A calculation method for fuel effective equivalence ratio for the simulation results of two-phase combustion in OpenFOAM

Abstract

The present invention relates to the technical field of post - processing and analysis of combustion numerical simulation results, and specifically discloses a method for calculating the fuel effective equivalence ratio for the simulation results of two - phase combustion in OpenFOAM, including the following steps: reading multiple discretized grid files and creating a case grid; creating a global blank file to store information such as transient positions and effective equivalence ratios at different times; writing variable names in the above - mentioned blank file; cyclically reading the component field data files in each time folder; creating a blank field file in each moment directory to store the mass fractions of carbon / hydrogen / oxygen elements, effective equivalence ratio, and mixture fraction at that moment; defining and calculating the mass fractions of carbon / hydrogen / oxygen elements, effective equivalence ratio, and mixture fraction in all components; extracting key information on the characteristic surface. By adopting the above - mentioned method for calculating the fuel effective equivalence ratio for the simulation results of two - phase combustion in OpenFOAM, the present invention can monitor the combustion organization of the power system in real - time and support its improved design.

Description

Technical Field

[0001] The present invention relates to the technical field of post-processing and analysis of combustion numerical simulation results, and in particular to a method for calculating the fuel effective equivalence ratio for the simulation results of two-phase combustion in OpenFOAM. Background Technique

[0002] With the rapid development of computer hardware and software technologies, computational fluid dynamics (CFD) has been widely used in simulating and studying chemical reaction flows. OpenFOAM is an object-oriented open-source C++ library based on the finite volume method, with significant advantages such as open code, free access, easy expansion, and support for large-scale parallel computing. Compared with commonly used commercial CFD software such as ANSYS Fluent, COMSOL Multiphysics, STAR-CCM+, etc., which have closed algorithms and expensive copyrights, the code of OpenFOAM is completely open, with extremely strong flexibility and easy expandability, and can be customized according to the research needs of users. It supports polyhedral meshes, can handle complex geometric configurations, and has powerful simulation and analysis capabilities for fluid flow, heat transfer, and multi-physics coupling problems. It has been widely used in fields such as aerospace and ordnance industries, ship and ocean, energy and power, vehicles and ground transportation, heavy industrial machinery, and electronic and electrical appliances.

[0003] Liquid fuels, especially liquid hydrocarbon fuels, have been widely used in various power systems such as internal combustion engines, gas turbines, aero-engines, rockets, and ramjets due to their significant advantages such as easy storage (thus enabling rapid response), easy transportation, low production cost, high volume energy density, and usability as coolants. As a fuel, liquid hydrocarbons need to undergo extremely complex physical-chemical processes such as continuous liquid-phase injection, primary atomization of liquid columns, secondary breakup of liquid clusters, turbulent dispersion of droplets, forced motion, endothermic evaporation, fuel vapor mixing, ignition, and flame propagation to achieve stable combustion and provide power. During the above processes, due to the limited penetration depth, turbulent transport, and convective diffusion of liquid jets, it is extremely easy to cause uneven spatial distributions of fuel droplet size, number density, and fuel-air equivalence ratio, etc. The uneven local equivalence ratio has a significant adverse impact on the ignition reliability, flame stability, combustion efficiency, and power smoothness of the power system. In severe cases, it may lead to damage to the power system and mission failure.

[0004] When liquid fuel burns, the gas-liquid two-phase always coexists, and the actual combustion process occurs in the gas phase. Therefore, when using OpenFOAM for simulation, it is difficult to obtain the gas-phase equivalence ratio that truly affects combustion performance, which is also a relatively weak point in the post-processing of OpenFOAM data. OpenFOAM outputs the calculation results of different field quantities in the form of scattered independent files, and the number of data files is relatively large. However, the configuration and mesh are comprehensively determined by multiple files, which is not convenient for quickly reading, refining, and analyzing the results. In addition, the chemical reaction mechanism of liquid hydrocarbon fuels is complex, and there are usually multiple combustible intermediate products containing carbon or hydrogen. Calculating the local equivalence ratio directly with a single component of hydrocarbon fuel vapor cannot reflect the real situation and may have large errors, which is not conducive to the refined design of the power system and the precise control of combustion organization. Therefore, for the two-phase combustion simulation results of OpenFOAM, a data post-processing algorithm that can quickly and accurately calculate the gas-phase equivalence ratio (referred to as the fuel effective equivalence ratio) is needed. Summary of the Invention

[0005] The object of the present invention is to provide a method for calculating the fuel effective equivalence ratio for the two-phase combustion simulation results of OpenFOAM, which can quickly, conveniently, and accurately calculate the effective equivalence ratio of the gas-phase fuel that has evaporated and even partially reacted in the two-phase combustion simulation results of OpenFOAM, and output it in an appropriate and easily readable file form; by adding a characteristic structure discrimination code, the evolution process of the effective equivalence ratio on characteristic surfaces such as shock fronts and flame surfaces can be obtained, so as to monitor the combustion organization of the power system in real time and provide a reference basis for the improved design of the power system.

[0006] To achieve the above object, the present invention provides a method for calculating the fuel effective equivalence ratio for the two-phase combustion simulation results of OpenFOAM, including the following steps:

[0007] S1. Set the current working path of OpenFOAM, read multiple discretized mesh files, and create a case mesh;

[0008] S2. Create a global blank file in the working directory to store information such as the transient positions and effective equivalence ratios of shock fronts and flame surface characteristic structures at different times;

[0009] S3. Write variable names in the blank file in step S2 above, and the variable names represent time information, three-dimensional coordinates of characteristic surfaces, heat release rate, mass fractions of carbon / hydrogen / oxygen elements, and effective equivalence ratio;

[0010] S4. Read the heat release rate, pressure gradient, and all component field data files containing carbon / hydrogen / oxygen elements in a single time folder, and traverse all times in the working directory;

[0011] S5. Create blank field files YC, YH, YO, EqvPhi, and Zo in each time directory to store the mass fractions of carbon / hydrogen / oxygen elements, the effective equivalence ratio, and the mixture fraction at that time.

[0012] S6. Define and calculate the mass fractions of carbon / hydrogen / oxygen elements in all components through regular expressions and save them in the form of OpenFOAM standard field data in each time directory.

[0013] S7. Define and calculate the effective equivalence ratio and the mixture fraction based on the element ratio through regular expressions and save them as field files.

[0014] S8. Define the shock front and flame front structures through regular expressions, extract the key information on the characteristic surfaces, and the key information is the time evolution process of the effective equivalence ratio for dynamic monitoring.

[0015] Preferably, in step S1, the case mesh is a static mesh, a dynamic mesh, a structured mesh, or an unstructured mesh. The static mesh means that the same mesh is used at all times and the mesh does not change during the numerical simulation process. The dynamic mesh refers to the mesh whose mesh topology or computational domain boundary changes during the numerical simulation.

[0016] Preferably, in step S2, the global blank file can be set in any file format as needed. The shock front is characterized by the maximum modulus of the pressure gradient, and the flame front is discriminated by the maximum value of the heat release rate. The time evolution information of the shock front and the flame front are respectively stored in two files SF.dat and RF.dat.

[0017] Preferably, in step S3, write the variable names time, XSF, YSF, ZSF, QdotSF, gradpSF, YCSF, YHSF, YOSF, and EqvPhiSF respectively at the first line of the SF.dat file to store the time information, the x / y / z axis coordinates on the shock front, the heat release rate, the pressure gradient, the mass fractions of C / H / O elements, and the effective equivalence ratio. Write the variable names time, XRF, YRF, ZRF, QdotRF, gradpRF, YCRF, YHRF, YORF, and EqvPhiSF at the first line of the RF.dat file to store the time information, the x / y / z coordinates on the shock front, the heat release rate, the pressure gradient, the mass fractions of C / H / O elements, and the effective equivalence ratio, and separate the variable names with commas.

[0018] Preferably, in step S4, read the calculation results of the components, the heat release rate, and the pressure gradient in each time directory in the OpenFOAM standard file reading and writing method, and traverse all times in the working directory through the forAll loop embedded in OpenFOAM.

[0019] Preferably, in step S5, a blank field file is still created in each time directory in the OpenFOAM standard file reading and writing manner to store the calculation results of some field quantities.

[0020] Preferably, in step S6, all components containing carbon / hydrogen / oxygen elements have the general formula C x H y O z , where x, y, and z are the numbers of C, H, and O atoms in the molecule respectively, and their mass fractions are:

[0021]

[0022] M C 、M H and M O are the molecular weights of C, H, and O elements respectively, and the summation symbol Σ indicates that the above calculations traverse all components containing C, H, and O elements.

[0023] Preferably, in step S7, based on the effective equivalence ratio φ e of the element and the mixture fraction Z O are respectively:

[0024]

[0025] is the mass fraction of oxygen element in the oxidizer. Since the mass fractions of all components or elements are calculated in the gas phase, the above formula naturally represents the effective equivalence ratio and mixture fraction of the gas-phase fuel and covers all components containing C / H / O elements.

[0026] Preferably, in step S8, for each moment, all computational grids are traversed with a forAll loop, and grid cells that meet the characteristics of the shock front and flame front are screened with an if judgment. According to the variable name order defined in step S3, the information on the characteristic grids is output to the global file, and the evolution process of the characteristic surface during this period is obtained by traversing all moments.

[0027] Therefore, the present invention adopts the above method for calculating the fuel effective equivalence ratio for the simulation results of two-phase combustion in OpenFOAM, and the beneficial effects are as follows:

[0028] (1) The present invention is oriented to the numerical simulation results of two-phase combustion in OpenFOAM, and can quickly and accurately calculate the equivalence ratio distribution on all grids of the liquid fuel power system, considering all intermediate components of incomplete evaporation and incomplete combustion of the fuel.

[0029] (2) The present invention can extract characteristic structures such as shock wave fronts (which are particularly important for internal combustion engine knock and air-breathing hypersonic power systems) and the time-evolution information of key variables on the flame surface, and can support the refined design of combustion organization.

[0030] (3) The calculation method of the present invention has good scalability. For any liquid hydrocarbon fuel and any reaction mechanism, only the components read in the fourth step and the regular expressions for calculating elemental mass fractions in the sixth step need to be modified accordingly.

[0031] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Description of the Drawings

[0032] Figure 1 is the effective equivalence ratio calculation flow chart of an embodiment of the fuel effective equivalence ratio calculation method for the OpenFOAM two-phase combustion simulation results of the present invention;

[0033] Figure 2 is the schematic diagram of the physical model of the n-heptane droplet / air one-dimensional detonation problem of an embodiment of the fuel effective equivalence ratio calculation method for the OpenFOAM two-phase combustion simulation results of the present invention;

[0034] Figure 3 is the spatio-temporal distribution of the effective equivalence ratio of the n-heptane droplet / air one-dimensional detonation of an embodiment of the fuel effective equivalence ratio calculation method for the OpenFOAM two-phase combustion simulation results of the present invention;

[0035] Figure 4 is the evolution of the effective equivalence ratio on the characteristic surface of the n-heptane droplet / air one-dimensional detonation of an embodiment of the fuel effective equivalence ratio calculation method for the OpenFOAM two-phase combustion simulation results of the present invention;

[0036] Figure 5 is the schematic diagram of the physical problem of the hydrogen-guided n-heptane droplet fuel scramjet combustion chamber of an embodiment of the fuel effective equivalence ratio calculation method for the OpenFOAM two-phase combustion simulation results of the present invention;

[0037] Figure 6 is the effective equivalence ratio cloud map of the scramjet combustion chamber of an embodiment of the fuel effective equivalence ratio calculation method for the OpenFOAM two-phase combustion simulation results of the present invention, with the n-heptane stoichiometric ratio contour line added;

[0038] Figure 7 is the mixture fraction cloud map of the scramjet combustion chamber of an embodiment of the fuel effective equivalence ratio calculation method for the OpenFOAM two-phase combustion simulation results of the present invention, with the hydrogen equivalence mixture fraction contour line added. Detailed Embodiments

[0039] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0040] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention pertains.

[0041] A method for calculating the fuel effective equivalence ratio for the simulation results of two-phase combustion in OpenFOAM includes the following steps:

[0042] S1. Set the current working path of OpenFOAM, read multiple discretized grid files and create a case grid; the case grid can be a static grid, a dynamic grid, a structured grid or an unstructured grid. A static grid means that the same grid is used at all times and the grid does not change during the numerical simulation process; a dynamic grid means a grid in which the grid topology or the computational domain boundary changes during the numerical simulation. For example, simulation methods such as rotating machinery, moving boundaries and adaptive mesh refinement, the grid changes dynamically during the calculation process.

[0043] S2. Create a global blank file in the working directory to store information such as the transient positions and effective equivalence ratios of the shock front and flame front characteristic structures at different times; the global blank file can be set in any file format as needed, such as the.dat format that is easily readable by common data processing software such as Origin and Tecplot.

[0044] The shock front is characterized by the maximum modulus of the pressure gradient, and the flame front is discriminated by the maximum value of the heat release rate. The time evolution information of the shock front and the flame front is stored in two files, SF.dat and RF.dat, respectively.

[0045] S3. Write variable names in the blank file in step S2 above. The variable names characterize time information, three-dimensional coordinates of the characteristic surface, heat release rate, mass fractions of carbon / hydrogen / oxygen elements, and effective equivalence ratio, etc.

[0046] Specifically, write the variable names time, XSF, YSF, ZSF, QdotSF, gradpSF, YCSF, YHSF, YOSF, and EqvPhiSF at the first line of the SF.dat file to store the time information, the x / y / z coordinates on the shock front, the heat release rate, the pressure gradient, the mass fractions of C / H / O elements, and the effective equivalence ratio respectively; write the variable names time, XRF, YRF, ZRF, QdotRF, gradpRF, YCRF, YHRF, YORF, and EqvPhiSF at the first line of the RF.dat file to store the time information, the x / y / z coordinates on the flame front, the heat release rate, the pressure gradient, the mass fractions of C / H / O elements, and the effective equivalence ratio respectively. Separate the variable names with commas so that different column data can be recognized when reading into common data software.

[0047] S4. Read the heat release rate, pressure gradient, and all component field data files containing carbon / hydrogen / oxygen elements in a single time folder, and traverse all time steps in the working directory; read the calculation results of components, heat release rate, and pressure gradient in each time step directory in the OpenFOAM standard file reading and writing mode (IOdictionary class), and traverse all time steps in the working directory through the forAll loop embedded in OpenFOAM. The specific components and their quantities are determined by the chemical reaction mechanism used in the actual calculation and can be flexibly modified according to needs.

[0048] S5. Create blank field files YC, YH, YO, EqvPhi, and Zo in each time step directory to store the mass fractions of carbon / hydrogen / oxygen elements, the effective equivalence ratio, and the mixture fraction at that time step; still create blank field files in each time step directory in the OpenFOAM standard file reading and writing mode to store the calculation results of some field quantities.

[0049] Therefore, the output files have the same organizational form as other field quantities output by OpenFOAM numerical calculations and also form a mapping relationship with the mesh files, facilitating further processing and analysis.

[0050] S6. Define and calculate the mass fractions of carbon / hydrogen / oxygen elements in all components through regular expressions and save them in the form of OpenFOAM standard field data in each time step directory; all components containing carbon / hydrogen / oxygen elements have the general formula C x H y O z , where x, y, and z are the numbers of C, H, and O atoms in the molecule respectively, and their mass fractions are as follows:

[0051]

[0052] M C 、F H and MO are the molecular weights of C, H, and O elements respectively, and the summation symbol Σ indicates that the above calculation traverses all components containing C, H, and O elements.

[0053] S7. Define and calculate the effective equivalence ratio and mixture fraction based on the element ratio through regular expressions, and save them as field files, covering all components such as combustible intermediates;

[0054] The effective equivalence ratio φ based on elements e and the mixture fraction Z O are respectively:

[0055]

[0056]

[0057] is the mass fraction of oxygen element in the oxidizer. Since the mass fractions of all components or elements are calculated in the gas phase, the above formula naturally represents the effective equivalence ratio and mixture fraction of the gas-phase fuel, and covers all components containing C / H / O elements.

[0058] S8. Define the shock front and flame front structures through regular expressions, extract key information on the characteristic surfaces, and the key information is the time evolution process of the effective equivalence ratio, which is used for dynamic monitoring.

[0059] For each moment, traverse all computational grids with a forAll loop, and use an if statement to filter out the grid cells that meet the characteristics of the shock front and flame front. According to the variable name order defined in step S3, output the information on the characteristic grids to the global file, and traverse all moments to obtain the evolution process of the characteristic surfaces during this period.

[0060] Through the above steps, a high-efficiency data post-processing method for calculating the effective equivalence ratio of a liquid fuel power system for the simulation results of OpenFOAM two-phase combustion is given, and the results are saved in an easy-to-read file format such as the common data processing software Origin, Tecplot, etc., which is convenient for further analysis.

[0061] The fuel effective equivalence ratio calculation process of the present invention for the simulation results of OpenFOAM two-phase combustion is as Figure 1 .

[0062] First, read the discretized grid file and multiple data files of the simulation results. If a static grid is used in the calculation, only read the grid file at the first moment; if a dynamic grid is used in the calculation, the corresponding grid file needs to be read again at each moment.

[0063] Secondly, establish the mapping relationship between the mesh file and the data file to complete the code preparation work. Meanwhile, create blank files SF.dat and RF.dat in the working directory based on the standard file reading and writing methods of OpenFOAM, and create blank field files YC, YH, YO, EqvPhi, and Zo in each time folder.

[0064] Thirdly, calculate the mass fractions of carbon, hydrogen, and oxygen elements through regular expressions (1)–(3), and then calculate the effective equivalence ratio and mixture fraction through regular expressions (4)–(5). Save the above results in each time folder, with the same file structure as other scalar fields in OpenFOAM.

[0065] Finally, define the shock front, flame front, etc. through regular expressions, and extract key information such as the effective equivalence ratio on the characteristic surface. Write the results into the files SF.dat and RF.dat every time a time folder is read, and traverse all time folders to obtain the time evolution process of the key quantities.

[0066] The functions and effects of the algorithm of the present invention will be further described below through two specific embodiments. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, rather than limiting the applicable scenarios of the present invention.

[0067] Embodiment 1

[0068] The schematic diagram of a one-dimensional detonation tube of n-heptane droplet / air is as Figure 2 , with a total length of 6 m and both ends closed, including a 2-m long pre-detonation tube and a 4-m long two-phase detonation section. The left end of the two-phase detonation section is denoted as x = 0, and the moment when the detonation front enters the two-phase region is denoted as t = 0. The pre-detonation tube is filled with a stoichiometric ratio of n-heptane vapor / air mixture; the two-phase detonation region is an n-heptane droplet / air mixture without fuel pre-evaporation. The initial diameter of the droplets is 10 μm, which are evenly distributed in the two-phase region. It is assumed that the effective equivalence ratio of the mixture formed after complete evaporation with air is 1.0. The initial temperature and pressure of the gas are 300 K and 0.1 MPa respectively, and the initial temperature of the droplets is also 300 K. All are in a static state at the initial moment.

[0069] A local high-temperature and high-pressure region (temperature 2500 K, pressure 5 MPa) with a thickness of 2 cm is set at the left end wall of the pre-detonation tube to induce the detonation wave to initiate. After the initial detonation wave is fully developed and reaches a stable state, it enters the two-phase region and continues to propagate. The n-heptane droplets quickly evaporate and burn under the action of the detonation wave, and there are unevaporated droplets and unreacted combustible intermediate products behind the detonation wave. After using OpenFOAM to complete the numerical simulation of this problem, the present invention algorithm is used to calculate the spatio-temporal distribution of the effective equivalence ratio in the entire two-phase region and the evolution process of the effective equivalence ratio on the dynamically propagating detonation front.

[0070] Figure 3 It is the distribution of the effective equivalence ratio in the time - space domain within the two - phase region (intercepting x = 0 - 2 m) obtained by the algorithm of the present invention. The middle red region is the region where the effective equivalence ratio is non - zero. Its right boundary is the space - time trajectory of the shock front, and its left boundary is the space - time trajectory of the reaction surface. The two blue regions on both sides have φ e →0. Among them, the right - hand blue region is because the shock front has not arrived yet, and the temperature of the n - heptane droplet is the same as that of the air and both are in a static state. The natural evaporation amount is extremely small within a time scale of milliseconds, so the effective equivalence ratio approaches 0. The left - hand blue region is because through the action of the shock front and the reaction surface, the n - heptane droplet is rapidly heated, evaporated, enters the gas phase and ignites, and burns fully within the flame zone. The fuel is exhausted behind the flame front, so the effective equivalence ratio approaches 0. As can be seen from the figure, the initially developed detonation wave in the gas phase (x = - 2 - 0 m, such as Figure 2 ) shows a decoupling trend after entering the two - phase region.

[0071] For example, at t = 0, the shock front and the reaction surface are tightly coupled. As the propagation distance increases, the distance between the two widens, and the detonation wave degenerates into a leading shock wave accompanied by a deflagration wave. In addition, due to the strong impact of the leading shock wave, the n - heptane droplets cannot be immediately accelerated to the gas - phase velocity, showing a significant aggregation effect. That is, in the region swept by the shock front, the n - heptane droplets are confined within a short distance between the shock front and the reaction surface. Although the initial equivalence ratio is 1, the actual local equivalence ratio is close to 20, and the real combustion state is not the initially set state. The calculation method of the fuel effective equivalence ratio developed by the present invention can accurately give the actual combustion state, which has more guiding value for the refined design and precise control of the combustion process.

[0072] Figure 4 is the time evolution process of the effective equivalence ratio on the shock front and the reaction surface after entering the two - phase region. On the shock front, Φ e has violent oscillations, mainly caused by the non - uniform distribution of the droplets. After the shock front sweeps over the droplets, it causes the macroscopic movement and local perturbation of the droplet positions, breaking the original uniform distribution state of the droplets within the computational domain. The non - uniform distribution of the droplets on the grid leads to a highly non - uniform effective equivalence ratio on the shock front after evaporation, showing violent oscillations. On the flame front, the oscillation of φ e is significantly weakened, but as the distance between the shock front and the flame front widens, it also shows a gradually increasing trend.

[0073] As can be seen above, even for a simple two - phase combustion model problem, its actual process is extremely complex. It is of great significance to master the real state and working conditions of two - phase combustion in real time, which is also one of the manifestations of the application value of the algorithm of the present invention.

[0074] Example Two

[0075] Schematic diagram of the physical problems of a scramjet combustor with a n - heptane droplet fuel model is as follows Figure 5 , the height of the combustor inlet (in the y - direction) is 50 mm, and the total length (in the x - direction) is 340 mm. At x 1 = 77 mm downstream of the combustor inlet, a strut with a length of 32 mm and a height of 6 mm is placed along the centerline of y = 25 mm. There is a circular hole with a diameter of 1 mm on the back of the strut (at x 0 = 109 mm) for injecting the hydrogen - n - heptane droplet mixture fuel. The upper wall of the combustor has a 3° inclination angle starting from x 2 = 100 mm. The Mach number of the air inflow at the combustor inlet is 2.0, the static temperature is 340 K, and the static pressure is 0.1 MPa. By mass fraction, the air composition is 73.6% nitrogen, 23.2% oxygen, and 3.2% water vapor. Hydrogen is injected into the combustor at a Mach number of 1.0, with a static temperature of 250 K and a static pressure of 0.1 MPa.

[0076] The liquid n - heptane fuel uses hydrogen as the carrier gas. After being fully atomized and broken up, it is injected into the combustor through the same nozzle. The initial diameter of the droplets is 15 μm, the initial temperature is 300 K, and the injection speed is the same as the hydrogen speed, 1200 m / s. The highly reactive hydrogen acts as a pilot flame, promoting the evaporation, ignition, and combustion of the n - heptane droplets after they are injected into the combustor. However, due to the high injection speed of n - heptane, it needs to go through the processes of heating, evaporation, and ignition, and there is a physical region where the droplets are not completely evaporated and the intermediate products are not fully burned. Therefore, this physical model is also a typical two - phase combustion problem, and involves characteristics such as supersonic flow, shock waves, and dual - fuel systems.

[0077] Figure 6 The contour map of the effective equivalence ratio distribution in the combustor behind the fuel strut is given. The white curve is the stoichiometric ratio contour of n - heptane / air (φ l = 1.0). After the gaseous hydrogen and n - heptane droplets are ejected from the back of the strut, due to the high - temperature and low - speed characteristics of the recirculation zone, the fuel has a long residence time, and the effective equivalence ratio is relatively high within a certain distance downstream of the strut. The ignition delay time of n - heptane is longer and the ignition energy is higher compared to hydrogen. As the airflow develops downstream, it is still not completely burned, and several isolated rich - fuel gas clusters are formed under the action of turbulent vortices, that is, the three regions limited by φ l = 1.0 in the downstream of the combustor shown in the figure.

[0078] Figure 7 The contour map of the mixture fraction distribution in the combustor behind the fuel strut is given. The white curve is the equivalence mixture fraction contour of hydrogen / air (Z g = 0.0282). The injection of n - heptane droplets generates some local unburned gas clusters, which carry hydrogen and move downstream. Several isolated hydrogen - rich gas clusters limited by Z g = 0.0282 also appear in the downstream of the combustor.

[0079] Therefore, by adopting the above method for calculating the fuel effective equivalence ratio for the simulation results of two-phase combustion in OpenFOAM, the effective equivalence ratio and the mixture fraction distribution of the simulation results of two-phase combustion in OpenFOAM can be calculated quickly and accurately, and the evolution process of key information on characteristic structures such as shock fronts and flame fronts can be extracted, supporting the refined design of the combustion organization of the power system.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements do not cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for calculating the fuel effective equivalent ratio based on OpenFOAM two-phase combustion simulation results, characterized in that: The following steps are involved: S1. Set the current working path of OpenFOAM, read multiple discretized grid files and create example grids; S2. Create a global blank file in the working directory to store the transient position and effective equivalent ratio information of the characteristic structures of the shock front and flame surface at different times; S3. Write variable names in the blank file of step S2 above, wherein the variable names represent time information, three-dimensional coordinates of characteristic surfaces, heat release rate, mass fraction of carbon / hydrogen / oxygen elements, and effective equivalent ratio; S4, read the heat release rate, pressure gradient, and all component field data files containing carbon / hydrogen / oxygen elements in a single time folder, and traverse all moments in the working directory; S5. Create blank field files YC, YH, YO, EqvPhi and Zo in the directory at each moment to store the mass fraction, effective equivalent ratio and mixture fraction of carbon / hydrogen / oxygen elements at that moment; S6. Define and calculate the mass fractions of carbon / hydrogen / oxygen elements in all components through regular expressions, and save them in the form of OpenFOAM standard field data in each time directory; S7. Define and calculate the effective equivalent ratio based on element ratio and mixture fraction through regular expressions and save them as field files; S8. Define the shock front and flame surface structure by regular expressions, and extract key information on the feature surface, where the key information is the time evolution process of the effective equivalence ratio for dynamic monitoring; In step S6, all components containing carbon / hydrogen / oxygen elements have the general formula C x H y O z , x, y, z are the number of C, H, and O atoms in the molecule, and their mass fractions are: M C 、M H and M O are the molecular weights of C, H, and O elements, respectively. The summation symbol Σ indicates that the above calculation traverses all components containing C, H, and O elements; In step S7, based on the effective equivalent ratio φ of the elements e and mixture fraction Z O They are: is the mass fraction of oxygen in the oxidant. Since the mass fractions of all components or elements are calculated in the gas phase, the above formula naturally characterizes the effective equivalence ratio and mixture fraction of the gas phase fuel, and covers all components containing C / H / O elements.

2. A method for calculating the fuel effective equivalent ratio based on OpenFOAM two-phase combustion simulation results according to claim 1, characterized in that: In step S1, the example grid is a static grid, a dynamic grid, a structured grid or an unstructured grid. The static grid refers to a grid that is the same at all times and does not change during the numerical simulation process; the dynamic grid refers to a grid whose grid topology or computational domain boundary changes during the numerical simulation.

3. A method for calculating the fuel effective equivalent ratio based on OpenFOAM two-phase combustion simulation results according to claim 2, characterized in that: In step S2, the global blank file is set to any file format as needed, the shock front is characterized by the maximum modulus of the pressure gradient, the flame surface is judged by the maximum value of the heat release rate, and the time evolution information of the shock front and the flame surface are stored in two files SF.dat and RF.dat, respectively.

4. A method for calculating the fuel effective equivalent ratio based on OpenFOAM two-phase combustion simulation results according to claim 3, characterized in that: In step S3, the variable names time, XSF, YSF, ZSF, QdotSF, gradpSF, YCSF, YHSF, YOSF and EqvPhiSF are written in the first line of the SF.dat file, respectively, to store time information, x / y / z axis coordinates on the shock front, heat release rate, pressure gradient, C / H / O element mass fraction and effective equivalent ratio; the variable names time, XRF, YRF, ZRF, QdotRF, gradpRF, YCRF, YHRF, YORF and EqvPhiSF are written in the first line of the RF.dat file, respectively to store time information, x / y / z axis coordinates on the shock front, heat release rate, pressure gradient, C / H / O element mass fraction and effective equivalent ratio, and the variable names are separated by commas.

5. A method for calculating the fuel effective equivalent ratio based on OpenFOAM two-phase combustion simulation results according to claim 4, characterized in that: In step S4, the components, heat release rate and pressure gradient calculation results in each moment directory are read in the OpenFOAM standard file reading and writing mode, and all moments in the working directory are traversed through the forAll loop embedded in OpenFOAM.

6. A method for calculating the fuel effective equivalent ratio based on OpenFOAM two-phase combustion simulation results according to claim 5, characterized in that: In step S5, a blank field file is created in each moment directory in the OpenFOAM standard file reading and writing mode to store the calculation results of some field quantities.

7. A method for calculating the fuel effective equivalent ratio based on OpenFOAM two-phase combustion simulation results according to claim 6, characterized in that: In step S8, for each moment, all calculation grids are traversed by the forAll loop, and the grid cells that meet the characteristics of the shock front and flame surface are selected by the if judgment. According to the order of variable names defined in step S3, the information on the characteristic grid is output to the global file, and all moments are traversed to obtain the evolution process of the characteristic surface during this period of time.

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