Calculation method for inhibiting thermoacoustic instability of hydrogen-doped combustion of gas turbine by electric field

Abstract

The invention discloses a calculation method for inhibiting thermoacoustic instability of hydrogen-doped combustion of a gas turbine by an electric field. In the combustion process, a flame area generates a large amount of charges, and when the charges are located in an electric field area, the motion state of the internal charges changes under the action of an electric field. The method comprises the following steps: determining an arrangement form of an electric field; establishing a numerical calculation model; determining a calculation mathematical model, determining material transport characteristics in a component transport equation, and selecting laminar flow diffusion or turbulent flow diffusion; determining combustion calculation boundary conditions, constructing a potential distribution equation in Maxwell, introducing a universal scalar equation UDS, and modifying the UDS equation to construct a potential equation; determining boundary conditions of the potential equation; and adding the generated electric field force into a component momentum equation source item, and carrying out coupling calculation. The method is used for calculating hydrogen-doped combustion thermoacoustic instability of the electric field inhibition gas turbine.

Description

Technical field:

[0001] The invention relates to the technical field of computational fluid dynamics, in particular to a calculation method for suppressing thermoacoustic instability of hydrogen-blended combustion in a gas turbine by electric field. Background technology:

[0002] The problem of combustion thermoacoustic instability is widely present in gas turbine combustion chambers. When the absolute value of the phase difference between the pressure and heat release rate fluctuations during the combustion process is between 0 and 90 degrees, the flame heat release rate oscillation will transfer energy to the sound field, thereby amplifying the effect of the sound field and producing larger combustion fluctuations.

[0003] In recent years, the hydrogen blending technology of gas turbines has gradually matured, and it is expected to become an effective means to control the low pollution emissions of gas turbines. Since the flame propagates quickly during hydrogen combustion, if the combustion is unstable, it is very easy to generate local high temperature and generate a large amount of hot NO. x , and flashback may occur. Especially in the process of changing the hydrogen blending ratio, it may overlap with the eigenfrequency of the components in the combustion chamber and cause resonance. Therefore, the thermoacoustic instability problem of hydrogen-blended gas turbine combustion needs to be paid special attention.

[0004] With the development of interdisciplinary studies, a variety of new methods for suppressing combustion instability have gradually emerged. Among them, the use of electric fields to suppress combustion instability has great potential. At present, a large number of experimental and theoretical studies have verified the effect of electric fields on suppressing combustion instability. During the combustion process, a large amount of charge is generated in the flame area. When it is located in the electric field area, the internal charge is affected by the electric field and its motion state changes. The migration process of positive and negative ions will collide with neutral reaction components and thus change the combustion process. When the combustion thermoacoustic instability occurs, the local pressure pulsation characteristics can be changed by adjusting the electric field form and change frequency, thereby avoiding resonance with sound waves and suppressing combustion instability. Summary of the invention:

[0005] The present invention is aimed at the above-mentioned problem of electric field suppression of hydrogen-added combustion instability. In order to overcome the limitations of existing research methods, a calculation method for electric field suppression of thermoacoustic instability of hydrogen-added combustion in a gas turbine is provided. The universal UDS equation is transformed into the Maxwell equation by using UDF, and it is coupled with the momentum equation and the component transport equation to numerically solve the pressure fluctuation and heat release rate fluctuation in the combustion chamber, thereby evaluating the effect of electric field suppression on combustion thermoacoustic instability, and providing engineering guidance for using electric field to suppress the instability of hydrogen-added combustion.

[0006] The above purpose is achieved through the following technical solutions:

[0007] A calculation method for suppressing thermoacoustic instability of hydrogen-blended combustion in a gas turbine by electric field, the method comprising the following steps:

[0008] Step 1: Based on the actual structure of the hydrogen-doped combustion chamber, a physical model matching it is constructed using modeling software, and the layout of the electric field is determined;

[0009] Step 2: Meshing the combustion chamber model with electrodes and establishing a numerical calculation model;

[0010] Step 3: Determine the mathematical model for calculation, simplify the Maxwell equation according to the internal combustion state in the actual combustion process, and construct the volume force term of the connection medium between the Maxwell equation and the NS equation. Determine the material transport characteristics in the component transport equation, and select laminar diffusion or turbulent diffusion;

[0011] Step 4: Determine the combustion calculation boundary conditions, and set the corresponding fuel flow, air flow, combustion chamber pressure, hydrogen blending ratio, etc. for different working conditions;

[0012] Step 5: Construct the electric potential distribution equation in Maxwell, introduce the universal scalar equation UDS, and modify the UDS equation to construct it as the electric potential equation;

[0013] Step 6: Determine the boundary conditions of the potential equation, set the grounding electrode potential to 0V, and set the high voltage electrode potential to the corresponding high voltage value;

[0014] Step 7: Set the boundary conditions of the charge transport equation. The surface charge density of the high-voltage electrode is given according to the actual situation, and the charge density of the ground electrode is set to δq / δn = 0. The space charge density is given according to the temperature and composition of the combustion area;

[0015] Step 8: Add the generated electric field force to the source term of the component momentum equation and perform coupled calculation.

[0016] The calculation method for suppressing thermoacoustic instability of hydrogen-blended combustion in a gas turbine by electric field, the specific process of step 1 is: constructing the electric potential distribution equation in Maxwell, introducing the universal scalar equation UDS, and modifying the UDS equation to construct it as a potential equation, activating the User-Define Scalar option, and constructing the first scalar equation UDS1;

[0017] In FLUENT, the universal form of the scalar transport equation is as follows:

[0018]

[0019] φ is the physical quantity that needs to be solved. Therefore, two scalar equations are used to solve the electric potential (Φ) equation and the charge (qc) distribution equation. Even if a strong electric field is applied in the combustion space, the current in the space is still very weak, so the magnetic effect of the current can be ignored. The electric field and charge in the system can be described by the Maxwell equations under quasi-electrostatic limit conditions. The distribution law of the electric potential in the space satisfies Gauss's law.

[0020] Since the potential equation has no convection term, the flux term is set to none, and the source term q c / ε k , using user-defined functions (UDFs) to programmatically calculate the source term, q c is the solution to the second scalar equation, ε k is the dielectric constant.

[0021] The calculation method for suppressing thermoacoustic instability of hydrogen-blended combustion in a gas turbine by electric field, the step six specifically comprises:

[0022] (1) Determine the boundary conditions of the potential equation, set the ground electrode potential to 0 V, set the high voltage electrode potential to the corresponding high voltage value, and solve the potential equation first to provide electric field strength data for solving the charge equation;

[0023] (2) Storing the electric field strength in space. The above equation solves the electric potential distribution in space, and subsequent calculations require electric field strength data. Therefore, C_UDMI needs to be called to store the three components of the electric field space:

[0024] C_UDMI(c0,t0,0)=-C_UDSI_G(c0,t0,0)[0];

[0025] C_UDMI(c0,t0,1)=-C_UDSI_G(c0,t0,0)[1];

[0026] C_UDMI(c0,t0,2)=-C_UDSI_G(c0,t0,0)[2];

[0027] (3) Establish the charge conservation equation:

[0028] (4) Add source terms to the potential equation;

[0029] Use the "DEFINE_SOURCE" macro that defines the source item:

[0030] vol=C_UDSI(c,t,1) / DIELECTRIC_CONSTANT;

[0031] (5) Add volume force source term to the momentum equation;

[0032] Add the electric field source terms in three directions to the momentum equation. Use the "DEFINE_SOURCE" macro to define the source terms of the momentum equation. The three components of the electric field force on the fluid are:

[0033]

[0034] Set the boundary conditions of the charge conservation equation: the surface charge density of the high-voltage electrode is given according to the actual situation, the charge density of the ground electrode is set to δq / δn=0, and the space charge density is given according to the temperature and composition of the combustion area.

[0035] The calculation method for suppressing thermoacoustic instability of hydrogen-blended combustion in a gas turbine by an electric field, wherein the charge conservation equation is established as follows: different charge concentrations are generated under different combustion environments, and the local charge concentration is closely related to the local chemical reaction rate. Therefore, the charge density distribution in space can be characterized by the combustion reaction rate;

[0036] The charge conservation equation is shown below:

[0037]

[0038] The movement of charge in the flow field includes three aspects, namely, migration along the direction of the electric field, movement with the flow field, and self-diffusion. Since the diffusion ability of the charge itself is weak, the equation is in the form of strong convection dominance, and its diffusion term is set by setting its diffusion coefficient D;

[0039] When the charge migrates along the electric field, it also moves along the flow field. Its speed along the flow field is the speed of the neutral fluid, and its speed along the electric field is the product of the ion mobility and the electric field strength: ion_vel[0] = C_U(c0, t0); ion_vel[1] = C_V(c0, t0); ion_vel[2] = C_W(c0, t0);

[0040] The three components of the electric field strength are the storage spaces of the electric potential in three directions in space: C_EE[0]=C_UDMI(c0,t0,0); C_EE[1]=C_UDMI(c0,t0,1); C_EE[2]=C_UDMI(c0,t0,2);

[0041] The convection term of the equation is:

[0042] NV_V_VS(current,=,ion_vel,+,C_EE,*,K);

[0043] The source term of the equation is:

[0044] The charge density generated in the combustion region is related to the reaction temperature, and its source term is qs=f(t).

[0045] Beneficial effects:

[0046] 1. The present invention conducts secondary development of Fluent based on UDF, manually constructs the Maxwell equation and couples it with the NS equation, which does not affect the operating steps of the combustion calculation part. It provides Fluent users with a new means to solve the electric field combustion coupling problem, making Fluent more efficient and quick in solving the problem of electric field suppressing combustion instability, and has strong universality for different research conditions. Description of the drawings:

[0047] Figure 1 The logic block diagram of the present invention is

[0048] Figure 2 This is the result diagram of the solution of the potential spatial distribution under the wire-tube structure;

[0049] Figure 3 This is the result diagram of charge spatial distribution solution under the wire-tube structure. Specific implementation method:

[0050] A calculation method for suppressing thermoacoustic instability of hydrogen-blended combustion in a gas turbine by electric field, the method comprising the following steps:

[0051] Step 1: Based on the actual structure of the hydrogen-doped combustion chamber, use modeling software to build a physical model that matches it. And determine the layout of the electric field;

[0052] Step 2: Mesh the combustion chamber model with electrodes and establish a numerical calculation model.

[0053] Step 3: Determine the mathematical model for calculation, simplify the Maxwell equations according to the internal combustion state in the actual combustion process, and construct the volume force term of the connection medium between the Maxwell equations and the NS equations. Determine the material transport characteristics in the component transport equations, and select laminar diffusion or turbulent diffusion.

[0054] Step 4: Determine the boundary conditions for combustion calculations, and set the corresponding fuel flow, air flow, combustion chamber pressure, hydrogen blending ratio, etc. for different working conditions. Solve the combustion characteristics under steady-state conditions.

[0055] Step 5: Construct the potential distribution equation in Maxwell, introduce the universal scalar equation UDS, modify the UDS equation, construct it as a potential equation, activate the User-Define Scalar option, and construct the first scalar equation UDS1.

[0056] In FLUENT, the universal form of the scalar transport equation is as follows:

[0057]

[0058] φ is the physical quantity that needs to be solved. Therefore, two scalar equations are used to solve the electric potential (Φ) equation and the charge (qc) distribution equation. Even if a strong electric field is applied in the combustion space, the current in the space is still very weak, so the current magnetic effect can be ignored. The electric field and charge in the system can be described by the Maxwell equations under quasi-electrostatic limit conditions. The law of electric potential distribution in space satisfies Gauss's law:

[0059]

[0060]

[0061] Since the potential equation has no convection term, the flux term is set to none. c / ε k , using user-defined functions (UDFs) to programmatically compute the source terms. c is the solution to the second scalar equation, ε k is the dielectric constant.

[0062] Step 6: (1) Determine the boundary conditions of the potential equation, set the ground electrode potential to 0 V, set the high voltage electrode potential to the corresponding high voltage value, and solve the potential equation first to provide electric field strength data for solving the charge equation.

[0063] (2) Storing the spatial electric field strength. The above equation solves the electric potential distribution in space, and subsequent calculations require electric field strength data. Therefore, C_UDMI needs to be called to store the three components of the electric field space.

[0064] C_UDMI(c0,t0,0)=-C_UDSI_G(c0,t0,0)[0];

[0065] C_UDMI(c0,t0,1)=-C_UDSI_G(c0,t0,0)[1];

[0066] C_UDMI(c0,t0,2)=-C_UDSI_G(c0,t0,0)[2];

[0067] (3) Establish the charge conservation equation

[0068] Different charge concentrations will be generated under different combustion environments, and the local charge concentration is closely related to the local chemical reaction rate. Therefore, the charge density distribution in space can be characterized by the combustion reaction rate.

[0069] The charge conservation equation is shown below

[0070]

[0071] The movement of charge in the flow field includes three aspects: migration along the electric field, movement with the flow field, and self-diffusion. Since the charge diffusion ability is weak, the equation is dominated by strong convection. The diffusion term is set by setting its diffusion coefficient D

[0072] When the charge migrates along the electric field, it also moves along the flow field. Its speed along the flow field is the speed of the neutral fluid, and its speed along the electric field is the product of the ion mobility and the electric field strength. ion_vel[0] = C_U(c0, t0); ion_vel[1] = C_V(c0, t0); ion_vel[2] = C_W(c0, t0);

[0073] The three components of the electric field strength are the storage space of the electric potential in three directions of space.

[0074] C_EE[0]=C_UDMI(c0,t0,0); C_EE[1]=C_UDMI(c0,t0,1); C_EE[2]=C_UDMI(c0,t0,2);

[0075] The convection term of the equation

[0076] NV_V_VS(current,=,ion_vel,+,C_EE,*,K);

[0077] The source term of the equation

[0078] The charge density generated in the combustion region is related to the reaction temperature, and its source term qs = f(t)

[0079] (4) Add source term to the potential equation

[0080] Use the "DEFINE_SOURCE" macro which defines the source item.

[0081] vol=C_UDSI(c,t,1) / DIELECTRIC_CONSTANT;

[0082] (5) Add volume force source term to momentum equation

[0083] Add three-dimensional electric force source terms to the momentum equation. Use the "DEFINE_SOURCE" macro to define the source terms of the momentum equation. The three components of the electric force on the fluid

[0084]

[0085] Set the boundary conditions of the charge conservation equation: the surface charge density of the high-voltage electrode is given according to the actual situation, and the charge density of the ground electrode is set to δq / δn = 0. The space charge density is given according to the temperature and composition of the combustion area.

[0086] This volume force is applied to each reaction component. Due to the differences in molecular weight of each component, the electric field force has different effects on different reaction components. In hydrogen-blended combustion, small molecular reactants account for a larger proportion, and the effect of the electric field on them is more obvious.

Claims

1. A calculation method for electric field suppression of thermoacoustic instability of hydrogen-blended combustion in a gas turbine, characterized by: The method comprises the following steps: Step 1: Based on the actual structure of the hydrogen-doped combustion chamber, a physical model matching it is constructed using modeling software, and the layout of the electric field is determined; Step 2: Meshing the combustion chamber model with electrodes and establishing a numerical calculation model; Step 3: Determine the mathematical model for calculation, simplify the Maxwell equation according to the internal combustion state in the actual combustion process, and construct the volume force term of the connection medium between the Maxwell equation and the NS equation. Determine the material transport characteristics in the component transport equation, and select laminar diffusion or turbulent diffusion; Step 4: Determine the combustion calculation boundary conditions, and set the corresponding fuel flow, air flow, combustion chamber pressure, hydrogen blending ratio, etc. for different working conditions; Step 5: Construct the electric potential distribution equation in Maxwell, introduce the universal scalar equation UDS, and modify the UDS equation to construct it as the electric potential equation; Step 6: Determine the boundary conditions of the potential equation, set the grounding electrode potential to 0V, and set the high voltage electrode potential to the corresponding high voltage value; Step 7: Set the boundary conditions of the charge transport equation. The surface charge density of the high-voltage electrode is given according to the actual situation, and the charge density of the ground electrode is set to δq / δn = 0. The space charge density is given according to the temperature and composition of the combustion area; Step 8: Add the generated electric field force to the source term of the component momentum equation and perform coupled calculation.

2. The calculation method for electric field suppression of thermoacoustic instability of hydrogen-blended combustion in a gas turbine according to claim 1 is characterized by: The specific process of the step 1 is as follows: construct the electric potential distribution equation in Maxwell, introduce the universal scalar equation UDS, modify the UDS equation, construct it as the electric potential equation, activate the User-Define Scalar option, and construct the first scalar equation UDS1; In FLUENT, the universal form of the scalar transport equation is as follows: φ is the physical quantity that needs to be solved. Therefore, two scalar equations are used to solve the electric potential (Φ) equation and the charge (qc) distribution equation. Even if a strong electric field is applied in the combustion space, the current in the space is still very weak, so the magnetic effect of the current can be ignored. The electric field and charge in the system can be described by the Maxwell equations under quasi-electrostatic limit conditions. The distribution law of the electric potential in the space satisfies Gauss's law. Since the potential equation has no convection term, the flux term is set to none, and the source term q c / ε k , using user-defined functions (UDFs) to programmatically calculate the source term, q c is the solution to the second scalar equation, ε k is the dielectric constant.

3. The calculation method for electric field suppression of thermoacoustic instability of hydrogen-blended combustion in a gas turbine according to claim 1 is characterized by: The step six specifically includes: (1) Determine the boundary conditions of the potential equation, set the ground electrode potential to 0 V, set the high voltage electrode potential to the corresponding high voltage value, and solve the potential equation first to provide electric field strength data for solving the charge equation; (2) Storing the electric field strength in space. The above equation solves the electric potential distribution in space, and subsequent calculations require electric field strength data. Therefore, C_UDMI needs to be called to store the three components of the electric field space: C_UDMI(c0,t0,0)=-C_UDSI_G(c0,t0,0)[0]; C_UDMI(c0,t0,1)=-C_UDSI_G(c0,t0,0)[1]; C_UDMI(c0,t0,2)=-C_UDSI_G(c0,t0,0)[2]; (3) Establish the charge conservation equation: (4) Add source terms to the potential equation; Use the "DEFINE_SOURCE" macro to define the source item: vol=C_UDSI(c,t,1) / DIELECTRIC_CONSTANT; (5) Add volume force source term to the momentum equation; Add three-directional electric field source terms to the momentum equation. Use the "DEFINE_SOURCE" macro to define the source terms of the momentum equation. The three components of the electric field force on the fluid are: Set the boundary conditions of the charge conservation equation: the surface charge density of the high-voltage electrode is given according to the actual situation, the charge density of the ground electrode is set to δq / δn=0, and the space charge density is given according to the temperature and composition of the combustion area.

4. The calculation method for electric field suppression of thermoacoustic instability of hydrogen-blended combustion in a gas turbine according to claim 3 is characterized by: The charge conservation equation is specifically established as follows: different charge concentrations will be generated under different combustion environments, and the local charge concentration is closely related to the local chemical reaction rate. Therefore, the charge density distribution in space can be characterized by the combustion reaction rate; The charge conservation equation is shown below: The movement of charge in the flow field includes three aspects, namely, migration along the direction of the electric field, movement with the flow field, and self-diffusion. Since the diffusion ability of the charge itself is weak, the equation is in the form of strong convection dominance, and its diffusion term is set by setting its diffusion coefficient D; While the charges migrate along the direction of the electric field, they also move along the flow field. Their speed along the flow field is the speed of the neutral fluid, and their speed along the electric field is the product of the ion mobility and the electric field strength: ion_vel[0]=C_U(c0,t0); ion_vel[1]=C_V(c0,t0); ion_vel[2]=C_W(c0,t0); The three components of the electric field strength are the storage spaces of the electric potential in three directions of space: C_EE[0]=C_UDMI(c0,t0,0); C_EE[1]=C_UDMI(c0,t0,1); C_EE[2]=C_UDMI(c0,t0,2); The convection term of the equation is: NV_V_VS(current,=,ion_vel,+,C_EE,*,K); The source term of the equation is: The charge density generated in the combustion region is related to the reaction temperature, and its source term is qs=f(t).

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