Method for determining thermo-acoustic oscillation monitoring threshold value of combustion chamber of gas turbine

Abstract

The invention relates to the technical field of thermoacoustic oscillation monitoring, in particular to a method for determining a thermoacoustic oscillation monitoring threshold value of a combustion chamber of a gas turbine. Comprising the following steps: S1, acquiring sound pressure field data corresponding to oscillation frequency; s2, obtaining a vibration stress value of each node of the flame tube at the oscillation frequency; s3, obtaining a thermal stress value of each node of the flame tube; s4, drawing a Goodman curve graph based on the obtained vibration stress value of the flame tube at each node of the oscillation frequency and the obtained thermal stress value of each node of the flame tube, and setting a safety coefficient in the drawn Goodman curve graph; s5, according to the Goodman curve graph drawn in the step S4, calculating a scaling ratio so as to calculate updated sound pressure field data, according to the updated sound pressure field data, judging whether the calculated scaling ratio is qualified or not, and according to a judgment result, determining a thermoacoustic oscillation pressure monitoring threshold value; and the monitoring threshold of the thermoacoustic oscillation of the combustion chamber is accurately determined.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoacoustic oscillation monitoring, and particularly to a method for determining the monitoring threshold of thermoacoustic oscillation in a gas turbine combustor. Background Art

[0002] Currently, most gas turbine combustors adopt dry low emission (DLN) technology to meet the increasingly strict emission standards. The DLN technology controls the combustion temperature by reducing the equivalence ratio in the combustion zone to achieve the purpose of reducing NO x emissions, but the DLN technology is prone to thermoacoustic oscillations. Thermoacoustic oscillation is an unstable combustion phenomenon caused by the mutual coupling of heat release fluctuations and pressure fluctuations in the combustor. Since the equivalence ratio in the combustion zone is relatively low, a small fluctuation in the equivalence ratio can cause a large heat release fluctuation. Therefore, the combustor using the DLN technology is prone to thermoacoustic instability, resulting in unstable combustion in the combustor, leading to phenomena such as increased emissions and flashback. More seriously, it will cause damage to the combustor and even gas turbine components, affecting the operating stability and safety of the gas turbine. Among them, the flame tube is one of the combustor components most easily damaged by thermoacoustic oscillations; as a thin-walled part that encloses the combustion flame, the flame tube is in a harsh working state of high temperature and high pressure for a long time; the occurrence of thermoacoustic oscillations will cause it to bear additional alternating stress, affecting its service life.

[0003] Industrial gas turbine units usually use the method of monitoring the characteristic quantity of pressure pulsation in the combustor to judge the thermoacoustic stability of the combustor. If the characteristic quantity of the pressure pulsation signal suddenly increases, it indicates that thermoacoustic oscillations occur in the combustor. The specific monitoring method is as follows: divide the spectrogram of the pressure pulsation signal into multiple monitoring frequency bands, set appropriate monitoring thresholds for each frequency band, and if the spectral amplitude exceeds the set monitoring threshold, it is judged that thermoacoustic oscillations occur. Therefore, the reasonable setting of the monitoring threshold is the key issue for the thermoacoustic oscillation monitoring of the combustor; too high a monitoring threshold will result in the inability to capture the thermoacoustic state in time; too low a monitoring threshold will cause the control system to react and operate frequently, affecting the normal operation of the gas turbine; therefore, the reasonable setting of the monitoring threshold is of great significance for both the thermoacoustic oscillation monitoring and the stable operation of the gas turbine.

[0004] Currently, the main methods for determining the monitoring threshold are the experimental method and the empirical method; although the experimental method can accurately obtain the oscillation data, it has high costs and a long cycle, and the experiment can only be carried out after the detailed design of the combustor is completed, making it difficult to guide the preliminary design. The empirical method is obtained from a large amount of operation data. For different manufacturers, the operation data are confidential and difficult to obtain.

[0005] Therefore, there is an urgent need to provide a method for determining the monitoring threshold of thermoacoustic oscillation in a gas turbine combustor, which can accurately determine the monitoring threshold of thermoacoustic oscillation in the combustor compared with the prior art. Summary of the Invention

[0006] The present invention solves the technical problems existing in the prior art, and provides a method for determining the monitoring threshold of thermoacoustic oscillation in a gas turbine combustor.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for determining the monitoring threshold of thermoacoustic oscillation in a gas turbine combustor, comprising the following steps:

[0009] S1. Construct a thermoacoustic coupling model of the combustor, obtain the oscillation frequency, and obtain the sound pressure field data corresponding to the oscillation frequency;

[0010] S2. Construct a finite element model of the solid domain of the flame tube, use the sound pressure field data obtained in step S1 as the excitation source, perform acoustic-vibration analysis on the finite element model of the solid domain of the flame tube, and obtain the vibration stress values of each node of the flame tube at the oscillation frequency;

[0011] S3. Adopt large eddy simulation technology to construct a thermal-solid coupling model of the flame tube, and obtain the thermal stress values of each node of the flame tube;

[0012] S4. Construct a Goodman curve graph with a safety factor, and based on the vibration stress values of each node of the flame tube at the oscillation frequency obtained in step S2 and the thermal stress values of each node of the flame tube obtained in step S3, plot each node of the flame tube in the Goodman curve graph;

[0013] S5. According to the Goodman curve graph drawn in step S4, calculate the scaling ratio, thereby calculate the updated sound pressure field data, and according to the updated sound pressure field data, judge whether the calculated scaling ratio is qualified. According to the judgment result, determine the thermoacoustic oscillation pressure monitoring threshold.

[0014] Further, S5 includes the following steps:

[0015] S51. Calculate the scaling ratio according to the Goodman curve graph drawn in step S4;

[0016] S52. Update the sound pressure field data according to the scaling ratio;

[0017] S53. According to the updated sound pressure field data, perform steps S2, S4, and S51 in sequence to obtain the updated vibration stress values, and calculate the judgment value corresponding to each node;

[0018] S54. Set a judgment threshold, compare the judgment value with the judgment threshold. When all the judgment values are less than or equal to the judgment threshold, judge that the calculated scaling ratio is qualified, and perform step S55. Otherwise, judge that the calculated scaling ratio is unqualified, and perform step S56;

[0019] S55. Determine the thermoacoustic oscillation pressure monitoring threshold as: i × P0, where i represents the scaling ratio and P0 represents the maximum amplitude corresponding to the normalized oscillation frequency;

[0020] S56. According to the updated vibration stress value, repeat steps S4, S51 - S54 until the calculated judgment value is qualified.

[0021] Furthermore, the scaling ratio in step S51 is calculated by the following formula:

[0022]

[0023] i = min(i m );

[0024] In the above formula, i m represents the scaling ratio corresponding to the m-th node, m takes values from 1 to D, σ am represents the vibration stress value corresponding to the m-th node, [σ am represents the allowable vibration stress value corresponding to the m-th node, i represents the scaling ratio, min(i m ) represents taking the minimum of the scaling ratios corresponding to D nodes as the scaling ratio, D represents the total number of nodes on the combustor liner; the allowable vibration stress value corresponding to the m-th node is the ordinate value of the point corresponding to the m-th node along the vertical coordinate direction on the Goodman curve.

[0025] Furthermore, the acoustic pressure field data updated according to the scaling ratio in step S52 is expressed as (x, y, z, i × P R , i × P i ), where x, y, and z respectively represent the distribution positions of the acoustic pressure field corresponding to P0 in the x, y, and z directions, P R represents the real part of P0, and P i represents the imaginary part of P0.

[0026] Furthermore, the judgment value in step S53 is calculated by the following formula:

[0027]

[0028] In the above formula, Q m represents the judgment value corresponding to the m-th node, and σ am ′ represents the updated vibration stress value corresponding to the m-th node.

[0029] Furthermore, S1 specifically includes the following steps:

[0030] S11. Use CFD software to calculate the flow field and temperature field inside the combustor liner to obtain the distribution of the sound speed field and density field inside the combustor liner;

[0031] S12. Use the acoustic calculation module in the CFD software to mesh the fluid domain inside the combustion chamber liner;

[0032] S13. Interpolate the sound speed field and density field obtained in step S11 into the fluid domain of the combustion chamber liner after meshing, and use the N-TAO model as the heat source model to solve the Helmholtz equation, thereby constructing a thermoacoustic coupling model of the combustion chamber;

[0033] S14. According to the thermoacoustic coupling model of the combustion chamber, obtain the sound pressure field data at different characteristic frequencies, and a growth rate is set for each characteristic frequency;

[0034] S15. Set the characteristic frequencies with negative growth rates as the oscillation frequencies, compare the amplitudes corresponding to all the oscillation frequencies, take the maximum amplitude, normalize it and denote it as P0, and obtain the sound pressure field data (x, y, z, P R , P i ).

[0035] Furthermore, the method of plotting each node of the combustion chamber liner in the Goodman curve in step S4 is: use a thermal stress value of the combustion chamber liner as the abscissa of a node and the corresponding vibration stress value as the ordinate of the node, so as to plot all the nodes in the Goodman curve.

[0036] Furthermore, S2 specifically includes the following steps:

[0037] S21. Set the displacement constraint boundary conditions, use the CFD software to mesh the solid domain of the combustion chamber liner, and use the displacement constraint boundary conditions for constraint while meshing, thereby establishing a finite element model of the solid domain;

[0038] S22. Interpolate the sound pressure field data obtained in step S1 on the inner wall nodes of the combustion chamber liner in the finite element model of the solid domain;

[0039] S23. Insert a damping term into the finite element model of the solid domain after being processed in step S22;

[0040] S24. For the finite element model of the solid domain after being processed in step S23, set the sweep frequency range and step size, set the frequency setting range, and encrypt the step size within the frequency setting range near the oscillation frequency;

[0041] S25. Perform a harmonic response analysis on the finite element model of the solid domain after being processed in step S24, so as to obtain the vibration stress values of each node at the oscillation frequency on the combustion chamber liner.

[0042] Even further, the damping term inserted in step S23 is expressed by the following formula:

[0043] [C] = α[M] + β[K];

[0044]

[0045] In the above formula, [C] represents the damping term, [M] represents the mass matrix, [K] represents the stiffness matrix, ξ represents the damping ratio, and w1 and w2 respectively represent two different angular frequencies.

[0046] Furthermore, S3 specifically includes the following steps:

[0047] S31. Calculate the boundary condition parameters of the flame tube temperature field calculation through the thermodynamic formula;

[0048] S32. Adopt the large eddy simulation technology, and then combine with the boundary condition parameters of the flame tube temperature field calculation obtained in step S31 to perform a coupled solution of the flame tube flow field and the solid temperature field, so as to obtain the temperature field distribution of the flame tube under the basic load condition;

[0049] S33. Calculate all the nodes of the solid domain of the flame tube through finite element software, and map the temperature values in the temperature field distribution obtained in step S32 onto each node calculated by the finite element software to form a thermal-solid coupling model of the flame tube;

[0050] S34. For the thermal-solid coupling model of the flame tube formed in step S33, carry out elastoplastic creep analysis by using finite element software to obtain the thermal stress values of each node of the flame tube.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0052] By designing multiple models for the flame tube during the design stage, the present invention calculates and judges values, sets a judgment threshold, and determines the monitoring threshold of the thermoacoustic oscillation pressure by comparing the judgment value with the judgment threshold. The method provided by the present invention can accurately determine the monitoring threshold of the thermoacoustic oscillation in the combustion chamber, providing a basis for predicting the thermoacoustic oscillation problem and the component life prediction during subsequent iterative design. Description of the Drawings

[0053] Figure 1 is the flowchart of the present invention.

[0054] Figure 2 is the schematic diagram of the sound pressure field distribution at different characteristic frequencies of the present invention.

[0055] Figure 3 is the schematic diagram of the sound pressure field distribution on the inner wall of the flame tube after interpolating the sound pressure field data into the finite element model of the solid domain of the present invention.

[0056] Figure 4 is the schematic diagram of the distribution of the vibration stress values of each node at the oscillation frequency on the flame tube of the present invention.

[0057] Figure 5 It is the Goodman curve diagram drawn for the present invention. Specific embodiments

[0058] The technical solution of the present invention will be clearly described below in conjunction with the accompanying drawings. Obviously, the described embodiments are not all embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0059] As Figure 1 shown, the present invention provides a method for determining the monitoring threshold of thermoacoustic oscillation in a gas turbine combustor, including the following steps:

[0060] S1. Construct a thermoacoustic coupling model of the combustor, obtain the oscillation frequency, and obtain the sound pressure field data corresponding to the oscillation frequency; specifically including the following steps:

[0061] S11. Use CFD software to calculate the flow field and temperature field in the flame tube to obtain the sound speed field and density field distributions in the flame tube.

[0062] S12. Use the acoustic calculation module in CFD software to mesh the fluid domain in the flame tube.

[0063] S13. Interpolate the sound speed field and density field obtained in step S11 into the fluid domain of the flame tube after meshing, and use the N-TAO model as the heat source model to solve the Helmholtz equation, thereby constructing a thermoacoustic coupling model of the combustor.

[0064] S14. According to the thermoacoustic coupling model of the combustor, obtain the sound pressure field data at different characteristic frequencies (as Figure 2 shown), and each characteristic frequency is correspondingly set with a growth rate.

[0065] S15. Set the characteristic frequencies with negative growth rates as the oscillation frequencies, compare the amplitudes in the sound pressure field data corresponding to all the oscillation frequencies, take the largest amplitude, normalize it and record it as P0, and export the real part and imaginary part of P0 to obtain the sound pressure field data (x, y, z, P R , P i ), where x, y, and z respectively represent the distribution positions of the sound pressure field corresponding to P0 in the x, y, and z directions, P R represents the real part of P0, and P i represents the imaginary part of P0.

[0066] S2. Construct a finite element model of the solid domain of the flame tube, use the sound pressure field data obtained in S1 as the excitation source, perform acoustic-vibration analysis on the finite element model of the solid domain of the flame tube, and obtain the vibration stress values of each node of the flame tube at the oscillation frequency; specifically including the following steps:

[0067] S21. Set the displacement constraint boundary condition, use CFD software to mesh the solid domain of the combustion chamber, and apply the displacement constraint boundary condition during meshing to establish a finite element model of the solid domain.

[0068] S22. Interpolate the sound pressure field data (x, y, z, P R , P i ) obtained in step S1 at the inner wall nodes of the combustion chamber in the finite element model of the solid domain (as shown in Figure 3 ).

[0069] S23. Insert a damping term into the finite element model of the solid domain processed in step S22. The damping term is expressed by the following formula:

[0070] [C] = αξ[M] + β[K];

[0071]

[0072] In the above formula, [C] represents the damping term, [M] represents the mass matrix, [K] represents the stiffness matrix, ξ represents the damping ratio, and ω1, ω2 respectively represent two different angular frequencies.

[0073] S24. For the finite element model of the solid domain processed in step S23, set the sweep frequency range f1~f2 and the step size Δf, set the frequency setting range, and encrypt the step size within the frequency setting range near the oscillation frequency to A times the original.

[0074] S25. Perform a harmonic response analysis on the finite element model of the solid domain processed in step S24 to obtain the vibration stress values of each node at the oscillation frequency on the combustion chamber (as shown in Figure 4 ).

[0075] S3. Use the large eddy simulation technique to obtain the temperature distribution of the internal flow field of the combustion chamber, establish a thermal-solid coupling model of the combustion chamber, and obtain the thermal stress values of each node of the combustion chamber. The thermal stress values of each node of the combustion chamber obtained in this step are set in one-to-one correspondence with the vibration stress values of each node at the oscillation frequency on the combustion chamber in step S2; specifically, it includes the following steps:

[0076] S31. Calculate the parameters of the temperature field calculation boundary condition of the combustion chamber through thermodynamic formulas.

[0077] S32. Use the large eddy simulation technique and combine the parameters of the temperature field calculation boundary condition of the combustion chamber calculated in step S31 to perform a coupled solution of the flow field and solid temperature field of the combustion chamber, so as to obtain the temperature field distribution of the combustion chamber under the basic load condition.

[0078] S33. Calculate all the nodes in the solid domain of the combustion chamber liner using finite element software, and map the temperature values in the temperature field distribution obtained in step S32 onto each node calculated by the finite element software to form a thermal-solid coupling model of the combustion chamber liner.

[0079] S34. For the thermal-solid coupling model of the combustion chamber liner formed in step S33, carry out elastoplastic creep analysis using finite element software to obtain the thermal stress values of each node of the combustion chamber liner.

[0080] S4. Construct a Goodman curve with a safety factor. Based on the vibration stress values of each node of the combustion chamber liner obtained in step S2 at various oscillation frequencies and the thermal stress values of each node of the combustion chamber liner obtained in step S3, plot each node in the Goodman curve.

[0081] Specifically, the constructed Goodman curve is as Figure 5 shown. It is constructed according to the material of the combustion chamber liner itself. The safety factor set in the plotted Goodman curve is denoted as n. Take a thermal stress value of the combustion chamber liner as the abscissa of a node and the corresponding vibration stress value as the ordinate of this node, so as to plot all the nodes in the Goodman curve. Figure 5 The position of the triangular point in

[0082] represents the position of a node in the Goodman curve.

[0083] S5. Calculate the scaling ratio, denoted as i. According to the scaling ratio, calculate the updated sound pressure field data. According to the updated sound pressure field data, judge whether the calculated scaling ratio is qualified. According to the judgment result, determine the monitoring threshold of the thermoacoustic oscillation pressure; specifically, it includes the following steps:

[0084]

[0085] i = min(i m );

[0086] In the above formula, i m represents the scaling ratio corresponding to the mth node, m takes values from 1 to D, σ am represents the vibration stress value corresponding to the mth node, [σ am represents the allowable vibration stress value corresponding to the mth node, i represents the scaling ratio, and min(i m ) represents taking the minimum of the scaling ratios corresponding to D nodes as the scaling ratio, and D represents the total number of nodes on the combustion chamber liner.

[0087] The allowable vibration stress value corresponding to the m-th node is the numerical value of the ordinate of the point corresponding to the m-th node along the vertical coordinate direction on the Goodman curve, that is Figure 5 The point in the triangle in Figure 5 is the position of the m-th node, and the point corresponding to it in the Goodman curve graph is the position of the circular point. Therefore, the ordinate of the circular point is the allowable vibration stress value corresponding to the m-th node.

[0088] S52. Update the sound pressure field data according to the scaling ratio. The updated sound pressure field data is expressed as: (x, y, z, i×P R , i×P i ).

[0089] S53. Perform steps S2, S4, and S51 in sequence according to the updated sound pressure field data to obtain the updated vibration stress value, and calculate the judgment value. Calculate the corresponding judgment value for the updated vibration stress value of each node. The judgment value corresponding to each node is calculated by the following formula:

[0090]

[0091] In the above formula, Q m represents the judgment value corresponding to the m-th node, and σ am ′ represents the vibration stress value corresponding to the updated m-th node.

[0092] S54. Set the judgment threshold, and compare each judgment value with the judgment threshold. When all the judgment values are less than or equal to the judgment threshold, it is judged that the calculated scaling ratio is qualified, and step S55 is performed. Otherwise, it is judged that the calculated scaling ratio is unqualified, and step S56 is performed; the judgment threshold is preferably 5%.

[0093] S55. Determine the monitoring threshold of the thermoacoustic oscillation pressure. The monitoring threshold of the thermoacoustic oscillation is: i×P0.

[0094] S56. According to the updated vibration stress value, repeat steps S4, S51 - S54 until the calculated judgment value is qualified.

[0095] In the present invention, by designing multiple models for the flame tube in the design stage, the judgment value is calculated, the judgment threshold is set, and by comparing the judgment value with the judgment threshold, the monitoring threshold of the thermoacoustic oscillation pressure is determined. The method provided by the present invention can accurately determine the monitoring threshold of the thermoacoustic oscillation in the combustion chamber, providing a basis for predicting the thermoacoustic oscillation problem and the component life prediction in the subsequent iterative design.

[0096] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than limiting the protection scope of the present invention. Any simple modification or equivalent replacement made by those of ordinary skill in the art to the technical solution of the present invention shall not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for determining a threshold value for monitoring thermoacoustic oscillations in a gas turbine combustion chamber, characterized in that: The following steps are involved: S1. Build a thermoacoustic coupling model of the combustion chamber, obtain the oscillation frequency, and obtain the sound pressure field data corresponding to the oscillation frequency; S2. Construct a solid domain finite element model of the flame tube, use the acoustic pressure field data obtained in step S1 as an excitation source, perform acoustic-vibration analysis on the solid domain finite element model of the flame tube, and obtain the vibration stress value of each node of the flame tube at the oscillation frequency; S3. Use large eddy simulation technology to build a flame tube thermal-solid coupling model to obtain the thermal stress value of each node of the flame tube; S4, constructing a Goodman curve diagram with a safety factor, based on the vibration stress value of each node of the flame tube at the oscillation frequency obtained in step S2 and the thermal stress value of each node of the flame tube obtained in step S3, plotting each node of the flame tube in the Goodman curve diagram; S5. Calculate the scaling ratio according to the Goodman curve drawn in step S4, thereby calculating the updated sound pressure field data, and determine whether the calculated scaling ratio is qualified according to the updated sound pressure field data, and determine the thermoacoustic oscillation pressure monitoring threshold according to the judgment result.

2. A method for determining a threshold value for monitoring thermoacoustic oscillations in a gas turbine combustion chamber according to claim 1, characterized in that: S5 includes the following steps: S51, calculating the scaling ratio according to the Goodman curve graph drawn in step S4; S52, updating the sound pressure field data according to the scaling ratio; S53, performing steps S2, S4, and S51 in sequence according to the updated sound pressure field data to obtain an updated vibration stress value, and calculating a judgment value corresponding to each node; S54, setting a judgment threshold, comparing the judgment value with the judgment threshold, when all the judgment values ​​are less than or equal to the judgment threshold, judging that the calculated scaling ratio is qualified, and proceeding to step S55, otherwise, judging that the calculated scaling ratio is unqualified, and proceeding to step S56; S55, determining the thermoacoustic oscillation pressure monitoring threshold value as: i×P0, where i represents a scaling ratio, and P0 represents a maximum amplitude corresponding to the standardized oscillation frequency; S56. Repeat steps S4, S51-S54 according to the updated vibration stress value until the calculated judgment value is qualified.

3. A method for determining a threshold value for monitoring thermoacoustic oscillations in a gas turbine combustion chamber according to claim 2, characterized in that: The scaling ratio in step S51 is calculated by the following formula: i=min(i m ); In the above formula, i m Indicates the scaling ratio corresponding to the mth node, m is 1-D, σ am represents the vibration stress value corresponding to the mth node, [σ am ] represents the allowable vibration stress value corresponding to the mth node, i represents the scaling ratio, min(i m ) means taking the smallest scaling ratio corresponding to D nodes as the scaling ratio, where D represents the total number of nodes on the flame tube; the allowable vibration stress value corresponding to the mth node is the value of the ordinate of the point corresponding to the mth node on the Goodman curve along the ordinate direction.

4. A method for determining a threshold value for monitoring thermoacoustic oscillations in a gas turbine combustion chamber according to claim 3, characterized in that: The sound pressure field data updated according to the scaling ratio in step S52 is expressed as (x, y, z, i×P R ,i×P i ), where x, y, and z represent the distribution positions of the sound pressure field corresponding to P0 in the x, y, and z directions, respectively. R represents the real part of P0, P i Represents the imaginary part of P0.

5. The method for determining the threshold value of thermoacoustic oscillation monitoring of a gas turbine combustion chamber according to claim 3, characterized in that: The judgment value in step S53 is calculated by the following formula: In the above formula, Q m represents the judgment value corresponding to the mth node, σ am ′ Represents the updated vibration stress value corresponding to the mth node.

6. A method for determining a threshold value for monitoring thermoacoustic oscillations in a gas turbine combustion chamber according to claim 4, characterized in that: S1 specifically includes the following steps: S11. Use CFD software to calculate the flow field and temperature field in the flame tube to obtain the sound velocity field and density field distribution in the flame tube; S12. Use the acoustic calculation module in the CFD software to mesh the fluid domain in the flame tube; S13, interpolating the sound velocity field and density field obtained in step S11 into the meshed flame tube fluid domain, and using the N-TAO model as a heat source model to solve the Helmholtz equation, thereby forming a combustion chamber thermal-acoustic coupling model; S14. According to the combustion chamber thermoacoustic coupling model, the acoustic pressure field data at different characteristic frequencies are obtained, and each characteristic frequency is correspondingly set with a growth rate; S15, set the characteristic frequency with a negative growth rate as the oscillation frequency, compare the amplitudes corresponding to all oscillation frequencies, take the largest amplitude, standardize it and record it as P0, and obtain the sound pressure field data (x, y, z, P R ,P i ).

7. A method for determining a threshold value for monitoring thermoacoustic oscillations in a gas turbine combustion chamber according to claim 1, characterized in that: The method for plotting each node of the flame tube on the Goodman curve diagram in step S4 is: taking a thermal stress value of the flame tube as the horizontal coordinate of a node and the corresponding vibration stress value as the vertical coordinate of the node, so that all nodes are plotted on the Goodman curve diagram.

8. The method for determining the threshold value of thermoacoustic oscillation monitoring of a gas turbine combustion chamber according to claim 1, characterized in that: S2 specifically includes the following steps: S21. Setting displacement constraint boundary conditions, using CFD software to mesh the solid domain of the flame tube, and using displacement constraint boundary conditions to constrain while meshing, thereby establishing a solid domain finite element model; S22, interpolating the acoustic pressure field data obtained in step S1 on the inner wall nodes of the flame tube in the solid domain finite element model; S23, inserting a damping term into the solid domain finite element model processed in step S22; S24, for the solid domain finite element model processed in step S23, setting the frequency sweep range and step length, setting the frequency setting range, and encrypting the step length within the frequency setting range near the oscillation frequency; S25. Perform harmonic response analysis on the solid domain finite element model processed in step S24 to obtain the vibration stress value of each node at the oscillation frequency on the flame tube.

9. A method for determining a threshold value for monitoring thermoacoustic oscillations in a gas turbine combustion chamber according to claim 8, characterized in that: The damping term inserted in step S23 is expressed as follows: [C] = α[M] + β[K]; In the above formula, [C] represents the damping term, [M] represents the mass matrix, [K] represents the stiffness matrix, ξ represents the damping ratio, and w1 and w2 represent two different angular frequencies respectively.

10. The method for determining a threshold value for monitoring thermoacoustic oscillation of a gas turbine combustion chamber according to claim 1, characterized in that: S3 specifically includes the following steps: S31, calculating the boundary condition parameters of the flame tube temperature field by thermodynamic formula; S32, using large eddy simulation technology, combined with the flame tube temperature field calculated in step S31 to calculate the boundary condition parameters, the flame tube flow field and the solid temperature field are coupled and solved, so as to obtain the temperature field distribution of the flame tube under the basic load condition; S33, calculating all nodes of the solid domain of the flame tube by finite element software, and mapping the temperature values ​​in the temperature field distribution obtained in step S32 to each node calculated by the finite element software, so as to form a thermal-solid coupling model of the flame tube; S34. For the flame tube thermal-solid coupling model constructed in step S33, finite element software is used to carry out elastic-plastic creep analysis to obtain the thermal stress value of each node of the flame tube.

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