High-precision total temperature probe based on double-filament thermocouple

Abstract

The invention relates to the technical field of total temperature testing, in particular to a high-precision total temperature probe based on a double-filament thermocouple, which comprises a stagnation cover, a probe support rod, an air inlet section, a contraction section, a square through hole, a thermocouple wire, a thermocouple wire lead pipeline, an air outlet section and a probe rear cover. The stagnation cover is formed by combining a cylinder and a fast convergence curve rotating body, the head of the stagnation cover is chamfered by 45 degrees, two thermocouple wire lead pipelines are arranged on the inner side of a square hole, and two thermocouple wires are arranged in parallel, tensioned in a linear shape and penetrate through the thermocouple wire lead pipelines. A probe rear cover is arranged on the side, back to the main flow, of the probe supporting rod. The side, back to the main flow, of the probe supporting rod extends out of the lead pipeline and is welded to the insulated wire. The invention provides a novel heat conduction error correction method which does not depend on the measurement of the temperature of the root of the thermocouple. Through experiments and theoretical analysis and in combination with computational fluid dynamics (CFD) simulation, key information can be directly extracted from measurement data of the thermocouple, so that heat conduction errors are accurately corrected, the measurement accuracy of the total temperature is remarkably optimized, and the total error is reduced to be smaller than 0.1%.

Description

Technical Field

[0001] The present invention relates to the technical field of total temperature testing, and in particular to a high-precision total temperature probe based on a double-filament thermocouple, which is suitable for correcting thermal conductivity errors using double-filament thermocouples under high subsonic conditions to achieve high-precision measurement of the total temperature of a flow field. Background Art

[0002] The compression system composed of fan / compressor is one of the three major components of an aircraft engine. Its efficiency will directly determine the performance of the aircraft engine. The efficiency of the fan / compressor is an indirect measurement. The temperature rise efficiency is one of the most commonly used methods to calculate its efficiency, especially for the single-stage efficiency of the compressor, which can only be measured by the temperature rise method. Therefore, accurately measuring the temperature rise of the inlet and outlet sections of the compression system is a key technical support for the development of high-performance aircraft engines. The calculation formula for measuring the compressor efficiency by the temperature rise method is as follows:

[0003]

[0004] where η c represents compressor efficiency, T t1 and T t2 Respectively represent the compressor inlet and outlet total temperatures, π c represents the total pressure ratio of the compressor, and k represents the specific heat ratio. For the temperature rise method to measure efficiency, the smaller the inlet and outlet temperature rise, the more difficult it is to accurately measure the efficiency. The main reason is that the relative measurement error of the inlet and outlet temperature rise is large.

[0005] When thermocouples measure temperature, the difference between the actual temperature of the gas under steady-state conditions mainly comes from the following three errors: velocity error, thermal conductivity error and radiation error. In the temperature range below 800K, the radiation error can be ignored.

[0006] The velocity error can be corrected by experimental calibration using the coefficient of restitution. However, thermal conductivity error is still a technical problem in the aerospace and energy fields and has not yet been effectively solved.

[0007] At present, the traditional thermocouple facing the incoming flow and the platinum resistance total temperature probe are usually used to measure the total temperature of the compressor flow field. There are five main defects: First, the thermal conductivity error of the thermocouple sensor is large; Second, the traditional thermal conductivity error correction method is based on the assumption of the hyperbolic cosine function. This assumption is often oversimplified in practical applications, resulting in a large deviation between the corrected temperature measurement result and the actual temperature, especially in situations where high-precision measurement is required; Third, the traditional thermal conductivity error correction method relies on the accurate measurement of the root temperature of the thermocouple. However, due to structural limitations, the single-wire thermocouple cannot directly provide this key temperature data, which introduces a large error when correcting the thermal conductivity error and cannot meet the requirements of high-precision measurement; Fourth, the layout of the traditional total temperature probe thermocouple wire is parallel to the incoming flow direction. This layout can provide relatively accurate measurement results under low-speed or subsonic conditions. However, under high-speed or supersonic conditions, due to the high-speed impact of the airflow, the thermocouple wire is easily blown and bent, resulting in distorted measurement results, which cannot meet the requirements of high-precision measurement. Fifth, under low-frequency temperature fluctuation conditions, the traditional total temperature probe has a significant thermal conductivity error in the measurement results of the thermocouple due to the large temperature difference between the hot node and the root. This error cannot be effectively solved by the traditional correction method, affecting the accuracy and reliability of temperature measurement.

[0008] Therefore, there is an urgent need to develop a total temperature probe that can perform high-precision total temperature measurement during compressor performance testing. Summary of the invention

[0009] The present invention is a self-correcting total temperature probe based on dual thermocouples. The probe adopts an "L"-shaped design as a whole. The sensing part is based on a thin-wire thermocouple temperature sensor. The two exposed thermocouple wires at the heads of the thermocouples are placed in parallel, tightened and in an "I" shape to solve the problem of insufficient total temperature measurement accuracy in compressor performance testing. The present invention proposes a new thermal conductivity error correction method that does not rely on the measurement of the root temperature of the thermocouple. Through experimental and theoretical analysis, combined with computational fluid dynamics (CFD) simulation, the present invention can directly extract key information from the measurement data of the thermocouple, thereby accurately correcting the thermal conductivity error.

[0010] The self-correcting total temperature probe of the dual thermocouple consists of a probe support rod and a stagnation cover. The probe support rod adopts an internal hollow cylindrical design. This structural design not only reduces fluid dynamics blockage, but also facilitates the arrangement and fixation of insulated wires. The hollow structure allows the wire to pass through while maintaining the overall strength and stability of the probe. The stagnation cover is made of high-temperature plastic. Through two cylindrical structures with different diameters and a transition in the form of double twisted wires at the junction, the fluid dynamics loss is effectively reduced and the fluid is ensured to form an ideal stagnation state at the front end of the probe. The velocity error is greatly reduced and the accuracy and stability of temperature measurement are improved. Two square holes are opened at a distance of 1mm from the entrance of the stagnation cover to accurately determine the position of the dual-wire thermocouple. In addition, two cylindrical holes are opened on the wall of the stagnation cover to guide the wires of the thermocouple to ensure smooth passage and fixation of the wires. The dual-wire thermocouple uses thin wires of 50 microns and 75 microns. In order to avoid electrical contact between bare wires and between wires and steel rods, the thin wires are connected to the thicker insulated wires by welding. In a double-wire thermocouple, the measured temperature T1 is greater than T2 because the larger diameter thermocouple has a higher thermal conductivity error. This difference reflects the effect of the thermocouple diameter on the measurement accuracy. In a double-wire thermocouple, two different temperatures are measured: T1 and T2. Through theoretical analysis, the relationship between the two thermocouple temperatures and the actual incoming flow temperature is determined as follows:

[0011]

[0012] Through wind tunnel calibration, the T1 and T2 values ​​at different incoming flow temperatures are obtained. Using these data, the parameter b is determined through linear regression analysis, which reflects the linear relationship between the two thermocouples. Based on the determined parameter b, the total temperature of the fluid can be accurately calculated.

[0013] The present invention provides a combined wire diameter thermocouple total temperature probe, and the technical problems to be solved are: first, the problem of poor accuracy of the total temperature probe of the existing thermocouple temperature sensor itself is solved. Second, the problem that the temperature of the root of the thermocouple needs to be provided in the existing thermocouple total temperature probe in order to correct the thermal conductivity error during measurement is solved. Third, the problem of low spatial resolution caused by the large spacing between the existing combined wire diameter thermocouple pairs is solved. Fourth, the problem of unreasonable layout of the existing combined wire diameter thermocouple total temperature probe and large loss of air flow capacity inside the stagnation hood channel is solved. Fifth, the problem of large speed error, thermal conductivity error and low measurement accuracy of the original "L" type total temperature probe is solved.

[0014] The technical solution of the present invention is:

[0015] 1. A combined wire diameter thermocouple total temperature probe, comprising a stagnation cover (1), a probe support rod (2), an air inlet section (3), a contraction section (4), a square through hole (5), a thermocouple wire (6), a wire lead pipe (7), an air outlet section (8), and a probe back cover (9), characterized in that: the stagnation cover (1) is composed of a cylinder and a fast convergence curve rotating body, the stagnation cover head (1) is chamfered at 45°, two wire lead pipes (7) are opened inside the square hole (5), two thermocouple wires (6) are placed in parallel, tightened and in an "I" shape and pass through the wire lead pipe (7); the probe support rod (2) is opened with a probe back cover (9) facing away from the mainstream, and the probe support rod (2) extends the lead pipe (7) away from the mainstream and is welded to the insulated wire.

[0016] 2. The stagnation hood (1) is made of polycarbonate and consists of two cylindrical sections with different diameters, namely an air inlet section (3) and an air outlet section (8). The cylinders with different diameters are connected by a contraction section (4). The inner diameter of the cylinder of the air inlet section (3) is 2 to 8 mm, the outer diameter is 3 to 12 mm, and the length is 7 to 36 mm. The meridian profile of the contraction section (4) is a lemniscate or a 30 to 60° arc line with a length of 1.5 to 8 mm. The inner diameter of the cylinder of the air outlet section (8) is 1 to 4 mm, the outer diameter is 2 to 8 mm, and the length is 3 to 9 mm.

[0017] 3. The stagnation cover (1) has two symmetrical square through holes (3) with a side length of 1 to 4 mm on the side of the cylinder. The front end of the square through hole is 1 to 4 mm away from the entrance of the stagnation cover. Two cylindrical thermocouple wire lead pipes (7) are opened along the mainstream direction at the rear ends of the two square through holes to lead out the thermocouple wires. The diameter of the pipes is 0.2 to 1 mm, and the distance between the pipes and the vertical plane of the cylinder is 0.2 to 1 mm.

[0018] 4. The two thermocouple wires (6) are K-type thermocouples, with wire diameters of 50 μm and 75 μm respectively. They are placed in parallel, tightened and in a "one" shape. The thermocouple measurement junction is located in the center, and the distance between the centers of the two measurement junctions is 0.4 mm to 1.6 mm. The wires are fixed in the wire lead pipe (7) by means of a heat-insulating adhesive material.

[0019] 5. The probe support rod (2) is a cylindrical tube with a length of 10 to 110 mm and is made of polycarbonate. The inner diameter of the cylindrical tube is 4 to 12 mm and the outer diameter is 6 to 18 mm. A probe rear cover (12) is provided on the cylindrical side facing away from the nozzle. The cross section of the probe rear cover is a fan ring with a central angle of 60° to 150°. The length of the rear cover is 2 to 15 mm. The top end of the rear cover along the axial direction of the cylinder is 3 to 8 mm away from the top end of the support rod (2).

[0020] The high-frequency dynamic three-dimensional full-parameter hot-wire probe of the present invention has the following beneficial effects:

[0021] Beneficial effect 1: The present invention uses CFD simulation technology to simulate the thermocouple measurement temperature under different working conditions by changing the stagnation hood temperature based on known incoming flow conditions. The linear relationship parameters between the two thermocouples are determined through linear regression analysis. By utilizing the linear relationship between the two thermocouples, the present invention can correct the thermal conductivity error without predicting the root temperature of the thermocouple in advance. This innovative method greatly simplifies the correction process and improves the measurement accuracy of the total temperature probe.

[0022] Beneficial effect 2: The thermocouple used in the present invention has a small diameter, which can greatly reduce the heat conduction between the thermocouple and the stagnation cover. At the same time, the present invention achieves extremely high spatial resolution by designing the measurement junction spacing of the double-wire thermocouple to be very small. This design enables the probe to capture more subtle temperature changes and is suitable for applications with extremely high requirements for temperature distribution.

[0023] Beneficial effect three: The probe stagnation cover of the present invention adopts heat-insulating material, which reduces the heat exchange between the stagnation cover and the probe support rod, thereby reducing the thermal conduction error caused by heat conduction.

[0024] Beneficial effect 4: The thermocouple wire is fixed and straightened by the wire support rod, forming a "-" shape, and the thermocouple temperature measurement junction is located in the center, facing the airflow direction, and the exposed wire and the wire support rod form a "П" shape. This support structure can ensure the strength of the thermocouple wire, and it is not easy to bend or break in the flow field.

[0025] Beneficial Effect 5: The two cylindrical structures with different diameters in the stagnation cover of the present invention and the double twisted wire transition at the junction effectively reduce the fluid dynamics loss and ensure that the fluid forms an ideal stagnation state at the front end of the probe, which greatly reduces the speed error. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of a high-precision total temperature probe based on a double-filament thermocouple in an embodiment of the present invention.

[0027] Figure 2 yes Figure 1 A-direction view.

[0028] Figure 3 yes Figure 1 B view.

[0029] Among them: 1-stagnation cover, 2-probe support rod, 3-air inlet section, 4-contraction section, 5-square through hole, 6-thermocouple wire, 7-wire lead pipe, 8-air outlet section, 9-probe back cover. DETAILED DESCRIPTION

[0030] The present invention is described in detail below in conjunction with the accompanying drawings and specific implementation examples so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0031] Embodiment 1: Figures 1 to 3 The present invention shows a high-precision total temperature probe based on a double-filament thermocouple, which is composed of a stagnation hood (1), a probe support rod (2), an air inlet section (3), a contraction section (4), a square through hole (5), a thermocouple wire (6), a wire lead pipe (7), an air outlet section (8), and a probe back cover (9). The stagnation hood (1) is composed of a cylinder and a fast convergence curve rotating body, the stagnation hood head (1) is chamfered at 45°, two wire lead pipes (7) are opened on the inner side of the square hole (5), and the two thermocouple wires (6) are placed in parallel, tightened and in an "I" shape and pass through the wire lead pipe (7); the probe support rod (2) is opened with a probe back cover (9) facing away from the mainstream, and the probe support rod (2) extends the lead pipe (7) away from the mainstream and is welded to the insulated wire.

[0032] The stagnation hood (1) is made of polycarbonate and consists of two cylindrical sections with different diameters, namely an air inlet section (3) and an air outlet section (8). The cylinders with different diameters are connected by a contraction section (4). The inner diameter of the cylinder at the air inlet end (3) is 2 mm, the outer diameter is 3 mm, and the length is 7 mm. The meridian profile of the contraction section (4) is a double twisted curve with a length of 2 mm. The inner diameter of the cylinder at the air outlet section (8) is 1 mm, the outer diameter is 2 mm, and the length is 3 mm.

[0033] 3. The stagnation cover (1) has two symmetrical square through holes (3) with a side length of 1 mm on the side of the cylinder. The front end of the square through hole is 1 mm away from the entrance of the stagnation cover. Two cylindrical thermocouple wire lead pipes (7) are opened along the mainstream direction at the rear ends of the two square through holes to lead out the thermocouple wires. The diameter of the pipe is 0.2 mm, and the distance between the pipe and the vertical plane of the cylinder is 0.2 mm.

[0034] 4. The two thermocouple wires (6) are K-type thermocouples with wire diameters of 50 μm and 75 μm respectively. They are placed in parallel, tightened and in a "one" shape. The thermocouple measurement point is located in the center. The distance between the centers of the two measurement points is 0.4 mm. The wires are fixed in the wire lead pipe (7) by a heat-insulating adhesive material.

[0035] 5. The probe support rod (2) is a 80 mm long cylindrical tube made of polycarbonate, with an inner diameter of 6 mm and an outer diameter of 8 mm. A probe rear cover (12) is provided on the cylindrical side facing away from the nozzle, and its cross section is a fan ring with a central angle of 90°. The length of the rear cover is 4 mm, and the distance between the top end of the rear cover and the support rod (2) along the axial direction of the cylinder and the top end is 5 mm.

[0036] The use process of the present invention is:

[0037] The present invention reveals the influence of thermocouple diameter on measurement accuracy in a double-wire thermocouple through experiments and theoretical analysis. In a double-wire thermocouple, the measured temperature T1 is greater than T2 because the larger diameter thermocouple has a higher thermal conductivity error. This difference reflects the influence of thermocouple diameter on measurement accuracy.

[0038] Temperature measurement relationship: Through experiments and theoretical analysis, the present invention determines the relationship between the temperature measurement of two thermocouples and the actual incoming flow temperature as follows:

[0039]

[0040] Among them, T1 and T2 are the temperatures measured by two thermocouples, b is a parameter reflecting the linear relationship between the two thermocouples, Tad is the actual incoming flow temperature, and m and C are constants.

[0041] Through wind tunnel calibration, the T1 and T2 values ​​at different incoming flow temperatures are obtained. Through linear regression analysis, the parameter b is determined, which reflects the linear relationship between the two thermocouples. In actual measurements, based on the determined parameter b, the total temperature of the fluid can be accurately calculated by measuring the indicated temperature of the two thermocouples. This method can still accurately correct the thermal conductivity error and accurately calculate the total temperature of the incoming flow under the condition of low-frequency temperature fluctuation of the incoming flow, that is, when the fluctuation frequency is lower than the response frequency of the thermocouple measurement junction but higher than the response frequency of the stagnation hood.

Claims

1. A combined wire diameter thermocouple total temperature probe, comprising a stagnation cover (1), a probe support rod (2), an air inlet section (3), a contraction section (4), a square through hole (5), a thermocouple wire (6), a wire lead pipe (7), an air outlet section (8), and a probe back cover (9), characterized in that: The stagnation cover (1) is composed of a cylinder and a fast convergence curve rotating body. The stagnation cover head (1) is chamfered at 45 degrees. Two thermocouple wires (6) are arranged in parallel, stretched and formed into a "one" shape and passed through the thermocouple wire lead pipes (7). The probe support rod (2) is provided with a probe rear cover (9) facing away from the mainstream. The probe support rod (2) extends out of the lead pipe (7) facing away from the mainstream and is welded to the insulated wire. The stagnation cover (1) is made of polycarbonate and is composed of two cylindrical sections with different diameters, namely an air inlet section (3) and an air outlet section (8). The cylinders with different diameters are connected by a contraction section (4). The inner diameter of the cylinder of the air inlet section (3) is 2 to 8 mm, the outer diameter is 3 to 12 mm, and the length is 7 to 36 mm. The meridian profile of the contraction section (4) is a lemniscate or a 30 to 60° arc line with a length of 1.5 to 8 mm. The inner diameter of the cylinder of the air outlet section (8) is 1 to 4 mm, the outer diameter is 2 to 8 mm, and the length is 3 to 9 mm. Two square through holes (3) with a side length of 1 to 4 mm are symmetrically opened on the side of the cylinder of the stagnation cover (1), and the front end of the square through hole is 1 to 4 mm away from the entrance of the stagnation cover. Two cylindrical wire lead pipes (7) are opened along the mainstream direction at the rear ends of the two square through holes to lead out the thermocouple wires. The diameter of the pipes is 0.2 to 1 mm, and the distance between the pipes and the vertical plane of the cylinder is 0.2 to 1 mm. The two thermocouple wires (6) are K-type thermocouples, with wire diameters of 50 microns and 75 microns respectively, placed in parallel, stretched and in a "single" shape, with the thermocouple measuring point located in the center, and the distance between the centers of the two measuring points being 0.4 mm to 1.6 mm, and the wires are fixed in the wire lead pipe (7) by means of a heat-insulating adhesive material; The probe support rod (2) is a cylindrical tube with a length of 10 to 110 mm and is made of polycarbonate. The inner diameter of the cylindrical tube is 4 to 12 mm and the outer diameter is 6 to 18 mm. A probe rear cover (12) is provided on the cylindrical side facing away from the nozzle. The cross section of the probe rear cover is a fan ring with a central angle of 60° to 150°. The length of the rear cover is 2 to 15 mm and the distance between the top end of the rear cover and the top end of the support rod (2) along the axial direction of the cylinder is 3 to 8 mm. The present invention proposes a temperature measurement correction method based on a double-wire thermocouple. In a double-wire thermocouple, the measured temperature T1 is greater than T2 because the larger diameter thermocouple has a higher thermal conductivity error. This difference reflects the influence of the thermocouple diameter on the measurement accuracy. In a double-wire thermocouple, two different temperatures are measured: T1 and T2. Through experimental and theoretical analysis, the relationship between the temperature measurement of the two thermocouples and the actual incoming flow temperature is determined as follows: Through wind tunnel calibration, the T1 and T2 values ​​at different incoming flow temperatures are obtained. Using these data, the parameter b is determined through linear regression analysis, which reflects the linear relationship between the two thermocouples. Based on the determined parameter b, the total temperature of the fluid can be accurately calculated.

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