Aircraft outer skin convective heat transfer coefficient ground test method and system

Abstract

The invention relates to a ground test method and system for a convective heat transfer coefficient of an aircraft outer skin, belongs to the technical field of aircraft heat dissipation, and aims to solve the problem that the convective heat transfer coefficient of the aircraft outer skin is difficult to test. The test method comprises the following steps: building a test system according to a test principle; determining a measuring point and calibrating a thermocouple; according to the estimated heat exchange capacity of the skin test piece, the power of a heating piece is set; the wind tunnel performs blowing test at the maximum wind speed to monitor whether the test system operates normally; setting an attack angle and a sideslip angle of the skin test piece, and feeding the five-axis servo control system to a specified position; setting a wind tunnel operation mach number and wind tunnel operation; a power supply and a PLC temperature controller in the test platform are started, and the test system operates; judging whether the test system is in a balanced state or not according to the temperature data displayed by the temperature data collector, and calculating a convective heat transfer coefficient; and adjusting the Mach number of the wind tunnel and the attack angle and sideslip angle of the skin test piece to enter the next test working condition, and repeating the steps S5-S8.

Description

Technical Field

[0001] The present invention relates to the technical field of aircraft heat dissipation, and in particular to a ground testing method and system for the convective heat transfer coefficient of an aircraft outer skin. Background Art

[0002] An aircraft flying in the atmosphere at a speed of less than Mach 1 and with a maximum level flight speed less than the speed of sound is a subsonic aircraft.

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

[0004] The convective heat transfer coefficient of the aircraft outer skin directly determines the application efficiency of the aircraft skin heat exchanger. However, the convective heat transfer coefficient of the aircraft outer skin is difficult to test and obtain. There is an urgent need to provide a test system and method for testing the convective heat transfer coefficient of the subsonic aircraft outer skin. Summary of the Invention

[0005] In view of the above analysis, the embodiments of the present invention aim to provide a ground test method and system for the convective heat transfer coefficient of an aircraft outer skin, so as to solve the problem that the convective heat transfer coefficient of an aircraft outer skin is difficult to test.

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

[0007] The present invention provides a method for testing the convective heat transfer coefficient of an aircraft outer skin, comprising the following steps:

[0008] S1: Build the test system according to the test principle;

[0009] S2: Determine the measuring points and calibrate the thermocouples in the test system;

[0010] S3: According to the estimated heat transfer capacity of the skin test piece, the power of the circular high-temperature ceramic heating plate on the skin test piece is set;

[0011] S4: The wind tunnel is blown at the maximum wind speed to test whether the test system operates normally, otherwise go to step S1;

[0012] S5: Set the attack angle and sideslip angle of the skin test piece, and the five-axis servo control system feeds it to the specified position;

[0013] S6: Set the wind tunnel operation Mach number and the wind tunnel starts running;

[0014] S7: Start the power supply and PLC temperature controller in the test platform, and the test system starts to operate;

[0015] S8: judging whether the test system is in equilibrium according to the temperature data displayed by the temperature data collector; if the test system is in equilibrium, recording or calculating the temperature of each measuring point and calculating the convective heat transfer coefficient; if the test system is not in equilibrium, waiting until the test system is in equilibrium, recording the temperature of each thermocouple and calculating the convective heat transfer coefficient;

[0016] S9: Adjust the wind tunnel Mach number, the angle of attack and the sideslip angle of the skin test piece to enter the next test condition, and repeat steps S5-S8.

[0017] Furthermore, in step S1, the test principle is: h = I*U / A / (T w -T a )

[0018] Where h is the convective heat transfer coefficient of the aircraft outer skin, W / (m 2 ℃);

[0019] I is the current supplied by the circular high-temperature ceramic heater, A (ampere);

[0020] U is the supply voltage of the circular high-temperature ceramic heater, V;

[0021] T w is the outer wall temperature of the skin test piece, °C;

[0022] T a is the incoming air temperature, ℃.

[0023] Furthermore, the incoming air temperature is calculated by the following formula: (T a / T t) ^3.5=(1atm / P t );

[0024] Among them, P t is the total pressure, KPa;

[0025] T t is the total temperature, °C;

[0026] T a is the incoming air temperature, ℃.

[0027] Furthermore, in step S3, the power of the circular high-temperature ceramic heating plate is P=h*A*ΔT*110%;

[0028] Where A is the outer wall area of the skin test piece, m 2 ;

[0029] ΔT is the estimated temperature difference between the outer wall of the skin test piece and the air, °C;

[0030] P is the power of the circular high-temperature ceramic heater, W;

[0031] h is the convective heat transfer coefficient of the skin test piece, W / (m 2 ℃).

[0032] Furthermore, in step S8, the equilibrium state of the test system is: the temperature fluctuation of each measuring point in the test system within 5 minutes is less than 1°C.

[0033] The present invention also provides a ground test system for the convective heat transfer coefficient of an aircraft outer skin, which is used for the above-mentioned test method and comprises a subsonic wind tunnel, a test platform and a five-axis servo control system;

[0034] The test platform includes a tooling, a skin test piece, and a PLC temperature controller;

[0035] The test platform is mounted on a five-axis servo control system and is located within the effective test area of the subsonic wind tunnel;

[0036] The tooling is a hollow cuboid, comprising an upper cover plate and a lower cover plate, which are fixed to the test platform with bolts;

[0037] The skin test piece is embedded in the center of the tooling upper cover plate.

[0038] Furthermore, the effective test area of the subsonic wind tunnel is within 100 to 150 mm of the wind tunnel outlet.

[0039] Furthermore, a circular high-temperature ceramic heating plate is attached to the inner wall of the skin test piece by means of high-temperature glue, and a thin-film thermocouple is attached to the outer wall of the skin test piece;

[0040] Parallel to the long side direction of the upper cover plate, a first thermocouple and a second thermocouple are symmetrically arranged at both ends of the circular high-temperature ceramic heating plate on the inner wall of the skin test piece.

[0041] Furthermore, square high-temperature ceramic heating plates are respectively attached to both sides of the upper cover plate inner wall skin test piece by using high-temperature glue;

[0042] The first thermocouple and the second thermocouple are located on the same straight line, and the third thermocouple and the fourth thermocouple are symmetrically arranged on the inner wall surface of the upper cover plate.

[0043] Furthermore, the distance between the first thermocouple and the third thermocouple is ≤5 mm, and the distance between the second thermocouple and the fourth thermocouple is ≤5 mm.

[0044] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0045] 1. The ground test system for the convective heat transfer coefficient of an aircraft outer skin of the present invention provides Mach numbers of different intensities through a subsonic wind tunnel, driving the skin test piece in the test platform to form various angles of attack and sideslip angles under the control of a five-axis servo control system. Different skin test piece angles of attack, sideslip angles, and Mach numbers can simulate different external flow fields of the skin test piece on the ground. That is, different skin test piece angles of attack, sideslip angles, and Mach numbers represent different flight conditions, thereby corresponding to different aircraft outer skin convective heat transfer coefficients, thereby realizing the measurement of the aircraft outer skin convective heat transfer coefficient in a ground state.

[0046] 2. The aircraft outer skin convective heat transfer coefficient ground test system of the present invention uses a small continuous subsonic wind tunnel and skin test pieces to measure the aircraft outer skin convective heat transfer coefficient, which is relatively low in cost.

[0047] 3. Through the testing system and method of the present invention, the convective heat transfer coefficient of the aircraft outer skin under different flight conditions can be measured in a ground state.

[0048] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0050] Figure 1 Schematic diagram of the test system structure of the present invention;

[0051] Figure 2 This is a schematic diagram of the test platform structure of the present invention;

[0052] Figure 3 Schematic diagram of the internal components of the tooling in the test platform of the present invention;

[0053] Figure 4 This is an external front view of the upper cover plate of the tooling in the test platform of the present invention;

[0054] Figure 5 This is a back view of the interior of the tooling upper cover plate in the test platform of the present invention;

[0055] Figure 6 Schematic diagram of the tilt-slip angle during the test process of the present invention;

[0056] Figure 7Schematic diagram of the angle of attack during the test process of the present invention.

[0057] Reference numerals:

[0058] 1-Subsonic wind tunnel; 2-Shareholder screws; 3-Tooling; 4-Test platform; 5-Skin test piece; 6-Five-axis servo control system; 7-Epoxy adhesive layer; 8-Thin film thermocouple; 9-PLC temperature controller; 10-Power supply; 11-Tooling upper cover; 12-Square high-temperature ceramic heating plate; 13-Polyimide insulation pad; 14-Circular high-temperature ceramic heating plate; 15-Thermal insulation felt; 16-Tooling lower cover; 17-First thermocouple; 18-Second thermocouple; 19-Third thermocouple; 20-Fourth thermocouple. DETAILED DESCRIPTION

[0059] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, and are not used to limit the scope of the present invention.

[0060] The present invention provides a method for testing the convective heat transfer coefficient of an aircraft outer skin, comprising the following steps:

[0061] S1: Build the test system according to the test principle;

[0062] S2: Determine the measuring points and calibrate the thermocouples in the test system;

[0063] S3: According to the estimated heat transfer capacity of the skin test piece, the power of the circular high-temperature ceramic heating plate on the skin test piece is set;

[0064] S4: The wind tunnel is blown at the maximum wind speed to test whether the test system operates normally, otherwise go to step S1;

[0065] S5: Set the attack angle and sideslip angle of the skin test piece, and the five-axis servo control system feeds it to the specified position;

[0066] S6: Set the wind tunnel operation Mach number and the wind tunnel starts running;

[0067] S7: Start the power supply and PLC temperature controller in the test platform, and the test system starts to operate;

[0068] S8: judging whether the test system is in equilibrium according to the temperature data displayed by the temperature data collector; if the test system is in equilibrium, recording or calculating the temperature of each measuring point and calculating the convective heat transfer coefficient; if the test system is not in equilibrium, waiting until the test system is in equilibrium, recording the temperature of each thermocouple and calculating the convective heat transfer coefficient;

[0069] S9: Adjust the wind tunnel Mach number, the angle of attack and the sideslip angle of the skin test piece to enter the next test condition, and repeat steps S5-S8.

[0070] Specifically, in step S1, the test system, such as Figure 1 The test system includes a subsonic wind tunnel, a test platform and a five-axis servo control system; the test platform includes a tooling, a skin test piece, a PLC temperature controller and a power supply;

[0071] The test platform is mounted on a five-axis servo control system and is located within the effective test area of the subsonic wind tunnel;

[0072] The wind tunnel is a subsonic, constant-temperature, constant-pressure continuous wind tunnel. The Mach number at the wind tunnel outlet is adjustable from 0.1 to 1.0, the outlet diameter is 65-75 mm, and the effective test area is within 100 to 150 mm of the wind tunnel outlet. A total pressure and total temperature sensor is installed in the wind tunnel. The total temperature and total pressure data measured by the total temperature and total pressure sensor can be used to determine whether the wind tunnel is in a stable state and to calculate the incoming air temperature.

[0073] The tooling is a hollow cuboid, comprising an upper cover plate and a lower cover plate, which is fixed to the test platform by fixing screws, and the skin test piece is embedded in the center of the tooling upper cover plate;

[0074] The skin test piece is a cylindrical piece with a diameter of 28-32 mm and a thickness of 1-4 mm. The material is consistent with the actual skin. A circular high-temperature ceramic heater is attached to the inner wall of the skin test piece using high-temperature glue, and a thin-film thermocouple is attached to the outer wall of the skin test piece. Parallel to the long side of the upper cover plate, a first thermocouple and a second thermocouple are symmetrically arranged at both ends of the circular high-temperature ceramic heater on the inner wall of the skin test piece, close to the polyimide insulation pad.

[0075] The space between the upper cover plate and the skin test piece is filled with epoxy glue, and polyimide thermal insulation pads and thermal insulation felt are installed, and then covered with the lower cover plate; the number of polyimide thermal insulation pads is 4, evenly distributed on the skin test piece;

[0076] Square high-temperature ceramic heating plates are respectively attached to both sides of the inner wall skin test piece of the upper cover plate of the tooling with high-temperature glue; the first thermocouple and the second thermocouple are located on the same straight line, and the third thermocouple and the fourth thermocouple are symmetrically arranged on the inner wall surface of the upper cover plate of the tooling; the spacing between the first thermocouple and the third thermocouple is ≤5mm, and the spacing between the second thermocouple and the fourth thermocouple is ≤5mm.

[0077] The thin film thermocouple, the first thermocouple, the second thermocouple, the third thermocouple and the fourth thermocouple are all connected to the input end of the PLC temperature controller, and the circular high-temperature ceramic heating plate and the square high-temperature ceramic heating plate are both connected to the output end of the PLC temperature controller through wires.

[0078] The power supply provides energy for the circular high-temperature ceramic heating plate and the square high-temperature ceramic heating plate;

[0079] It should be noted that the test platform is installed on a five-axis servo control system, which can accurately control the spatial position and spatial angle of the skin test piece. The test piece is fixed in the effective test area of the subsonic continuous wind tunnel according to the set posture; epoxy glue is filled between the upper cover of the tooling and the skin test piece, and polyimide insulation pads are added to reduce heat conduction between the skin test piece and the tooling, and insulation felt is added to isolate the convection heat transfer on the rear side of the tooling during the test; the inner wall of the skin test piece is glued with high-temperature glue to a circular high-temperature ceramic heating piece for heating the skin test piece; the outer wall of the skin test piece is glued with a thin-film thermocouple for Used to measure the outer wall temperature of the skin test piece; square high-temperature ceramic heating plates are respectively attached to both sides of the inner wall of the skin test piece on the tooling cover plate with high-temperature glue to heat the tooling; the first thermocouple, the second thermocouple, the third thermocouple and the fourth thermocouple are used to measure the temperature of the corresponding positions. The PLC temperature controller ensures that the tooling and the skin test piece are close to the same temperature by monitoring the temperatures of the first thermocouple, the second thermocouple, the third thermocouple and the fourth thermocouple, isolates the temperature transfer between the tooling and the skin test piece, and ensures that all the heat generated by the circular high-temperature ceramic heating plate on the skin test piece is carried away by the external incoming air.

[0080] It should be noted that the PLC control strategy of the test platform's PLC temperature controller is as follows: the circular high-temperature ceramic heater on the inner wall of the skin test piece operates at constant power to heat the skin test piece. When the PLC temperature controller detects that the tooling temperature is more than 1°C lower than the skin test piece, the square high-temperature ceramic heaters on both sides of the skin test piece on the inner wall of the tooling cover begin to heat the tooling. When the temperature difference between the tooling temperature and the skin test piece temperature is ≤1°C, the PLC temperature controller cuts off the power to the square high-temperature ceramic heaters, and the square high-temperature ceramic heaters stop heating. The square high-temperature ceramic heaters have high power consumption, generally more than 10 times that of circular high-temperature ceramic heaters, and have a rapid heating effect. The temperature difference between the tooling and the skin test piece can be stably controlled to within 1°C through negative feedback PLC control constructed using the PLC temperature controller and four thermocouples in the tooling.

[0081] Specifically, in step S1, the test principle is: in the test system, active insulation measures (PLC temperature controller) and passive insulation measures (epoxy adhesive layer, polyimide insulation pad and insulation felt between the tooling and the skin test piece) are adopted. It can be considered that the boundary surfaces of the skin test piece except the outer wall surface are all insulating surfaces. Therefore, when the test system is stable, the heat power consumption of the circular high-temperature ceramic heating plate on the skin test piece is equal to the heat exchanged between the skin heat exchanger and the incoming air.

[0082] According to Newton's cooling formula, the convective heat transfer coefficient of the aircraft outer skin is h, the outer wall area of the skin test piece is A, and the wall temperature measured by the thin film thermocouple on the outer wall of the skin is T w The total pressure and total temperature sensors in the wind tunnel calculate the incoming air temperature to be T a The circular high-temperature ceramic heating plate on the skin test piece is supplied with a current of I and a voltage of U. According to the law of conservation of energy, the following relationship exists:

[0083] I*U=h*A*(T w -T a )

[0084] Therefore, the convective heat transfer coefficient is

[0085] h=I*U / A / (T w -T a )

[0086] Where h is the convective heat transfer coefficient of the aircraft outer skin, W / (m 2 ℃);

[0087] I is the current supplied by the circular high-temperature ceramic heater, A (ampere);

[0088] U is the supply voltage of the circular high-temperature ceramic heater, V;

[0089] T w is the outer wall temperature of the skin test piece, °C;

[0090] T a is the incoming air temperature, ℃.

[0091] Among them, T a Calculated by the following formula:

[0092] (T a / T t) ^3.5=(1atm / P t )

[0093] P t is the total pressure, KPa;

[0094] T t is the total temperature, °C;

[0095] T a is the incoming air temperature, ℃.

[0096] Specifically, in step S2, the measuring points are: a measuring point on the outer wall of the skin test piece, an air measuring point in the wind tunnel, a measuring point at the first thermocouple and a measuring point at the second thermocouple symmetrically arranged at both ends of the circular high-temperature ceramic heating plate on the inner wall of the skin test piece, and a measuring point at the third thermocouple and a measuring point at the fourth thermocouple symmetrically arranged on the inner wall of the tooling upper cover.

[0097] Specifically, in step S2, the method for calibrating the thermocouples in the test system is: placing a standard thermocouple and a calibrated thermocouple in the same environment, changing the ambient temperature, and measuring the electromotive force and temperature relationship curve of the calibrated thermocouple.

[0098] Specifically, in step S3, the power of the circular high-temperature ceramic heater on the skin test piece is set based on the estimated heat transfer capacity of the skin test piece: before the test, the convective heat transfer coefficient h of the skin test piece can be estimated through theoretical calculation. The heater power P can then be set to P = h * A * ΔT * 110%, where A is the outer wall area of the skin test piece, ΔT is the estimated temperature difference between the outer wall of the skin test piece and the air, and 110% is an increment set to take into account the margin.

[0099] It should be noted that the theoretical estimated value of the convective heat transfer coefficient h of the skin test piece is calculated by the following formula:

[0100] h=Nu*k / x=0.0296rho 0.8 v 0.8 x -0.2 mu -0.8 Pr 0.6 k

[0101] Among them, Nu is the Nusselt number, a dimensionless number;

[0102] Re is the Reynolds number, a dimensionless number;

[0103] Pr is the air Prandtl number, a dimensionless number;

[0104] x is the length of the skin test piece, m;

[0105] k is the thermal conductivity of air, W / (m℃)

[0106] rho is the air density, kg / m 3 ;

[0107] mu is the air dynamic viscosity, Pa*s;

[0108] v is the flight speed of the aircraft, m / s.

[0109] Specifically, in step S4, the wind tunnel is blown at a maximum Mach number to monitor whether the test system is operating normally. Otherwise, the process proceeds to step S1, wherein the maximum Mach number is 1.0 and the blown test lasts for 25-35 minutes. During the test, the total temperature and total pressure sensors and the measured temperatures of each thermocouple in the wind tunnel of the test system are checked to see whether they are within a normal and reasonable range. If all are within the normal and reasonable range, the test system is operating normally. If any thermocouple measured temperature is not within the normal and reasonable range, the process returns to step S1.

[0110] Specifically, in step S5, the attack angle and sideslip angle of the skin test piece are manually set: first, the wind tunnel axis is defined as the Y axis, the X axis and the Z axis are perpendicular to the Y axis, the plane formed by the X axis and the Y axis is the horizontal plane, and the plane formed by the Z axis and the Y axis is the vertical plane. Then, the sideslip angle is the angle between the long side of the tooling and the wind tunnel axis in the horizontal plane ( Figure 6 ), the angle of attack is the angle between the long side of the tooling and the axis of the wind tunnel in the vertical plane ( Figure 7 ), different sideslip angles and angles of attack represent different flight conditions, and their sizes depend on the range of sideslip angles and angles of attack that the actual aircraft can achieve; the test platform is installed on a five-axis servo control system and is set in the effective test area of the subsonic wind tunnel. The five-axis servo control system can drive the test platform to move and feed it to the specified position according to the set angle of attack and sideslip angle of the skin test piece, and accurately control the spatial position, sideslip angle and angle of attack of the skin test piece.

[0111] Specifically, in step S8, the equilibrium state of the test system means that the temperature fluctuation of each measuring point within 5 minutes is less than 1°C.

[0112] Specifically, in step S9, the wind tunnel Mach number, the angle of attack and sideslip angle of the skin test piece are adjusted to enter the next test flight condition, and steps S5-S8 are repeated to calculate the convective heat transfer coefficient. It should be noted that different skin test piece angles of attack, sideslip angles and Mach numbers can simulate different external flow fields of the skin test piece on the ground, that is, different skin test piece angles of attack, sideslip angles and Mach numbers represent different flight conditions, thereby corresponding to different aircraft outer skin convective heat transfer coefficients, and finally a table of aircraft outer skin convective heat transfer coefficients is obtained.

[0113] The present invention also provides an aircraft outer skin convective heat transfer coefficient testing system for implementing the above-mentioned testing method, comprising a subsonic wind tunnel, a test platform, and a five-axis servo control system; the test platform comprises a tooling, a skin test piece, a PLC temperature controller, and a power supply;

[0114] The test platform is mounted on a five-axis servo control system and is located within the effective test area of the subsonic wind tunnel;

[0115] The wind tunnel is a subsonic, constant-temperature, constant-pressure continuous wind tunnel. The Mach number at the wind tunnel outlet is adjustable from 0.1 to 1.0, the outlet diameter is 65-75 mm, and the effective test area is within 100 to 150 mm of the wind tunnel outlet. A total pressure and total temperature sensor is installed in the wind tunnel. The total temperature and total pressure data measured by the total temperature and total pressure sensor can be used to determine whether the wind tunnel is in a stable state and to calculate the incoming air temperature.

[0116] The tooling is a hollow cuboid, comprising an upper cover plate and a lower cover plate, which is fixed to the test platform by fixing screws, and the skin test piece is embedded in the center of the tooling upper cover plate;

[0117] The skin test piece is a cylindrical piece with a diameter of 28-32 mm and a thickness of 1-4 mm. The material is consistent with the actual skin. A circular high-temperature ceramic heater is attached to the inner wall of the skin test piece using high-temperature glue, and a thin-film thermocouple is attached to the outer wall of the skin test piece. Parallel to the long side of the upper cover plate, a first thermocouple and a second thermocouple are symmetrically arranged at both ends of the circular high-temperature ceramic heater on the inner wall of the skin test piece, close to the polyimide insulation pad.

[0118] The space between the upper cover plate and the skin test piece is filled with epoxy glue, and polyimide thermal insulation pads and thermal insulation felt are installed, and then covered with the lower cover plate; the number of polyimide thermal insulation pads is 4, evenly distributed on the skin test piece;

[0119] Square high-temperature ceramic heating plates are respectively attached to both sides of the inner wall skin test piece of the upper cover plate of the tooling with high-temperature glue; the first thermocouple and the second thermocouple are located on the same straight line, and the third thermocouple and the fourth thermocouple are symmetrically arranged on the inner wall surface of the upper cover plate of the tooling; the spacing between the first thermocouple and the third thermocouple is ≤5mm, and the spacing between the second thermocouple and the fourth thermocouple is ≤5mm.

[0120] The thin film thermocouple, the first thermocouple, the second thermocouple, the third thermocouple and the fourth thermocouple are all connected to the input end of the PLC temperature controller, and the circular high-temperature ceramic heating plate and the square high-temperature ceramic heating plate are both connected to the output end of the PLC temperature controller through wires.

[0121] The present invention provides Mach numbers of different intensities through a subsonic wind tunnel, driving the skin test piece in the test platform to form various angles of attack and sideslip angles under the control of a five-axis servo control system. Different skin test piece angles of attack, sideslip angles and Mach numbers can simulate different external flow fields of the skin test piece on the ground, that is, different skin test piece angles of attack, sideslip angles and Mach numbers represent different flight conditions, thereby corresponding to different aircraft outer skin convective heat transfer coefficients, and realizing the measurement of the aircraft outer skin convective heat transfer coefficient in the ground state, with low cost.

[0122] Example 1

[0123] This embodiment provides a ground test system for the convective heat transfer coefficient of an aircraft outer skin. Figure 1 shown.

[0124] It includes a subsonic wind tunnel, a test platform and a five-axis servo control system; the test platform includes a tooling, a skin test piece, a PLC temperature controller and a power supply;

[0125] The test platform is mounted on a five-axis servo control system and is located 120 mm outside the subsonic wind tunnel;

[0126] The wind tunnel is a subsonic, constant temperature and constant pressure continuous wind tunnel, the Mach number at the wind tunnel outlet is adjustable in the range of 0.1 to 1.0, the outlet diameter is 70 mm, and a total pressure and total temperature sensor is installed in the wind tunnel;

[0127] The tooling is a hollow cuboid, comprising an upper cover plate and a lower cover plate, and the skin test piece is embedded in the center of the tooling upper cover plate;

[0128] The skin test piece is a cylindrical piece with a diameter of 30 mm and a thickness of 2 mm. The material is consistent with the actual skin. A circular high-temperature ceramic heater is attached to the inner wall of the skin test piece using high-temperature glue, and a thin-film thermocouple is attached to the outer wall of the skin test piece. Parallel to the long side of the upper cover plate, a first thermocouple and a second thermocouple are symmetrically arranged at both ends of the circular high-temperature ceramic heater on the inner wall of the skin test piece, close to the polyimide insulation pad.

[0129] The space between the upper cover plate and the skin test piece is filled with epoxy glue, and polyimide thermal insulation pads and thermal insulation felt are installed, and then covered with the lower cover plate; the number of polyimide thermal insulation pads is 4, evenly distributed on the skin test piece;

[0130] Square high-temperature ceramic heating plates are glued to both sides of the inner wall skin test piece of the upper cover plate of the tooling with high-temperature glue; the first thermocouple and the second thermocouple are located on the same straight line, and the third thermocouple and the fourth thermocouple are symmetrically arranged on the inner wall surface of the upper cover plate of the tooling; the spacing between the first thermocouple and the third thermocouple is 3mm, and the spacing between the second thermocouple and the fourth thermocouple is 3mm.

[0131] The thin film thermocouple, the first thermocouple, the second thermocouple, the third thermocouple and the fourth thermocouple are all connected to the input end of the PLC temperature controller, and the circular high-temperature ceramic heating plate and the square high-temperature ceramic heating plate are both connected to the output end of the PLC temperature controller through wires.

[0132] Example 2

[0133] The aircraft outer skin convective heat transfer coefficient testing method of this embodiment is performed using the testing system of Example 1. The skin test piece in the testing system can accurately simulate the aircraft outer skin heat exchanger, and includes the following steps:

[0134] S1: Build the test system and determine the test points according to the test principle;

[0135] The measuring points are: the outer wall measuring point of the skin test piece, the air measuring point in the wind tunnel, the first thermocouple measuring point and the second thermocouple measuring point symmetrically set at both ends of the circular high-temperature ceramic heating plate on the inner wall of the skin test piece, and the third thermocouple measuring point and the fourth thermocouple measuring point symmetrically set on the inner wall of the tooling upper cover.

[0136] S2: Calibrate the thermocouples in the test system;

[0137] Place the standard thermocouple and the four calibrated thermocouples in the same environment, change the ambient temperature, and measure the relationship curve between the electromotive force and temperature of the calibrated thermocouples.

[0138] S3: According to the estimated heat transfer capacity of the skin test piece, the power of the circular high-temperature ceramic heating plate on the skin test piece is set;

[0139] Before testing, theoretical calculations were performed:

[0140] h=Nu*k / x=0.0296rho 0.8 v 0.8 x -0.2 mu -0.8 Pr 0.6 k

[0141] By looking up the table to obtain the relevant parameter values, it can be estimated that the convective heat transfer coefficient h of the aircraft outer skin heat exchanger is about 200W / (m 2 ℃), the heating plate power P can be set to P = h * A * Δ T * 110% = 200W / (m 2 ℃)*0.072m 2 *20℃*110%=31.38W; where A is the outer wall area of the skin test piece, ΔT is the estimated temperature difference between the outer wall of the skin test piece and the air, and 110% is the increment set to take into account the margin.

[0142] S4: The wind tunnel is blown at the maximum wind speed to test whether the test system operates normally, otherwise go to step S1;

[0143] The maximum Mach number is 1.0, and the wind test lasts 30 minutes. During the test, the measurement temperatures of the total temperature and total pressure sensors inside the wind tunnel and each thermocouple in the test system were detected to be within the normal and reasonable range, and the test system operated normally.

[0144] S5: Set the attack angle and sideslip angle of the skin test piece, and the five-axis servo control system feeds it to the specified position;

[0145] The angle of attack is 0° and the sideslip angle is 0°;

[0146] S6: Set the wind tunnel operation Mach number and the wind tunnel starts running;

[0147] Mach number Mach = 0.2;

[0148] S7: Start the power supply and PLC temperature controller in the test platform, and the test system starts to operate;

[0149] S8: Determine whether the test system is in equilibrium based on the temperature data displayed by the temperature data collector (the temperature fluctuation of each measuring point within 5 minutes is less than 1°). If the test system is in equilibrium, record or calculate the temperature of each measuring point:

[0150] Skin test piece outer wall temperature T w =52.5℃

[0151] The total temperature T measured by the wind tunnel total temperature and total pressure sensor t =34.5℃, total pressure P t =0.103MPaSubstitute into the following formula:

[0152] (T a / T t )^3.5=(1atm / Pt)

[0153] Get the incoming air temperature T a =32.1℃;

[0154] In the test system, I is the current supplied by the circular high-temperature ceramic heater I = 1.3A, the voltage supplied by the circular high-temperature ceramic heater U = 2.8V, and the surface area of the outer wall of the skin test piece A = 7.07e-4m 2 ;

[0155] Substituting h=I*U / A / (Tw-Ta), we can get h=252.4W / (m 2 ℃).

[0156] S9: Adjust the wind tunnel Mach number, the angle of attack and sideslip angle of the skin test piece to enter the next test condition, repeat steps S5-S8, and measure the convective heat transfer coefficient of the skin test piece corresponding to the following conditions: angle of attack of 0°, sideslip angle of 0°, Mach number Mach = 0.4; angle of attack of 0°, sideslip angle of 0°, Mach number Mach = 0.5; angle of attack of 2°, sideslip angle of 0°, Mach number Mach = 0.5; angle of attack of 0°, sideslip angle of 5°, Mach number Mach = 0.5. Specific data are shown in Table 1.

[0157] Table 1 Convective heat transfer coefficient data of the skin test piece of the embodiment

[0158]

[0159]

[0160] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for testing the convective heat transfer coefficient of an aircraft outer skin, characterized in that: The following steps are involved: S1: Build the test system according to the test principle; S2: Determine the measuring points and calibrate the thermocouples in the test system; S3: According to the estimated heat transfer capacity of the skin test piece, the power of the circular high-temperature ceramic heating plate on the skin test piece is set; S4: The wind tunnel is blown at the maximum wind speed to test whether the test system operates normally, otherwise go to step S1; S5: Set the attack angle and sideslip angle of the skin test piece, and the five-axis servo control system feeds it to the specified position; S6: Set the wind tunnel operation Mach number and the wind tunnel starts running; S7: Start the power supply and PLC temperature controller in the test platform, and the test system starts to operate; S8: judging whether the test system is in equilibrium according to the temperature data displayed by the temperature data collector; if the test system is in equilibrium, recording or calculating the temperature of each measuring point and calculating the convective heat transfer coefficient; if the test system is not in equilibrium, waiting until the test system is in equilibrium, recording the temperature of each thermocouple and calculating the convective heat transfer coefficient; S9: Adjust the wind tunnel Mach number, the angle of attack and the sideslip angle of the skin test piece to enter the next test condition, and repeat steps S5-S8.

2. The testing method according to claim 1, wherein: In step S1, the test principle is: h = I*U / A / (T w -T a ) Where h is the convective heat transfer coefficient of the aircraft outer skin, W / (m 2 ℃); I is the current supplied by the circular high-temperature ceramic heater, A (ampere); U is the supply voltage of the circular high-temperature ceramic heater, V; T w is the outer wall temperature of the skin test piece, °C; T a is the incoming air temperature, ℃.

3. The testing method according to claim 2, wherein: The incoming air temperature is calculated by the following formula: (T a / T t) ^3.5=(1atm / P t ); Among them, P t is the total pressure, KPa; T t is the total temperature, °C; T a is the incoming air temperature, ℃.

4. The testing method according to claim 3, wherein: In step S3, the power of the circular high-temperature ceramic heating plate is P=h*A*ΔT*110%; Where A is the outer wall area of the skin test piece, m 2 ; ΔT is the estimated temperature difference between the outer wall of the skin test piece and the air, °C; P is the power of the circular high-temperature ceramic heater, W; h is the convective heat transfer coefficient of the skin test piece, W / (m 2 ℃).

5. The testing method according to claim 4, characterized in that: In step S8, the equilibrium state of the test system is: the temperature fluctuation of each measuring point in the test system is less than 1°C within 5 minutes.

6. A ground test system for aircraft outer skin convective heat transfer coefficient, used to implement the test method according to any one of claims 1 to 6, characterized in that: Includes a subsonic wind tunnel, test platform, and five-axis servo control system; The test platform includes a tooling, a skin test piece, and a PLC temperature controller; The test platform is mounted on a five-axis servo control system and is located within the effective test area of the subsonic wind tunnel; The tooling is a hollow cuboid, comprising an upper cover plate and a lower cover plate, which are fixed to the test platform with bolts; The skin test piece is embedded in the center of the tooling upper cover plate.

7. The test system according to claim 6, characterized in that: The effective test area of the subsonic wind tunnel is within 100 to 150 mm of the wind tunnel outlet.

8. The test system according to claim 7, characterized in that: A circular high-temperature ceramic heating plate is attached to the inner wall of the skin test piece by high-temperature glue, and a thin-film thermocouple is attached to the outer wall of the skin test piece; Parallel to the long side direction of the upper cover plate, a first thermocouple and a second thermocouple are symmetrically arranged at both ends of the circular high-temperature ceramic heating plate on the inner wall of the skin test piece.

9. The test system according to claim 8, characterized in that: Square high-temperature ceramic heating plates are respectively attached to both sides of the upper cover plate inner wall skin test piece using high-temperature glue; The first thermocouple and the second thermocouple are located on the same straight line, and the third thermocouple and the fourth thermocouple are symmetrically arranged on the inner wall surface of the upper cover plate.

10. The test system according to claim 9, characterized in that: The distance between the first thermocouple and the third thermocouple is ≤5 mm, and the distance between the second thermocouple and the fourth thermocouple is ≤5 mm.

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