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

Abstract

The utility model 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.

Description

Technical Field

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

[0002] The fan / compressor compression system is one of the three major components of an aircraft engine, and its efficiency directly determines the performance of the aircraft engine. The efficiency of the fan / compressor is an indirect measurement, and temperature rise efficiency is one of the most commonly used methods to calculate its efficiency. In particular, the single-stage efficiency of the compressor can only be measured using 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 compressor efficiency using the temperature rise method is as follows:

[0003]

[0004] where η c represents the compressor efficiency, T t1 and T t2 Respectively represent the total temperature of the compressor inlet and outlet, π c represents the compressor's total pressure ratio, and k represents the specific heat ratio. When measuring efficiency using the temperature-rise method, the smaller the inlet and outlet temperature rise, the more difficult it is to accurately measure efficiency. This is primarily due to the large relative measurement error of the inlet and outlet temperature rises.

[0005] The difference between the temperature measured by a thermocouple and the actual gas temperature under steady-state conditions is primarily due to three types of errors: velocity error, thermal conductivity error, and radiation error. Radiation error is negligible in the temperature range below 800K.

[0006] Velocity errors can be corrected experimentally using the coefficient of restitution. However, thermal conductivity errors remain a technical challenge in the aerospace and energy fields and have yet to be effectively addressed.

[0007] Currently, traditional thermocouples facing the incoming flow and platinum resistance total temperature probes are commonly used to measure the total temperature of the compressor flow field. These methods have five major drawbacks: 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, which is often oversimplified in practical applications, resulting in large deviations between the corrected temperature measurement results and the actual temperature, especially in applications requiring high-precision measurements. Third, the traditional thermal conductivity error correction method relies on accurate measurement of the thermocouple root temperature. However, due to structural limitations, single-wire thermocouples cannot directly provide this critical temperature data, which introduces significant errors when correcting the thermal conductivity error and fails to meet the requirements of high-precision measurements. Fourth, the traditional total temperature probe thermocouple wire is arranged parallel to the incoming flow direction. This layout provides relatively accurate measurement results under low or subsonic conditions. However, under high or supersonic conditions, the thermocouple wire is easily bent by the high-speed impact of the airflow, resulting in distorted measurement results and failing to meet the requirements of high-precision measurement. Fifth, under low-frequency temperature fluctuations, traditional total temperature probes suffer from significant thermal conductivity errors in thermocouple measurements due to the large temperature difference between the hot node and the root. This error cannot be effectively addressed using traditional correction methods, affecting the accuracy and reliability of temperature measurements.

[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 provides a high-precision total temperature probe based on a double-filament thermocouple. The probe adopts an "L"-shaped design as a whole. The sensing part is based on a thin-filament thermocouple temperature sensor. The two exposed thermocouple wires at the head of the thermocouple are placed in parallel, tightened and in an "I" shape, so as 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] A high-precision total temperature probe based on a dual-filament thermocouple consists of a probe support rod and a stagnation shroud. The probe support rod features a hollow cylindrical design. This structural design not only reduces fluid dynamic obstruction but also facilitates the placement and securement of the insulated wires. The hollow structure allows the wires to pass through while maintaining the overall strength and stability of the probe. The stagnation shroud is made of high-temperature plastic. Its two cylindrical structures of different diameters and the use of a twisted-pair transition at the junction effectively reduce fluid dynamic losses and ensure an ideal stagnation state at the probe tip. This significantly minimizes velocity error and improves the accuracy and stability of temperature measurements. Two square holes are provided 1 mm from the entrance of the stagnation shroud to precisely determine the position of the dual-filament thermocouple. In addition, two cylindrical holes are provided in the stagnation shroud wall to guide the thermocouple wires, ensuring smooth passage and securement. The dual-filament thermocouples use 50- and 75-micron fine wires. To prevent electrical contact between the bare wires and between the wires and the steel rod, the fine wires are connected to the thicker insulated wires by welding. In a twin-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. In a twin-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] Wind tunnel calibration is used to obtain T1 and T2 values ​​at different incoming flow temperatures. Using this data, linear regression analysis is used to determine the parameter b, which reflects the linear relationship between the two thermocouples. Based on this parameter b, the total flow temperature 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, it solves the problem of poor accuracy of the total temperature probe of the existing thermocouple temperature sensor itself. Second, it solves the problem that the temperature of the root of the thermocouple needs to be provided when measuring with the existing thermocouple total temperature probe in order to correct the thermal conductivity error. Third, it solves the problem that the spacing between the two pairs of the existing combined wire diameter thermocouple is too large, resulting in low spatial resolution. Fourth, it solves the problem that the layout of the existing combined wire diameter thermocouple total temperature probe is unreasonable, and the airflow capacity loss inside the stagnation hood channel is large. Fifth, it solves the problem that the original "L" type total temperature probe has large speed error, thermal conductivity error, and low measurement accuracy.

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

[0015] 1. A high-precision total temperature probe based on a double-filament thermocouple, 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 (1) is chamfered at 45°, two wire lead pipes (7) are opened on the inner side of the square through hole (5), the two thermocouple wires (6) are placed in parallel, tightened and in a "one" shape and pass through the wire lead pipe (7); the probe support rod (2) is provided 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 cover (1) is made of polycarbonate and consists of two cylindrical sections with different diameters, namely the air inlet section (3) and the 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 double-hedged curve or a 30 to 60° arc line, and the length is 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. Two square through holes (5) with a side length of 1 to 4 mm are symmetrically opened on the side of the cylinder of the stagnation cover (1). The front end of the square through hole (5) is 1 to 4 mm away from the entrance of the stagnation cover. Two cylindrical thermocouple wire lead pipes (7) are opened at the rear end of the two square through holes (5) along the main flow direction to lead out the thermocouple wire. The diameter of the pipe is 0.2 to 1 mm, and the distance between the pipe 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 "U" shape. The thermocouple measuring point is located in the center. The distance between the centers of the two measuring points is 0.4 mm to 1.6 mm. The wires are fixed in the wire lead pipe (7) by 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 (9) is provided on the side of the cylinder 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 rear cover is 2 to 15 mm long and the top end of the rear cover along the cylindrical axis is 3 to 8 mm away from the top end of the support rod (2).

[0020] The present invention provides a high-precision total temperature probe based on a double-filament thermocouple, which has the following beneficial effects:

[0021] Beneficial Effect 1: This invention utilizes CFD simulation technology to simulate thermocouple temperature measurements under different operating conditions by varying the stagnation hood temperature, based on known incoming flow conditions. Linear regression analysis determines the linear relationship parameters between the two thermocouples. By leveraging this linear relationship, the invention can correct thermal conductivity errors without requiring advance prediction of the thermocouple root temperatures. This innovative approach significantly simplifies the correction process and improves the measurement accuracy of the total temperature probe.

[0022] Second beneficial effect: The small diameter of the thermocouple used in this invention significantly reduces heat conduction between the thermocouple and the stagnation shield. Furthermore, by designing the measurement junction spacing of the double-wire thermocouple to be very small, this invention achieves extremely high spatial resolution. This design enables the probe to capture even subtler temperature changes, making it suitable for applications with extremely high temperature distribution requirements.

[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 secured and straightened by the wire support rod, forming a "-" shape. 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 ensures the strength of the thermocouple wire, preventing it from bending or breaking 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 fluid dynamics losses and ensure that the fluid forms an ideal stagnation state at the front end of the probe, greatly reducing velocity errors. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure 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-direction 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 with reference to 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 precise definition of the protection scope of the present invention.

[0031] Example 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 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). The present invention is characterized in that: the stagnation cover (1) is composed of a cylinder and a fast convergence curve rotating body, the stagnation cover (1) is chamfered at 45 degrees, two wire lead pipes (7) are opened on the inner side of the square through hole (5), 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 cover (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-hedged 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. Two square through holes (5) with a side length of 1 mm are symmetrically opened on the side of the cylinder of the stagnation cover (1). The front end of the square through hole (5) is 1 mm away from the entrance of the stagnation cover. Two cylindrical wire lead pipes (7) are opened at the rear end of the two square through holes (5) along the main flow direction to lead out the thermocouple wire. 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 "U" shape. The thermocouple measuring point is located in the center, and the distance between the centers of the two measuring points is 0.4 mm. The wires are fixed in the wire lead pipe (7) by an insulating adhesive material.

[0035] 5. The probe support rod (2) is an 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 (9) is provided on the side of the cylinder facing away from the nozzle. The cross section of the probe rear cover is a fan-shaped ring with a central angle of 90°. The rear cover is 4 mm long and the top end of the rear cover along the cylindrical axis is 5 mm away from the top end of the support rod (2).

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

[0037] Through experimental and theoretical analysis, this paper reveals the influence of thermocouple diameter on measurement accuracy in twin-wire thermocouples. In twin-wire thermocouples, 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 has determined the relationship between the temperature measured by 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] Wind tunnel calibration was performed to obtain T1 and T2 values ​​at different incoming flow temperatures. Linear regression analysis determined the parameter b, 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 inferred from the indicated temperatures of the two thermocouple measurement junctions. This method can accurately correct thermal conductivity errors and accurately infer the total outflow temperature even under conditions of low-frequency temperature fluctuations in the incoming flow—that is, when the fluctuation frequency is lower than the response frequency of the thermocouple measurement junctions but higher than the response frequency of the stagnation hood.

Claims

1. A high-precision total temperature probe based on a double-filament thermocouple, 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 rear cover (9), characterized in that: The stagnation cover (1) is composed of a cylinder and a fast convergence curve rotating body. The stagnation cover (1) is chamfered at 45 degrees. Two thermocouple wires (6) are opened inside the square through hole (5). Two thermocouple wires (6) are placed in parallel, tightened and in a "one" shape and pass through the thermocouple wire lead pipes (7). The probe support rod (2) is opened 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 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 double-negative curve or a 30 to 60° arc line, and the length is 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 (5) with a side length of 1 to 4 mm are symmetrically opened on the side of the cylindrical body of the stagnation cover (1). The front end of the square through hole (5) is 1 to 4 mm away from the entrance of the stagnation cover (1). Two cylindrical thermocouple wire lead pipes (7) are opened along the main flow direction at the rear end of the two square through holes (5) to lead out the thermocouple wire. The diameter of the pipe is 0.2 to 1 mm, and the distance between the pipe 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. They are placed in parallel, stretched and formed into a "single" shape. The thermocouple measuring junction is located in the center, and the distance between the centers of the two measuring junctions is 0.4 mm to 1.6 mm. The wires are fixed in the wire lead pipe (7) by 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 (9) 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.

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