that: The specific process of step (5) is as follows: (5-1) Calculate the spectral radiation emittance M of the aircraft surface based on the temperature distribution of the aircraft skin surface obtained in step (3) λ : Where 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 radiation 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 the surface radiation to the radiance of the black body radiation at the same temperature; M λ is the spectral radiation emittance of the fuselage surface; λ is the wavelength; (5-3) calculating the infrared radiation amplitude brightness of the tail flame according to the temperature distribution of the aircraft tail flame gas obtained in step (2) and the infrared emissivity model of the tail flame established in step (4), specifically including: The tail flame is divided into several gas layers. The infrared radiation absorption and emission of each gas layer need to be considered from bottom to top during calculation. The infrared radiation absorption of the gas layer is directly calculated using the spectral infrared radiation transmittance obtained by searching the HITEMP database in step (4). The infrared radiation radiance calculation method generated by the gas layer is the same as the infrared radiation radiance calculation method of the skin surface in (5-1) and (5-2).

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