Airplane deicing / electromagnetic low-scattering compatible structure and design method thereof

Abstract

The invention relates to the field of electronic materials, in particular to an airplane deicing / electromagnetic low-scattering compatible structure and a design method thereof. The periodic high-wave-transmission electric heating impedance network is adopted, the impedance network is conformal to the wave absorbing structure, and the high-wave-transmission-rate performance is achieved through the patterning design of the impedance network; and the key icing area on the surface of the wave-absorbing structure is optimized to carry out partition resistance regulation and control, so that the purposes of partition heating and heat concentration adjustment are achieved, and more targeted deicing is achieved. According to the invention, the functions of electric heating deicing and electromagnetic low scattering can be realized at the same time, the deicing requirement of an airplane in a high-altitude or cold environment can be met, so that the flight safety of the airplane is protected, and the electromagnetic low scattering function of the airplane is not influenced. The method is expected to be applied to safety protection and electromagnetic compatibility of low detectable aircrafts in the future and becomes an important technical accumulation.

Description

Technical Field

[0001] The present invention relates to the field of electronic materials, and in particular to an aircraft deicing / electromagnetic low scattering compatible structure and a design method thereof. Background Art

[0002] When an aircraft encounters clouds containing supercooled water droplets during flight, its surface parts exposed to the environment are prone to rapid accumulation and freezing of supercooled water droplets into ice, which is called aircraft icing. Aircraft icing seriously endangers the flight safety of the aircraft, such as destroying the aerodynamic shape of the airfoil, resulting in a decrease in the lift coefficient and lift-to-drag ratio, and may cause the aircraft to stall prematurely. Aircraft anti-icing technology is an important means to reduce icing accidents and improve aircraft safety performance.

[0003] At present, the de-icing systems on aircraft are mainly divided into the following categories according to different usage methods: liquid ice protection system, mechanical ice protection system, thermal ice protection system and other ice protection systems. Among them, the basic principle of the electric thermal de-icing system is to convert electrical energy into thermal energy through the heating elements on the inner surface of the aircraft, and conduct the heat to the outer surface of the aircraft to achieve the purpose of anti-icing and de-icing. Due to its advantages such as high efficiency, good reliability and easy control, it is currently one of the most widely used and most promising aircraft de-icing methods.

[0004] For low-detectable aircraft targets, due to the complexity of their mission environment, in addition to considering the possible icing problem of the aircraft, the electromagnetic compatibility problem caused by its complex electromagnetic environment must also be considered. In order to prevent the deicing part of the aircraft from affecting the electromagnetic scattering function, it is necessary to design a deicing / electromagnetic low-scattering compatible structure. Although the electric heating deicing system is suitable for aircraft deicing due to its advantages of simple structure and high deicing efficiency; however, the electric heating system will inevitably bring about electromagnetic scattering problems due to the introduction of metal networks; therefore, how to achieve high-efficiency deicing and electromagnetic low-scattering compatibility has become the focus and difficulty of the design. At present, there is little research on how to reasonably use the electric heating anti-deicing system on such aircraft, and there is a gap in the research on the anti-deicing / electromagnetic low-scattering compatible structure. Summary of the invention

[0005] In view of the above-mentioned problems or shortcomings, and to solve the problem that existing low-detectable aircraft can simultaneously realize electromagnetic compatibility function and efficient de-icing function, the present invention provides an aircraft de-icing / electromagnetic low-scattering compatible structure and a design method thereof, which adopts a periodic high-transmittance electric heating impedance network, conformally forms the impedance network to the absorbing structure, and realizes high-transmittance performance through patterned design of the impedance network, and adjusts its heating power by optimizing the size and resistance of the pattern.

[0006] The technical solution of the present invention is as follows:

[0007] A design method for an aircraft deicing / electromagnetic low scattering compatible structure comprises the following steps:

[0008] Step 1, design a periodic patterned impedance network with high transmittance; the basic unit of the impedance network is a square, which is a double-layer structure composed of a bottom substrate and a patterned upper resistor film. The same basic units are periodically arranged in a matrix to form an impedance network, which meets the -1dB transmission frequency band of 2-16GHz and the relative bandwidth of 155.56%; within 2-18GHz, all are low reflection frequency bands below -10dB.

[0009] The patterned impedance network design can obtain a high transmittance structure. The use of a periodic impedance network pattern can distribute the heat generated by power supply as evenly as possible over the entire covering surface of the wing while obtaining high transmittance.

[0010] Step 2: Use the Navier-Stokes equations to solve the model of the target aircraft wing in the wing air flow field analysis; the three equations including mass conservation, momentum conservation and energy conservation are comprehensively expressed as the integral form of the Navier-Stokes equations:

[0011]

[0012] Among them, F C represents the convective flux, F v represents the viscous flux, W is the conserved variable, Ω is the control volume, Q is the heat flux, and S is the surface of the wing (control volume).

[0013] Then introduce the perfect gas thermodynamic relationship and Stokes ideal gas assumption to close the above Navier-Stokes equation, and we get:

[0014]

[0015] ρH=ρE+P

[0016] γ is the adiabatic coefficient, which is 1.4 for air, (μ, v, ω) represent the three components of velocity, ρ represents density, P represents pressure, H represents total enthalpy, and E represents energy.

[0017] The pressure (flow parameters) of the air flow field of the wing is obtained under different working conditions, providing data for the calculation of water droplet impact characteristics and wing icing conditions.

[0018] Then, the water drop impact characteristics are calculated and expressed by the water drop collection coefficient, which refers to the actual impact amount W of water droplets impacting on the unit wingspan length per unit time. m With its maximum possible impact amount W max The ratio of E mIndicates that E m =W m / W, where W m The definition of is:

[0019] W m =V0(Y ou -Y ol )LWC=V0(y ou -y ol )LWC·L

[0020] V0 is the aircraft speed, Y ou , Y ol is the starting coordinate of the water droplet trajectory tangent to the upper and lower surfaces of the wing in the chord length direction in the far field, y ou ,y ol Y ou , Y ol The ratio of LWC to the chord length, LWC is the liquid water content, and L is the characteristic size of the object (chord length).

[0021] W max The definition of is:

[0022] W max =V0·M·LWC=V0·h·LWC·L

[0023] M is the projected height of the wing in the chord length direction, and h is the ratio of M to the chord length.

[0024] Substituting the liquid water content, average diameter of water droplets and the calculated pressure of the air flow field into the water droplet impact calculation, the water droplet impact coefficient at the leading edge of the wing is obtained (the water droplet impact coefficient is the largest at the leading edge of the wing), and the icing situation is also the most serious at the leading edge of the wing. After calculating different working conditions, the length L1 of the target wing icing area in the chord length direction is obtained.

[0025] Step 3: Conformally distribute the impedance network designed in step 1 on the surface of the absorbing structure of the target wing, and then redesign the basic unit of the impedance network in the corresponding wing leading edge area S+ obtained by drawing a perpendicular line in the chord length direction according to L1 solved in step 2, and increase the resistance value R of the impedance film in the basic unit of the S+ area.

[0026] According to the characteristic that ice accumulation on the leading edge of the wing is serious, the present invention proposes a design method for concentrating heat in the S+ area of ​​the leading edge of the wing; this is because the length L2 of the wing's absorbing structure in the chord length direction is greater than L1, and the electric heating system inevitably brings about electromagnetic scattering problems due to the introduction of the metal network. It cannot be directly connected to electricity only in the key icing area of ​​the absorbing structure, and it is necessary to connect electricity at the end of the absorbing structure; therefore, the present invention achieves this purpose by performing voltage division design on different areas of the impedance network.

[0027] According to the formula of resistance value R:

[0028]

[0029] Where S1 is the cross-sectional area of ​​the current flowing through the impedance network, ρ′ is the resistivity, and L3 is the length of the resistor film; if the cross-sectional area S1 is reduced, the resistance value of this part will increase, thereby increasing the voltage division of the DC power supply in this part. According to the average power density formula:

[0030]

[0031] P d is the average power per unit area, and U is the voltage; at this time, the heating power of this part increases. When the heating power of the S+ area increases relative to the non-S+ area, the purpose of concentrating heat is achieved. The area with increased heating power just covers the area with severe ice accumulation (S+ area) of the target wing, thereby achieving a more targeted deicing purpose.

[0032] Step 4: Perform electromagnetic simulation on the impedance network model redesigned in step 3 to ensure that the target wing still meets the performance requirements of electromagnetic low scattering; if not, return to step 3 to redesign the pattern shape of the impedance film in the basic unit of the wing leading edge area S+ until the target wing meets the performance requirements of electromagnetic low scattering.

[0033] Furthermore, in step 3, the resistance value of the impedance film is increased by reducing the width of the impedance film.

[0034] Furthermore, in step 3, the resistance value of the impedance film is increased by redesigning the pattern of the resistance film.

[0035] Furthermore, the resistance value of the impedance film in step 3 is increased by reducing the resistance value of the basic unit in the non-wing leading edge area S+.

[0036] Furthermore, the resistance value of the basic unit in the non-wing leading edge area S+ is reduced by increasing the width of the impedance film.

[0037] Furthermore, the resistance value of the basic unit in the non-wing leading edge area S+ is reduced by redesigning the pattern of the resistance film.

[0038] An aircraft deicing / electromagnetic low scattering compatible structure is designed using the above method. When in use, the wing leading edge area S+ is adaptively and conformally covered with the basic unit redesigned in step 3, and the non-wing leading edge area S+ of the absorbing structure is also adaptively and conformally covered, and then electrically heated for deicing.

[0039] In summary, the present invention has designed a multifunctional electromagnetic functional structure that can simultaneously realize the functions of electric heating deicing and electromagnetic low scattering, which can not only meet the deicing needs of aircraft at high altitude or in cold environments, thereby protecting the flight safety of the aircraft, but also ensure that the electromagnetic low scattering function of the aircraft is not affected. It is expected to be applied to the safety protection and electromagnetic compatibility of future low-detectable aircraft, becoming an important technical accumulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the structure of the periodic unit used in the embodiment;

[0041] Figure 2 The water droplet impact coefficient distribution cloud diagram of the NACA0012 airfoil in the embodiment;

[0042] Figure 3 The water droplet impact coefficient distribution curve of the NACA0012 airfoil in the embodiment;

[0043] Figure 4 The ice shape diagram (left) and icing condition cloud diagram (right) of the NACA0012 airfoil in the embodiment;

[0044] Figure 5 The icing intensity distribution curve of the NACA0012 airfoil in the embodiment;

[0045] Figure 6 A three-dimensional structural diagram of the final non-uniform electric heating impedance network designed in the embodiment;

[0046] Figure 7 is a temperature distribution diagram of the non-uniform impedance network in the embodiment;

[0047] Figure 8 It is a diagram of the electromagnetic performance simulation result of the non-uniform impedance network in the embodiment;

[0048] Fig. 9 This is a diagram of the RCS simulation results of the wing loaded with the impedance network in the embodiment;

[0049] Fig.10 A sample physical picture of a non-uniform impedance network of an embodiment;

[0050] Fig.11 A sample test environment for an embodiment;

[0051] Fig.12 Comparison between the sample test curve and the simulation curve of the embodiment;

[0052] Fig.13 This is an infrared image of the electrical heating of the non-uniform impedance network in the room temperature environment of the embodiment;

[0053] Fig.14It is a melting curve diagram of ice cubes on a non-uniform impedance network in a cold environment in an embodiment. DETAILED DESCRIPTION

[0054] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0055] This embodiment uses the aircraft wing airfoil NACA0012 as an example to simulate water drop impact and icing, and studies the specific distribution of ice accumulation on the wing surface. The ice presents the characteristics of a trumpet shape of "thick at both ends and thin in the middle". The impedance network is designed with partitioned loading impedance, and the resistance of the middle area is increased by changing the size of the structure, thereby achieving partitioned heating. The impedance network structure designed by this method has a -1dB transmittance band of 2-16.7GHz and a relative bandwidth of 157.22%; within 2-18GHz, all are low-reflection bands below -10dB. The simulation and experimental structures are consistent, proving that this design can have high wave transmittance while effectively de-icing. This design provides an effective solution for the integrated de-icing / electromagnetic low-scattering design of aircraft, and it is easy to operate and implement.

[0056] The design of this embodiment adopts a non-uniform pattern arrangement, and prints the following on a 0.1 mm thick polyimide film: Figure 1 The cross hollow pattern shown (yellow is the substrate), the thermal conductivity of the polyimide is 2W·m -1 ·K -1 , using carbon paste as the printing material, the square resistance of the printed pattern is The pattern width in the middle area is 0.8mm, and the pattern width on both sides is 1.5mm, showing the characteristics of non-uniform distribution. After connecting the electrodes on both sides, they are covered on the leading edge of the wing (i.e. the surface of the absorbing structure), and finally the functions of electric heating and electromagnetic scattering can be integrated.

[0057] An integrated electric heating / electromagnetic scattering design for aircraft deicing includes the following steps:

[0058] Step 1: The basic unit structure of the impedance network pattern designed in this embodiment is as follows: Figure 1 As shown, a cross-shaped hollow impedance network is used, and the square resistance is Printed on polyimide film, it achieves performance with a transmittance of more than 80% and a reflectivity of less than 10% in the range of 2-18GHz.

[0059] Step 2: For the study of icing on aircraft wings, this embodiment uses the NACA0012 wing model as the research object and uses the Navier-Stokes equation to solve the wing air flow field analysis.

[0060] Select the working conditions, determine the ambient temperature, water content, flight speed, and average diameter of water droplets. The ambient temperature is -5°C and the water content is 1g / m 3 , the flight speed is 80m / s, the average diameter of the water droplets is 20 microns, and the pressure of the air flow field of the wing is obtained. This parameter and the working conditions are used to calculate the water droplet impact characteristics and the icing condition of the wing. In this embodiment, the chord length of the wing is 1m.

[0061] The calculated water droplet impact area of ​​the NACA0012 wing is concentrated on the leading edge, such as Figure 2 As shown, it shows a trend of being the largest in the middle and gradually decreasing on both sides. The curve changes as Figure 3 As shown in (the Y direction is the chord length direction). The icing condition of the wing is also concentrated in the leading edge, as shown in Figure 4 As shown in the figure, it presents a trumpet shape with thick ends and thinner in the middle, and no ice is accumulated when it extends to the rear of the wing. At this time, the ice area is within the area perpendicular to the chord length (-0.04m, 0.04m), as shown in the figure. Figure 5 shown.

[0062] Step 3: After obtaining the situation of the icing area, on the premise of step 2, the non-uniform design of the impedance network pattern is performed, and the width of the impedance network pattern in the middle area is reduced. The basic unit width of the original model is 1.35mm. The width of the unit in the middle area of ​​the impedance network is reduced to 0.55mm, and the resistance value of this area is increased. The width of the unit in the area on both sides of the impedance network is increased to 1.55mm, and the resistance value of this area is reduced. Thus, a non-uniformly distributed impedance network structure is formed, such as Figure 6 As shown. In the comsol multi-physics field simulation calculation, the results show that the temperature rise is basically concentrated in the middle area, and the temperature distribution is as follows Figure 7 shown.

[0063] Furthermore, the width of the impedance network pattern in other areas (non-S+ areas) can also be increased at the same time, the cross-sectional area increases, resulting in a decrease in the resistance of this part, thereby reducing the voltage division of the DC power supply in this part, and reducing the heat generation power of this part. When the heat generation power of the middle S+ area increases and the heat generation power of the non-S+ areas on both sides decreases, the purpose of better heat concentration is achieved. And this part of the area with increased heat generation power just covers the area with severe ice accumulation (S+ area) of the target wing, thereby achieving the purpose of more targeted deicing.

[0064] Step 4: Use cst electromagnetic simulation software to perform electromagnetic simulation on the designed non-uniform structure, such as Figure 8As shown in the simulation of the planar structure, the -1dB transmittance band of the structure is 2-16.7GHz, and the relative bandwidth is 157.22%; within 2-18GHz, it is a low reflection band below -10dB. It has high transmittance and low reflectivity, and is an impedance film with excellent electromagnetic wave transmission performance.

[0065] The impedance network is covered to the leading edge of the wing loaded with the absorbing structure, such as Fig. 9 As shown in the figure, the RCS reduction curve is obtained. It can be seen that in the azimuth of (-90°, +90°), the model loaded with the non-uniform impedance network not only does not cause the RCS to increase, but also has a slight reduction effect on the RCS. This shows that the impedance network will not affect the electromagnetic scattering performance of the aircraft and is suitable for aircraft wings or similar curved structures.

[0066] Step 5: In order to verify the engineering feasibility of the model solution, the model unit is designed to be 198mm*198mm in size and processed. Fig.10 The free space method is used to test the reflection and transmission performance of the sample. The test environment is as follows: Fig.11 As shown. Analyze the error between the simulation results and the test results, and get the simulation test comparison ( Fig.12 ) It can be seen that the difference is not big, the expected effect is achieved, and the effectiveness of the structure is verified. Copper electrodes are attached to both ends of the impedance network, and then a DC source is loaded to test the electric heating characteristics of the sample. At room temperature, a voltage of 120V is loaded. After the temperature stabilizes, the infrared image of the sample is measured as follows Fig.13 As shown, the calculated heat power of the middle part is 1450w / m 2 Then, the electric heating and deicing of ice on the surface of the impedance network was tested at an ambient temperature of about -8°C. The temperature change curve is shown in the figure below. Fig.14 As shown in Figure 2, it fully demonstrates the effectiveness of the non-uniform impedance network design for temperature concentration.

[0067] It can be seen from the above embodiments that this embodiment uses the aircraft wing airfoil NACA0012 as an example to simulate water drop impact and icing, and studies the specific distribution of ice accumulation on the wing surface. The ice presents the characteristics of a trumpet shape of "thick at both ends and thin in the middle". The impedance network is designed with partitioned loading impedance, and the resistance of the region is increased by changing the size of the structure in the middle region to achieve partitioned heating. The impedance network structure designed by this method has a -1dB transmission frequency band of 2-16.7GHz and a relative bandwidth of 157.22%; all low reflection frequency bands within 2-18GHz are below -10dB. The impedance network is loaded onto the leading edge of the NACA0012 airfoil, and the impedance network model with partitioned loading impedance is subjected to electromagnetic simulation. The model still has a very high transmittance and a very low reflectivity, and the effect is very good under both TE and TM polarizations, and the RCS will show a slight decrease, which shows that the impedance network will not affect the electromagnetic scattering performance of the aircraft. The structures of simulation and experiment are consistent, proving that this design can effectively de-ice while having high wave transmittance. This design provides an effective solution for the integrated de-icing / electromagnetic low-scattering design of aircraft, and it is easy to operate and implement.

[0068] In summary, the present invention adopts a periodic high-transmittance electric heating impedance network, conforms the impedance network to the absorbing structure, and achieves high-transmittance performance through patterned design of the impedance network; and by optimizing the key icing areas on the surface of the absorbing structure, the resistance value is adjusted in different zones to achieve the purpose of zoned heating and concentrated heat adjustment, thereby achieving more targeted deicing. The present invention can simultaneously realize the functions of electric heating deicing and electromagnetic low scattering, which can not only meet the needs of aircraft deicing at high altitudes or in cold environments, thereby protecting the flight safety of the aircraft, but also ensure that the aircraft's electromagnetic low scattering function is not affected. It is expected to be applied to future low-detectable aircraft safety protection and electromagnetic compatibility, and become its important technical accumulation.

Claims

1. A design method for an aircraft deicing / electromagnetic low scattering compatible structure, characterized in that: The following steps are involved: Step 1, designing a periodically patterned impedance network with high transmittance; The basic unit of the impedance network is a square, which is a double-layer structure composed of a bottom substrate and a patterned upper resistor film. The same basic units are periodically arranged in a matrix to form an impedance network. The -1dB transmission frequency band is 2-16GHz, and the relative bandwidth is 155.56%; within 2-18GHz, all are low reflection bands below -10dB; Step 2: Use the Navier-Stokes equations to solve the model of the target aircraft wing in the wing air flow field analysis; the three equations including mass conservation, momentum conservation and energy conservation are comprehensively expressed as the integral form of the Navier-Stokes equations: Among them, F c represents the convective flux, F v represents the viscous flux, W is the conserved variable, Ω is the airfoil, Q is the heat flux, and S is the surface of the airfoil; Then introduce the perfect gas thermodynamic relationship and Stokes ideal gas assumption to close the above Navier-Stokes equation, and we get: pH=ρE+P γ is the adiabatic coefficient, which is 1.4 for air; μ, v, ω represent the three components of velocity, ρ represents density, P represents pressure, H represents total enthalpy, and E represents energy; Obtain the pressure of the air flow field of the wing under different working conditions; Then, the water drop impact characteristics are calculated and expressed by the water drop collection coefficient, which refers to the actual impact amount W of water droplets impacting on the unit wingspan length per unit time. m With its maximum possible impact amount W max The ratio of E m Indicates that E m =W n / W, where W m The definition of is: W m =V0(Y ou -Y ol )LWC=V0(y ou -y ol )LUCK·L V0 is the aircraft speed, Y ou , Y ol is the starting coordinate of the water droplet trajectory tangent to the upper and lower surfaces of the wing in the chord length direction in the far field, y ou ,y ol Y ou , Y ol The ratio of LWC to the chord length is 1:1, LWC is the liquid water content, L is the characteristic size of the object, i.e., the chord length; W max The definition of is: W max =V0·M·LWC=V0·h·LWC·L M is the projected height of the wing in the chord length direction, and h is the ratio of M to the chord length; Substitute the liquid water content, average diameter of water droplets and the calculated air flow field pressure into the water droplet impact calculation to obtain the water droplet impact coefficient of the wing leading edge; after calculations under different working conditions, the length L1 of the target wing ice area in the chord length direction is calculated; Step 3: The impedance network designed in step 1 is conformally distributed on the surface of the absorbing structure of the target wing, and then the basic unit of the impedance network is redesigned in the corresponding wing leading edge area S+ obtained by making a perpendicular line in the chord length direction according to L1 solved in step 2, and the resistance value of the impedance film in the basic unit of the S+ area is increased. According to the formula of the resistance value R: Where S1 is the cross-sectional area of ​​the current flowing through the impedance network, ρ′ is the resistivity, and L3 is the length of the resistor film; According to the average power density formula: P d is the average power per unit area, and U is the voltage; Step 4: Perform electromagnetic simulation on the impedance network model redesigned in step 3 to ensure that the target wing still meets the performance requirements of electromagnetic low scattering; if not, return to step 3 to redesign the pattern shape of the impedance film in the basic unit of the wing leading edge area S+ until the target wing meets the performance requirements of electromagnetic low scattering.

2. The design method of the aircraft deicing / electromagnetic low scattering compatible structure as claimed in claim 1, characterized in that: The resistance value of the impedance film in step 3 is increased by reducing the width of the impedance film.

3. The design method of the aircraft deicing / electromagnetic low scattering compatible structure as claimed in claim 1, characterized in that: The design method for increasing the resistance value of the impedance film in step 3 is to redesign the pattern of the resistance film.

4. The design method of the aircraft deicing / electromagnetic low scattering compatible structure as claimed in claim 1, characterized in that: The design method of increasing the resistance value of the impedance film in step 3 is to reduce the resistance value of the basic unit in the non-wing leading edge area S+.

5. The design method of the aircraft deicing / electromagnetic low scattering compatible structure as claimed in claim 4, characterized in that: The resistance value of the basic unit in the non-wing leading edge area S+ is reduced by increasing the width of the impedance film.

6. The design method of the aircraft deicing / electromagnetic low scattering compatible structure as claimed in claim 4, characterized in that: The method for reducing the resistance value of the basic unit in the non-wing leading edge area S+ is to redesign the pattern of the resistance film.

7. The design method of the aircraft deicing / electromagnetic low scattering compatible structure as claimed in claim 1, characterized in that: The substrate in the basic unit is a 0.1 mm thick polyimide film with a thermal conductivity of 2 W·m -1 ·K -1 ; Carbon paste is used as the printing material for the resistor film, and the square resistance of the printed pattern is 660Ω / □.

8. An aircraft deicing / electromagnetic low scattering compatible structure, characterized in that: The design is carried out by the method as described in any one of claims 1 to 7. When in use, the wing leading edge area S+ is adaptively and conformally covered with the basic unit redesigned in step 3, and the non-wing leading edge area S+ of the absorbing structure is also adaptively and conformally covered, and then electrically heated for de-icing.

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