A Method for Database Component Simplification and Reconstruction Applicable to Flamelet Models

Abstract

The present invention belongs to the fields of engine combustion and computational fluid dynamics, and discloses a method for database component reduction and reconstruction applicable to the flamelet model. The method for database component reduction and reconstruction applicable to the flamelet model of the present invention includes specifying the names of the reserved components; traversing the flamelet database and deleting the non-reserved components; calculating the coefficients A 1 to A 7; adding new coefficients A 1 to A 7 in the flamelet database to form a new flamelet database; reassigning the thermochemical parameters of the numerical simulation calculation program. The method for database component reduction and reconstruction applicable to the flamelet model of the present invention reduces the storage amount of the flamelet database and the interpolation calculation amount of the components by storing seven new coefficients and deleting a large amount of useless component information, and improves the calculation efficiency of the flamelet combustion model without reducing the prediction accuracy of the combustion flow field.

Description

Technical Field

[0001] The present invention belongs to the fields of engine combustion and computational fluid dynamics, and particularly relates to a method for reducing and reconstructing database components applicable to the flamelet model. Background Art

[0002] With the development of computational fluid dynamics, the role of numerical simulation in the design process of engine combustion chambers has become increasingly obvious. It can shorten the R & D cycle and reduce R & D costs, but at the same time, it also poses high requirements for both the accuracy and efficiency of numerical simulation. The key to numerical simulation of combustion chambers is the interaction between turbulence and combustion. Since the flamelet combustion model decouples turbulent flow and chemical reactions, it greatly reduces the amount of calculation. At the same time, detailed chemical reaction kinetic mechanisms can be used to depict the details of combustion flow, and it has been widely applied to the design and evaluation of engine combustion chambers.

[0003] The flamelet combustion model needs to store the component values corresponding to different mixture fractions and reaction progress variables in the flamelet database in advance. During calculation, the mass fractions of each component are obtained by looking up tables and interpolating according to the flow field parameters of the local grid, and then the temperature and density are calculated based on the mass fractions of the components. Currently, the fuels used in engines are usually large - molecule hydrocarbon fuels, and their chemical reaction kinetic mechanisms are very complex. For example, aviation engines use aviation kerosene as fuel, and the number of components in its chemical reaction kinetic mechanism is greater than 200. At this time, the calculation efficiency of the flamelet combustion model will be greatly affected. To address this problem, it is necessary to reduce and reconstruct the database of the flamelet model without affecting the overall prediction accuracy to improve the calculation efficiency of the flamelet combustion model.

[0004] Currently, there is an urgent need to develop a method for reducing and reconstructing database components applicable to the flamelet model. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for reducing and reconstructing database components applicable to the flamelet model.

[0006] The method for reducing and reconstructing database components applicable to the flamelet model of the present invention includes the following steps:

[0007] Step1. Specify the names of the components to be retained;

[0008] Specify N 0 names of components to be retained in the flamelet database Flamelet.dat as the judgment criterion for whether a component needs to be removed;

[0009] Step2. Traverse the flamelet database and delete non - retained components;

[0010] Open the flamelet database Flamelet.dat and iterate through the names of all components. If the name of a component is the same as the reserved component name, retain this component and its corresponding parameters; if it is different from the reserved component name, delete this component and its corresponding parameters from the flamelet database Flamelet.dat and store this component and its corresponding parameters in the temporary database Temp.dat;

[0011] Step3. Calculate the coefficients A 1~ A 7;

[0012] Based on the data in the temporary database Temp.dat, solve for the coefficients respectively by solving a system of simultaneous equations A 1, A 2, A 3, A 4, A 5, A 6, A 7;

[0013] Step4. Add the coefficients to the flamelet database A 1~ A 7 to form a new flamelet database;

[0014] Add the coefficients to the flamelet database Flamelet.dat A 1, A 2, A 3, A 4, A 5, A 6, A 7 to form a new flamelet database Flamelet_new.dat;

[0015] Step5. Reassign the thermochemical parameters of the numerical simulation calculation program;

[0016] According to the order of the components in the new flamelet database Flamelet_new.dat file, reassign the thermochemical parameters of the numerical simulation calculation program to ensure one-to-one correspondence; the thermochemical parameters include the names of each component, as well as the molecular weights, thermodynamic coefficients, and transport coefficients corresponding to the names of each component respectively.

[0017] Furthermore, the calculation process of the coefficients A 1~ A 7 in Step3 is as follows:

[0018] Step301. Determine that the key technical parameter of the flamelet combustion model is the component mass fraction;

[0019] The flame surface combustion model calculates the temperature value by combining the component mass fractions with the enthalpy value, calculates the density by combining the component mass fractions with the molar mass, and determines that the key technical parameter of the flame surface combustion model is the component mass fraction, which is obtained by looking up and interpolating in the flame surface database;

[0020] Step302. Define the coefficients A 1 to A 6, and give a method for solving the temperature of the gas mixture;

[0021] The product of the combustion of fuel and air is a gas mixture. For a gas mixture containing n components, the enthalpy h and the enthalpy of each component h i and the mass fraction Y i have the following relationship:

[0022] ;

[0023] The enthalpy of a single component in the gas mixture and the temperature T have the following relationship:

[0024] ;

[0025] Among them, M i is the molar mass of component i , R u is the universal gas constant, is the fitting coefficient of component i ;

[0026] Set the components of the mass fractions retained in the flame surface database to 1, 2... N 0, and the components of the mass fractions to be deleted are N 0 + 1, N 0 + 2... n , combine equations (1) and (2) to get:

[0027] ;

[0028] Let

[0029] ;

[0030] Then

[0031] ;

[0032] It can be seen from equation (10) that only components 1, 2... need to be stored in the flame surface database NMass fraction and coefficient of 0 A 1、 A 2、 A 3、 A 4、 A 5、 A 6, the temperature of the gas mixture can be solved through the enthalpy of the gas mixture without storing the mass fractions of the components N 0 + 1、 N 0 + 2…… n of the mass fraction;

[0033] Step303. Define the coefficient A 7, a method for solving the density of the gas mixture is given;

[0034] For a gas mixture containing n components, the pressure p and the density ρ have the following relationship:

[0035] ;

[0036] Let

[0037] ;

[0038] Then

[0039] ;

[0040] It can be seen from equation (13) that in the flamelet database, only the mass fractions and coefficients of components 1, 2... N 0 and A 7 need to be stored, and the density of the gas mixture can be solved through the pressure and temperature of the gas mixture without storing the mass fractions of components N 0 + 1、 N 0 + 2…… n of the mass fraction;

[0041] Step304. Obtain the coefficient A 1~ A 7;

[0042] According to equations (4)-(9) and (12), solve the coefficients A 1、 A 2、 A 3、 A 4、 A 5、 A 6、 A 7.

[0043] The method for database component reduction and reconstruction applicable to the flamelet model of the present invention reduces the storage amount of the flamelet database and the interpolation calculation amount of components by storing seven new coefficients and deleting a large amount of useless component information, and improves the calculation efficiency of the flamelet combustion model without reducing the prediction accuracy of the combustion flow field. Description of the Drawings

[0044] Figure 1 It is a flow chart of a method for database component reduction and reconstruction applicable to the flamelet model of the present invention;

[0045] Figure 2 It is a comparison curve of the radial temperature distribution coefficients at the combustor outlet obtained by two methods for constructing the flamelet database. Detailed Embodiments

[0046] The present invention will be described in detail below with reference to the drawings and embodiments.

[0047] As Figure 1 shown, the method for database component reduction and reconstruction applicable to the flamelet model of the present invention includes the following steps:

[0048] Step1. Specify the names of the components to be retained;

[0049] Specify N the names of 0 components that need to be retained in the flamelet database Flamelet.dat as the judgment criteria for whether a component needs to be removed;

[0050] Step2. Traverse the flamelet database and delete the non-retained components;

[0051] Open the flamelet database Flamelet.dat and traverse the names of all components. If the name of a component is the same as the name of the retained component, then retain this component and the corresponding parameters; if it is different from the name of the retained component, then delete this component and the corresponding parameters in the flamelet database Flamelet.dat, and store this component and the corresponding parameters in the temporary database Temp.dat;

[0052] Step3. Calculate the coefficients A 1~ A 7;

[0053] Based on the data in the temporary database Temp.dat, solve the coefficients A 1, A 2, A 3, A 4, A 5, A 6, A 7 respectively by solving the simultaneous equations;

[0054] Step4. Add coefficients to the flamelet database A 1 to A 7 to form a new flamelet database;

[0055] Add coefficients 1, A 1, A 2, A 3, A 4, A 5, A 6, A 7 to the flamelet database Flamelet.dat to form a new flamelet database Flamelet_new.dat;

[0056] Step5. Reassign the thermochemical parameters of the numerical simulation calculation program;

[0057] According to the order of the components in the new flamelet database Flamelet_new.dat file, reassign the thermochemical parameters of the numerical simulation calculation program to ensure one-to-one correspondence; the thermochemical parameters include the names of each component, as well as the component molecular weights, thermodynamic coefficients, and transport coefficients corresponding to the names of each component respectively.

[0058] Furthermore, the coefficients of Step 3 A 1 to A 7 are calculated as follows:

[0059] Step301. Determine that the key technical parameter of the flamelet combustion model is the component mass fraction;

[0060] The flamelet combustion model calculates the temperature value by combining the component mass fraction with the enthalpy value, calculates the density by combining the component mass fraction with the molar mass. Determine that the key technical parameter of the flamelet combustion model is the component mass fraction, and obtain the component mass fraction by looking up the table and interpolating in the flamelet database;

[0061] Step302. Define coefficients A 1 to A 6 and give a method for solving the temperature of the gas mixture;

[0062] The product of fuel and air combustion is a gas mixture. For a gas mixture containing n components, the enthalpy h and the enthalpy of each component h i and the mass fraction Y i have the following relationship:

[0063] ;

[0064] Enthalpy and temperature of individual components in the gas mixture T There is the following relationship:

[0065] ;

[0066] Among them, M i is the molar mass of component i ; R u is the universal gas constant, is the fitting coefficient of component i ;

[0067] Set the components with mass fractions retained in the flamelet database as 1, 2... N 0, and the components with mass fractions deleted are N 0 + 1, N 0 + 2... n , Combine equations (1) and (2) to obtain:

[0068] ;

[0069] Let

[0070] ;

[0071] Then

[0072] ;

[0073] It can be seen from equation (10) that in the flamelet database, only the mass fractions and coefficients of components 1, 2... N 0 need to be stored A 1, A 2, A 3, A 4, A 5, A 6, then the temperature of the gas mixture can be solved through the enthalpy of the gas mixture, and there is no need to store the mass fractions of components N 0 + 1, N 0 + 2... n ;

[0074] Step303. Define the coefficient A 7 and give a method for solving the density of the gas mixture;

[0075] For a gas mixture containing n components, the pressure p and the density ρ have the following relationship:

[0076] ;

[0077] Let

[0078] ;

[0079] Then

[0080] ;

[0081] As can be seen from Equation (13), in the flamelet database, only the mass fractions and coefficients of components 1, 2,... N 0 need to be stored, and A 7. Then, the density of the gas mixture can be solved through the pressure and temperature of the gas mixture, without storing the mass fractions of components N 0 + 1, N 0 + 2... n ;

[0082] Step304. Obtain the coefficients A 1 to A 7;

[0083] According to Equations (4)-(9) and (12), solve the coefficients A 1, A 2, A 3, A 4, A 5, A 6, A 7 respectively.

[0084] Example: In this example, a single-head combustion chamber is used to test the method for reducing and reconstructing the database components applicable to the flamelet model of the present invention.

[0085] The combustion medium of the single-head combustion chamber is aviation kerosene. The calculation adopts a detailed mechanism with 203 components and 1592 chemical reactions; the method for reducing and reconstructing the database components applicable to the flamelet model in this example retains 10 components, namely: CO2, CO, H2O, O2, N2, H2, CH4, OH, CH, and CH2O; among them, the first level is the main products, including CO2 and H2O; the second level is the intermediate products, including CO, OH, CH, H2, CH4, and CH2O; the third level is the oxidants, including O2 and N2;

[0086] In this example, the radial temperature distribution coefficient at the outlet of the combustion chamber is calculated respectively through the traditional method for constructing the flamelet database and the method for reducing and reconstructing the database components applicable to the flamelet model of the present invention.

[0087] The inflow conditions of the single-head combustion chamber are shown in Table 1. To reduce the calculation amount, during the calculation, gaseous fuel is adopted, fuel atomization is ignored, and at the same time, the cooling holes of the flame tube are simplified, and the total number of grids is about 1.3 million.

[0088] Table 1 Inflow Conditions of Single-Head Combustor

[0089]

[0090] Figure 2 The comparison curve of the radial temperature distribution coefficient at the combustor outlet obtained by two flamelet database construction methods is given. It can be seen that the results obtained by the two flamelet database construction methods are completely coincident, indicating that the database component reduction and reconstruction method applicable to the flamelet model of the present invention has no influence on the accuracy of numerical simulation.

[0091] Table 2 gives the numerical simulation time consumed by two flamelet database construction methods. It can be seen that the database component reduction and reconstruction method applicable to the flamelet model of the present invention shortens the calculation time by about 20% compared with the traditional flamelet database construction method, and has higher calculation efficiency.

[0092] Table 2 Comparison of Calculation Times

[0093]

[0094] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and embodiments. For those skilled in the art, without departing from the principle of the present invention, all the features disclosed in the present invention, or all the steps in the disclosed methods or processes, except for the mutually exclusive features and / or steps, can be combined in any way. The present invention is not limited to the specific details and the illustrated examples here.

Claims

1. A method for database component reduction and reconstruction applicable to the flamelet model, characterized in that The described method for database component reduction and reconstruction includes the following steps: Step1. Specify the names of the retained components; Given N 0 component names to be retained in the Flamelet.dat database as the criterion for judging whether a component needs to be removed; Step2. Traverse the flamelet database and delete non-retained components; Open the flamelet database Flamelet.dat and traverse the names of all components. If the name of a component is the same as the name of the retained component, retain this component and its corresponding parameters; if it is different from the name of the retained component, delete this component and its corresponding parameters in the flamelet database Flamelet.dat, and store this component and its corresponding parameters in the temporary database Temp.dat; Step3. Calculate the coefficient A 1 to A 7; Based on the data in the temporary database Temp.dat, the coefficients are solved separately through the simultaneous equations. A 1. A 2. A 3. A 4. A 5. A 6. A 7; coefficient A 1~ A The calculation process of 7 is as follows: Step301. Determine that the key technical parameter of the flamelet combustion model is the component mass fraction; The flamelet combustion model calculates the temperature value by combining the component mass fraction with the enthalpy value, and calculates the density by combining the component mass fraction with the molar mass. Determine that the key technical parameter of the flamelet combustion model is the component mass fraction, and obtain the component mass fraction by looking up and interpolating in the flamelet database; Step302. Define coefficients A 1~ A 6, and give a method for solving the temperature of the gas mixture; The products of fuel and air combustion are a gas mixture. For a gas mixture containing n components, the enthalpy h has the following relationship with the enthalpy h i and mass fraction Y i : ； Enthalpy and temperature of individual components in a gas mixture T There is the following relationship between them: ； Among them, M i is the molar mass of the component i ; R u is the universal gas constant is the fitting coefficient of the component i ; Set the components of the mass fractions retained in the flamelet database to 1, 2... N 0, and the components of the mass fractions to be deleted are N 0 + 1, N 0 + 2... n , Combine equations (1) and (2) to obtain: ； Let ； Then ； As can be seen from Equation (10), in the flamelet database, only the mass fractions and coefficients of components 1, 2... N 0 need to be stored A 1, A 2, A 3, A 4, A 5, A 6, and the temperature of the gas mixture can be solved by the enthalpy of the gas mixture without storing the mass fractions of components N 0 + 1, N 0 + 2... n ; Step303. Define coefficients A 7. Provide a method for solving the density of a gas mixture For a gas mixture containing n components, the pressure p and the density ρ are related as follows: ； Let ； Then ； As can be seen from Equation (13), in the flamelet database, only the mass fractions and coefficients of components 1, 2... N 0 need to be stored A 7. Then, the density of the gas mixture can be solved from the pressure and temperature of the gas mixture without storing the mass fractions of components N 0+1, N 0+2... n ; Step304. Obtain the coefficient A 1 to A 7; Solve the coefficients respectively according to equations (4)-(9) and (12). A 1、 A 2、 A 3、 A 4、 A 5、 A 6、 A 7; Step4. Add coefficients to the flame surface database A 1 to A 7 to form a new flame surface database; Add coefficients to the flamelet database Flamelet.dat A 1、 A 2、 A 3、 A 4、 A 5、 A 6、 A 7, to form a new flamelet database Flamelet_new.dat; Step5. Reassign the thermochemical parameters of the numerical simulation calculation program; According to the order of the components in the new flamelet database Flamelet_new.dat file, reassign the thermochemical parameters of the numerical simulation calculation program to ensure one-to-one correspondence; the thermochemical parameters include the names of each component, as well as the component molecular weights, thermodynamic coefficients, and transport coefficients corresponding to the names of each component respectively.

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