A numerical calculation method for pollutant NOx considering the influence of combustion temperature fluctuation

Abstract

The present invention discloses a method for numerically calculating NOx pollutants that considers the effects of combustion temperature fluctuations. The method defines a resolution control function; calculates the filter scale coefficient in the resolution control function based on the Smagorinsky subgrid stress model, and calculates the resolution control function size; adaptively controls the smooth switching between the unsteady RANS mode, the LES mode, and the DNS mode during the calculation process through the resolution function; remodels the model turbulent viscosity coefficient based on the resolution function; constructs a partially premixed FGM laminar flow thermodynamic table based on the characteristic variables mixture fraction and reaction progress variable to calculate flow field information; and solves the NOx transport equation and defines a temperature fluctuation coefficient to correct the NOx generation amount to calculate NOx generation. The present invention can accurately predict the NOx generation distribution during the combustion process in a combustion chamber at a relatively low grid resolution.

Description

Technical Field

[0001] The present invention belongs to the field of numerical simulation of turbulent combustion of aviation engines, and in particular relates to a numerical calculation method for pollutants NOx taking into account the influence of combustion temperature pulsation. Background Art

[0002] The International Civil Aviation Organization has established strict limits on aviation engine pollutant emissions. With the continuous introduction of new emission standards, NOx emission requirements have been reduced by 50% compared to the original requirements, indicating that the environmental hazards of NOx pollutants are receiving increasing attention and attention. In the process of promoting low-pollution combustion engine design, developing high-precision combustion chamber pollutant NOx prediction methods has been a hot topic and a challenge in research.

[0003] The interior of an aircraft engine combustion chamber involves numerous complex physical phenomena, including high premixing, unstable combustion, and large-timescale NOx emissions. To quickly and accurately simulate the flow field within the combustion chamber, the numerical calculation process requires the selection of an appropriate turbulence model. Numerous turbulence computation methods have been proposed for turbulent eddies of varying scales. These methods, ranked in descending order of their degree of modeling of turbulent kinetic energy, include the Reynolds-averaged numerical simulation (RANS), the hybrid Reynolds-averaged large eddy simulation (hybridRANS-LES), the large eddy simulation (LES), and the direct numerical simulation (DNS). RANS methods, however, model turbulent kinetic energy at all global scales and are insufficient to accurately describe the complex turbulent combustion conditions within the combustion chamber. While LES and DNS achieve the required accuracy, they require high computational resources, making them unsuitable for immediate engineering applications. To balance accuracy and cost, hybrid RANS-LES methods have rapidly developed in engineering applications in recent years, resulting in numerous computational methods such as DES, VLES, and PANS.

[0004] NOx, the exhaust pollutant from aircraft engines and gas turbines, is typically composed of nitric oxide (NO), nitrogen dioxide (NO2), and nitrous oxide (N2O), with NO accounting for over 95% of the total. Therefore, predicting NO formation within the combustion chamber is crucial for accurate NOx prediction. Calculating NO formation typically requires detailed chemical reaction mechanisms to account for combustion intermediates. Traditional combustion models consume significant computational resources, hindering widespread engineering application. The FGM combustion model, developed in recent years by van Oijen et al., represents a representative approach to detailed chemical thermodynamics. By solving the transport equations for characteristic scalars, the FGM combustion model can significantly reduce computational resources. However, because the FGM combustion model is based on short timescales, it cannot accurately describe the formation of pollutants such as NOx on larger timescales, leading to a lack of a unified simulation method.

[0005] In summary, NOx is a significant pollutant in aircraft engine exhaust. Due to the high temporal fluctuations of the turbulent combustion process within the combustion chamber, current NOx prediction methods are inaccurate and require significant computational resources, hindering their practical application in engineering. Therefore, developing numerical methods that can rapidly and accurately calculate NOx generation is crucial for the development of low-pollution aircraft engines. Summary of the Invention

[0006] In order to solve the problems of low NOx pollutant prediction accuracy and high computing resource requirements in the existing technology, the purpose of the present invention is to provide a numerical calculation method for NOx pollutants that takes into account the influence of combustion temperature pulsation, which can perform high-precision calculation of the detailed distribution of NOx pollutants inside the combustion chamber at a lower grid resolution.

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

[0008] A numerical calculation method for pollutants NOx taking into account the influence of combustion temperature fluctuations, the steps are as follows:

[0009] 1) Define the resolution control function F r ;

[0010] 2) Calculating the filter scale coefficient C in the resolution control function in step 1) based on the Smagorinsky subgrid stress model x , and further calculate the resolution control function F r size;

[0011] 3) as the grid resolution changes, based on the BSLk-ω turbulence model, adaptive adjustment is performed through the resolution control function in step 1) to achieve adaptive transition between the unsteady RANS mode, LES mode, and DNS mode in the calculation process;

[0012] 4) Based on the resolution control function F r , remodeling the turbulent viscosity coefficient μ in the BSL k-ω turbulence model t , and the corrected turbulent viscosity coefficient is obtained

[0013] 5) Based on the characteristic variable mixture fraction Z and reaction progress variable Y c Construct a partially premixed FGM laminar flow thermodynamic table to complete the calculation of unsteady flame flow field.

[0014] 6) Solve the NOx transport equation and correct the NOx generation by defining the temperature fluctuation coefficient.

[0015] Furthermore, the step 1) is specifically as follows:

[0016] Define the resolution control function F r The expression is:

[0017]

[0018] Where, is the minimum function, exp(d)=e d is a natural exponential function, n = 2 and β = 0.002 are empirical constants, L i , L c and L k are the integral length scale, the turbulence cutoff length scale and the Kolmogorov length scale, respectively, and their expressions are:

[0019] L c =C x (Δ x Δ y Δ z ) 1 / 3

[0020] L i =k 3 / 2 / (β * kω)

[0021] L k =ν 3 / 4 / (β * kω) 1 / 4

[0022] Where C x is the filter scale coefficient; Δ x Δ y Δ z are the scales of the grid in the x, y, and z directions, which are determined by the discrete process; ν is the fluid viscosity coefficient; k is the turbulent kinetic energy, ω is the turbulent specific dissipation rate, and β * =0.09 is the model constant.

[0023] Furthermore, the step 2) is specifically as follows:

[0024] Calculation of filter scale coefficient C based on Smagorinsky sub-grid stress model x , the expression is:

[0025]

[0026] Where C μ =0.09 is the model constant, C s is the model constant, ranging from 0.05 to 0.18, Δ is the spatial resolution; S is the strain rate amplitude.

[0027] Furthermore, the step 3) is specifically as follows:

[0028] When the resolution control function F r When the size of approaches 1, the unsteady RANS mode dominates, and most of the turbulence is solved by the RANS method; when the resolution control function F r As the grid resolution decreases, the proportion of the unsteady RANS mode gradually decreases, and the proportion of the DNS mode gradually increases. At this time, the LES mode is restored, and the proportion of turbulence solved directly increases. When the resolution control function F r When it approaches 0, the DNS mode becomes dominant and all turbulence is directly solved.

[0029] Furthermore, the step 4) is specifically as follows:

[0030] BSL k-ω Turbulent viscosity coefficient μ in turbulence model t The definition is as follows:

[0031] μ t =ρk / ω

[0032] Where ρ is the fluid density, k is the turbulent kinetic energy, and ω is the turbulent specific dissipation rate;

[0033] The turbulent viscosity coefficient μ in the BSL k-ω turbulence model t Modification is made, and the modified turbulent viscosity coefficient Its expression is:

[0034]

[0035] Furthermore, the specific steps of step 5) are as follows:

[0036] 51) Using partially premixed FGM laminar flow thermodynamics to build a table based on the characteristic variable mixture fraction Z and reaction progress variable Y c Construct thermodynamic table; use β-PDF method; specific calculation only needs to calculate the mixture fraction and variance Reaction progress variables and variance The transport equation is as follows:

[0037]

[0038]

[0039]

[0040]

[0041] In the formula, the superscript “—” indicates spatial filtering, and “~” indicates Fave filtering; Sc t =0.7 is the Schmitdt number; λ = μC p / Pr is the molecular thermal diffusion coefficient, μ is the dynamic viscosity, C p is the heat capacity coefficient, Pr=0.85; C g =2.86, C d =2.0; is the source term of the reaction progress variable, which is closed by the Zimont model; c φ =2.0; τ turb =k / ε is the turbulence time scale;

[0042] 52) Use the re-modeled and partially premixed FGM thermodynamic tables, perform unsteady calculations on the combustion chamber pollutants, and obtain the distributions of flow field velocity, temperature, components, and characteristic scalars.

[0043] Furthermore, the specific steps of step (6) are as follows:

[0044] 61) Due to the relatively long time scale of NOx generation, it is difficult to couple it well in a CFD model. Therefore, NOx calculations are usually solved by introducing a separate NOx model after the flow field calculations are completed. The NOx transport equation is as follows:

[0045]

[0046] Where S NO It is the source term of the equation and needs to be modeled according to different NO species.

[0047] For thermal NO, the following equation is used to calculate the closed transport equation for the source term:

[0048]

[0049]

[0050] Where k f，1 =1.8×10 8 e -38370 / T , k f，2 =1.8×10 4 Te -4680 / T , k f，3 =7.1×10 7 e -450 / T , k r，1 =3.8×10 7 e -425 / T , k r，2 =3.81×10 3Te -20820 / T , k r，3 =1.7×10 8 e -24560 / T is the reaction rate coefficient related to the reaction temperature T; “[]” indicates the concentration of the corresponding reaction component; M w，NO is the molar mass of NO.

[0051] For fast NO, the following equation is used to calculate the closed transport equation for the source term:

[0052]

[0053]

[0054] Where, f = 4.75 + 0.0819n - 23.2φ + 32φ 2 -12.2φ 3 , k′ pr =6.4×106(RT / p)a+1,E a =303474.125, n is the number of carbon atoms in the fuel, and φ is the equivalence ratio.

[0055] 62) Define the temperature fluctuation coefficient to correct the NO generation:

[0056] T′ max =T mαx *T m

[0057]

[0058] Among them, T max is the maximum temperature of the flow field; T′ max is the corrected maximum temperature of the flow field, which is used to calculate the integral upper limit of the NO generation rate affected by turbulence; T m is the temperature fluctuation coefficient, which is used to correct the effect of transient high temperature on NO generation; T mean is the time-averaged temperature of the flow field; T rms is the pulsating temperature.

[0059] The beneficial effects of the present invention are as follows:

[0060] The method of the present invention calculates the filter scale coefficient C through the Smagorinsky sub-grid model x , defines the resolution control function F r , achieving high-precision solution of the flow field in the combustion chamber, coupling the partially premixed FGM laminar flow thermodynamic table building method, and finally achieving high-precision and efficient unsteady calculation of flow field characteristic information (especially temperature field pulsation values).

[0061] Subsequently, by solving the NOx pollutant equation and correcting the NOx generation and distribution by defining the temperature pulsation coefficient, efficient and accurate prediction of NOx pollutants can be achieved, providing strong support for the design of low-pollution aircraft engines. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 Flowchart of the method of the present invention.

[0063] Figure 2 Schematic diagram of the structure of the Sandia combustion experimental device in an embodiment of the present invention.

[0064] Figure 3 The transient and average NOx distribution diagram inside the burner of the embodiment of the present invention

[0065] Figure 4 This is a comparison chart of the calculation results of the main reaction components of the burner in the embodiment of the present invention.

[0066] Figure 5 This is a comparison chart of the calculation results of the burner pollutant NOx in the embodiment of the present invention. DETAILED DESCRIPTION

[0067] In order to facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and drawings. The contents mentioned in the embodiments are not intended to limit the present invention.

[0068] Reference Figure 1 As shown in FIG, a numerical calculation method for pollutants NOx considering the influence of combustion temperature fluctuations is as follows:

[0069] 1) Define the resolution control function F r ; The details are as follows:

[0070] Define the resolution control function F r The expression is:

[0071]

[0072] Where, is the minimum function, exp(d)=e d is a natural exponential function, n = 2 and β = 0.002 are model constants, L i , L c and L k are the integral length scale, the turbulence cutoff length scale and the Kolmogorov length scale, respectively, and their expressions are:

[0073] L c =C x (Δ x Δ y Δz ) 1 / 3

[0074] L i =k 3 / 2 / (β * kω)

[0075] L k =ν 3 / 4 / (β * kω) 1 / 4

[0076] Where C x is the filter scale coefficient; Δ x Δ y Δ z are the scales of the grid in the x, y, and z directions, which are determined by the discrete process; v is the fluid viscosity coefficient; k is the turbulent kinetic energy, ω is the turbulent specific dissipation rate, β * =0.09 is the model constant.

[0077] 2) Calculating the filter scale coefficient C in the resolution control function in step 1) based on the Smagorinsky subgrid stress model x , and further calculate the resolution control function F r Size; details are as follows:

[0078] Calculation of filter scale coefficient C based on Smagorinsky sub-grid stress model x , the expression is:

[0079]

[0080] Where C μ =0.09 is the model constant, C s is the model constant, ranging from 0.05 to 0.18, Δ is the spatial resolution; S is the strain rate amplitude.

[0081] 3) As the grid resolution changes, adaptive adjustment is performed through the resolution control function in step 1) to achieve adaptive transition between the unsteady RANS mode, LES mode, and DNS mode in the calculation process; specifically, as follows:

[0082] When the resolution control function F r When the size of approaches 1, the unsteady RANS mode dominates, and most of the turbulence is solved by the RANS method; when the resolution control function F r As the grid resolution decreases, the proportion of the unsteady RANS mode gradually decreases, and the proportion of the DNS mode gradually increases. At this time, the LES mode is restored, and the proportion of turbulence solved directly increases. When the resolution control function Fr When it approaches 0, the DNS mode becomes dominant and all turbulence is directly solved.

[0083] 4) Based on the resolution control function F r , remodeling the turbulent viscosity coefficient μ in the BSL k-ω turbulence model t , and the corrected turbulent viscosity coefficient is obtained The details are as follows:

[0084] 41) Turbulent viscosity coefficient μ in the BSL k-ω turbulence model t The definition is as follows:

[0085] μ t =ρk / ω

[0086] Where ρ is the fluid density, k is the turbulent kinetic energy, and ω is the turbulent specific dissipation rate;

[0087] The turbulent viscosity coefficient μ in the BSL k-ω turbulence model t Modification is made, and the modified turbulent viscosity coefficient Its expression is:

[0088]

[0089] 5) Based on the characteristic variable mixture fraction Z and reaction progress variable Y c Construct a partially premixed FGM laminar flow thermodynamic table to complete the unsteady flame flow field calculation. The details are as follows:

[0090] 51) Using partially premixed FGM laminar flow thermodynamics to build a table based on the characteristic variable mixture fraction Z and reaction progress variable Y c Construct thermodynamic table; use β-PDF method; specific calculation only needs to calculate the mixture fraction and variance Reaction progress variables and variance The transport equation is as follows:

[0091]

[0092]

[0093]

[0094]

[0095] In the formula, the superscript “—” indicates spatial filtering, and “~” indicates Fave filtering; Sc t =0.7 is the Schmitdt number; λ = μC p / Pr is the molecular thermal diffusion coefficient, μ is the dynamic viscosity, C p is the heat capacity coefficient, Pr=0.85; C g =2.86, G d =2.0; is the source term of the reaction progress variable, which is closed by the Zimont model; c φ =2.0; τ turb =k / ε is the turbulence time scale;

[0096] 52) Use the re-modeled and partially premixed FGM thermodynamic tables, perform unsteady calculations on the combustion chamber pollutants, and obtain the distributions of flow field velocity, temperature, components, and characteristic scalars.

[0097] 6) Solve the NOx transport equation and correct the NOx generation by defining the temperature fluctuation coefficient, as follows:

[0098] 61) Due to the relatively long time scale of NOx generation, it is difficult to couple it well in a CFD model. Therefore, NOx calculations are usually solved by introducing a separate NOx model after the flow field calculations are completed. The NOx transport equation is as follows:

[0099]

[0100] Where S NO It is the source term of the equation and needs to be modeled according to different NO species.

[0101] For thermal NO, the following equation is used to calculate the closed transport equation for the source term:

[0102]

[0103]

[0104] Where k f，1 =1.8×10 8 e -38370 / T , k f，2 =1.8×10 4 Te -4680 / T , k f,3 =7.1×10 7 e -450 / T , k r，1 =3.8×10 7 e -425 / T , k r,2 =3.81×10 3 Te -20820 / T , k r,3 =1.7×108 e -24560 / T is the reaction rate coefficient related to the reaction temperature T; “[]” indicates the concentration of the corresponding reaction component; M w,NO is the molar mass of NO.

[0105] For fast NO, the following equation is used to calculate the closed transport equation for the source term:

[0106]

[0107]

[0108] Where, f = 4.75 + 0.0819n - 23.2φ + 32φ 2 -12.2φ 3 , k′ pr =6.4×106(RT / p)a+1,E a =303474.125, n is the number of carbon atoms in the fuel, and φ is the equivalence ratio.

[0109] 62) Define the temperature fluctuation coefficient to correct the NO generation:

[0110] T′ max =T max *T m

[0111]

[0112] Among them, T max is the maximum temperature of the flow field; T′ max is the corrected maximum temperature of the flow field, which is used to calculate the integral upper limit of the NO generation rate affected by turbulence; T m is the temperature fluctuation coefficient, which is used to correct the effect of transient high temperature on NO generation; T mean is the time-averaged temperature of the flow field; T rms is the pulsating temperature.

[0113] like Figure 2 As shown in the basic structure, the Sandia combustion experimental device is used in this embodiment to verify the numerical calculation method of the pollutant NOx that takes into account the influence of combustion temperature fluctuations of the present invention. The calculation domain is discretized using a hexahedral structured grid, and the simulation results are compared and verified with the traditional RANS-FGM calculation method.

[0114] The Sandia flame combustion device features a stable, controlled flame at the fuel inlet, serving as a heat source to maintain stable combustion. The main fuel inlet has a diameter of D = 7.2 mm and receives a mixture of 25% CH4 and 75% air. The annular control stage (ignoring the wall thickness between the main stage and control stage) has a diameter ranging from 1.0D to 2.62D and receives a mixture of C2H2, H2, air, CO2, and N2. The composition, enthalpy, and equivalence ratio of the mixture are equivalent to a methane-air mixture with a 0.77 ratio. The chemical reaction mechanism utilizes the Gri3.0 methane combustion mechanism with detailed intermediate reactions to solve for intermediate reaction products. Air wake flows outside the control stage inlet. This simulation relies on the finite volume numerical method, employing the SIMPLEC algorithm for pressure-velocity coupling, distance-weighted high-order velocity interpolation for mass flux calculation, and element-based gradient least squares discretization for gradients. The time is advanced using a second-order implicit discretization scheme, the convection term is discretized using a central difference scheme, the pressure term is discretized using the PRESTO! scheme, and the turbulence scalar is discretized using a second-order upwind scheme.

[0115] The code of the model method of the present invention is embedded in the CFD software and compiled and executed. The NOx distribution obtained by numerical calculation is as follows: Figure 3 As shown, the left figure shows the transient NO distribution of the central section, and the right figure shows the time-averaged NO distribution of the central section; the simulation results are compared with the experimental results, respectively. Figure 4 and Figure 5 The main components and NOx pollutant distribution shown in the figure. Under this invention, the main combustion reaction components and NOx peak, inflection point and axial distribution trend are in good agreement with the experimental values, with high calculation accuracy.

[0116] The present invention has many specific application paths. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principles of the present invention. These improvements should also be considered as the scope of protection of the present invention.

Claims

1. A method for numerical calculation of pollutants NOx taking into account the influence of combustion temperature fluctuations, characterized in that: Here are the steps: 1) Define the resolution control function F r ; 2) Calculating the filter scale coefficient C in the resolution control function in step 1) based on the Smagorinsky subgrid stress model x , and further calculate the resolution control function F r size; 3) as the degree of grid discretization changes, based on the BSLk-ω turbulence model, adaptive adjustment is performed through the resolution control function in step 1) to achieve adaptive transition between the unsteady RANS mode, LES mode, and DNS mode in the calculation process; 4) Based on the resolution control function F r , remodeling the turbulent viscosity coefficient μ in the BSLk-ω turbulence model t , and the corrected turbulent viscosity coefficient is obtained 5) Based on the characteristic variable mixture fraction Z and reaction progress variable Y c Construct a partially premixed FGM laminar flow thermodynamic table to complete the calculation of unsteady flame flow field; 6) Solve the NOx transport equation and correct the NOx generation by defining the temperature fluctuation coefficient; The step 5) is specifically as follows: 51) Using partially premixed FGM laminar flow thermodynamics to build a table based on the characteristic variable mixture fraction Z and reaction progress variable Y c Construct thermodynamic tables; use the β-PDF method; calculate mixture fractions and variance Reaction progress variables and variance The transport equation is as follows: In the formula, the superscript "—" indicates spatial filtering, "~" indicates Fave filtering; Sc t =0.7 is the Schmitdt number; λ = μ p / Pr is the molecular thermal diffusion coefficient, μ is the dynamic viscosity, C p is the heat capacity coefficient, Pr=0.85; C g =2.86, C d =2.0; is the source term of the reaction progress variable, which is closed by the Zimont model; c φ =2.0; τ turb =k / ε is the turbulence time scale; 52) Use the re-modeled and partially premixed FGM thermodynamic tables to perform unsteady calculations on the combustion chamber pollutants and obtain the flow field velocity, temperature, composition and characteristic scalar distribution; The step 6) is specifically as follows: 61) Since the time scale of NOx generation is relatively large, it is difficult to couple it well in a CFD model. Therefore, the calculation of NOx should be solved by introducing a separate NOx model after the flow field calculation is completed. The NOx transport equation is as follows: Where S NO is the source term of the equation, and is modeled according to different NO species; For thermal NO, the following equation is used to calculate the closed transport equation for the source term: Where k f,1 =1.8×10 8 e -38370 / T , k f，2 =1.8×10 4 Te -4680 / T , k f，3 =7.1×10 7 e -450 / T , k r,1 =3.8×10 7 e -425 / T , k r，2 =3.81×10 3 te -20820 / T , k r,3 =1.7×10 8 e -24560 / T is the reaction rate coefficient related to the reaction temperature T; "[]" indicates the concentration of the corresponding reaction component; M w,NO is the molar mass of NO; For fast NO, the following equation is used to calculate the closed transport equation for the source term: Where, f = 4.75 + 0.0819n - 23.2φ + 32φ 2 -12.2φ 3 , k′ pr =6.4×106(RT / p)a+1,E a =303474.125, n is the number of carbon atoms in the fuel, φ is the equivalence ratio; 62) Define the temperature fluctuation coefficient to correct the NO generation: T′ max =T max *T m Among them, T max is the maximum temperature of the flow field; T′ max is the corrected maximum temperature of the flow field, which is used to calculate the integral upper limit of the NO generation rate affected by turbulence; T m is the temperature fluctuation coefficient, which is used to correct the effect of transient high temperature on NO generation; T mean is the time-averaged temperature of the flow field; T rms is the pulsating temperature.

2. The method for calculating the NOx pollutant numerical value considering the influence of combustion temperature fluctuation according to claim 1, characterized in that: The step 1) is specifically as follows: Define the resolution control function F r The expression is: Where, is the minimum function, exp(d)=e d is a natural exponential function, n = 2 and β = 0.002 are empirical constants, L i , L c and L k are the integral length scale, the turbulence cutoff length scale and the Kolmogorov length scale, respectively, and their expressions are: L c =C x (D x D y D z ) 1 / 3 L i =k 3 / 2 / (b * (kω) L k =n 3 / 4 / (b * (kω) 1 / 4 Where C x is the filter scale coefficient; Δ x Δ y Δ z are the scales of the grid in the x, y, and z directions, which are determined by the discrete process; v is the fluid viscosity coefficient; k is the turbulent kinetic energy, ω is the turbulent specific dissipation rate, β * =0.09 is the model constant.

3. The method for calculating the NOx pollutant numerical value considering the influence of combustion temperature fluctuation according to claim 1, characterized in that: The step 2) is specifically as follows: Calculation of filter scale coefficient C based on Smagorinsky sub-grid stress model x , the expression is: Where C μ =0.09 is the model constant, C s is the model constant, ranging from 0.05 to 0.18, Δ is the spatial resolution; S is the strain rate amplitude.

4. The method for calculating the NOx pollutant numerical value considering the influence of combustion temperature fluctuation according to claim 1, characterized in that: The step 3) is as follows: When the resolution control function F r When the size of approaches 1, the unsteady RANS mode becomes dominant and the turbulence is solved by the RANS method; when the resolution control function F r As the grid resolution decreases, the proportion of the unsteady RANS mode gradually decreases, and the proportion of the DNS mode gradually increases. At this time, the LES mode is restored, and the proportion of turbulence solved directly increases. When the resolution control function F r When it approaches 0, the DNS mode becomes dominant and all turbulence is directly solved.

5. The method for calculating the NOx pollutant numerical value considering the influence of combustion temperature fluctuation according to claim 1, characterized in that: The step 4) is specifically as follows: Turbulent viscosity coefficient μ in the BSL k-ω turbulence model t The definition is as follows: m t =ρk / ω Where ρ is the fluid density, k is the turbulent kinetic energy, and ω is the turbulent specific dissipation rate; The turbulent viscosity coefficient μ in the BSL k-ω turbulence model t Modification is made, and the modified turbulent viscosity coefficient Its expression is:

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