Aircraft outer skin convective heat transfer coefficient ground test system based on incubator

Abstract

The invention relates to an aircraft outer skin convective heat transfer coefficient ground test system based on an incubator, belongs to the technical field of aircraft heat dissipation, and aims to solve the problem that the existing method cannot accurately simulate the flight condition in a low-temperature and low-pressure environment and cannot measure and obtain the convective heat transfer coefficient of the aircraft outer skin in the low-temperature and low-pressure environment. An aircraft outer skin convective heat transfer coefficient ground test system based on an incubator comprises a low-temperature and low-pressure incubator, a centrifugal fan, a skin heat exchanger, a temperature collector, a circulating pump, a thermocouple and a simulation heat source. Different external flow fields of the skin heat exchanger are simulated on the ground through the wind speed generated by the centrifugal fan, different high-altitude low-temperature and low-pressure environments are simulated through the low-temperature and low-pressure incubator, and measurement of the convective heat transfer coefficient of the outer skin of the aircraft is completed on the ground.

Description

Technical Field

[0001] The present invention relates to the technical field of aircraft heat dissipation, and particularly to a ground test system for the convective heat transfer coefficient of the outer skin of an aircraft based on a temperature chamber. Background Art

[0002] When an aircraft flies in the atmosphere at a speed less than Mach 1, an aircraft with a maximum level flight speed less than the speed of sound is a subsonic aircraft.

[0003] A subsonic aircraft can use the outer skin of the aircraft for environmental control, use part of the outer skin as a heat exchanger, conduct the heat in the cabin to the outer skin, and then transfer it to the low-temperature ram air outside. Compared with engine bleed air or compressor refrigeration, the aircraft skin heat exchanger has high efficiency, small volume and weight, and does not require additional equipment. It is a relatively economical and reliable environmental control measure under a certain flight profile.

[0004] The convective heat transfer coefficient of the outer skin of an aircraft directly determines the application efficiency of the aircraft skin heat exchanger. However, it is difficult to measure the convective heat transfer coefficient of the outer skin of an aircraft. Some existing test systems cannot accurately simulate the flight conditions of a low-temperature and low-pressure environment. There is an urgent need to provide a test system and method for measuring the convective heat transfer coefficient of the outer skin of a subsonic aircraft. Summary of the Invention

[0005] In view of the above analysis, embodiments of the present invention aim to provide a ground test system for the convective heat transfer coefficient of the outer skin of an aircraft based on a temperature chamber to solve at least one of the following problems: 1. It is difficult to measure the convective heat transfer coefficient of the existing outer skin of an aircraft; 2. Existing test systems and methods cannot accurately simulate the flight conditions of a low-temperature and low-pressure environment and cannot measure the convective heat transfer coefficient of the outer skin of an aircraft under a low-temperature and low-pressure environment.

[0006] The object of the present invention is mainly achieved through the following technical solutions:

[0007] The present invention provides a ground test system for the convective heat transfer coefficient of the outer skin of an aircraft based on a temperature chamber, including a flight condition simulation unit and a test unit;

[0008] The flight condition simulation unit includes a low-temperature and low-pressure temperature chamber and a centrifugal fan;

[0009] The test unit includes a skin heat exchanger, a temperature collector, a circulation pump, a thermocouple and a simulated heat source.

[0010] Further, the low-temperature and low-pressure temperature chamber is used to simulate the high-altitude low-temperature and low-pressure environment;

[0011] The centrifugal fan is used to generate airflows with different wind speeds to simulate different external flow fields of the skin heat exchanger on the ground;

[0012] The temperature collector is used to record and store the instantaneous temperature data measured by the thermocouple and synchronously display the data through a digital display function;

[0013] The circulation pump is used to provide the kinetic energy for the flow of the working medium, and by adjusting the rotation speed, the working medium has different flow rates and head in the flow channels of the skin heat exchanger;

[0014] The simulated heat source is used to heat the working medium.

[0015] Furthermore, heat insulation felts are laid on the inner wall surface of the skin heat exchanger.

[0016] Furthermore, the low-temperature and low-pressure thermostat is an open-close type cuboid box, which is internally provided with a vacuum pump and a compressor;

[0017] The centrifugal fan and the skin heat exchanger are respectively placed on the left and right sides inside the low-temperature and low-pressure thermostat. The skin heat exchanger is internally provided with heat dissipation channels, and is supported and fixed by a fixed bracket, so that the outer wall surface of the skin heat exchanger is in the core area of the centrifugal fan outlet.

[0018] Furthermore, the circulation pump, the temperature collector and the simulated heat source are arranged outside the low-temperature and low-pressure thermostat;

[0019] The skin heat exchanger, the circulation pump and the simulated heat source are connected in series through skin pipelines to form a closed-loop circuit.

[0020] Furthermore, the thermocouples are respectively arranged at the outer wall surface of the skin heat exchanger, one end of the skin inlet pipeline connecting to the inner wall surface of the skin heat exchanger, and one end of the skin outlet pipeline connecting to the inner wall surface of the skin heat exchanger, and are all connected to the temperature data collector.

[0021] Furthermore, the simulated heat source is a heat source plate with a thin film heating sheet laid on it.

[0022] Furthermore, the core area of the centrifugal fan outlet refers to the area where the distance from the centrifugal fan outlet is less than or equal to the diameter of the centrifugal fan outlet.

[0023] Furthermore, the wind speed in the core area of the centrifugal fan outlet is 10 - 30 m / s.

[0024] The present invention also provides a method for ground testing the convective heat transfer coefficient of the outer skin of an aircraft by using the above ground testing system.

[0025] Compared with the prior art, the present invention can at least achieve one of the following beneficial effects:

[0026] 1. The ground test system for the convective heat transfer coefficient of the outer skin of an aircraft based on an incubator simulates different external flow fields of the skin heat exchanger on the ground by generating wind speeds through a centrifugal fan, and simulates different high-altitude low-temperature and low-pressure environments through a low-temperature and low-pressure incubator, and measures the convective heat transfer coefficient of the outer skin of the aircraft on the ground.

[0027] 2. Through the test system of the present invention, the convective heat transfer coefficient of the outer skin of the aircraft under different flight conditions can be measured under ground conditions.

[0028] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combination schemes. Other features and advantages of the present invention will be described in the subsequent specification, and some advantages can be made obvious from the specification, or understood by implementing the present invention. The objectives and other advantages of the present invention can be realized and obtained through the content specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings are only for the purpose of showing specific embodiments and are not considered as limiting the present invention. Throughout the drawings, the same reference signs denote the same components.

[0030] Figure 1 It is a schematic structural diagram of the test system of the present invention;

[0031] Figure 2 It is a schematic connection diagram of the skin heat exchanger, the circulation pump and the simulated heat source of the present invention.

[0032] Reference Signs:

[0033] 1 - Low-temperature and low-pressure incubator; 2 - Centrifugal fan; 3 - Fixed bracket; 4 - Skin heat exchanger; 5 - Circulation pump; 6 - Temperature collector; 7 - Thin film heating sheet; 8 - Heat source plate; 9 - Skin inlet pipeline; 10 - Skin outlet pipeline. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The following will specifically describe the preferred embodiments of the present invention with reference to the drawings, wherein the drawings form a part of this application and are used together with the embodiments of the present invention to explain the principles of the present invention, and are not used to limit the scope of the present invention.

[0035] The present invention provides a ground test system for the convective heat transfer coefficient of the outer skin of an aircraft based on an incubator, including a flight condition simulation unit and a test unit;

[0036] The flight condition simulation unit includes a low-temperature and low-pressure incubator and a centrifugal fan;

[0037] The test unit includes a skin heat exchanger, a temperature collector, a circulation pump, a thermocouple and a simulated heat source;

[0038] The low-temperature and low-pressure incubator is an openable and closable cuboid box with an openable and closable door on the front side, and symmetrically arranged holes on the left and right sides; a vacuum pump and a compressor system are provided inside the low-temperature and low-pressure box to ensure a low-pressure and low-temperature environment;

[0039] The centrifugal fan and the skin heat exchanger are respectively placed on the left and right sides inside the low-temperature and low-pressure incubator. The skin heat exchanger is provided with a heat dissipation flow channel and is supported and fixed by a fixing bracket, so that the outer wall surface of the skin heat exchanger is in the core area of the centrifugal fan outlet; the core area of the outlet refers to: the distance from the centrifugal fan outlet ≤ D, where D is the diameter of the centrifugal fan outlet;

[0040] The circulating pump, the temperature collector and the simulated heat source are arranged outside the low-temperature and low-pressure incubator;

[0041] The skin heat exchanger, the circulating pump and the simulated heat source are connected in series through skin pipelines to form a closed-loop circuit; among them, one end of the skin heat exchanger is connected to one end of the circulating pump through a skin inlet pipeline, and the other end of the skin heat exchanger is connected to the simulated heat source through a skin outlet pipeline; the circulating pump and the simulated heat source are connected through a separate pipeline; the skin inlet pipeline and the skin outlet pipeline pass through the holes on the side of the box body and penetrate out of the box body;

[0042] The thermocouples are respectively arranged on the outer wall surface of the skin heat exchanger, one end of the skin inlet pipeline connected to the inner wall surface of the skin heat exchanger, and one end of the skin outlet pipeline connected to the inner wall surface of the skin heat exchanger, and are all connected to the temperature data collector;

[0043] The low-temperature and low-pressure incubator can provide a low-temperature and low-pressure environment of normal temperature to -80°C and normal pressure to 1Kpa, and can simulate the low-temperature and low-pressure environmental conditions at an altitude of 5km to 20km;

[0044] The power of the centrifugal fan is 18000 - 18500W, and a wind speed of 10 - 30m / s can be generated in the core area of the outlet, which is used to simulate different external flow fields of the skin heat exchanger on the ground;

[0045] The simulated heat source is a heat source plate with a thin film heating sheet laid on it, which is used to heat the working medium;

[0046] The circulating pump is used to provide the kinetic energy for the flow of the working medium, and by adjusting the rotation speed, the working medium has different flow rates and head in the flow channel of the skin heat exchanger;

[0047] The thermocouples are used to measure the temperatures at the skin inlet pipe, the skin outlet pipe and the outer wall surface of the skin. The temperature data collector records and stores the instantaneous temperature data measured by the thermocouples and synchronously displays the data through the digital display function;

[0048] In order to avoid the loss of the heat of the working medium during the flow and conduction process, heat insulation felts are laid on the inner wall surface of the skin heat exchanger.

[0049] When the test system is operating, a simulated heat source provides heat, and a circulation pump provides the flow of the working fluid, causing the working fluid to flow in a closed loop in the skin inlet pipeline and the skin outlet pipeline, flowing from the skin inlet pipeline to the skin outlet pipeline, and exchanging the heat provided by the simulated heat source with the ram air on the outer wall surface of the skin heat exchanger.

[0050] The present invention also provides a ground test method for the convective heat transfer coefficient of the outer skin of an aircraft based on a temperature chamber, which is completed by the above test system and includes the following steps:

[0051] S1: According to the test principle, build a test system and determine the measuring points;

[0052] S2: Calibrate the thermocouples at each measuring point;

[0053] S3: Set the rotational speed of the centrifugal fan, and at the same time, set the rotational speed of the circulation pump according to the flow resistance of the test system;

[0054] S4: Set the power of the thin film heating sheet according to the estimated heat transfer capacity of the skin heat exchanger;

[0055] S5: Debug the test system to ensure that the test system operates correctly;

[0056] S6: Design the flight altitude, query the meteorological data to obtain the temperature and air pressure values at this flight altitude, set the temperature and air pressure values in the low-temperature and low-pressure temperature chamber according to the meteorological data, and start the low-temperature and low-pressure temperature chamber;

[0057] S7: Start the centrifugal fan and adjust the outlet speed of the fan;

[0058] S8: Judge whether the test system is in a balanced state according to the temperature data displayed by the temperature data collector. If the test system is in a balanced state, record the temperatures at each measuring point and calculate the convective heat transfer coefficient; if the test system is not in a balanced state, continue to wait until the test system is in a balanced state, then record the temperatures at each measuring point and calculate the convective heat transfer coefficient;

[0059] S9: Change the rotational speed of the centrifugal fan, repeat steps S7 - S8, obtain more than 3 groups of corresponding data of wind speed and convective heat transfer coefficient, and use the least squares method to fit to obtain the definite functional relationship between the convective heat transfer coefficient and the flight speed;

[0060] S10: Determine the next flight altitude, query the meteorological data to obtain the temperature and air pressure values at this flight altitude, repeat steps S7 - S9, and obtain the definite functional relationship between the convective heat transfer coefficient and the flight speed at this flight altitude.

[0061] Specifically, in step S1, the test principle is:

[0062] After the test system reaches equilibrium, according to the law of conservation of energy, there is the following relationship: the working fluid exchanges the heat provided by the simulated heat source with the ram air on the outer wall of the skin heat exchanger, and the heat taken away by the working fluid is equal to the heat exchanged between the skin and the ram air:

[0063] Rho*Cp*V*(Ti - To) = h*A*(Tw - Ta)

[0064] Therefore,

[0065] h = Rho*Cp*V*(Ti - To) / A / (Tw - Ta)

[0066] where Ti is the temperature at the inlet pipe of the skin heat exchanger, °C;

[0067] To is the temperature at the outlet pipe of the skin heat exchanger, °C;

[0068] Ta is the temperature of the incoming air, °C;

[0069] T W is the temperature of the outer wall of the skin, °C;

[0070] Cp is the specific heat capacity of the working fluid, J / (kg°C);

[0071] Rho is the density of the working fluid, kg / m 3 ;

[0072] V is the volume flow rate of the working fluid, m 3 / s;

[0073] A is the outer wall area of the skin heat exchanger, m 2 ;

[0074] According to the heat transfer coefficient correlation for air flowing over a flat plate surface,

[0075] Nu = 0.0296*Re 0.8 *Pr 0.6

[0076] Nu = h*x / k

[0077] Re = rho*v*x / mu

[0078] We get: h = Nu*k / x = 0.0296*rho 0.8 *v 0.8 *x 0.8 / mu 0.8 *Pr 0.6 *k / x = C*v 0.8

[0079] where Nu is the Nusselt number, a dimensionless number;

[0080] Re is the Reynolds number, a dimensionless number;

[0081] Pr is the Prandtl number of air, a dimensionless number;

[0082] x is the length of the skin heat exchanger, in m;

[0083] k is the thermal conductivity of air, in W / (m℃);

[0084] rho is the air density, in kg / m 3

[0085] mu is the dynamic viscosity of air, in Pa*s;

[0086] v is the flight speed, in m / s;

[0087] Among them, C is a parameter related to the physical properties of air, which is a function of temperature T and pressure P. The functional relationship is:

[0088] C = 0.0296 * rho 0.8 * x -0.2 / mu 0.8 * Pr 0.6 * k = f(T, P)

[0089] Therefore, under the conditions of constant temperature and pressure and unchanged relative positions of the centrifugal fan and the skin heat exchanger, C is a constant, and h is 0.8 positively correlated with v.

[0090] By adjusting the wind speed in the core area of the centrifugal fan outlet, the convective heat transfer coefficients at different wind speeds are obtained, and the least squares method is used to fit h = C * v 0.8 , and the value of C is calculated, so as to obtain the definite functional relationship between the convective heat transfer coefficient and the flight speed, that is:

[0091] h = f(v)

[0092] According to the meteorological conditions at different flight altitudes, the air pressure and temperature at a specific altitude are adjusted, and the curve of the convective heat transfer coefficient varying with the flight speed at different flight altitudes can be obtained. The altitude is H, and h H = f(v).

[0093] Specifically, in step S1, the measurement points are respectively the skin inlet pipe measurement point, the skin outlet pipe measurement point, and the skin outer wall measurement point set at the skin inlet pipe, the skin outlet pipe, and the skin outer wall.

[0094] Specifically, in step S2, the method for calibrating the thermocouples at each measurement point is: placing the standard thermocouple and the thermocouple to be calibrated in the same environment, changing the environmental temperature, and measuring the curve of the electromotive force and temperature relationship of the thermocouple to be calibrated.

[0095] Specifically, in step S3, the rotational speed of the circulation pump is set according to the flow resistance of the test system. The flow resistance has been measured during the design of the aircraft skin heat exchanger. The higher the rotational speed of the circulation pump, the stronger its driving ability and the greater the flow resistance it can overcome. Based on the performance curve of the circulation pump and the flow resistance, the rotational speed of the circulation pump is determined.

[0096] Specifically, in step S4, the power of the heating element is set according to the estimated heat transfer capacity of the skin heat exchanger. Before the test, the convective heat transfer coefficient h of the aircraft outer skin heat exchanger can be estimated through theoretical calculations. Then, the power P of the heating element can be set as P = h * A * ΔT * 110%, where A is the outer wall area of the skin heat exchanger, ΔT is the temperature difference between the estimated outer wall of the skin heat exchanger and the air, and 110% is the increment set considering the margin. Among them, the heating element is a polyimide film heating element.

[0097] It should be noted that the theoretical estimated value of the convective heat transfer coefficient h of the aircraft outer skin heat exchanger is calculated through the following formula:

[0098] h = Nu * k / x = 0.0296rho 0.8 v 0.8 x -0.2 mu -0.8 Pr 0.6 k

[0099] Among them, Nu is the Nusselt number, a dimensionless number;

[0100] Re is the Reynolds number, a dimensionless number;

[0101] Pr is the Prandtl number of air, a dimensionless number;

[0102] x is the length of the skin heat exchanger, m;

[0103] k is the thermal conductivity of air, W / (m℃)

[0104] rho is the air density, kg / m 3 ;

[0105] mu is the dynamic viscosity of air, Pa*s;

[0106] v is the flight speed of the aircraft, m / s.

[0107] Specifically, in step S5, the test system is operated on the ground. After debugging, ensure that the temperatures measured by each thermocouple in the test system are consistent with the ground temperature, and the power and rotational speed of the circulation pump are within the normal range to ensure that the test system is error-free.

[0108] Specifically, in step S8, the balanced state of the test system means that the temperature fluctuations of each measuring point within 5 minutes are < 1℃.

[0109] The ground test system for the convective heat transfer coefficient of the outer skin of an aircraft based on an incubator can simulate different external flow fields of the skin heat exchanger on the ground by generating wind speeds with a centrifugal fan, and simulate different high-altitude low-temperature and low-pressure environments with a low-temperature and low-pressure incubator, thus completing the measurement of the convective heat transfer coefficient of the outer skin of the aircraft on the ground.

[0110] Embodiment 1

[0111] The ground test system for the convective heat transfer coefficient of the outer skin of an aircraft based on an incubator in this embodiment includes a low-temperature and low-pressure incubator, a centrifugal fan, a skin heat exchanger, a temperature collector, a circulation pump, a thermocouple, and a simulated heat source; as Figure 1 shown.

[0112] The low-temperature and low-pressure incubator is an open-close cuboid box body with an openable and closable door on the front side, and symmetrically arranged holes on the left and right sides; a vacuum pump and a compressor system are provided inside the low-temperature and low-pressure box to ensure a low-pressure and low-temperature environment;

[0113] The centrifugal fan and the skin heat exchanger are respectively placed on the left and right sides inside the low-temperature and low-pressure incubator. The skin heat exchanger is provided with a heat dissipation flow channel and is supported and fixed by a fixed bracket, so that the outer wall surface of the skin heat exchanger is in the core area of the centrifugal fan outlet; the core area of the outlet means that the distance from the centrifugal fan outlet ≤ D (30 mm), and D is the diameter of the centrifugal fan outlet;

[0114] The circulation pump, the temperature collector, and the simulated heat source are arranged outside the low-temperature and low-pressure incubator;

[0115] The skin heat exchanger, the circulation pump, and the simulated heat source are connected in series through skin pipelines to form a closed-loop circuit; among them, one end of the skin heat exchanger is connected to one end of the circulation pump through a skin inlet pipeline, and the other end of the skin heat exchanger is connected to the simulated heat source through a skin outlet pipeline; the circulation pump and the simulated heat source are connected through a separate pipeline; the skin inlet pipeline and the skin outlet pipeline pass through the holes on the side of the box body and penetrate the box body;

[0116] The thermocouples are respectively arranged on the outer wall surface of the skin heat exchanger, one end of the skin inlet pipeline connected to the inner wall surface of the skin heat exchanger, and one end of the skin outlet pipeline connected to the inner wall surface of the skin heat exchanger, and are all connected to the temperature data collector;

[0117] The simulated heat source is a heat source plate with a thin film heating sheet laid on it;

[0118] The inner wall surface of the skin heat exchanger is laid with heat insulation felt.

[0119] When the test system is operating, the simulated heat source provides heat, and the circulation pump provides the flow of the working fluid, causing the working fluid to flow in a closed loop in the skin inlet pipeline and the skin outlet pipeline, flowing from the skin inlet pipeline to the skin outlet pipeline, and exchanging the heat provided by the simulated heat source with the ram air on the outer wall surface of the skin heat exchanger.

[0120] Embodiment 2

[0121] The ground test method for the convective heat transfer coefficient of the outer skin of an aircraft based on an incubator in this embodiment is completed through the above test system, and includes the following steps:

[0122] S1: According to the test principle, build a test system and determine the measuring points.

[0123] The measuring points are respectively the skin inlet pipe measuring point, the skin outlet pipe measuring point, and the skin outer wall surface measuring point set at the skin inlet pipe, the skin outlet pipe, and the skin outer wall surface.

[0124] S2: Calibrate the thermocouples at each measuring point.

[0125] Place the standard thermocouple and the three thermocouples to be calibrated in the same environment, change the environmental temperature, and measure the relationship curve between the electromotive force and temperature of the thermocouples to be calibrated.

[0126] S3: Set the rotational speed of the centrifugal fan, and at the same time, set the rotational speed of the circulation pump according to the flow resistance of the test system.

[0127] The rotational speed of the centrifugal fan is: 1500 rpm.

[0128] The flow resistance of the test system is 1057.95 Pa. According to the performance curve and flow resistance of the circulation pump, the rotational speed of the circulation pump is determined to be 10000 rpm.

[0129] S4: Set the power of the thin film heating sheet according to the estimated heat transfer capacity of the skin heat exchanger.

[0130] Before the test, through theoretical calculation:

[0131] h = Nu * k / x = 0.0296 rho 0.8 v 0.8 x -0.2 mu -0.8 Pr 0.6 k

[0132] Look up the table to obtain the numerical values of relevant parameters, and it can be estimated that the convective heat transfer coefficient h of the outer skin heat exchanger of the aircraft is about 200 W / (m 2 ℃) under the flight conditions of a flight altitude of 1049 m and a flight speed of 155 km / h. Then the power P of the heating sheet can be set to P = h * A * ΔT * 110% = 200 W / (m 2 ℃) * 0.072 m2 *20 °C * 110% = 31.38 W; where A is the outer wall area of the skin heat exchanger, ΔT is the temperature difference between the estimated outer wall of the skin heat exchanger and the air, and 110% is the increment set to account for the margin.

[0133] S5: Debug the test system to ensure that the test system operates correctly;

[0134] Operate the test system on the ground. After debugging, ensure that the temperatures measured by each thermocouple in the test system are consistent with the ground temperature, and the power and speed of the circulation pump are within the normal range.

[0135] S6: Design the flight altitude, query the meteorological data to obtain the temperature and pressure values at this flight altitude, set the temperature and pressure values in the low-temperature and low-pressure incubator according to the meteorological data, and start the low-temperature and low-pressure incubator;

[0136] Flight altitude h = 1000 m, atmospheric temperature = 8.5 °C, atmospheric pressure = 89.9 Kpa;

[0137] S7: Start the centrifugal fan and adjust the fan outlet speed;

[0138] Fan outlet speed 10 m / s;

[0139] S8: Judge that the test system is in a balanced state according to the temperature data displayed by the temperature data collector (the temperature fluctuation of each measuring point within 5 minutes < 1 °C), and record the temperature of each measuring point:

[0140] Temperature at the inlet pipe of the skin heat exchanger Ti = 58.8 °C;

[0141] Temperature at the outlet pipe of the skin heat exchanger To = 57.1 °C;

[0142] Incoming air temperature Ta = 8.5 °C;

[0143] Temperature of the outer wall of the skin T W = 47.7 °C;

[0144] The working fluid is selected as No. 65 aviation coolant. Looking up the table, the density of the working fluid Rho = 1063.69 kg / m 3 , the specific heat capacity of the working fluid Cp = 3258 J / (kg °C), the outer wall area of the skin A = 0.072 m 2 , the volume flow rate of the working fluid V = 5.20E-05 m 3 / s. Substitute into h = Rho * Cp * V * (Ti - To) / A / (Tw - Ta), and we can get h = 55.1 W / (m 2 °C).

[0145] C is a parameter related to the physical properties of air and is a function of the atmospheric temperature T and the atmospheric pressure P. The functional relationship is: C = 0.0296 * rho 0.8 *x -0.2 / mu 0.8 *Pr 0.6 *k = f(T, P). After calculation, C1 = 8.73;

[0146] S9: Change the rotational speed of the centrifugal fan. The wind speeds of the centrifuge are 20 m / s and 30 m / s respectively. Repeat steps S7 - S8 to obtain more than 3 groups of corresponding data of wind speed and convective heat transfer coefficient, as shown in Table 1. C = (C1 + C2 + C3) / 3 = (8.73 + 8.68 + 8.59) / 3 = 8.7. Using the least squares method to fit, when the flight altitude is 1000 m, the determined functional relationship between the convective heat transfer coefficient and the flight speed is: h 1000m = 8.7v 0.8 ;

[0147] S10: Determine the next flight altitude as 1500 m. Query the meteorological data to obtain the temperature (5.25 °C) and air pressure value (84.5 KPa) at this flight altitude. Using the least squares method to fit, when the flight altitude is 1500 m, the determined functional relationship between the convective heat transfer coefficient and the flight speed is: h 1500m = 7.6v 0.8 , as shown in Table 2.

[0148] Table 1 Data table of the test process of the convective heat transfer coefficient of the outer skin of the aircraft at a flight altitude of 1000 m

[0149] Item 1-1 1-2 1-3 Height / m 1000 1000 1000 Atmospheric temperature / °C 8.5 8.5 8.5 Atmospheric pressure / KPa 89.9 89.9 89.9 <![CDATA[V / m 3 / s]]> 5.20E-05 5.20E-05 5.20E-05 Rotational speed of centrifugal fan / rpm 1500 3000 6000 Outlet air velocity of centrifugal fan / 10 20 30 Ti / °C 58.8 54.6 50.2 To / °C 57.1 51.9 47.1 Tw / °C 47.7 44.4 38.6 Ta / °C 8.5 8.5 8.5 <![CDATA[A / m 2 > 0.142 0.142 0.142 <![CDATA[Rho / kg / m 3 > 1063.7 1063.7 1063.7 C 8.73 8.68 8.59 <![CDATA[h / (m 2 °C)]]> 55.1 95.4 130.5

[0150] Table 2 Data table of the test process of the convective heat transfer coefficient of the outer skin of the aircraft at a flight altitude of 1500 m

[0151]

[0152]

[0153] In this embodiment, a low - temperature and low - pressure environment is simulated through a ground test system, the measurement of the convective heat transfer coefficient of the outer skin of the aircraft at different flight altitudes is completed, and a determined functional relationship between the convective heat transfer coefficient of the outer skin of the aircraft and the flight speed is established.

[0154] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A ground test system for the convective heat transfer coefficient of the outer skin of an aircraft based on an incubator, characterized in that, It includes a flight condition simulation unit and a test unit; The flight condition simulation unit includes a low-temperature and low-pressure incubator and a centrifugal fan; The test unit includes a skin heat exchanger, a temperature collector, a circulation pump, a thermocouple, and a simulated heat source.

2. The ground test system according to claim 1, wherein The low-temperature and low-pressure incubator is used to simulate the high-altitude low-temperature and low-pressure environment; The centrifugal fan is used to generate airflows with different wind speeds to simulate different external flow fields of the skin heat exchanger on the ground; The temperature collector is used to record and store the instantaneous temperature data measured by the thermocouple and synchronously display the data through the digital display function; The circulation pump is used to provide the kinetic energy of the working medium flow, and by adjusting the rotational speed, the working medium has different flow rates and head in the flow channels of the skin heat exchanger; The simulated heat source is used to heat the working medium.

3. The ground test system according to claim 1, wherein Heat insulation felts are laid on the inner wall surface of the skin heat exchanger.

4. The ground test system according to claim 3, wherein, The low-temperature and low-pressure incubator is an open-close type cuboid box body, and a vacuum pump and a compressor are arranged inside; The centrifugal fan and the skin heat exchanger are respectively placed on the left and right sides inside the low-temperature and low-pressure incubator. The skin heat exchanger is provided with a heat dissipation flow channel, which is supported and fixed by a fixing bracket, so that the outer wall surface of the skin heat exchanger is in the core area of the centrifugal fan outlet.

5. The ground test system according to claim 4, wherein The circulation pump, the temperature collector, and the simulated heat source are arranged outside the low-temperature and low-pressure incubator; The skin heat exchanger, the circulation pump, and the simulated heat source are connected in series through skin pipelines to form a closed-loop circuit.

6. The ground test system according to claim 5, wherein, The thermocouples are respectively arranged at the outer wall surface of the skin heat exchanger, at one end of the skin inlet pipeline connecting to the inner wall surface of the skin heat exchanger, and at one end of the skin outlet pipeline connecting to the inner wall surface of the skin heat exchanger, and are all connected to the temperature data collector.

7. The ground test system according to claim 6, wherein, The simulated heat source is a heat source plate with a thin film heating sheet laid on it.

8. The ground test system according to claim 7, wherein The core area of the centrifugal fan outlet refers to the area where the distance from the centrifugal fan outlet is less than or equal to the diameter of the centrifugal fan outlet.

9. The ground test system according to claim 8, wherein The wind speed in the core area of the centrifugal fan outlet is 10 - 30 m / s.

10. A method for ground testing the convective heat transfer coefficient of the outer skin of an aircraft using the ground testing system according to any one of claims 1 - 9.

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