Simulation calculation method for external flow field and infrared radiation characteristics of invisible aircraft

Abstract

The invention relates to the technical field of aircraft infrared radiation characteristic simulation, in particular to an invisible aircraft external flow field and infrared radiation characteristic simulation calculation method. According to the simulation method provided by the invention, firstly, a geometric model of the stealth aircraft is simplified and an external flow field of the stealth aircraft is constructed, secondly, the whole model is subjected to unstructured grid division, then flow field feature calculation is performed on the basis of an obtained grid, and finally, infrared radiation feature calculation is performed on the stealth aircraft on the basis of a flow field calculation result. The infrared radiation characteristic simulation data of the stealth aircraft attenuated by the atmosphere can be obtained, and the design requirement of a novel infrared detection system is met.

Description

Technical Field

[0001] The invention relates to a simulation calculation method for the external flow field and infrared radiation characteristics of a stealth aircraft, and belongs to the technical field of aircraft simulation. Background Art

[0002] At present, the detection of aircraft mainly adopts radar or infrared means. Due to the use of stealth technology, the radar cross section (RCS) of aircraft is extremely small, especially for stealth aircraft that can actively detect and avoid enemy detection radars. The frontal radar cross section has been as low as 0.001 and 0.1m respectively. 2 , which forces the opponent to increase the radar search energy and scanning beam density, which is undoubtedly conducive to the stealth aircraft to evade the enemy radar, but increases the difficulty of detection. Therefore, the existing radar detection means can no longer meet the detection needs of stealth aircraft. Compared with radar signals, any object above absolute zero radiates infrared energy all the time. Even aircraft that have taken a series of stealth measures will inevitably radiate energy when flying at high speed due to the presence of engine tail flame and skin aerodynamic heat. Therefore, it is an effective means to detect stealth aircraft using the infrared radiation characteristics of stealth aircraft. This requires the radiation characteristic data of typical stealth aircraft as the design basis of infrared detection system. However, the existing research results only consider the intrinsic radiation intensity of advanced stealth aircraft, and the situation after atmospheric attenuation has not been fully studied. Actual testing is not a feasible solution, which is not conducive to the accurate design of infrared detection system. Therefore, it is urgent to carry out simulation research on infrared radiation characteristics of advanced stealth aircraft after atmospheric attenuation. Summary of the invention

[0003] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art and provide a simulation calculation method for the external flow field and infrared radiation characteristics of a stealth aircraft, which can obtain the temperature and pressure distribution characteristics of the external flow field of the stealth aircraft, and then obtain the simulation data of the infrared radiation characteristics of the aircraft after atmospheric attenuation, so as to meet the design requirements of the infrared detection system.

[0004] The technical solution of the present invention is: a method for simulating and calculating the external flow field and infrared radiation characteristics of a stealth aircraft, comprising:

[0005] The aircraft geometry model is simplified, only the external skin and engine nozzle are retained, and its external flow field is constructed;

[0006] Perform unstructured meshing on the entire model;

[0007] Calculate the flow field characteristics based on the obtained grid;

[0008] Based on the calculation results of flow field characteristics, the infrared radiation characteristics of stealth aircraft attenuated by atmosphere are calculated.

[0009] Preferably, when constructing the external flow field, the geometric dimension L in the axial direction of the aircraft fuselage is taken as a reference, and the length of the external flow field model is 10L to 30L and the diameter is 5L to 15L.

[0010] Preferably, the external flow field model adopts a 1 / 2 cylinder model.

[0011] Preferably, when the whole model is divided into unstructured grids, the first layer height is generated at the outer skin and the near wall of the engine nozzle to meet y + The boundary layer grid of >20 is locally refined near the engine nozzle and tail flame, where y + Represents the normal distance to the wall and is used to describe the relative position within the boundary layer.

[0012] Preferably, the length of the encrypted area is 1.5 to 3 times the geometric dimension L of the aircraft fuselage in the axial direction, that is, 1.5L to 3L.

[0013] Preferably, when calculating flow field characteristics, the model to be considered is:

[0014] The turbulence model is selected as GEKO k-ω model, BSL k-ω model or SST k-ω model;

[0015] Select density-based implicit algorithm or pressure-based coupled algorithm as solver type;

[0016] The discretization method of momentum equation, energy equation and continuity equation is first-order upwind difference format or second-order upwind difference format;

[0017] Discrete coordinates model is selected for radiation heat transfer on solid surface;

[0018] Gas Component Model Select the component transport model.

[0019] Preferably, when calculating flow field characteristics, the parameters that need to be considered are:

[0020] The flight altitude is selected to be 5 to 20 km;

[0021] The flight Mach number is selected between 0.8 and 2;

[0022] The boundary condition type of the nozzle inlet section is pressure inlet, with total temperature and total pressure of 573-673K and 0.1-0.2MPa respectively;

[0023] The atmospheric environment boundary condition type is pressure far field, the temperature and pressure are 217~256K and 5529~54048Pa respectively, and the density type is ideal gas;

[0024] The emissivity of the inner wall of the nozzle is 0.7 to 0.8;

[0025] The remaining solid walls are 0.2 to 0.3, and no-slip boundary conditions are used on all walls.

[0026] Preferably, when calculating infrared radiation characteristics, the parameters are set as follows:

[0027] The calculation altitude is selected as 5 to 20 km;

[0028] Select 400-600 for pixel density control factor and 10-20 for ray density;

[0029] The pitch angle of the detection point is -90°~90°, and the yaw angle is 0°~360°. The direction directly behind the tail of the aircraft is the 0° detection point, and the direction directly facing the head is the 180° detection point.

[0030] The spectral range was set to 1–14 μm, and the spectral resolution was 0.05–0.1 μm;

[0031] The detection distance is set to 1~10km;

[0032] The emissivity of the inner wall of the nozzle is 0.7-0.8, and that of the other solid walls is 0.2-0.3.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] (1) The method of the present invention can obtain infrared radiation characteristic data of stealth aircraft attenuated by the atmosphere at any detection angle and in any band, filling the gap in the relevant field;

[0035] (2) The method described in the present invention is highly feasible and easy to operate. The data obtained can meet the design requirements of new infrared detection systems and is easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A geometric model structure diagram of an embodiment of the present invention;

[0037] Figure 2 It is an unstructured grid division diagram of an embodiment of the present invention;

[0038] Figure 3 It is a temperature field result diagram of an embodiment of the present invention;

[0039] Figure 4 It is a pressure field result diagram of an embodiment of the present invention;

[0040] Figure 5 This is a graph showing the angular distribution of the integrated radiation intensity of the main parts of the stealth aircraft attenuated by the atmosphere on the 0° pitch plane according to an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The present invention provides a method for simulating and calculating the external flow field and infrared radiation characteristics of a stealth aircraft, comprising the following steps: firstly simplifying a geometric model of the stealth aircraft and constructing its external flow field; secondly performing unstructured grid division on the entire model; then calculating the flow field characteristics based on the obtained grid; and finally completing the calculation of the infrared radiation characteristics of the stealth aircraft attenuated by the atmosphere based on the flow field calculation results.

[0042] In the simulation method, when simplifying the geometric model, small parts are removed from the target aircraft nose, fuselage, wings, tail and engine nozzle while ensuring that the geometric dimensions of the target aircraft nose, fuselage, wings, tail and engine nozzle remain unchanged, leaving only the external skin and nozzle;

[0043] In the present invention, considering that the infrared radiation characteristics of stealth aircraft are mainly related to the skin temperature, tail flame temperature and the components of the absorptive-radiative gas in the tail flame, the removal of small surface components will not have a significant impact on the aircraft flow field results and infrared radiation results. Therefore, removing these small structures can reduce the number of grids generated, reduce the difficulty of grid generation, and help the convergence of subsequent flow field calculations.

[0044] When constructing the external flow field, the geometric dimension L in the axial direction of the aircraft fuselage is used as a reference. The length of the external flow field model is 10 to 30 times the length of the aircraft fuselage, and the diameter is 5 to 15 times the length of the aircraft fuselage, that is, the length of the external flow field model is 10L to 30L, and the diameter is 5L to 15L. The advantage of controlling the size of the external flow field within the above range is that it can ensure that the flow field calculation domain is large enough compared to the aircraft, so that the subsequent flow field calculation results are accurate. Since the aircraft is a bilaterally symmetrical structure, a 1 / 2 model is used for processing, and the external flow field model also uses a 1 / 2 cylindrical model. The present invention does not impose any special restrictions on the modeling software, and commercial software familiar to those skilled in the art can be used.

[0045] When performing unstructured meshing, the flow effect is considered and the first layer height is generated to meet y near the wall of the skin and the engine nozzle. + >20 boundary layer grids, where y + It indicates the normal distance to the wall, which is used to describe the relative position in the boundary layer. It is locally encrypted near the nozzle and tail flame, and the length of the encrypted area is 1.5 to 3 times the length of the aircraft fuselage (1.5L to 3L). The advantage of using unstructured grids is that it is conducive to processing the parts with large changes in curvature of the aircraft surface; + The advantage of taking a value greater than 20 is that the flow field near the solid wall of the aircraft can be accurately captured; the advantage of local encryption is that the calculation error of the tail flame flow field can be reduced; in the present invention, no special limitation is made to the grid division software, and commercial software familiar to technical personnel in this field can be used.

[0046] When calculating flow field characteristics, the turbulence model selects the GEKO k-ω model, the BSL k-ω model, or the SST k-ω model; the solver type selects the density-based implicit algorithm or the pressure-based coupling algorithm; the discretization method of the momentum equation, the energy equation, and the continuity equation is preferably the first-order upwind difference format or the second-order upwind difference format, and the second-order upwind difference format is more preferred; the radiation heat transfer on the solid surface selects the discrete coordinate model (DO model); the gas component model selects the component transport model (Species Transport model); the flight altitude is selected to be 5 to 20 km, preferably 7 to 10 km, and the flight Mach number is selected to be 0.8 to 2, preferably 1.3 to 1.5; the nozzle inlet section boundary condition type is a pressure inlet, and the total temperature and total pressure are 573 to 673 K and 0.1 to 0.2 MPa, preferably 573 to 583 K and 0.12 to 0.15 MPa, respectively; the atmospheric environment boundary condition type is a pressure far field, and the temperature and pressure are 217 to 256 K and 5529 to 54048 Pa, respectively, preferably 223 to 243 K and 26500 to 41105 Pa, and the density type is an ideal gas; the emissivity of the inner wall of the nozzle is 0.7 to 0.8, preferably 0.7 to 0.75; the remaining solid wall is 0.2 to 0.3, preferably 0.2 to 0.25, and all walls adopt no-slip boundary conditions. The present invention does not make any special restrictions on the flow field characteristic calculation software, and commercial software well known to those skilled in the art can be used.

[0047] When calculating the infrared radiation characteristics, the calculation altitude is selected to be 5-20km, preferably 7-10km; the pixel density control factor is selected to be 400-600, more preferably 400-450, and the ray density is selected to be 10-20, preferably 15-20; the pitch angle of the detection point is -90°~90°, preferably -30°~30°, the yaw angle is 0°~360°, the direction directly behind the tail of the aircraft is the 0° detection point, and the direction directly facing the head is the 180° detection point; the spectral range is set to 1-14μm, preferably 3-5μm, and the spectral resolution is 0.05-0.1μm, preferably 0.05-0.075μm; the detection distance is set to 1-10km, preferably 3-5km; the emissivity of the inner wall of the nozzle is 0.7-0.8, more preferably 0.7-0.75, and the emissivity of the remaining solid walls is 0.2-0.3, more preferably 0.2-0.25. In the present invention, no special limitation is imposed on the infrared radiation characteristic calculation software, and commercial software well known to those skilled in the art may be used.

[0048] Example:

[0049] First, while ensuring that the original geometric dimensions of the target aircraft's nose, fuselage, wings, tail and engine nozzle remain unchanged, the small parts are removed and only the external skin and nozzle are retained. Since the aircraft is a bilaterally symmetrical structure, a 1 / 2 model is used for calculation. The aircraft's external flow field also uses a 1 / 2 cylinder with a length of 12L and a diameter of 5L, where L is the geometric dimension of the aircraft's fuselage axis.

[0050] For the simplified model, unstructured grids are used for three-dimensional grid division, and the first layer height that satisfies y is generated near the skin, wing and engine nozzle wall. + =30 boundary layer grids are locally encrypted near the nozzle and tail flame. The length of the encrypted area is 2L, where L is the geometric dimension of the aircraft fuselage axis direction. Finally, 3.6 million grids are obtained.

[0051] Secondly, the obtained grid file is imported into the flow field calculation software for flow field characteristic calculation, and the SSTk-ω model is selected as the turbulence model; the density-based implicit algorithm is selected as the solver type; the second-order upwind difference format is selected as the discretization method of the momentum equation, energy equation and continuity equation; the discrete coordinate model (DO model) is selected as the radiation heat transfer on the solid surface; the species transport model (Species Transport model) is selected as the gas component model; the flight altitude is selected as 10km, and the flight Mach number is selected as 1.3; the boundary condition type of the nozzle inlet section is set to pressure inlet, and the total temperature and total pressure are taken as 575K and 0.15MPa respectively; the atmospheric environment boundary condition type is set to pressure far field, and the temperature and pressure are taken as 223K and 26500Pa respectively, and the density type is set to ideal gas; the emissivity of the inner wall of the nozzle is set to 0.7, and the other solid wall surfaces are set to 0.2, and all wall surfaces adopt no-slip boundary conditions.

[0052] Finally, the obtained flow field result file is imported into the infrared radiation characteristic calculation software for calculation, and the calculation altitude is selected as 10km; the pixel density control factor is selected as 400, and the ray density is selected as 20; the pitch angle is 0°, the yaw angle is 0°~360°, the direction directly behind the tail of the aircraft is the 0° detection point, and the direction directly ahead is the 180° detection point; the spectral range is set to 3~5μm, and the spectral resolution is 0.05μm; the detection distance is set to 5km; the emissivity of the inner wall of the nozzle is 0.7, and the emissivity of the other solid walls is 0.2; the angular distribution result of the 3~5μm integrated radiation intensity of the stealth aircraft attenuated by the atmosphere on the 0° pitch surface can be obtained.

[0053] in, Figure 1 is the geometric model structure diagram, Figure 2 is the unstructured grid partition diagram, Figure 3 is the temperature field result diagram, Figure 4 is the pressure field result diagram, Figure 5is the angular distribution curve of the integrated radiation intensity of each main part of the stealth aircraft attenuated by the atmosphere on the 0° pitch plane. Figure 1 and Figure 2 It can be seen that the external flow field range is appropriate, and the grid size and number are appropriate. Figure 3 It can be seen that the high-temperature area of ​​the external flow field is mainly concentrated in the center of the tail flame. The highest temperature is located near the nozzle, not exceeding 625.10K. In the direction of the nozzle axis, with the increase of the distance from the nozzle, the tail flame temperature gradually decreases. The temperature distribution on the surface of the aircraft is relatively uniform, generally between 275 and 290K. Figure 4 The pressure distribution trend of the external flow field is similar to the temperature distribution trend. The maximum pressure is still located in the center of the tail flame, and the maximum value appears at the nozzle, not exceeding 0.16MPa. As the distance from the nozzle increases, the pressure gradually decreases. The higher pressure on the aircraft surface appears at the leading edge of the nose cone, the junction between the fuselage and the front wing, and the tail surface. Figure 5 It can be seen that the direction with stronger infrared radiation after atmospheric attenuation is mainly behind the tail, and the maximum value of the overall integrated radiation intensity appears near the detection angles of 20° and 340°, and the minimum is in the head-on direction of 180°. Since the tail flame part is mainly gas radiation, it is greatly affected by atmospheric attenuation, and the nozzle and skin parts are mainly solid radiation, which are less affected. The overall integrated radiation intensity after attenuation is mainly composed of the radiation of the nozzle and the skin and mainly presents the radiation characteristics of the nozzle part. At the same time, the nozzle integrated radiation intensity only dominates the overall contribution at the detection angles of 0°~50° and 310°~360°, and the skin part is second, but it contributes to the overall in the entire detection range. The gas radiation of the tail flame part contributes very little to the overall in the entire detection range.

[0054] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

[0055] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in this field.

Claims

1. A method for simulating and calculating the external flow field and infrared radiation characteristics of a stealth aircraft, characterized in that include: The aircraft geometry model is simplified, only the external skin and engine nozzle are retained, and its external flow field is constructed; Perform unstructured meshing on the entire model; Calculate the flow field characteristics based on the obtained grid; Based on the calculation results of flow field characteristics, the infrared radiation characteristics of stealth aircraft attenuated by atmosphere are calculated.

2. The method for simulating and calculating the external flow field and infrared radiation characteristics of a stealth aircraft according to claim 1, characterized in that: When constructing the external flow field, the geometric dimension L in the axial direction of the aircraft fuselage is taken as a reference. The length of the external flow field model is 10L~30L and the diameter is 5L~15L.

3. The method for simulating and calculating the external flow field and infrared radiation characteristics of a stealth aircraft according to claim 2, characterized in that: The external flow field model adopts a 1 / 2 cylinder model.

4. The method for simulating and calculating the external flow field and infrared radiation characteristics of a stealth aircraft according to claim 1, characterized in that: When the whole model is meshed with unstructured grids, the first layer height is generated to meet the y + The boundary layer grid of >20 is locally refined near the engine nozzle and tail flame, where y + Represents the normal distance to the wall and is used to describe the relative position within the boundary layer.

5. The method for simulating and calculating the external flow field and infrared radiation characteristics of a stealth aircraft according to claim 4 is characterized in that: The length of the encrypted area is 1.5 to 3 times the geometric dimension L of the aircraft fuselage axis direction, that is, 1.5L to 3L.

6. The method for simulating and calculating the external flow field and infrared radiation characteristics of a stealth aircraft according to claim 1, characterized in that: When calculating flow field characteristics, the models that need to be considered are: The turbulence model is selected as GEKO k-ω model, BSL k-ω model or SST k-ω model; Select density-based implicit algorithm or pressure-based coupled algorithm as solver type; The discretization method of momentum equation, energy equation and continuity equation is first-order upwind difference format or second-order upwind difference format; Discrete coordinates model is selected for radiation heat transfer on solid surface; Gas Component Model Select the component transport model.

7. The method for simulating and calculating the external flow field and infrared radiation characteristics of a stealth aircraft according to claim 6, characterized in that: When calculating flow field characteristics, the parameters that need to be considered are: The flight altitude is selected to be 5 to 20 km; The flight Mach number is selected between 0.8 and 2; The boundary condition type of the nozzle inlet section is pressure inlet, with total temperature and total pressure of 573-673K and 0.1-0.2MPa respectively; The atmospheric environment boundary condition type is pressure far field, the temperature and pressure are 217~256K and 5529~54048Pa respectively, and the density type is ideal gas; The emissivity of the inner wall of the nozzle is 0.7 to 0.8; The remaining solid walls are 0.2 to 0.3, and no-slip boundary conditions are used on all walls.

8. The method for simulating and calculating the external flow field and infrared radiation characteristics of a stealth aircraft according to claim 1, characterized in that: When calculating infrared radiation characteristics, the parameter settings are as follows: The calculation altitude is selected as 5 to 20 km; Select 400-600 for pixel density control factor and 10-20 for ray density; The pitch angle of the detection point is -90°~90°, and the yaw angle is 0°~360°. The direction directly behind the tail of the aircraft is the 0° detection point, and the direction directly facing the head is the 180° detection point. The spectral range was set to 1–14 μm, and the spectral resolution was 0.05–0.1 μm; The detection distance is set to 1~10km; The emissivity of the inner wall of the nozzle is 0.7-0.8, and that of the other solid walls is 0.2-0.3.

Images