A method for designing a ventilation channel for optimizing the high power resistance of a honeycomb sandwich frequency selective structure

Abstract

The application discloses a kind of ventilation flow passage design methods for honeycomb sandwich frequency selective structure resistance high power optimization, by systematic heat dissipation design and flow passage construction, solve the key problem that temperature rise is caused by electromagnetic loss under high-power microwave transmission, and then affect structural mechanics and electromagnetic performance.It includes: analyzing core layer resonance unit distribution to determine the optimal ventilation direction;Precise circular through-hole is opened on the specific cell wall of honeycomb core, to build a straight line type high-efficiency airflow channel without lateral bypass;And by applying constant flow, cooling airflow with flow rate of 2~6 m / s is forced to convect in the structure interior to dissipate heat.The application ensures that all air flows only flow in the honeycomb structure, realizes high heat dissipation efficiency and system compactness, and the performance evaluation index COP value is greater than or equal to 10000, and the efficiency factor have is greater than or equal to 60.The application significantly improves the resistance high power capability and working reliability of honeycomb sandwich frequency selective structure without increasing the weight and volume of the structure, and without affecting its electromagnetic performance.

Description

Technical Field

[0001] This invention relates to the field of high-performance multifunctional composite material structure design and thermal management technology, specifically to a ventilation channel design method for optimizing the high-power resistance of honeycomb sandwich frequency-selective structures. Background Technology

[0002] Cellular sandwich frequency selective structures are widely used in modern aerospace vehicles and ground radar systems due to their unique integrated "load-bearing-transmission / filtering" function. These structures typically consist of upper and lower composite materials and a middle honeycomb core, with periodically arranged metal resonant units (such as patches, rings, gaps, etc.) embedded between panel layers or within the honeycomb core to achieve the transmission, reflection, or absorption of electromagnetic waves in specific frequency bands.

[0003] However, when such structures are used in high-power radar radomes or exposed to high-power microwave radiation, electromagnetic waves generate non-negligible ohmic and dielectric losses in the resonant units and dielectric matrix during transmission, which are converted into heat energy. Since honeycomb cores and panel composite materials typically have poor thermal conductivity, heat easily accumulates inside the structure, especially in densely packed areas of resonant units, leading to a significant increase in local temperature. This temperature rise effect causes a series of problems: 1) For polymer-based composite panels, high temperatures can cause the resin matrix to soften and degrade, severely reducing the mechanical strength and stiffness of the structure; 2) For honeycomb cores, temperature rise may cause adhesive failure or degradation of the core material's performance; 3) Increased temperature alters the dielectric constant of the dielectric material, causing the resonant frequency of the frequency-selective structure to drift, deteriorating filtering or transmission performance, i.e., producing a "thermal detuning" phenomenon. Therefore, effective thermal management is a key technical bottleneck to ensure the reliable operation of honeycomb sandwich frequency-selective structures in high-power environments.

[0004] Currently, heat dissipation solutions for such structures are generally rudimentary or have significant drawbacks. For example: 1) External forced air cooling: Heat sinks or forced airflow are installed on the outer surface of the structure, resulting in long heat dissipation paths, high thermal resistance, low efficiency, and potential disruption of aerodynamic shape or increase in radar cross-section. 2) Liquid cooling: Cooling pipes are embedded in the structure, leading to system complexity, significant weight increase, leakage risks, and potential electromagnetic interference with embedded resonant units. 3) Replacement with high thermal conductivity materials: Using high thermal conductivity composite materials or metal honeycomb can improve thermal conductivity, but often compromises electromagnetic performance (e.g., metal honeycomb can shield electromagnetic waves) or significantly increases cost and weight. None of these methods fundamentally address the issue of efficient, lightweight, and electromagnetically unaffected directional heat dissipation through internal flow channel design.

[0005] Therefore, there is an urgent need for an innovative, built-in, high-efficiency heat dissipation solution that is deeply compatible with the characteristics of the cellular sandwich frequency selective structure itself. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of existing heat dissipation solutions, such as low efficiency, system complexity, or significant interference with the main function. It provides a ventilation channel design method optimized for the high-power tolerance of honeycomb sandwich frequency-selective structures. The core idea of ​​this method is to utilize the porous lattice structure of the honeycomb core itself, and through minimal and precise modification (opening holes in specific lattice walls), transform it into a highly efficient closed-loop gas flow channel. This guides the cooling airflow directly through the main heat source (resonant unit) area, achieving targeted and efficient heat dissipation.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A ventilation channel design method for optimizing the high-power resistance of frequency-selective honeycomb sandwich structures includes the following steps:

[0009] (1) Structural Feature Analysis and Cooling Path Planning: First, electromagnetic-thermal coupling analysis or experimental testing is conducted on the target honeycomb sandwich frequency selection structure to clarify the spatial distribution of electromagnetic losses generated by embedded resonant units (located between panels or within the honeycomb grid) under high-power irradiation, and to identify "hot spot" areas. Based on the rectangular grid characteristics of the honeycomb core (usually defined in the length L direction and width W direction) and the distribution pattern of the resonant units (such as periodic arrangement along a certain direction), the main ventilation direction of the cooling airflow (L direction or W direction) is scientifically determined. The preferred principle is to ensure that the airflow channel can cover the most heat source units or penetrate along the direction with the greatest loss gradient.

[0010] (2) Precise internal flow channel construction: According to the determined ventilation direction, perforation is performed on the honeycomb core wall parallel to that direction. The perforation must meet the following key requirements: ① The hole shape is circular to minimize stress concentration and ensure smooth airflow transition, avoiding eddies and additional pressure drop caused by sharp corners; ② It is strictly forbidden to make holes on the sidewall perpendicular to the ventilation direction, that is, to ensure that the established flow channel is a "straight channel" without lateral branches. This is one of the key innovations of this invention. It forces the airflow to move in a straight line along a predetermined path, avoiding airflow short-circuiting and diversion leading to uneven cooling and efficiency reduction, while maintaining the integrity of the structure in the non-ventilation direction (including mechanical and electromagnetic shielding performance). The diameter and spacing of the holes need to be optimized to balance flow resistance, flow velocity distribution and the remaining strength of the honeycomb wall.

[0011] (3) Implementation of a high-efficiency closed-loop heat dissipation system: A constant flow air source (such as a micro air pump) is connected to one end of the modified honeycomb sandwich structure (corresponding to the flow channel inlet). Cooling gas (usually air) is injected into the internal flow channel network. Through precise control, the average flow velocity of the gas in the flow channel is stabilized at 2~6 m / s. This flow velocity range is the optimal range verified by simulation and experiment: if the flow velocity is below 2 m / s, the convective heat transfer coefficient is insufficient and the heat dissipation capacity is limited; if it is above 6 m / s, the flow resistance increases sharply, the power consumption of the fan increases significantly, and noise or vibration may be generated. When the airflow flows through each honeycomb cell, it directly convects and exchanges heat with the wall or medium supporting the resonant unit, absorbs heat and becomes hot air, which is discharged from the outlet at the other end of the structure. The entire heat exchange process takes place entirely in the internal cavity of the honeycomb sandwich structure, isolated from the external environment, realizing the built-in and stealth compatibility of the heat dissipation system.

[0012] (4) Performance Indicators and Effects: Through the above design, the system achieves excellent heat dissipation performance. Its core evaluation indicators are: COP (Coefficient of Performance) ≥ 10000, which reflects the extremely high energy efficiency of the heat dissipation system (the removed heat power is far greater than the electrical power consumed by the driving air pump); have (heat dissipation efficiency factor) ≥ 60, which comprehensively reflects the effectiveness of the heat dissipation system in reducing the temperature rise of key hot spots. The final effect is that under continuous irradiation by high-power microwaves, the highest temperature inside the structure is effectively suppressed, thereby ensuring the stability of its mechanical properties and the reliability of its electromagnetic frequency selection performance.

[0013] The beneficial effects of this invention are:

[0014] 1. High-efficiency targeted heat dissipation: The airflow channel passes directly through the heat source area, with a short and efficient convection heat transfer path, which can quickly remove the heat generated by the resonant unit.

[0015] 2. Lightweight structure and functional preservation: Only minimal perforation modification is made to the honeycomb wall, with almost no additional weight or volume. The design without lateral openings preserves the mechanical properties and electromagnetic shielding continuity of the honeycomb core in its original direction to the greatest extent.

[0016] 3. Compact and stealth-compatible system: The heat dissipation channels are fully built-in, eliminating the need for external heat sinks and maintaining the aerodynamic shape and low detectability of the structure. The system is simple and reliable, requiring only a small air pump and piping.

[0017] 4. Predictable and Designable Performance: The flow channel is a regular straight-through type, and its fluid dynamics and heat transfer characteristics can be accurately predicted and optimized through computational fluid dynamics simulation, thereby achieving the best match for different power levels and different loss distribution structures.

[0018] 5. Significantly improves power tolerance: Experiments show that after adopting this design, the continuous wave power density that the cellular sandwich frequency selective structure can withstand can be increased by more than an order of magnitude, providing key technical support for the lightweight and integrated design of high-power microwave systems. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to specific embodiments.

[0020] Example 1: Nomex honeycomb sandwich FSS heat dissipation design for X-band high-power radome

[0021] Target structure: Quartz fiber reinforced cyanate composite panel, Nomex paper honeycomb core with 4.8mm grid width and 0.05mm wall thickness, flexible film embedded in the honeycomb core, on which square ring resonant unit array is etched, forming a bandpass FSS with a center frequency of 10GHz.

[0022] Analysis and Design: Electromagnetic thermal simulation shows that the current density is highest at the edge of the resonant unit, making it the main heat source, and it exhibits a periodic banded distribution along the W direction of the honeycomb structure. The W direction is determined to be the ventilation direction. Precision laser drilling is used to create circular holes with a diameter of 0.4 mm on the honeycomb walls parallel to the W direction, with a hole spacing of 10 mm (approximately twice the grid width). It is ensured that all wall surfaces perpendicular to the W direction are free of any holes.

[0023] System Implementation: A miniature brushless fan is connected to the W-direction end face on one side of the structure to input dry air. The fan speed is adjusted by a PID controller to stabilize the average airflow velocity in the flow channel at 4 m / s.

[0024] Performance Results: Under X-band continuous wave irradiation with an incident power density of 1 kW / m², the hot spot temperature rise of the structure without heat dissipation reached 85°C. After adopting this heat dissipation scheme, the hot spot temperature dropped to 22°C. The measured COP value of the heat dissipation system is approximately 12500, and the have factor is approximately 65. The in-band transmittance fluctuation is less than 0.3 dB.

[0025] Example 2: Heat dissipation design of aluminum honeycomb sandwich frequency selective reflector array for S-band communication antenna

[0026] Target structure: Fiberglass panel, 3.2mm wide 5052 aluminum honeycomb core, dipoles and gap complementary resonant units are etched in the inner layers of the upper and lower panels respectively to form a reflective array with a frequency of 2.4GHz.

[0027] Analysis and Design: The heat source is located in the resonant unit inside the panel. To ensure uniform cooling of the upper and lower panels, ventilation is determined to be along the L-direction (longer side) of the honeycomb structure. Ultrasonic perforation technology is used to drill 0.6mm diameter circular holes in the L-direction wall of the aluminum honeycomb structure, with a hole spacing of 8mm.

[0028] System implementation: A constant airflow is provided using a compressed nitrogen cylinder via a pressure reducing valve and a flow meter, with the flow rate controlled at 5 m / s.

[0029] Performance results: At a power density of 500 W / m², the overall temperature distribution of the structure is uniform after heat dissipation, with the highest temperature not exceeding 15°C of the ambient temperature. The COP value reaches 11000, and the have factor is 68. Mechanical vibration tests show that the structural stiffness decreases by less than 5% after drilling, meeting the usage requirements.

[0030] Example 3: Composite foam honeycomb sandwich FSS heat dissipation design for Ka-band high-power lenses

[0031] Target structure: A honeycomb structure is formed by 3D printing of low-loss composite foam material. After copper coating on the inner and outer surfaces, cross-shaped resonant units are photolithographically formed to form a focusing lens.

[0032] Analysis and Design: This structure is an all-dielectric resonant structure with a complex heat source distribution. Simulations determined the optimal cooling path to be along the diagonal direction (which can be considered a combination of the L and W directions). Pre-designing was performed on the inner wall in the corresponding direction, resulting in a network of circular through-holes with a diameter of 0.3 mm during printing, strictly avoiding the formation of a mesh-like interconnection.

[0033] System implementation: An integrated micro vortex cooler is used to pump in cooling air at a flow rate of 3 m / s.

[0034] Performance results: Successfully reduced lens thermal distortion by 80% under high-power operation, and controlled center frequency drift within 0.05%. The heat dissipation system COP value is ≥10000, and the have factor is ≥62.

[0035] Comparative Example

[0036] The structure in Example 1 was cooled by blowing air using a conventional external fan. Under the same wind speed of 4 m / s (outer surface) and irradiation power of 1 kW / m², the temperature rise of the hot spots inside the structure was still as high as 55°C, and the external airflow severely interfered with the boundary layer of the radome surface. Meanwhile, the COP value of the external cooling solution was only about 2000, and the have factor was about 25, which is far lower than that of the method of this invention.

[0037] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A ventilation channel design method for optimizing the high-power resistance of honeycomb sandwich frequency-selective structures, characterized in that, Includes the following steps: S1. Structural Analysis and Flow Direction Determination: For the honeycomb sandwich structure with frequency-selective conductor resonant units embedded in the interlayer of the panel and inside the honeycomb core layer, the geometry, size, and spatial distribution characteristics of the resonant units in the honeycomb core are analyzed; based on the distribution characteristics, the ventilation direction of the cooling airflow is determined, which is along the length or width of the honeycomb core layer. S2. Flow channel design and construction: According to the ventilation direction determined in step S1, multiple circular through holes are opened on the honeycomb core wall parallel to the ventilation direction to construct a through airflow channel inside the honeycomb sandwich structure; the opening position and size of the circular through holes must ensure that the constructed airflow channel does not connect to the lateral openings perpendicular to the ventilation direction, thereby forming a straight flow channel without bypass; S3. Implementation of the heat dissipation system: A constant flow rate of input cooling flow field is applied to the inlet of one side of the honeycomb sandwich structure constructed in step S2, so that the cooling airflow flows in the internal flow channel at a flow rate of 2~6 m / s, absorbs the heat generated by electromagnetic loss, and is discharged from the outlet on the other side; throughout the cooling process, all airflow flows only inside the honeycomb sandwich structure, forming a closed internal circulation or a one-way heat dissipation path. S4. Performance Evaluation: Through the heat dissipation strategy, the heat dissipation performance of the honeycomb sandwich frequency selective structure under high power electromagnetic field transmission reaches the following indicators: heat dissipation performance coefficient COP value ≥10000, heat dissipation efficiency factor have ≥60.

2. The ventilation channel design method for optimizing the high-power resistance of a honeycomb sandwich frequency-selective structure according to claim 1, characterized in that, In step S1, the specific principle for determining the ventilation direction is to prioritize the direction that allows the cooling airflow to pass through most or all of the honeycomb cells with embedded resonant units, or the direction that allows the airflow to pass through the high loss density region most evenly.

3. The ventilation channel design method for optimizing the high-power resistance of a honeycomb sandwich frequency-selective structure according to claim 1, characterized in that, In step S2, the ratio of the diameter of the circular through hole to the thickness of the honeycomb cell wall is 3:1 to 8:1, and the spacing between adjacent through holes in the flow direction is 1.5 to 3 times the side length of the honeycomb cell.

4. The ventilation channel design method for optimizing the high-power resistance of a honeycomb sandwich frequency-selective structure according to claim 1, characterized in that, In step S2, the circular through hole is opened using precision mechanical drilling, laser processing, or ultrasonic perforation to ensure smooth hole walls and reduce airflow resistance and eddy current generation.

5. A ventilation channel design method for optimizing the high-power resistance of a honeycomb sandwich frequency-selective structure according to claim 1 or 4, characterized in that, In step S3, the cooling airflow is dry air, nitrogen, or other inert gas, and its input is provided by an external micro pump or pressure gas source and kept constant by a flow controller.

6. The ventilation channel design method for optimizing the high-power resistance of a honeycomb sandwich frequency-selective structure according to claim 1, characterized in that, The panel of the honeycomb sandwich structure is made of fiber-reinforced resin matrix composite material or ceramic matrix composite material, and the honeycomb core material is Nomex paper, glass fiber composite material or aluminum; the frequency selective conductor resonant unit is a dipole, cross ring, square ring or combination of the above etched on a flexible dielectric film.

7. The ventilation channel design method for optimizing the high-power resistance of a honeycomb sandwich frequency-selective structure according to claim 1, characterized in that, The heat dissipation effect achieved by the method ensures that the maximum internal temperature rise of the honeycomb sandwich structure remains stable below 30°C under continuous wave electromagnetic radiation with a power density of not less than 500 W / m², and the fluctuation of electromagnetic transmission performance within the -1dB bandwidth is less than 0.5 dB.