Dynamic temperature probe based on double-wire thermocouple

Abstract

The invention relates to the technical field of dynamic temperature testing, in particular to a dynamic temperature probe based on a double-filament thermocouple, which comprises a thermocouple wire support rod, a probe support rod, a thermocouple measuring contact and a thermocouple wire, the thermocouple wire support rod is made into a wedge shape and supports the thermocouple wire, the double-filament thermocouple is arranged at the front edge of the support rod and is parallel to incoming flow, and the probe support rod is connected with the thermocouple measuring contact. The thermocouple wire is straightened through the thermocouple wire supporting rod and is in a linear shape, and the thermocouple measuring contact is located in the middle. The two thermocouples are arranged in parallel in the airflow direction, and it is ensured that the same temperature point is measured. The exposed thermocouple wire and the thermocouple wire supporting rod form an n shape which can ensure that the thermocouple is in full contact with a flow field, and the thermocouple wire is convenient to replace. The invention provides a novel dynamic error correction method which is a temperature measurement method based on a second-order compensation strategy, and compensation parameters can be adjusted according to actual temperature dynamic changes. Through experiments and theoretical analysis, in combination with computational fluid dynamics (CFD) simulation, key information can be directly extracted from the measurement data of the thermocouple, so that the dynamic response of the thermocouple is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of aviation engine temperature testing, and in particular relates to a double-wire thermocouple dynamic temperature probe. Background Art

[0002] When an aircraft engine is installed and running, dynamic temperature distortion may occur at the fan / compressor inlet due to environmental factors. For example, when the aircraft inhales the exhaust gas discharged by the missile during high-maneuvering flight, launches a missile, inhales the engine return exhaust gas and water vapor during ejection from the deck of a carrier-based aircraft, and the anti-icing device in the inlet is heated, the engine inlet dynamic temperature distortion will occur. When this dynamic temperature distortion passes through the inlet, the increase in air flow velocity may cause the boundary layer separation at the large curvature bend, disrupting the uniformity of the inlet air flow field; for a turboshaft engine, the air flow must also pass through a particle separator to produce pre-swirl diffusion. After the dynamic temperature distortion that has undergone the above development reaches the inlet of the fan / compressor, it will cause changes in the working environment and load of the fan compressor. Dynamic temperature distortion will not only affect the surge boundary of the engine (in severe cases, it may even directly cause surge), but also affect the common working line of the engine, which has an unignorable impact on the aerodynamic stability of the engine. In order to accurately understand the impact of engine inlet dynamic temperature distortion on fan / compressor aerodynamic stability, it is necessary to carry out relevant compression system inlet dynamic temperature distortion tests to simulate the changes in fan / compressor characteristics under various dynamic temperature distortion conditions. This requires accurate measurement of the compression system inlet dynamic temperature distortion (mainly temperature rise rate) and its development in subsequent compressors of various levels, so as to provide support for accurately grasping the aerodynamic stability of the compression system under various distortion conditions.

[0003] At present, for the dynamic temperature distortion of imports, various domestic research institutions have carried out theoretical analysis and research on experimental testing technology with small inertia thermocouples, combined wire diameter thermocouples and hot wire / hot film thermometers as the main channels. However, in terms of frequency response, temperature measurement accuracy, temperature field test method, data processing method, dynamic temperature calibration method, etc., there are problems that cannot meet the model requirements, and there is also a large gap with the advanced level abroad. There are four main defects: First, the response speed of the thermocouple sensor is closely related to the diameter of the wire. Although the extremely fine wire can provide a fast response speed to meet the needs of high-frequency measurement, the material strength of this extremely fine wire limits its application in harsh test environments. Too thin wires are prone to physical damage or performance degradation when facing high temperature gradients, high-speed airflows and other harsh conditions, so it is difficult to achieve the required high-frequency response characteristics. Second, in the prior art, the temperature compensation scheme of thermocouples usually relies on the first-order compensation method. Although this method is simple, it often leads to large errors when dealing with complex dynamic temperature changes. Third, in the prior art, in the design of traditional double-wire thermocouples, the distance between the two wires is usually large, which leads to low spatial resolution when measuring dynamic temperature changes. When dealing with measurement tasks of complex dynamic temperature fields such as aircraft engines, this poor spatial resolution will greatly reduce the accuracy of the test. In addition, the larger double-wire spacing will affect the accuracy of the compensation scheme. Fourth, the traditional total temperature probe thermocouple wire layout is parallel to the incoming flow direction. This layout can provide more 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 bent, which greatly affects the response frequency of the thermocouple.

[0004] Therefore, there is an urgent need to develop a high-precision, stable operation, small spatial resolution and fan / compressor inlet dynamic temperature distortion test probe that can simultaneously measure the dynamic temperature distortion, so as to achieve accurate measurement of the dynamic temperature distortion and provide direct data support for high-performance design of fans / compressors at all levels. Summary of the invention

[0005] The present invention discloses a dynamic temperature probe based on a double thermocouple. The probe is composed of a thermocouple wire support rod, a probe support rod, a thermocouple measuring junction and a thermocouple wire. In order to reduce the vortex generated by the thermocouple wire support rod in the flow field, which may interfere with the temperature measurement of the thermocouple measuring junction, the thermocouple wire support rod is made into a wedge shape. The thermocouple wire support rod supports the thermocouple wire. The double-wire thermocouple is placed at the front edge of the support rod, parallel to the incoming flow, to reduce the influence of the vortex on the measuring junction and improve the response frequency of the temperature probe. The thermocouple wire is straightened by the thermocouple wire support rod to form an "I" shape, and the thermocouple measuring junction is located in the middle. Facing the airflow direction, two thermocouples are placed in parallel to ensure the measurement of the same temperature point. The exposed thermocouple wire and the thermocouple wire support rod form an "П" shape, which can ensure that the thermocouple is in full contact with the flow field and is convenient for replacing the thermocouple wire.

[0006] Compared with the traditional thermocouple dynamic temperature probe, the present invention proposes a new type of double-wire thermocouple dynamic temperature probe. Through in-depth research on the dynamic relationship between different wire diameters, a temperature measurement method based on a second-order compensation strategy is proposed, which can adjust the compensation parameters according to the actual temperature dynamic changes. This design enables the thermocouple wire to maintain strength and rigidity under the impact of high-speed airflow and is not prone to bending and deformation. Through the compensation strategy, the same dynamic response as the ideal thin-wire thermocouple is achieved. The second-order transfer function relationship of the thermocouple is as follows:

[0007]

[0008] The second-order transfer function is considered to be the sum of two first-order transfer functions, which are related to the thermocouple measurement junction and the thermocouple wire respectively. The specific expression is:

[0009]

[0010] H(z)=m1H1(z)+m2H2(z)

[0011] Four parameters that affect the dynamic characteristics of thermocouples are obtained, namely m1, m2, τ1, and τ2. The present invention systematically analyzes the four key parameters that affect the dynamic characteristics of thermocouples through CFD simulation technology: m1, m2, τ1, and τ2. After simulation analysis under a variety of different working conditions, it is finally concluded that thermocouples with different wire diameters remain unchanged in the values ​​of m1 and m2, and the ratio of τ1 and τ2 is closely related to the wire diameter of the thermocouple. By averaging the m1 and m2 values ​​of two thicker thermocouples, we can approximately estimate the m1 and m2 values ​​of the thinner thermocouple. This method not only simplifies the actual measurement process, but also can predict the performance of thin-wire thermocouples without directly measuring them. Furthermore, by analyzing the ratio of τ1 and τ2 of two thermocouples, we can determine the τ1 and τ2 parameters of the thin-wire thermocouple, thereby accurately obtaining its transfer function.

[0012] The present invention provides a double-wire thermocouple dynamic temperature probe that can measure the dynamic temperature distortion of the fan / compressor inlet. The technical problems to be solved are: first, the contradiction between the high response frequency and high strength of the existing small inertia thermocouples is solved. Second, the temperature measurement method by introducing the second-order compensation strategy solves the significant deviation between the rapid change of the existing temperature field and the prediction of the first-order model, which greatly improves the accuracy and reliability of the overall measurement. Third, the problems of large size, large interference to the flow field, and low spatial resolution caused by the large spacing between the combined wire diameter thermocouple pairs are solved. Fourth, the problem that when the existing dynamic temperature probe measures high Mach airflow, the thermocouple wire is difficult to maintain strength and rigidity under the impact of high-speed airflow and is prone to bending and deformation is solved.

[0013] The technical solution of the present invention is:

[0014] 1. A dynamic temperature probe based on a double thermocouple, comprising a thermocouple support rod (1), a probe support rod (2), a corundum tube (3), a thick thermocouple measuring junction (4), a thin thermocouple measuring junction (5), a thick thermocouple wire (6), and a thin thermocouple wire (7), characterized in that: the thermocouple support rod (1) is connected to the probe support rod (2), two "G"-shaped through holes are opened at the front edge of the thermocouple support rod (1) and penetrate the probe support rod (2), and the truncated cone-shaped probe support rod (2) is reduced The small support rod interferes with the flow field. The corundum tube (3) is fixed in the "Г"-shaped through hole of the thermocouple support rod (1) and the probe support rod (2) and is used for heat insulation of the thick thermocouple wire (6) and the thin thermocouple wire (7). The thick thermocouple wire (6) and the thin thermocouple wire (7) are led out through the inner hole of the corundum tube (3). The exposed thermocouple wire at the head of the double-wire thermocouple probe is tightened and in a "-" shape. The thick thermocouple measuring junction (4) and the thin thermocouple measuring junction (5) are located in the middle of the exposed thermocouple wire.

[0015] 2. The even-wire support rod (1) is made of a high-temperature resistant alloy material. The even-wire support rod (1) is a wedge-shaped support rod, and the interior is a hollow "Г"-shaped cylindrical support rod, which is composed of a semi-cylinder and a triangular prism. The diameter of the semi-cylinder is 2 to 4 mm, and the height is 8 to 20 mm. The side length of the triangular prism is 4 to 8 mm. The diameter of the hollow "Г"-shaped cylinder is 1 to 2 mm, and the height is 6 to 15 mm. The even-wire support rod (1) adopts an elbow design to avoid the even-wire from breaking and prolong the service life of the even-wire. The distance between the central axis of the even-wire support rod (1) and the central axis of the probe support rod (2) is 4 to 6 mm.

[0016] 3. The shape of the probe support rod (2) is a frustum, which helps to reduce the disturbance of the probe support rod in the flow field. The frustum is designed to be small at the top and large at the bottom. The diameter of the upper circle is 6 to 12 mm, and the diameter of the lower circle is 10 to 20 mm. A through hole with a diameter of 1 to 2 mm is opened at the fixed position of the even-wire support rod (1).

[0017] 4. The corundum tube (3) has an F-shaped through hole for passing the thick thermocouple wire (6) and the thin thermocouple wire (7), the diameter of which is 0.2 mm to 0.5 mm. The corundum tube (3) is fixed to the wire support rod (1) and the probe support rod (2) by means of a heat-insulating adhesive material.

[0018] 5. The thick thermocouple wire (6) and the thin thermocouple wire (7) are passed through and fixed in the corundum tube (3) and are straightened by the wire support rod (1). The exposed parts of the thick thermocouple wire (6) and the thin thermocouple wire (7) are parallel to the upper surface of the head of the probe support rod (2) and are in the shape of "-". The thick thermocouple measuring junction (4) and the thin thermocouple measuring junction (5) are located in the middle of the exposed thermocouple wire and face the incoming flow direction. The exposed parts of the thick thermocouple wire (6) and the thin thermocouple wire (7) are in the shape of "P" with the two wire support rods respectively. The diameter of the thick thermocouple wire (6) is 50 microns to 100 microns, and the diameter of the thin thermocouple wire (7) is 25 microns to 50 microns.

[0019] The present invention provides a dynamic temperature probe based on a double-wire thermocouple, which has the following beneficial effects:

[0020] Beneficial effect 1: After steady-state and dynamic calibration in a calibration wind tunnel, the present invention uses two thicker thermocouples through compensation technology to obtain the rapid response of thinner thermocouples, and can accurately capture rapidly changing temperature fields. These wires are far superior to traditional small-inertia thermocouples in physical strength and stability, and provide a reliable and accurate means for dynamic temperature distortion testing of fan / compressor inlets in practical applications.

[0021] Beneficial effect 2: By analyzing and simulating the behavior of different wire diameters under dynamic temperature changes, the present invention introduces an accurate temperature measurement method based on a second-order compensation strategy, improves the traditional first-order compensation scheme, optimizes the compensation method, and makes the compensation result more accurate. Through this strategy, we can effectively compensate two thicker thermocouple wires.

[0022] Beneficial effect three: The present invention achieves extremely high spatial resolution by designing the distance between the measuring junctions 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 4: The thermocouple wire of the present invention is fixed and straightened by the wire support rod to form 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. The support structure can ensure the strength of the thermocouple wire, and it is not easy to bend or break in the flow field.

[0024] Beneficial Effect 5: The probe head of the present invention has a simple and compact structure, is "I" shaped, and has a small size. The double-wire parallel hot wires are arranged vertically without crossing or affecting each other. It is also suitable for measurement between narrow fan / compressor and turbine stages.

[0025] Beneficial effect six: The bending part of the thermocouple support rod of the present invention adopts an arc design, which effectively protects the thermocouple wire and makes it difficult to break. At the same time, the thermocouple support rod is designed to be a wedge shape, which greatly reduces the interference with the flow field.

[0026] Beneficial effect seven: The thermocouple wire of the present invention passes through the corundum tube, which can play an insulating and heat-insulating role for the thermocouple wire, and is convenient for replacing the wire. The thermocouple can be different types of thermocouples such as K type, J type, T type, etc. The double wire diameter ratio can be a combination of different thicknesses such as 1.5, 2, 2.5, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of a dynamic temperature probe based on a double-wire thermocouple in an embodiment of the present invention.

[0028] Figure 2 yes Figure 1 Top view of the .

[0029] Among them: 1-wire support rod, 2-probe support rod, 3-corundum tube, 4-thick thermocouple measuring junction, 5-thin thermocouple measuring junction, 6-thick thermocouple wire, 7-thin thermocouple wire. 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] like Figures 1-2 The invention shows a dynamic temperature probe based on a double-wire thermocouple. The double-wire support rod (1) is connected to the probe support rod (2). Two "G"-shaped through holes are opened at the front edge of the double-wire support rod (1) and penetrate the probe support rod (2). The truncated cone-shaped probe support rod (2) is used to reduce the interference of the support rod on the flow field. The corundum tube (3) is fixed in the "G"-shaped through holes of the double-wire support rod (1) and the probe support rod (2) and is used for heat insulation of the thick thermocouple wire (6) and the thin thermocouple wire (7). The thick thermocouple wire (6) and the thin thermocouple wire (7) are led out through the inner hole of the corundum tube (3). The exposed wire at the head of the double-wire thermocouple probe is tightened and in a "-" shape. The thick thermocouple measurement junction (4) and the thin thermocouple measurement junction (5) are located in the middle of the exposed wire.

[0032] The even-wire support rod (1) is made of a high-temperature resistant alloy material. The even-wire support rod (1) is a wedge-shaped support rod, and the interior is a hollow "G"-shaped cylindrical support rod, which is composed of a semi-cylinder and a triangular prism. The semi-cylinder has a diameter of 3 mm and a height of 10 mm. The side length of the triangular prism is 6 mm. The hollow "G"-shaped cylinder has a diameter of 2 mm and a height of 8 mm. The even-wire support rod (1) adopts an elbow design to avoid the even-wire from breaking and prolong the service life of the even-wire. The distance between the central axis of the even-wire support rod (1) and the central axis of the probe support rod (2) is 2 mm.

[0033] The shape of the probe support rod (2) is a frustum, which helps to reduce the disturbance of the probe support rod in the flow field. The frustum is designed to be small at the top and large at the bottom, with an upper circle diameter of 8 mm and a lower circle diameter of 10 mm. A 2 mm through hole is opened at the fixed position of the even-wire support rod (1).

[0034] 4. The corundum tube (3) has an F-shaped through hole for passing the thick thermocouple wire (6) and the thin thermocouple wire (7), and the diameter of the through hole is 0.5 mm. The corundum tube (3) is fixed to the wire support rod (1) and the probe support rod (2) by means of a heat-insulating adhesive material.

[0035] 5. The thick thermocouple wire (6) and the thin thermocouple wire (7) are passed through and fixed in the corundum tube (3) and are straightened by the wire support rod (1). The exposed parts of the thick thermocouple wire (6) and the thin thermocouple wire (7) are parallel to the upper surface of the head of the probe support rod (2) and are in the shape of "-". The thick thermocouple measuring junction (4) and the thin thermocouple measuring junction (5) are located in the middle of the exposed thermocouple wire and face the incoming flow direction. The exposed parts of the thick thermocouple wire (6) and the thin thermocouple wire (7) are in the shape of "P" with the two wire support rods. The diameter of the thick thermocouple wire (6) is 100 microns, and the diameter of the thin thermocouple wire (7) is 50 microns.

[0036] This invention proposes a new type of double-wire thermocouple dynamic temperature probe. Through in-depth research on the dynamic relationship between different wire diameters, a temperature measurement method based on a second-order compensation strategy is proposed, which can adjust the compensation parameters according to the actual temperature dynamic changes. This design enables the thermocouple wire to maintain strength and rigidity under the impact of high-speed airflow and is not prone to bending and deformation. Through the compensation strategy, the same dynamic response as the ideal thin-wire thermocouple is achieved. The second-order transfer function relationship of the thermocouple is as follows:

[0037]

[0038] The second-order transfer function is considered to be the sum of two first-order transfer functions, which are related to the thermocouple measurement junction and the thermocouple wire respectively. The specific expression is:

[0039]

[0040] The analysis shows that the values ​​of m1 and m2 remain unchanged for thermocouples with different wire diameters, and the relationship between τ1 and Reynolds number satisfies the formula:

[0041] log(Δ)=a0+a1 log(Re),Δ=(m1 / τ1+m2 / τ2)

[0042] The relationship between τ2 and Reynolds number satisfies the formula:

[0043] log(τ2)=β0+β1log(Re)

[0044] Under the same inlet flow conditions, the ratio of τ2 between different wire diameters is a constant. The τ2 of the thinner thermocouple can be inferred from the ratio of τ2 between the two thicker thermocouples, and the τ1 value of the thinner thermocouple can be obtained through the above relationship. By processing the m1 and m2 values ​​of the two thicker thermocouples, the m1 and m2 values ​​of the thinner thermocouple can be approximately estimated, and the second-order transfer function of the thinner thermocouple can be obtained.

Claims

1. A dynamic temperature probe based on dual thermocouples, comprising a thermocouple wire support rod (1), a probe support rod (2), a corundum tube (3), a thick thermocouple measuring junction (4), a thin thermocouple measuring junction (5), a thick thermocouple wire (6), and a thin thermocouple wire (7), characterized in that: The wire support rod (1) is connected to the probe support rod (2). Two "G"-shaped through holes are opened at the front edge of the wire support rod (1) and penetrate the probe support rod (2). The truncated cone-shaped probe support rod (2) is used to reduce the interference of the support rod on the flow field. The corundum tube (3) is fixed in the "G"-shaped through holes of the wire support rod (1) and the probe support rod (2) and is used for heat insulation of the thick thermocouple wire (6) and the thin thermocouple wire (7). The thick thermocouple wire (6) and the thin thermocouple wire (7) are led out through the inner hole of the corundum tube (3). The exposed wires at the head of the double-wire thermocouple probe are tightened and in a "-" shape. The thick thermocouple measurement junction (4) and the thin thermocouple measurement junction (5) are located in the middle of the exposed wires. The even-wire support rod (1) is made of a high-temperature resistant alloy material. The even-wire support rod (1) is a wedge-shaped support rod, and the interior is a hollow "G"-shaped cylindrical support rod, which is composed of a semi-cylinder and a triangular prism. The semi-cylinder has a diameter of 2 to 4 mm and a height of 8 to 20 mm. The side length of the triangular prism is 4 to 8 mm. The hollow "G"-shaped cylinder has a diameter of 1 to 2 mm and a height of 6 to 15 mm. The even-wire support rod (1) adopts an elbow design to avoid the even-wire from breaking and prolong the service life of the even-wire. The distance between the central axis of the even-wire support rod (1) and the central axis of the probe support rod (2) is 4 to 6 mm. The probe support rod (2) is in the shape of a truncated cone, which helps to reduce the disturbance of the probe support rod in the flow field. The truncated cone is designed to be small at the top and large at the bottom, with an upper circle diameter of 6 to 12 mm and a lower circle diameter of 10 to 20 mm. A through hole with a diameter of 1 to 2 mm is opened at the fixed position of the even-wire support rod (1); The corundum tube (3) has an "F"-shaped through hole for passing a thick thermocouple wire (6) and a thin thermocouple wire (7), the diameter of which is 0.2 mm to 0.5 mm. The corundum tube (3) is fixed to the wire support rod (1) and the probe support rod (2) by means of a heat-insulating adhesive material; The thick thermocouple wire (6) and the thin thermocouple wire (7) are passed through and fixed in the corundum tube (3) and are straightened by the wire support rod (1). The exposed parts of the thick thermocouple wire (6) and the thin thermocouple wire (7) are parallel to the upper surface of the head of the probe support rod (2) and are in a "-" shape. The thick thermocouple measuring point (4) and the thin thermocouple measuring point (5) are located in the middle of the exposed thermocouple wire and face the incoming flow direction. The exposed parts of the thick thermocouple wire (6) and the thin thermocouple wire (7) are in a "P" shape with the two wire support rods. The diameter of the thick thermocouple wire (6) is 50 microns to 100 microns, and the diameter of the thin thermocouple wire (7) is 25 microns to 50 microns. The present invention proposes a temperature measurement correction method based on a double-wire thermocouple. The dynamic characteristics of the thermocouple can be described by a second-order transfer function, which is expressed as follows: This function can be considered as the superposition of two first-order transfer functions, which are related to the thermocouple measurement junction and the thermocouple wire respectively. Its specific expression is H(z)=m1H1(z)+m2H2(z) The analysis shows that the values ​​of m1 and m2 remain unchanged for thermocouples with different wire diameters, and the relationship between τ1 and Reynolds number satisfies the formula: log(Δ)=a0+a1log(Re),Δ=(m1 / τ1+m2 / τ2) The relationship between τ2 and Reynolds number satisfies the formula: log(τ2)=β0+β1log(Re) Under the same inlet flow conditions, the ratio of τ2 between different wire diameters is a constant. The τ2 of the thinner thermocouple can be inferred from the ratio of τ2 between the two thicker thermocouples, and the τ1 value of the thinner thermocouple can be obtained through the above relationship. By processing the m1 and m2 values ​​of the two thicker thermocouples, the m1 and m2 values ​​of the thinner thermocouple can be approximately estimated, and the second-order transfer function of the thinner thermocouple can be obtained.

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