Temperature acquisition component and method for measuring surface heat flux density of flat plate specimen in arc wind tunnel

Abstract

The present invention provides a temperature acquisition device and a method for measuring the surface heat flux density of a flat specimen in an arc wind tunnel. The device includes a metal plate, a heat insulation frame, and thermocouples. The heat insulation frame surrounds the periphery of the metal plate. Two thermocouples are installed at the center of the lower surface of the metal plate, and the distances from the two thermocouple probes to the upper surface of the metal plate are different. The temperature acquisition component is arranged at the position to be measured at the outlet of the arc wind tunnel nozzle. The temperature acquisition component can measure the temperature for a long time and repeatedly, calculate the heat flux density through the temperature data, and in combination with the heat flux density measurement method of the present invention, it can not only measure the change process of the transient heat flux density in a short time, but also measure the steady-state heat flux density and the radiation equilibrium temperature for a long time.

Description

Technical Field

[0001] The present invention belongs to the technical field of arc wind tunnel tests, and particularly relates to a temperature acquisition component and a method for measuring the surface heat flux density of a flat specimen in an arc wind tunnel. Background Technique

[0002] Arc wind tunnel tests are always carried out in various links of aircraft development. Conducting wind tunnel tests directly on the entire aircraft is often costly. Under cost constraints, it becomes a more reasonable choice to intercept local structural features of the aircraft for testing. The flat plate arc wind tunnel test is one of the most common ones.

[0003] Before conducting a flat plate arc wind tunnel test, it is necessary to calibrate the incoming flow state of the wind tunnel to ensure that the airflow state at the outlet of the wind tunnel nozzle can meet the requirements. Among them, the heat flux density q on the flat plate surface surface is one of the basic bases for judging whether the airflow parameters meet the requirements and needs to be measured emphatically.

[0004] Currently, the main means for measuring the heat flux density in arc wind tunnel tests are water calorimeters, thin-walled calorimeters, and plug calorimeters. The water calorimeter measures the heat flux density by measuring the steady-state temperature rise of the cooling water. It has a slow response time and can only measure the steady-state heat flux density, and cannot measure the real-time change process of the heat flux density. The thin-walled calorimeter and the plug calorimeter have the same measurement principle, which is to measure the back temperature of the metal under heating conditions, and obtain the time change rate of the temperature by fitting the linear segment of the temperature rise curve, so as to calculate the surface heat flux density. However, the thin-walled calorimeter is limited by the small wall thickness of the outer shell and small heat sink, and there is a strict limit on the longest working time. Although the plug calorimeter has a slightly longer working time than the thin-walled calorimeter, its life is shorter, and it requires a long cooling time after the test and cannot be tested multiple times in a short time.

[0005] In summary, there are still problems with the existing heat flux density measurement methods in flat plate arc wind tunnel tests, and it is still necessary to explore heat flux density measurement means that are more convenient, effective, and have fewer usage restrictions. Summary of the Invention

[0006] The purpose of the present invention is to provide a temperature acquisition device and a method for measuring the surface heat flux density of a flat specimen in an arc wind tunnel. This temperature acquisition component can measure temperature for a long time and repeatedly, and calculate the heat flux density through temperature data. The heat flux density measurement method of the present invention is convenient, effective, and reusable. It can measure the change process of transient heat flux density in a short time, and can also measure the steady-state heat flux density and radiation equilibrium temperature for a long time, so as to make up for the deficiencies of current heat flux density measurement means and provide a new idea for measuring the surface heat flux density of flat specimens in arc wind tunnels.

[0007] The technical solution adopted by the present invention to achieve the above purpose is as follows:

[0008] The present invention provides a temperature acquisition component, including a metal flat plate, a heat insulation frame, and a thermocouple. The heat insulation frame surrounds the periphery of the metal flat plate. Two thermocouples are installed at the center position of the lower surface of the metal flat plate, and the distances from the two thermocouple probes to the upper surface of the metal flat plate are different. The temperature acquisition component is arranged at the position to be measured at the outlet of the arc wind tunnel nozzle.

[0009] Further, 2 holes are arranged within a range of a radius of 6 mm at the geometric center of the lower surface of the metal flat plate. The diameter of a single hole is not greater than 2 mm. The bottom of the 2 holes is respectively at a distance of x 1 mm and x 2 mm from the upper surface of the metal flat plate. x 1 takes 1 - 3 mm, and x 2 is 1 - 2 mm larger than x 1 .

[0010] Further, the material of the metal flat plate is an isotropic metal material with a melting point higher than the stagnation temperature of the wind tunnel flow field by more than 100 degrees Celsius. The size range of the length and width of the metal flat plate is 80 mm - 280 mm, and the size range of the thickness of the metal flat plate is 10 mm - 30 mm.

[0011] Further, the material of the heat insulation frame is a lightweight heat insulation material with a thermal conductivity lower than 0.5 W / (m·K), a density lower than 650 kg / m 3 , and a temperature resistance higher than the stagnation temperature of the wind tunnel flow field. The thickness range of the heat insulation frame is 20 mm - 40 mm.

[0012] Further, the thermocouple is a K - type armored thermocouple, adopting a needle - type structure. The diameter of the probe is between 1 mm and 1.5 mm, and the length of the probe is more than 3 mm greater than the thickness of the metal flat plate. The pressing force between the tip of the thermocouple probe and the bottom of the hole in the metal flat plate is not less than 8 N.

[0013] The present invention also provides a method for measuring the surface heat flux density of a flat plate specimen in an arc wind tunnel, including the following steps

[0014] Obtain the temperatures at different distances from the upper surface of the flat plate specimen through the temperature acquisition component;

[0015] According to the method of separation of variables, preset the surface temperature expression of the flat plate specimen as a form of the sum of the products of several time functions and coordinate functions;

[0016] Use the temperature data obtained by the temperature acquisition component to perform the first inverse solution correction on the temperature expression;

[0017] Use the Savitzky - Golay filtering function to perform the second correction on the temperature expression;

[0018] The surface temperature of the flat specimen is obtained by using the second - corrected temperature expression, and the heat flux density of the hot wall on the surface of the flat specimen is obtained by substituting it into Fourier's law of heat conduction.

[0019] Furthermore, it is characterized in that the preset surface temperature expression of the flat specimen is

[0020]

[0021] where n is 4, g i (x) is a coordinate function, f i (t) is a time function, t is time, and x is the distance variable from the upper surface of the metal plate.

[0022] Furthermore, the coordinate function selects polynomials or spline functions of different orders;

[0023] The temperature expression is inversely solved and corrected for the first time using the temperature data obtained by the temperature acquisition component. Specifically, the time function is solved by the following formula and substituted into the temperature expression to achieve the first modification,

[0024]

[0025]

[0026]

[0027]

[0028] where x 1 、x 2 are the distances from the temperature acquisition points to the upper surface of the flat specimen respectively, T 1 and T 2 are the temperatures obtained by two temperature acquisition points of the temperature acquisition component, and are the time change rates of the temperature, λ is the material thermal conductivity of the metal plate, ρ is the material density of the metal plate, and c is the material specific heat capacity of the metal plate.

[0029] Furthermore, the second correction of the temperature expression using the Savitzky - Golay filtering function is specifically as follows: The original temperature data T 1 、T 2 are filtered by the following formula, and the filtered temperature and temperature change rate are substituted into the temperature expression for the second correction,

[0030]

[0031] where m is a positive integer of any size, a k and b kIt is the weight coefficient in the filtering function.

[0032] Furthermore, the temperature on the surface of the flat specimen is

[0033] T surface = T(t, 0) = J(T 1 , T 2 , x 1 , x 2 , 0)

[0034] The heat flux density on the surface of the flat specimen is

[0035]

[0036] Advantages of the present invention compared with the prior art:

[0037] The temperature measurement component proposed by the present invention relies on the high thermal conductivity of the metal material to directly conduct heat energy to the tip of the thermocouple probe in the measurement hole, and the temperature response is sensitive enough; the melting point of the metal flat plate itself is more than 100 degrees Celsius higher than the stagnation temperature of the wind tunnel flow field, which can resist the erosion of high-temperature air flow for a long time, can be reused multiple times, does not require cooling measures, has a simple structure and high reliability.

[0038] The method for measuring the heat flux density on the surface of the flat specimen in the arc wind tunnel proposed by the present invention is to infer the surface heat flux density based on the measured temperature data. This method can not only calculate the real-time change law of the transient heat flux density through the transient change of temperature, but also measure the steady-state heat flux density and the surface radiation equilibrium temperature through the data at thermal equilibrium. It effectively makes up for the deficiency that only the cold wall heat flux density can be obtained under short-time heating conditions during the measurement of the heat flux density in the current arc wind tunnel, and the hot wall heat flux density and the radiation equilibrium temperature cannot be obtained under long-time heating conditions.

[0039] The method for measuring the heat flux density on the surface of the flat specimen in the arc wind tunnel proposed by the present invention uses the Savitzky-Golay filtering function to correct the temperature data, establishes the correlation between the temperature at the current moment and the change rate of the temperature and the temperatures at the adjacent moments before and after, weakens the numerical noise caused by the original data, and reduces the oscillation of the solution. Description of the Drawings

[0040] The accompanying drawings included are used to provide a further understanding of the embodiments of the present invention, which form a part of the specification, are used to illustrate the embodiments of the present invention, and are used to explain the principles of the present invention together with the text description. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts.

[0041] Figure 1Schematic diagram of the temperature acquisition component structure provided by a specific embodiment of the present invention;

[0042] Figure 2 For the specific embodiment of the present invention under a heat flux density condition of 300 KW / m 2 Surface temperature and heat flux density curves obtained by the surface heat flux density measurement method of the flat plate specimen of the arc wind tunnel under the heat flux density condition.

[0043] Among them, the above-mentioned drawings include the following reference numerals:

[0044] 1. Arc wind tunnel nozzle, 2. Thermal insulation frame, 3. Metal flat plate, 4. Armored thermocouple. Specific implementation mode

[0045] The following details the specific embodiments of the present invention. In the following description, for purposes of explanation rather than limitation, specific details are set forth to facilitate a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may also be practiced in other embodiments without these specific details.

[0046] It should be noted here that in order to avoid obscuring the present invention with unnecessary details, only the device structures and / or processing steps closely related to the solution of the present invention are shown in the drawings, while other details less related to the present invention are omitted.

[0047] The present invention provides a temperature acquisition component, as Figure 1 shown, including a metal flat plate 3, a thermal insulation frame 2, and two K-type armored thermocouples 4. The metal material of the metal flat plate 3 should be isotropic and have a melting point higher than the stagnation temperature of the wind tunnel flow field by more than 100 degrees Celsius; the length and width dimensions range from 80 mm to 280 mm, and the thickness dimension range is from 10 mm to 30 mm; there are two holes within a radius of 6 mm from the geometric center of the lower surface of the metal flat plate. Within the allowable range of the processing technology, the two holes are made as close as possible to avoid distortion of the heat flux density measurement result due to excessive temperature difference. The diameter of a single hole is not greater than 2 mm, avoiding obvious influence on the temperature distribution caused by too large a hole; the bottom of the two holes is respectively x 1 mm and x 2 mm from the upper surface of the metal flat plate. x 1 takes 1 to 3 mm, and x 2 is 1 to 2 mm larger than x 1 . Designing the bottom distance of the holes between 1 and 2 mm is to make the temperature gradient within a reasonable range and conducive to the convergence of the solution.

[0048] The material of the thermal insulation frame 2 is selected with a thermal conductivity lower than 0.5 W / (m·K) and a density lower than 650 kg / m 3, a lightweight thermal insulation material with a temperature resistance higher than the stagnation temperature of the wind tunnel flow field; the entire heat insulation frame 2 is in a "return" structure and is wrapped around the four sides of the metal flat plate 3 to ensure that the surroundings of the metal flat plate are approximately an adiabatic boundary, isolating heat conduction in all directions, so that only the upper surface of the metal flat plate 3 receives heat transfer, and the wrapping thickness is between 20 mm and 40 mm.

[0049] The structural form of the 2 K-type armored thermocouples 4 is needle-shaped, the probe diameter is between 1 mm and 1.5 mm, the probe length is more than 3 mm greater than the thickness of the metal flat plate, the thermocouple probes are inserted into two holes on the lower surface of the metal flat plate 3, and the pressing force between the probe tip and the bottom of the hole is not less than 8 N. The thermocouple needs to record the complete change process T of the temperatures at the bottoms of the two holes 1 、T 2 。 By designing the probe diameter, on the one hand, the probe strength is ensured and it is not easy to bend, and on the other hand, the opening of the metal flat plate is not large, and the interference with the temperature field is small. A pressing force is applied between the probe tip and the bottom of the hole so that the two do not separate, and the contact thermal resistance can be ignored without interfering with the measurement results.

[0050] The present invention provides a method for measuring the surface heat flux density of an arc wind tunnel flat specimen, and the specific implementation steps are as follows:

[0051] Step 1: Heat the temperature acquisition component with the arc wind tunnel air flow to be measured to obtain the temperature data T at different wall thicknesses x 1 、x 2 from the upper surface of the temperature acquisition component 1 、T 2 。

[0052] The center of the upper surface of the metal flat plate is at the position to be measured at the outlet of the arc wind tunnel nozzle. Two thermocouples are installed at the center position of the lower surface of the metal flat plate. The distances from the two thermocouple probes to the upper surface of the metal flat plate are different. The high-temperature air flow of the arc wind tunnel passes through the upper surface of the metal flat plate, and the two thermocouples measure the temperature data at different wall thicknesses on the surface.

[0053] Step 2: Adopt the method of separation of variables, and assume that the surface temperature expression of the flat specimen is in the form of the sum of the products of several time functions and coordinate functions:

[0054]

[0055] In formula (1), n is a positive integer greater than 0, and n takes 4 in this embodiment; the 4 coordinate functions g i (x) (i = 1, 2, 3, 4) can select polynomial or spline functions of different orders; the 4 time functions f i (t) (i = 1, 2, 3, 4) are regarded as the 4 unknowns in the first inverse solution. t is time, and x is the distance variable from the upper surface of the metal flat plate.

[0056] Step 3: Use the temperature acquisition component to obtain the bottom temperature T 1 and T 2 , find the time rate of change of temperature and The temperature data T 1 , T 2 Substituting into equation (1), we obtain equations (2) and (3):

[0057]

[0058]

[0059] The time rate of change of temperature Substituting into the one-dimensional transient heat conduction differential equation, we obtain equations (4) and (5):

[0060]

[0061]

[0062] Among them, λ is the thermal conductivity of the metal plate, ρ is the material density of the metal plate, and c is the specific heat capacity of the metal plate.

[0063] The four time functions f can be obtained by inversely solving equations (2), (3), (4), and (5) i (t)(i=1, 2, 3, 4), the four time functions f i (t)(i=1, 2, 3, 4) is substituted back into formula (1) to complete the first correction of the temperature expression. The temperature T(t, x) in formula (1) is corrected to be only related to the variable x and the bottom temperature T 1 and T 2 , the distance between the bottom of the hole and the surface x 1 and x 2 , the time rate of change of the bottom hole temperature and The relevant function is shown in formula (6):

[0064]

[0065] Step 4: The temperature expression (6) after the first correction needs to be corrected for the second time using the Savitzky-Golay filter function to establish a correlation between the current temperature and the temperature change rate and the temperature of the previous and next neighboring moments, weaken the numerical noise caused by the original data, and reduce the oscillation of the solution, as shown in Equation 7:

[0066]

[0067] In the formula, m is a positive integer of any size, a k and b kis the weight coefficient in the filtering function, and the magnitude of m determines the number of weight coefficients.

[0068] The original temperature data T 1 , T 2 is processed by Equation (7) to obtain the filtered temperature and the temperature change rate.

[0069] Substitute the temperature T 1 and T 2 in Equation (6), the time change rate of temperature and with Equation (7), and complete the second correction of the temperature expression. The temperature T(t, x) in Equation (6) is corrected to a function that only depends on the variables x, the bottom hole temperature T 1 , T 2 , the distance x 1 between the bottom hole and the surface, and x 2 as shown in Equation (8):

[0070] T(t, x) = J(T 1 , T 2 , x 1 , x 2 , x) (8)

[0071] Step 5: According to the second-corrected temperature expression (8), let x be 0 to obtain the temperature on the surface of the metal plate; substitute Equation (8) into Fourier's law of heat conduction and let x be 0 to obtain the heat flux density on the surface of the metal plate, as shown in Equations (9) and (10):

[0072] T surface = T(t, 0) = J(T 1 , T 2 , x 1 , x 2 , 0) (9)

[0073]

[0074] To verify the effectiveness and correctness of the heat flux density measurement method provided by the present invention, an arc wind tunnel test on the heat flux density measurement of a flat plate was carried out under the heating condition of a heat flux density of 300 KW / m 2 . The original data and the measurement results are given in Figure 2 , and Figure 2 T 1 , T 2 in are the temperature data at different wall thicknesses x 1 , x 2 from the surface obtained by the temperature acquisition component. Based on this set of original data, the heat flux density measured by the method provided by the present invention is 313 KW / m2 , the deviation from the true value of 300 is only 4.3%, and this error is completely within the acceptable range in the engineering field. Additionally, the method also measures the temperature on the flat surface and can be used to obtain the surface radiation equilibrium temperature during long-term hot commissioning.

[0075] Features described and / or illustrated for one embodiment above can be used in the same or similar manner in one or more other embodiments, and / or combined with or replace features in other embodiments.

[0076] It should be emphasized that the term "comprising / including" as used herein refers to the presence of features, whole units, steps or components, but does not exclude the presence or addition of one or more other features, whole units, steps, components or combinations thereof.

[0077] Many features and advantages of these embodiments are clear from this detailed description, and thus the appended claims are intended to cover all such features and advantages of these embodiments that fall within their true spirit and scope. Additionally, since many modifications and changes are readily conceivable by those skilled in the art, the embodiments of the present invention are not to be limited to the exact structures and operations illustrated and described, but may cover all suitable modifications and equivalents that fall within their scope.

[0078] The above description is only the preferred embodiments of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0079] The parts not detailed in the present invention are well-known technologies to those skilled in the art.

Claims

1. A method for measuring the surface heat flux density of a flat plate specimen in an arc wind tunnel, characterized in that, it includes the following steps Obtain the temperatures at different distances from the upper surface of the flat plate specimen through a temperature acquisition component; According to the method of separation of variables, preset the surface temperature expression of the flat plate specimen as a form of the sum of the products of several time functions and coordinate functions; Perform the first inverse solution correction on the temperature expression using the temperature data obtained by the temperature acquisition component; Perform the second correction on the temperature expression using the Savitzky-Golay filtering function; Obtain the surface temperature of the flat plate specimen using the temperature expression corrected for the second time, and substitute it into Fourier's law of heat conduction to obtain the surface heat flux density of the hot wall of the flat plate specimen; The preset surface temperature expression of the flat plate specimen is where n is 4, g i (x) is a coordinate function, f i (t) is a time function, t is time, and x is the distance variable from the upper surface of the metal plate; The coordinate function selects polynomials or spline functions of different orders; The first inverse solution correction of the temperature expression using the temperature data obtained by the temperature acquisition component is specifically to solve the time function through the following formula and substitute it into the temperature expression to achieve the first modification, where x 1 and x 2 are the distances of the temperature acquisition points from the upper surface of the flat specimen, T 1 and T 2 are the temperatures obtained by the two temperature acquisition points of the temperature acquisition component, and are the time change rates of the temperature, λ is the material thermal conductivity of the metal plate, ρ is the material density of the metal plate, and c is the specific heat capacity of the material of the metal plate.

2. The method for measuring the surface heat flux density of a flat plate specimen in an arc wind tunnel according to claim 1, characterized in that, The second correction of the temperature expression using the Savitzky-Golay filtering function is specifically as follows. The original temperature data T 1 , T 2 are filtered, and the filtered temperature and temperature change rate are substituted into the temperature expression for the second correction. where m is a positive integer of any size, a k and b k are weight coefficients in the filtering function.

3. The method for measuring the surface heat flux density of a flat plate specimen in an arc wind tunnel according to claim 2, characterized in that, The temperature on the surface of the flat plate specimen is T surface = T(t, 0) = J(T 1 , T 2 , x 1 , x 2 , 0) The heat flux density on the surface of the flat plate specimen is 4. The method for measuring the surface heat flux density of a flat plate specimen in an arc wind tunnel according to claim 1, characterized in that, The temperature acquisition component includes a metal plate, a heat insulation frame, and thermocouples. The heat insulation frame surrounds the periphery of the metal plate. Two thermocouples are installed at the center position of the lower surface of the metal plate. The distances from the two thermocouple probes to the upper surface of the metal plate are different. The temperature acquisition component is arranged at the position to be measured at the outlet of the arc wind tunnel nozzle.

5. The method for measuring the surface heat flux density of a flat plate specimen in an arc wind tunnel according to claim 4, characterized in that, Two holes are provided within a range of 6 mm radius from the geometric center of the lower surface of the metal flat plate, the diameter of a single hole is not greater than 2 mm, and the bottom surfaces of the two holes are respectively at a distance of x 1 mm and x 2 mm from the upper surface of the metal flat plate, where x 1 is taken as 1 to 3 mm, and x 2 is 1 to 2 mm larger than x 1 .

6. The method for measuring the surface heat flux density of a flat plate specimen in an arc wind tunnel according to claim 5, characterized in that, The metal plate is made of an isotropic metal material with a melting point more than 100 degrees Celsius higher than the stagnation temperature of the wind tunnel flow field; the size range of the length and width of the metal plate is 80 mm to 280 mm, and the size range of the thickness of the metal plate is 10 mm to 30 mm.

7. The method for measuring the surface heat flux density of a flat plate specimen in an arc wind tunnel according to claim 4, characterized in that, The heat-insulating frame is made of a lightweight heat-insulating material with a thermal conductivity lower than 0.5 W / (m K), a density lower than 650 kg / m 3 , and a temperature resistance higher than the stagnation temperature of the wind tunnel flow field. The thickness range of the heat-insulating frame is 20 mm to 40 mm.

8. The method for measuring the surface heat flux density of a flat plate specimen in an arc wind tunnel according to claim 4, characterized in that, The thermocouple is a K-type armored thermocouple, adopting a needle type structure, with the probe diameter between 1 mm and 1.5 mm, and the probe length is more than 3 mm greater than the thickness of the metal plate; the pressing force between the tip of the thermocouple probe and the bottom of the hole of the metal plate is not less than 8 N.

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