A method for detecting a dynamic blade tip clearance of an aero-engine

Abstract

The application discloses a kind of detection methods of aero-engine dynamic screen blade tip clearance.It is first improved to traditional plane rectangular sensor, designs curved surface rectangular capacitive sensor, and installs the curved surface rectangular capacitive sensor designed on casing, then the capacitance value when all screen blade is measured by curved surface rectangular capacitive sensor to face curved surface rectangular capacitive sensor, then consider additional capacitance generated except screen blade tip position, and relative dielectric constant and temperature and pressure are nonlinear relationship under high temperature and high pressure environment in aero-engine, establish the relationship between tip clearance and the capacitance value measured by curved surface rectangular capacitive sensor when all screen blade is to face curved surface rectangular capacitive sensor, obtain the tip clearance value under dynamic condition.The application can obtain the tip clearance value under dynamic condition with higher accuracy, provide more accurate judgment basis for subsequent tip clearance adjustment, and guarantee the safe operation of aero-engine.

Description

Technical Field

[0001] This invention belongs to the field of aero-engine monitoring technology, specifically relating to a method for detecting the tip clearance of dynamic serrated blades in aero-engines. Background Technology

[0002] The blade tip clearance of an aero-engine (the radial clearance between the blade tip and the casing) has a crucial impact on the engine's performance, efficiency, and reliability. A suitable blade tip clearance can improve engine efficiency, reduce fuel consumption, reduce wear between the blades and the casing, and extend the engine's service life. However, during engine operation, the blade tip clearance changes dynamically due to factors such as blade vibration, thermal expansion, and casing deformation and wear. If the blade tip clearance cannot be maintained within a suitable range, it is necessary to adjust it in a timely manner to ensure the safe operation of the aero-engine. Currently, among non-contact measurement methods for blade tip clearance, capacitance measurement is widely used due to its advantages such as low cost and wide applicability. However, existing capacitance sensors have some problems when measuring the dynamic blade tip clearance of aero-engines. The main problem is that the detection surface of traditional capacitance sensors is a plane, which is different from the arc shape of the inner wall of the casing. This leads to measurement errors caused by the unequal gap between the detection surface of the capacitance sensor and the blade tip, resulting in inaccurate measurement results and thus low accuracy in calculating blade tip clearance. Furthermore, since aero-engines operate under high temperature and high pressure conditions, the relative permittivity may have a non-linear relationship with temperature and pressure. However, the relative permittivity used in existing technologies for calculating blade tip clearance has a linear relationship with temperature and pressure, further reducing the accuracy of blade tip clearance calculation. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the existing technology and propose a method for detecting the tip clearance of dynamic serrated blades in aero engines.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] This invention discloses a method for detecting the tip clearance of dynamic serrated blades in an aero-engine, as detailed below:

[0006] Step 1: Improve the shape of the core electrode detection surface to an arc shape, a rectangular projection, an arc radius equal to the arc radius of the inner wall of the casing, and an arc chord length not greater than the arc chord length of the blade tip of the comb tooth; install the curved rectangular capacitive sensor on the inner wall of the aero-engine casing, and arrange the core electrode detection surface of the curved rectangular capacitive sensor concentrically with the inner wall of the casing.

[0007] Step 2: When the aero-engine is operating, the rotating shaft and the toothed blades corresponding to the curved rectangular capacitive sensor sweep across the sensor, generating capacitance between them and the core of the sensor. The curved rectangular capacitive sensor converts the detected capacitance value into a signal value output. By using the relationship between the peak value of the signal output by the curved rectangular capacitive sensor and the detected capacitance value, the capacitance value detected by the curved rectangular capacitive sensor when all the toothed blades are facing it is calculated.

[0008] Step 3: Consider the capacitance generated between the curved rectangular capacitive sensor and the tip of the toothed blade, as well as the additional capacitance generated between the excess portion of the curved rectangular capacitive sensor (wider than the toothed blade) and the rotation axis. Establish the relationship between the tip gap and the capacitance value measured by the curved rectangular capacitive sensor when all the toothed blades are facing the sensor. Combine this with the capacitance value detected by the curved rectangular capacitive sensor when all the toothed blades are facing the sensor obtained in Step 2 to obtain the tip gap value under dynamic conditions.

[0009] Preferably, the curved rectangular capacitive sensor converts the detected capacitance value into a swing voltage signal. When all the toothed blades are facing the curved rectangular capacitive sensor, the capacitance value detected by the curved rectangular capacitive sensor is:

[0010]

[0011] In the formula, V1 is the peak value of the swing voltage output by the curved rectangular capacitive sensor, and m is the amplification factor for converting the capacitance value into the swing voltage signal.

[0012] Preferably, in step three, when all the comb blades are aligned with the curved rectangular capacitive sensor, the relationship between the capacitance measured by the curved rectangular capacitive sensor and the blade tip gap is expressed as follows:

[0013]

[0014] In the formula, L is the arc length of the core electrode of the curved rectangular capacitive sensor, ε is the absolute dielectric constant of air between the serrated blade and the curved rectangular capacitive sensor, a is the axial movement, n is the width of the serrated blade, d is the blade tip gap, d1 is the distance between the core electrode of the curved rectangular capacitive sensor and the rotation axis, and W is the width of the detection surface of the core electrode of the curved rectangular capacitive sensor.

[0015] More preferably, the absolute air permittivity ε between the serrated blades and the curved rectangular capacitive sensor is...

[0016] ε=ε r ×ε0

[0017] In the formula, ε r ε is the relative permittivity, and ε0 is the absolute permittivity of vacuum;

[0018] In aero-engines, the relative permittivity exhibits a non-linear relationship with temperature and pressure, specifically:

[0019]

[0020] In the formula, α and β are both coefficients;

[0021] Temperature T and pressure P are measured by temperature sensors and pressure sensors installed on the inner wall of the aero-engine casing.

[0022] More preferably, the formula for calculating the tip clearance under dynamic conditions is:

[0023]

[0024] The present invention has the following beneficial effects:

[0025] This invention improves the detection accuracy of capacitive sensors by modifying their shape. It also considers the additional capacitance generated beyond that at the blade tip, and the non-linear relationship between the relative permittivity and temperature and pressure under the high temperature and high pressure environment inside aero-engines. This allows for the acquisition of highly accurate blade tip clearance values ​​under dynamic conditions. Specifically, this invention designs a curved rectangular capacitive sensor. The core detection surface of the curved rectangular capacitive sensor is arc-shaped, with a rectangular projection. The radius of the arc is equal to the radius of the arc on the inner wall of the casing, and the chord length of the arc is no greater than the chord length of the arc at the blade tip. During installation, the core detection surface of the curved rectangular capacitive sensor is concentrically arranged with the inner wall of the casing, ensuring a match between the core detection surface of the curved rectangular capacitive sensor and the inner wall of the casing and the blade tip. This avoids measurement errors caused by unequal clearances between the core detection surface of a planar capacitive sensor and the blade tip, thereby improving accuracy. This invention improves measurement accuracy, and the rectangular design effectively reduces the impact of axial movement, further enhancing measurement precision. Furthermore, it considers the additional capacitance generated between the excess portion of the curved rectangular capacitive sensor core electrode detection surface (wider than the toothed blade) and the rotation axis, thereby improving the accuracy of tip clearance calculation. Additionally, it addresses the nonlinear relationship between the relative permittivity and temperature and pressure under the high-temperature and high-pressure environment inside aero-engines, establishing a nonlinear relationship between the relative permittivity and temperature and pressure, further improving the accuracy of tip clearance calculation. This invention can obtain highly accurate tip clearance values ​​under dynamic conditions, providing a more accurate basis for subsequent tip clearance adjustments and ensuring the safe operation of aero-engines. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the curved rectangular capacitive sensor in this invention;

[0027] Figure 2 This is a schematic diagram of the comb blades sweeping across the curved rectangular capacitive sensor in this invention;

[0028] Figure 3 for Figure 2 The front view;

[0029] Figure 4 for Figure 3 Enlarged view of section A;

[0030] Figure 5 This is a schematic diagram of the axial movement of the comb blades. Detailed Implementation

[0031] The present invention will now be further described with reference to the accompanying drawings.

[0032] This invention discloses a method for detecting the tip clearance of dynamic serrated blades in an aero-engine, as detailed below:

[0033] Step 1, such as Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, a curved rectangular capacitive sensor is designed. The core detection surface of the curved rectangular capacitive sensor is arc-shaped, with a rectangular projection. The radius of the arc is equal to the radius of the arc on the inner wall of the aero-engine casing, and the chord length b1 of the arc is no greater than the chord length b of the arc at the tip of the serrated blade. A temperature sensor, a pressure sensor, and the curved rectangular capacitive sensor are installed on the inner wall of the casing, with the core detection surface of the curved rectangular capacitive sensor arranged concentrically with the inner wall of the casing. Compared with the traditional planar rectangular capacitive sensor, the core detection surface of the curved rectangular capacitive sensor matches the inner wall of the casing. Furthermore, because the arc at the tip of the serrated blade is concentric with the arc on the inner wall of the casing, the core detection surface of the curved rectangular capacitive sensor can match the tip of the serrated blade. This avoids the measurement error caused by the unequal gap between the core detection surface of the traditional planar capacitive sensor and the tip of the serrated blade, thus improving measurement accuracy. The temperature sensor and pressure sensor are used to detect the temperature T and pressure P between the curved rectangular capacitive sensor and the serrated blade.

[0034] Step 2: The core electrode of the curved rectangular capacitive sensor, the corresponding parts of the rotating shaft and the toothed blades constitute the two plates of the capacitor. That is, the corresponding parts of the rotating shaft and the toothed blades form one plate. When the aero-engine operates, the rotating shaft and the toothed blades corresponding to the curved rectangular capacitive sensor continuously sweep across the sensor at a preset speed, generating capacitance between them and the core electrode. The curved rectangular capacitive sensor is an amplitude-modulated capacitive sensor. The detected capacitance value is converted into a swing voltage signal V with peaks and valleys through a conditioning circuit. The relationship between the swing voltage signal V output by the curved rectangular capacitive sensor and the detected capacitance value C is as follows:

[0035] V = mC

[0036] In the formula, m is the amplification factor of the conditioning circuit, which is obtained through preliminary experiments;

[0037] When all the toothed blades are aligned with the curved rectangular capacitive sensor, the swing voltage signal V output by the sensor reaches its peak value V1 (because the distance from the sensor core to the tip of the toothed blade is minimal). Therefore, the capacitance value C1 detected by the sensor when all the toothed blades are aligned with it is...

[0038]

[0039] Step 3: Referring to the expression relating the capacitance value to the blade tip gap measured by a traditional planar rectangular sensor, the expression relating the capacitance value to the blade tip gap measured by a curved rectangular capacitive sensor is as follows:

[0040]

[0041] In the formula, L is the arc length of the core electrode of the curved rectangular capacitive sensor, ε is the absolute dielectric constant of air between the grating blade and the curved rectangular capacitive sensor, a is the axial movement, n is the width of the grating blade, and d is the distance from the core electrode of the curved rectangular capacitive sensor to the tip of the grating blade, i.e., the tip gap.

[0042] Among them, the expression for the relationship between capacitance and tip clearance measured by a traditional planar rectangular capacitance sensor only considers the influence of axial movement on capacitance, such as... Figure 5As shown, the dashed rectangles on both sides represent the positions of the ferrule blades after axial displacement 'a' to both sides, while the solid rectangles represent the positions where the ferrule blades have not undergone axial displacement. However, this calculation does not consider the additional capacitance generated by the excess portion of the core electrode detection surface wider than the ferrule blade and the rotation axis, resulting in inaccurate tip clearance calculations. Therefore, by introducing the additional capacitance generated by the excess portion of the core electrode detection surface wider than the ferrule blade and the rotation axis of the curved rectangular capacitive sensor, a corrected expression is obtained for the relationship between the capacitance measured by the curved rectangular capacitive sensor and the tip clearance when all the ferrule blades are aligned with the sensor.

[0043]

[0044] In the formula, d1 is the distance between the core electrode of the curved rectangular capacitive sensor and the rotation axis, measured in a static state; W is the width of the detection surface of the core electrode of the curved rectangular capacitive sensor; n is the width of the sieve blade; and Wn is the length of the curved rectangular capacitive sensor that is wider than the sieve blade. This refers to the capacitance generated between the curved rectangular capacitive sensor and the tip of the comb blade. This refers to the additional capacitance generated between the excess portion of the curved rectangular capacitive sensor (wider than the toothed blade) and the rotating shaft.

[0045] The absolute dielectric constant ε of the air between the serrated blades and the curved rectangular capacitive sensor is

[0046] ε=ε r ×ε0(1.3)

[0047] In the formula, ε r Let ε be the relative permittivity, and ε0 be the absolute permittivity of vacuum, and ε0 = 8.85 × 10⁻⁶. -12 F / m.

[0048] Although existing relative permittivity models take into account the effects of temperature and pressure, approximating the relationship between the relative permittivity and temperature T and pressure P as a linear one is...

[0049]

[0050] In the formula, α is a coefficient;

[0051] Under the high temperature and high pressure environment inside an aero-engine, the relative permittivity exhibits a nonlinear relationship with temperature and pressure. Therefore, the existing formula for the relationship between the relative permittivity and temperature and pressure needs to be modified.

[0052]

[0053] In the formula, β is also a coefficient. The values ​​of α and β can be obtained through preliminary experiments. In this embodiment, α = 0.000537 and β = 1.2 × 10⁻⁶. -7 ;

[0054] Combining equations (1.1), (1.2), (1.3), and (1.4), the formula for calculating the tip clearance under dynamic conditions is obtained as follows:

[0055]

[0056] Then, the tip clearance value under dynamic conditions is obtained through calculation.

[0057] Furthermore, if the deviation between the blade tip clearance d under dynamic conditions and the blade tip clearance d0 measured under static conditions is within a preset range, then no adjustment is made to the blade tip clearance; otherwise, the blade tip clearance is adjusted. In this embodiment, the preset range of deviation is -0.25mm.

Claims

1. A method for detecting the tip clearance of dynamic serrated blades in an aero-engine, characterized in that: Specifically as follows: Step 1: Design a curved rectangular capacitive sensor with an arc-shaped core detection surface, a rectangular projection, an arc radius equal to the arc radius of the inner wall of the casing, and an arc chord length no greater than the arc chord length of the tip of the comb-tooth blade; install the curved rectangular capacitive sensor on the inner wall of the aero-engine casing, with the core detection surface of the curved rectangular capacitive sensor arranged concentrically with the inner wall of the casing; Step 2: When the aero-engine is running, the rotating shaft and the toothed blades corresponding to the curved rectangular capacitive sensor sweep across the sensor, generating capacitance between them and the core of the sensor. The curved rectangular capacitive sensor converts the detected capacitance value into a signal value output. By using the relationship between the peak value of the signal output by the curved rectangular capacitive sensor and the detected capacitance value, the capacitance value detected by the curved rectangular capacitive sensor when all the toothed blades are facing it is calculated. Step 3: Consider the capacitance generated between the curved rectangular capacitive sensor and the tip of the toothed blade, as well as the additional capacitance generated between the excess part of the curved rectangular capacitive sensor (wider than the toothed blade) and the rotation axis. Establish the relationship between the tip gap and the capacitance value measured by the curved rectangular capacitive sensor when all the toothed blades are facing the curved rectangular capacitive sensor. Combine this with the capacitance value detected by the curved rectangular capacitive sensor when all the toothed blades are facing the curved rectangular capacitive sensor obtained in Step 2 to obtain the tip gap value under dynamic conditions. The formula for calculating tip clearance under dynamic conditions is as follows: ； In the formula, m is the amplification factor for converting the capacitance value into a swing voltage signal, L is the arc length of the core electrode of the curved rectangular capacitive sensor, n is the width of the toothed blade, d is the blade tip gap, d1 is the distance between the core electrode of the curved rectangular capacitive sensor and the rotation axis, W is the width of the detection surface of the core electrode of the curved rectangular capacitive sensor, and V is the swing voltage signal output by the curved rectangular capacitive sensor. It is the absolute permittivity of vacuum. and All are coefficients, where T is temperature and P is pressure; If the deviation between the dynamic tip clearance d and the static tip clearance d0 is within a preset range, no adjustment is made to the tip clearance; otherwise, the tip clearance is adjusted. The preset range for the deviation is... .

2. The method for detecting the tip clearance of dynamic serrated blades in an aero-engine according to claim 1, characterized in that: The curved rectangular capacitive sensor converts the detected capacitance value into a swing voltage signal. When all the toothed blades are facing the curved rectangular capacitive sensor, the capacitance value detected by the sensor is: In the formula, V1 is the peak value of the swing voltage output by the curved rectangular capacitive sensor.

3. The method for detecting the tip clearance of dynamic serrated blades in an aero-engine according to claim 2, characterized in that: In step three, the relationship between the tip gap and the capacitance value measured by the curved rectangular capacitive sensor when all the toothed blades are aligned with the sensor is as follows: In the formula, Let be the absolute dielectric constant of the air between the toothed blades and the curved rectangular capacitive sensor, and 'a' be the axial displacement.

4. The method for detecting the tip clearance of dynamic serrated blades in an aero-engine according to claim 3, characterized in that: The absolute dielectric constant of air between the serrated blades and the curved rectangular capacitive sensor for In the formula, It is the relative permittivity; In aero-engines, the relative permittivity exhibits a nonlinear relationship with temperature T and pressure P, specifically: Temperature T and pressure P are measured by temperature and pressure sensors installed on the inner wall of the aircraft engine casing.

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