A Ground Environment Test Method for the Equipment Compartment of a Solar UAV

Abstract

The present invention discloses a method for ground environmental testing of an electronic equipment cabin of a solar unmanned aerial vehicle, which includes three steps: obtaining a comprehensive temperature that integrates the influence of external convective heat transfer and solar radiation, simulating an equivalent heat transfer channel outside the equipment cabin, and conducting environmental tests under extreme high / low temperature and low pressure conditions. The present invention is mainly applied to the ground environmental testing of the electronic equipment cabin of a solar unmanned aerial vehicle, evaluating the thermal environment of the equipment cabin and the effectiveness of thermal control measures during the performance investigation stage, and solving the problem that the influence of external convective heat transfer and solar radiation needs to be considered simultaneously in the ground environmental testing under extreme high / low temperature and low air pressure conditions. The present invention can not only conveniently simulate and adjust the external heat transfer conditions, thereby enabling full-envelope ground environmental testing of the electronic equipment cabin of a solar unmanned aerial vehicle, but also greatly reduce the complexity of the environmental test system and the refrigeration capacity requirement under extreme low temperature conditions, effectively saving the cost of ground environmental testing.

Description

Technical Field

[0001] The present invention relates to the field of thermal engineering technology, and particularly to a method for ground environmental testing of an equipment cabin of a solar-powered unmanned aerial vehicle in the field of aircraft environmental control technology. Background Art

[0002] Solar-powered unmanned aerial vehicles have the characteristics of slow climb / cruise / descent speed and high cruise altitude, and will experience extreme temperatures and low air pressures and other harsh working conditions in the flight envelope. In GJB1172.12, the national working extreme value of low air temperature with a time risk rate of 20% can reach -80°C at an altitude of 0 - 20 km, while the hot weather limit at 0 km is 40°C. The equipment cabin of a solar-powered unmanned aerial vehicle carries various electronic devices, and the normal operation of the electronic devices requires suitable environmental temperature conditions. Therefore, during the development process of a solar-powered unmanned aerial vehicle, it is necessary to add thermal control measures to the equipment cabin and evaluate the thermal environment characteristics of the equipment cabin and the effectiveness of the thermal control measures in the flight envelope through ground environmental tests.

[0003] Solar-powered unmanned aerial vehicles generally use composite material fuselages. The equipment cabin is a part of the fuselage, that is, the outer skin of the equipment cabin exchanges convective heat with the oncoming air from the outside. At the same time, due to the very high cruise altitude, the effect of solar radiation needs to be considered. Therefore, different from conventional environmental tests, the ground environmental test of this type of equipment cabin requires not only simulating the flight altitude and extreme high / low temperatures in a vacuum chamber, but also simultaneously simulating the convective heat transfer and solar radiation heat transfer conditions outside the skin. However, general thermal environment test systems mainly provide conditions such as extreme high / low temperatures and low air pressures. The simulation of solar radiation requires designing and adding relevant radiation simulation devices, and at the same time, they do not have the ability to simulate the large-area oncoming wind speed. The extreme low temperature condition (-80°C) also poses higher requirements for the capacity of low-temperature refrigeration equipment; the simulation of the oncoming wind speed needs to be carried out using a wind tunnel, while general wind tunnel test systems lack the simulation of high altitude, extreme high / low temperatures and solar radiation, and the test cost of a wind tunnel test system that can simultaneously simulate wind speed, high altitude, extreme high / low temperatures and solar radiation is huge.

[0004] In fact, conditions such as external convective heat transfer and radiation heat transfer mainly affect the thermal environment inside the cabin through the heat transfer of the skin of the equipment cabin. During the performance investigation test stage in the development process, on the basis of the original thermal environment simulation test system, it is possible to explore an equivalent test method that can simultaneously simulate convective heat transfer and solar radiation, which is of great significance for reducing the complexity of the test system and the test cost. Summary of the Invention

[0005] The present invention provides a ground environment test method for a solar-powered UAV equipment cabin. The method converts the equivalent temperature generated by the thermal effects of external airflow and solar radiation on the cabin into a comprehensive temperature, and constructs tiny channels on the periphery of the cabin to simulate the convective heat transfer coefficient of the external airflow, thereby achieving a comprehensive equivalent simulation of the external heat exchange conditions.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for testing the ground environment of a solar-powered UAV equipment cabin comprises the following steps:

[0008] The first step is to integrate the effects of external convective heat transfer and solar radiation in the form of comprehensive temperature, which mainly includes the calculation of external convective heat transfer coefficient and comprehensive temperature.

[0009] The second step is to simulate the design of equivalent heat exchange outside the equipment cabin. By constructing an air flow channel outside the equipment cabin to simulate the external convective heat transfer coefficient and comprehensive temperature of the equipment cabin, and ensuring that the inlet and outlet heat exchange temperature difference is within 1-3°C, equivalent simulation of external heat exchange conditions is achieved.

[0010] The third step is to build a thermal environment test system for the solar drone equipment cabin. Combining the comprehensive temperature and air supply flow obtained in the previous two steps, the thermal environment test of the equipment cabin under high temperature, low temperature and low pressure conditions is carried out to further evaluate the effectiveness of the thermal control measures when the electronic equipment is working.

[0011] Specifically:

[0012] The first step is to integrate the effects of external convective heat transfer and solar radiation intensity in the form of comprehensive temperature, specifically including the calculation of external convective heat transfer coefficient and comprehensive temperature:

[0013] (1.1) Calculation of external convection heat transfer coefficient of equipment compartment

[0014] There are two main methods for calculating the convective heat transfer coefficient outside the equipment compartment: engineering calculations and numerical simulations. During the performance testing phase of the development process, engineering calculations are more efficient, while numerical simulations offer a more refined approach. Ultimately, both methods yield the surface convective heat transfer coefficient. During actual flight, the heat transfer coefficient of the electronic equipment compartment's exterior surface can be approximated by the heat transfer coefficient of a flat plate outflow for engineering calculations.

[0015] Consider the boundary layer development process from the nose to the front of the equipment cabin, and judge the flow condition on the equipment cabin surface according to the position of the turning point and the front of the equipment cabin. Define the distance between the turning point and the front of the equipment cabin and the nose as x c and x s The flow conditions on the surface of the electronic equipment compartment can be divided into full laminar flow (x c >l), mixed flow (xs <x c <l) and fully turbulent (x s >x c ), the expressions for the average convective heat transfer coefficients in the three flow cases are as follows:

[0016]

[0017] In the formula, α is the convective heat transfer coefficient, l is the length of the entire flat plate, α x，l and α x，t are the laminar and turbulent convective heat transfer coefficients at a distance x from the front end of the equipment cabin to the nose of the aircraft respectively. Existing calculation formulas for convective heat transfer coefficients can be selected.

[0018] (1.2) Calculation of the comprehensive temperature of the air outside the equipment cabin considering solar radiation heat transfer

[0019] The external thermal environment of the electronic equipment cabin at high altitude mainly includes two parameters: convective heat transfer and radiation heat transfer with the external air flow. To reduce the radiation simulation equipment, the comprehensive temperature is used for equivalence. The external comprehensive temperature is an external meteorological parameter synthesized from the equivalent temperatures generated by the thermal effects of the external air flow and solar radiation on the structure. There are various types of calculation methods, and one that can be adopted is:

[0020]

[0021] α0 = α c + α r (3)

[0022] α r = C·θ (4)

[0023] In the formula, t sa - external comprehensive temperature, K;

[0024] t0 - ambient temperature, K. Since the cruising speed of the solar-powered unmanned aircraft is very low, it is considered that the recovery temperature of the boundary layer is the ambient temperature;

[0025] I - solar radiation intensity, W / m 2 , the radiation intensity at 18 km is 1300 W / m 2 , which can be obtained specifically according to meteorological data;

[0026] ρ s - radiation absorptivity of the equipment cabin surface. For carbon fiber materials, it can be taken as 0.8, or it can be selected according to the actual material properties;

[0027] α0 - heat transfer coefficient of the outer surface, including the convective heat transfer coefficient α c and the long-wave radiation heat transfer coefficient α r ;

[0028] C - The radiant coefficient of two objects participating in radiation heat transfer, W / (m 2 ·K 4 );

[0029] θ - Temperature factor, K 3 ;

[0030] (1.3) Since solar radiation is directional, it is necessary to calculate the corresponding radiation components according to the solar radiation angle at the flight location. It can be processed in two ways: one is to solve the comprehensive temperature for each surface of the equipment cabin separately, and the other is to evenly distribute the radiation heat transfer to each surface of the equipment cabin. The first way calculates the comprehensive temperature of each surface of the equipment cabin, which can simulate the radiation heat transfer more carefully. The second way can simplify the air supply distribution simulation and evenly distribute the total radiation heat transfer between the electronic equipment cabin and the outside world to each side, so as to ensure that the total radiation heat is consistent with the actual situation.

[0031] The second step is to design the size parameters and air supply parameters of the heat transfer simulation channels outside the equipment cabin, specifically including:

[0032] (2.1) Since the comprehensive temperature already includes the effect of solar radiation, therefore, the external convective heat transfer of the equipment cabin is simulated by the air flow through the peripheral micro-channels, and the temperature difference between the inlet and outlet is ensured to be at a small level, so as to form a stable simulation of the external heat transfer conditions. Peripheral channels with equal height or variable height can be constructed according to the shape of the equipment cabin. Since the cross-section of the cabin is generally rectangular, four rectangular channels can be used outside the cabin to simulate the external convective heat transfer.

[0033] (2.2) The convective heat transfer coefficient in the channel can be calculated by numerical simulation methods or by engineering methods such as the Dittus-Boelter turbulent flow correlation in pipes. If it is a rectangular channel, its width b is determined by the side width of the equipment cabin. Assuming the channel height h, it is ensured that the convective heat transfer coefficient of each side surface of the equipment cabin in the channel should be approximately equal to the heat transfer coefficient α in the first step (1.1), so that the flow rate of the channel can be obtained. If the air supply parameters of each channel are controlled separately, the flow rate of each channel can be obtained, so as to realize the separate adjustment of the comprehensive temperature and air supply flow rate of each channel.

[0034] (2.3) Check and control the temperature difference between the inlet and outlet of the channel. When the heat transfer amount on the surface of the equipment cabin reaches thermal equilibrium, we get

[0035] φ = G·C p ·Δt (5)

[0036] In the formula, Cp - The specific heat capacity at constant pressure of the air flow in the channel, J / (kg·K); Δt - The temperature difference between the inlet and outlet of the air flow in the channel, K; G - The air flow rate for the test, kg / s; φ - The heat generation of the test piece in the equipment cabin.

[0037] The temperature difference between the inlet and outlet calculated by Equation (5) should ensure that the heat transfer temperature difference Δt is within 1 - 3 °C. If the requirements are not met, reselect the channel cross-sectional size (channel height) and repeat the calculations in (2.2) and (2.3) until the requirements are satisfied.

[0038] (2.4) Although the air supply flow rate and the comprehensive temperature of each channel can be controlled separately, since the cross-section of the cabin is often square in engineering, using the average air supply parameters can reduce the complexity of the upstream air supply system. That is, when calculating the comprehensive temperature in the first step, the solar radiation heat is evenly distributed to the four surfaces, and each channel uses the same air supply flow rate and comprehensive temperature, and centralized air supply can be adopted upstream.

[0039] The third step: Build a thermal environment test system for the equipment cabin of the solar UAV and conduct thermal environment tests for the equipment cabin under high temperature, low temperature and low air pressure conditions.

[0040] (3.1) Place the test piece of the electronic equipment cabin in the external heat transfer simulation channel, and place both in the vacuum chamber. The outer periphery of the channel is covered with a heat insulation layer of types such as aerogel to reduce the energy exchange with the outside world. Connect the air supply pipeline and the measuring equipment to build a thermal environment test system for the equipment cabin of the solar UAV.

[0041] (3.2) Turn on the air supply system, obtain the comprehensive temperature and air supply flow rate according to the previous two steps, adjust the air supply flow rate and temperature, turn on the vacuum system, and adjust the atmospheric height and air supply parameters in the cabin to reach the required test conditions.

[0042] (3.3) Turn on the power supply of the heat generation simulation component in the electronic equipment cabin and adjust the required heat generation power.

[0043] (3.4) Record parameters such as air supply parameters, atmospheric height, air temperature in the electronic equipment cabin, and surface temperature of the electronic equipment. After the test parameters are stable, turn off the heating element, vacuum system and air supply system in sequence to end the test.

[0044] (3.5) In addition to conducting steady-state tests, it is also possible to adjust the air supply parameters according to the envelope change to conduct dynamic environment tests within the entire envelope and evaluate the effectiveness of the thermal control measures.

[0045] The present invention is mainly used for ground environmental simulation tests of solar-powered UAV equipment cabins. By introducing a comprehensive temperature and convection heat transfer equivalent simulation channel, it makes up for the shortcomings of wind speed simulation in general environmental test simulation cabins, simplifies the simulation of solar radiation, and solves the problem of simultaneously simulating external convection heat transfer and radiation heat transfer in the equipment cabin under extreme high / low temperature and low pressure conditions. The invention includes three steps: obtaining a comprehensive temperature that integrates the influence of external convection heat transfer and solar radiation, simulating an equivalent heat transfer channel outside the equipment cabin, and conducting environmental tests under extreme high / low temperature and low pressure conditions. It can significantly reduce the complexity of the environmental test system during the performance assessment stage of solar-powered UAV development. At the same time, since the introduction of solar radiation generally makes the comprehensive temperature higher than the ambient temperature, it can reduce the demand for refrigeration capacity in extreme low temperature conditions, effectively saving the cost of ground environmental testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1(a) shows the calculation of the radiation component of each surface of the equipment cabin separately;

[0047] Figure 1(b) shows that the radiation heat transfer in the equipment cabin is evenly distributed to each surface;

[0048] Figure 2 It is the cross section of the tiny heat exchange channel outside the equipment cabin;

[0049] Figure 3 It is the schematic diagram of the equipment cabin ground environment simulation test system. DETAILED DESCRIPTION

[0050] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0051] The present invention provides a ground environmental test method for a solar-powered UAV equipment cabin, which includes three steps: obtaining a comprehensive temperature that integrates the influence of external convection heat transfer and solar radiation, simulating an equivalent heat exchange channel outside the equipment cabin, and conducting environmental tests under extremely high / low temperature and low pressure conditions. The method can perform equivalent simulations of external convection heat transfer and solar radiation heat transfer in the equipment cabin under extremely high / low temperature and low pressure conditions, and evaluate the thermal environment of the electronic equipment cabin and the effectiveness of thermal control measures.

[0052] The first step specifically includes:

[0053] (1.1) Calculation of external convection heat transfer coefficient of equipment compartment

[0054] Because engineering calculations are more efficient, we provide an engineering calculation method to obtain the surface convective heat transfer coefficient. The heat transfer coefficient of the electronic equipment cabin's exterior surface during actual flight is approximated by the flat plate outflow heat transfer coefficient.

[0055] The convective heat transfer correlation for a laminar outward-swept flat plate is:

[0056]

[0057] In the formula, x is the distance from the fixed dimension to the leading edge of the flat plate; Pr is the Prandtl number; Re x is the local Reynolds number; Nu x is the local Nusselt number, and its expression is:

[0058]

[0059] Applicable parameter range: 0.6 < Pr < 50; Re x < 5×10 5 , where λ is the thermal conductivity; α x is the local convective heat transfer coefficient. Combining with Equation (6), the local convective heat transfer coefficient of the laminar flat plate can be obtained:

[0060]

[0061] The correlation equation for convective heat transfer of turbulent flow over a flat plate is:

[0062]

[0063] Applicable parameter range: 0.6 < Pr < 60; 5×10 5 < Re x < 10 7 . Therefore, the local convective heat transfer coefficient of the turbulent flat plate can be obtained:

[0064]

[0065] For the case where the flow over the entire flat plate is laminar, the average value of the convective heat transfer coefficient can be obtained by integrating over the entire flat plate, that is:

[0066]

[0067] In the formula, l is the length of the entire flat plate.

[0068] For the average convective heat transfer coefficient of turbulent convective heat transfer, it cannot be simply determined by a method similar to that of laminar flow. In the case of a mixed boundary layer (both laminar and turbulent), the average convective heat transfer coefficient of the entire flat plate surface can be regarded as the weighted average of the laminar section (0 ≤ x ≤ x c ) and the turbulent section (x c ≤ x ≤ l), that is:

[0069]

[0070] In the formula, x c is the critical length at which the flow transitions from laminar to turbulent. Substituting the local convective heat transfer coefficients corresponding to laminar and turbulent flows into the above formula, we can further obtain:

[0071]

[0072] Define Re c as the critical Reynolds number when laminar flow transitions to turbulent flow. Substitute it into the above equation and integrate, and finally we can get:

[0073]

[0074] In the formula, Re l is the Reynolds number defined with the flat plate length l as the characteristic dimension.

[0075] To calculate the convective heat transfer of the electronic equipment compartment at high altitude, it can be regarded as the convective heat transfer of a flat plate with a length of l in cross flow. When calculating the average convective heat transfer coefficient on the outside of the equipment compartment, it cannot be simply considered that the flow starts to develop from the front end of the equipment compartment. It is necessary to pay attention to the development process of the boundary layer from the nose to the front of the equipment compartment, and judge the flow situation on the surface of the equipment compartment according to the position of the transition point and the front end of the equipment compartment. Define the distances from the transition point and the front end of the equipment compartment to the nose as x c and x s , respectively. The flow situation on the surface of the electronic equipment compartment can be divided into full laminar flow (x c > l), mixed flow (x s < x c < l) and full turbulent flow (x s > x c ). The expressions of the average convective heat transfer coefficient for the three flow situations are shown in Equation (1).

[0076] The convective heat transfer coefficient can also be obtained by numerical simulation methods, that is, generating a computational grid for the cabin including the nose and performing an external flow field calculation; first, perform a calculation with an adiabatic wall condition to obtain the boundary layer recovery temperature distribution on the surface, and then set the wall to a constant heat flux or constant wall temperature condition for calculation to obtain the convective heat transfer coefficient referenced to the oncoming flow temperature. Finally, convert this convective heat transfer coefficient to the convective heat transfer coefficient referenced to the boundary layer recovery temperature; since the flight Mach number of a solar-powered unmanned aerial vehicle is generally very small, the convective heat transfer coefficient referenced to the oncoming flow temperature can be directly used.

[0077] (1.2) Use the synthetic temperature to equivalent the external convective heat transfer coefficient and solar radiation heat transfer. The external synthetic temperature is an external meteorological parameter synthesized by the equivalent temperature generated by the thermal effects of the external airflow and solar radiation on the structure. The calculation method used is shown in Equation (2).

[0078] (1.3) Since solar radiation is directional, it is necessary to calculate the corresponding radiation components according to the solar radiation angle at the flight location, which can be processed in two ways: one is to solve the comprehensive temperature of each surface of the equipment cabin separately, and the other is to evenly distribute the radiation heat transfer to each surface of the equipment cabin, as shown in Figures 1(a) and 1(b). The first method uses formula (2) to calculate the comprehensive temperature of each surface of the equipment cabin, which can simulate the radiation heat transfer more meticulously and provide a basis for the separate control of heat transfer on each subsequent surface. The second method can simplify the upstream air supply system and evenly distribute the total amount of radiation heat transfer between the electronic equipment cabin and the outside world to each side, so as to ensure that the total radiation heat is consistent with the actual situation.

[0079] (1.4) If the method of evenly distributing solar radiation to the four surfaces is adopted, when the environmental temperature is -80 °C, the altitude is 0 km, and the speed is 8 m / s under the extreme low temperature condition, if the distance between the starting point of the equipment cabin and the nose of the aircraft is 1100 mm, the convective heat transfer coefficient of 36.614 W / (m²·K) can be obtained, and the comprehensive temperature is -70 °C, which is 10 °C higher than the actual environmental temperature, reducing the demand for the refrigeration equipment capacity under the extreme low temperature condition.

[0080] The second step specifically includes:

[0081] (2.1) Construct the peripheral microchannels, use the air flow in the channels to simulate the external convective heat transfer of the equipment cabin, and ensure that the temperature difference between the inlet and outlet is within 1 - 3 °C to form a stable simulation of the external heat transfer conditions. The peripheral channels are as Figure 2 shown.

[0082] (2.2) The calculation of the flow heat transfer in the channels can adopt numerical simulation methods or engineering calculation methods. For example, for rectangular channels, the Dittus - Boelter turbulent flow correlation in the pipe can be used:

[0083]

[0084] where, T w - the temperature of the equipment cabin wall, K; T f - the temperature of the air flow in the channel, K; Pr f - the Prandtl number of the air flow in the channel.

[0085] The applicable parameter range of formula (16): 0.7 ≤ Pr ≤ 100; 2000 ≤ Re ≤ 10 6 , where:

[0086]

[0087]

[0088] where μ is the aerodynamic viscosity, Pa·s; d is the equivalent diameter, m; α is the convective heat transfer coefficient, W / (m 2 ·K); λ is the thermal conductivity of air, W / (m·K).

[0089] The widths b1 and b2 of the rectangular channels are determined by the side width of the equipment cabin. Figure 2 As shown, assuming the channel height h, to ensure that the convective heat transfer coefficient on each side surface of the equipment cabin in the channel is approximately equal to the heat transfer coefficient α in the first step (1.1), the fluid velocity v under each working condition can be calculated from the above relational expressions.

[0090] Then the air supply flow rate for each channel is:

[0091] G = v·b·h·ρ (18)

[0092] where ρ is the density of the test air flow, kg / m 3 , and v is the air flow in the test channel, m / s.

[0093] If the air supply parameters for each channel are controlled separately, the flow rate of each channel can be obtained using the above formula. The sum of the total flow rates of the 4 channels is the required total air supply volume. At the same time, the comprehensive temperature of each channel can also be adjusted individually.

[0094] (2.3) Control of the temperature difference between the inlet and outlet of the channel. When the heat transfer amount on the surface of the equipment cabin reaches thermal equilibrium, the following can be obtained:

[0095] φ = G·C p ·Δt (19)

[0096] where Cp is the specific heat capacity at constant pressure of the air flow in the channel, J / (kg·K); Δt is the temperature difference between the inlet and outlet of the air flow in the channel, K; G is the air flow rate for the test, kg / s; and φ is the heat generation amount of the test piece in the equipment cabin.

[0097] The temperature difference between the inlet and outlet calculated from Equation (19) should ensure that the heat transfer temperature difference Δt is within 1 - 3°C. If the requirements are not met, reselect the channel cross-sectional dimensions (channel height), and repeat the calculations in (2.2) and (2.3) until the requirements are met.

[0098] (2.4) Although the air supply flow rate and comprehensive temperature of each channel can be controlled separately, since the cross-section of the cabin is often square in engineering, using average air supply parameters can reduce the complexity of the upstream air supply. That is, when calculating the comprehensive temperature in the first step, the solar radiation heat is evenly distributed to the four surfaces, and each channel uses the same air supply flow rate and comprehensive temperature, and centralized air supply can be adopted upstream.

[0099] (2.5) When centralized gas supply is adopted upstream, the side width of the equipment cabin is 280 mm. When the channel height of 40 mm is selected, the required gas supply flow rate of 1160 kg / h can be obtained. Smaller channel heights can also be selected to reduce the gas supply flow rate requirements.

[0100] The third step specifically includes:

[0101] (3.1) According to Figure 3 the schematic diagram of the test system shown, place the test piece of the electronic equipment cabin in the external heat exchange simulation channel, and place both in the vacuum chamber. An aerogel thermal insulation layer is laid outside the peripheral channel. Connect the gas supply pipeline and measuring equipment to build a thermal environment test system for the equipment cabin of the solar UAV. The test system with a single gas supply parameter is given here. If the heat transfer conditions of each surface of the equipment cabin are simulated, the gas supply to each channel can also be adjusted separately.

[0102] (3.2) Turn on the gas supply system. According to the comprehensive temperature (-70 °C) and gas supply flow rate (1160 kg / h) obtained in the previous two steps, adjust the gas supply flow rate and temperature. Turn on the vacuum system and adjust the atmospheric height and gas supply parameters in the cabin to reach the required test conditions.

[0103] (3.3) Turn on the power supply of the heat generation simulation component in the electronic equipment cabin and adjust the required heat generation power.

[0104] (3.4) Record parameters such as gas supply parameters, atmospheric height, air temperature inside the electronic equipment cabin, and surface temperature of the electronic equipment. After the test parameters are stable, turn off the heating element, vacuum system, and gas supply system in sequence to end the test.

[0105] (3.5) In addition to conducting steady-state tests, dynamic environment tests can also be carried out by adjusting the gas supply parameters according to the envelope change, and the effectiveness can be evaluated after adding thermal control measures.

Claims

1. A ground environment test method for the equipment cabin of a solar-powered unmanned aerial vehicle, characterized in that, It includes the following steps: The first step is to integrate the effects of external convective heat transfer and solar radiation in the form of synthetic temperature, including the calculation of the external convective heat transfer coefficient and the synthetic temperature; Specifically, it includes the following sub-steps: (1.1) Calculate the external convective heat transfer coefficient of the equipment cabin according to the flight conditions, which serves as the basis for the convective heat transfer coefficient in the subsequent equivalent external heat transfer simulation, and is obtained by engineering calculation and numerical simulation methods; when using the engineering calculation method, the correlation formula for the convective heat transfer coefficient of flat plate flow is adopted, considering the development process of the boundary layer from the nose to the front of the equipment cabin, and judging the flow conditions on the surface of the equipment cabin according to the position of the transition point and the front end of the equipment cabin; when performing numerical simulation, a computational grid is generated for the cabin body including the nose to calculate the external flow field, and the distribution of the convective heat transfer coefficient on the outer surface of the equipment cabin is obtained, and the average convective heat transfer coefficient is adopted in the subsequent steps; (1.2) Calculate the synthetic temperature of the air surrounding the equipment cabin considering solar radiation heat transfer. The external synthetic temperature is an external meteorological parameter that synthesizes the equivalent temperature generated by the thermal effects of the external air flow and solar radiation on the cabin body; this temperature serves as the ambient temperature in the subsequent equivalent external heat transfer simulation, and the calculation formula used is: ， In the formula, — external comprehensive temperature, ; — Ambient temperature, , since the cruising speed of the solar UAV is very low, it is considered that the recovery temperature of the boundary layer is the ambient temperature; — solar radiation intensity, , the radiation intensity at is , which is specifically obtained according to meteorological data; — Surface radiation absorptivity of the equipment cabin, which can be taken as that of carbon fiber material , or selected according to the actual material properties; — The external surface heat transfer coefficient, including the convective heat transfer coefficient and the long-wave radiation heat transfer coefficient ; — the radiation coefficient of heat conduction between two objects participating in radiative heat transfer, ; — Temperature factor, ; The second step is the design of the equivalent external heat transfer simulation of the equipment cabin. By constructing an air flow channel around the equipment cabin to simulate the external convective heat transfer coefficient and synthetic temperature of the equipment cabin, and ensuring that the heat transfer temperature difference between the inlet and outlet is within 1 - 3 °C, the equivalent simulation of the external heat transfer conditions is realized; The third step is to build a thermal environment test system for the equipment cabin of the solar-powered unmanned aerial vehicle. Combining the synthetic temperature and the air supply flow rate obtained in the previous two steps, conduct thermal environment tests on the equipment cabin under high temperature, low temperature, and low air pressure conditions, and further evaluate the effectiveness of the thermal control measures when the electronic equipment is working.

2. The method for ground environment test of the equipment cabin of a solar-powered unmanned aerial vehicle according to claim 1, wherein: In step (1.2) of the first step, consider the radiation heat transfer amount on different surfaces of the equipment cabin caused by the directivity of solar radiation, and perform corresponding radiation component calculations according to the solar radiation angle at the flight location; it is processed in two ways: one is to solve the synthetic temperature for each surface of the equipment cabin separately, and the other is to evenly distribute the radiation heat transfer to each surface of the equipment cabin.

3. A method for ground environmental testing of the equipment cabin of a solar UAV according to claim 1, characterized in that: The second step specifically includes the following sub-steps: (2.1) Construct a micro air flow channel around the equipment cabin to simulate the external convective heat transfer coefficient of the equipment cabin. The air temperature in the channel adopts the synthetic temperature obtained in step (1.2) of the first step, and ensure that the heat transfer temperature difference between the inlet and outlet is within 1 - 3 °C, so as to form a stable simulation of the external heat transfer conditions; since the cross-section of the cabin body is rectangular, four rectangular channels are used around the cabin body to simulate the external convective heat transfer; (2.2) Determine the gas flow rate of the peripheral channel. On the basis of selecting the basic dimensions of the micro channel, change the air flow rate and calculate the convective heat transfer coefficient, ensuring that the convective heat transfer coefficient on each side surface of the equipment cabin in the channel should deviate from the heat transfer coefficient in step (1.1) of the first step by within 5%; (2.3) Check and control the temperature difference between the inlet and outlet of the channel. When the heat transfer amount on the surface of the equipment cabin reaches thermal equilibrium, the following relationship exists: ， where — specific heat capacity at constant pressure of the air flow in the channel, ; — Temperature difference between the inlet and outlet of the air flow in the channel, ; — Air flow rate for testing, ; — Heat generation of the test piece in the equipment compartment; The heat transfer temperature difference obtained from the above formula should be ensured within 1 - ; If the requirements are not met, reselect the channel cross-sectional dimensions and repeat the calculations in (2.2) and (2.3) until the requirements are met.

4. A method for ground environmental testing of a solar drone equipment compartment according to claim 3, characterized in that: In step (2.2) of the second step, the air supply parameters for each channel are calculated separately to obtain the comprehensive temperature and air supply flow rate for each channel. In the test system, the comprehensive temperature and air supply flow rate for each channel are controlled separately to achieve a more refined simulation of the heat transfer on the outer surface of the cabin.

5. A method for ground environment testing of a solar UAV equipment cabin according to claim 3, characterized in that: In step (2.2) of the second step, the average air supply parameters are used to reduce the complexity of the upstream air supply. That is, when calculating the comprehensive temperature in the first step (1.2), the solar radiation heat is evenly distributed to the four surfaces, so that each channel uses the same air supply flow rate and comprehensive temperature.

6. A method for ground environmental testing of a solar unmanned aerial vehicle equipment cabin according to claim 1, characterized in that: The third step specifically includes the following sub-steps: (3.1) Install the test piece of the electronic equipment cabin in the external heat transfer simulation channel, and place the two in the vacuum chamber. An aerogel type thermal insulation layer is laid outside the peripheral channel. Connect the air supply pipeline and the measuring equipment to set up the thermal environment test system for the solar UAV equipment cabin. (3.2) Turn on the air supply system. According to the comprehensive temperature and air supply flow rate obtained in the first step and the second step, adjust the air supply flow rate and temperature. Turn on the vacuum system and adjust the atmospheric height and air supply parameters in the cabin to reach the required test conditions. (3.3) Turn on the power supply of the heat generation simulation component in the electronic equipment cabin and adjust the required heat generation power. (3.4) Record the air supply parameters, atmospheric height, air temperature in the electronic equipment cabin, and surface temperature parameters of the electronic equipment. After the test parameters are stable, turn off the heating element, vacuum system, and air supply system in sequence to end the test. (3.5) In addition to conducting steady-state tests, the air supply parameters can also be adjusted according to the envelope change to conduct dynamic environment tests, and evaluate its effectiveness after adding thermal control measures.

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