Filter pressure calculation method and system in large eddy simulation of compressible turbulent combustion

Abstract

A method and system for calculating filtered pressure in large eddy simulation of compressible turbulent combustion, a multi-component ideal gas model for large eddy simulation is established for the flow combustion process, the grids and particles in the area where the gas model is located are initialized, and the filter density, filter temperature, number of components of the multi-component gas, filter mass fraction of each component, and particle position, particle temperature, and particle mass fraction of each grid are obtained; based on the filter density, filter temperature, number of components of the multi-component gas, and filter mass fraction of each grid, the large eddy simulation solvable pressure is calculated; based on the filter density of each grid and the temperature and particle mass fraction of the particles themselves in the current grid, the particle solvable pressure and the particle average pressure are calculated. The present invention obtains the filtered pressure in large eddy simulation based on the relationship between the solvable pressure of large eddy simulation, the average pressure of particles, and the solvable pressure of particles. The present invention can effectively improve the robustness of numerical calculations and maintain a high accuracy when the combustion heat release is strong.

Description

Technical Field

[0001] The invention relates to the field of turbulent combustion numerical simulation, and in particular to an accurate filtering pressure calculation method and system suitable for large eddy simulation of compressible turbulent combustion. Background Art

[0002] Hypersonic vehicles powered by scramjets have shown great potential in both military and civilian applications. The supersonic combustion process in scramjets is extremely complex and has not yet been fully understood, which has also limited the further improvement of scramjets' performance and stability.

[0003] With the development of computational fluid dynamics and computational combustion, numerical simulation has gradually become an indispensable means to understand the supersonic combustion process. Currently, large eddy simulation (LES) has been widely used to simulate supersonic combustion processes. Despite its great success, there are still many key issues to be clarified, especially the closure of some sub-grid models. Among them, one of the most important closed models is the turbulent combustion model, which is usually used to close the chemical reaction source term of the filter.

[0004] The basis of the probability density function (PDF) method is the random assumption, that is, it is assumed that the physical quantities in the turbulent flow field are random variables. Starting from the random method, all single-point single-time processes are strictly closed, no matter how complex the process is. Therefore, the turbulence-chemical reaction interaction can be accurately closed by the probability density function method. In order to improve the robustness of the probability density function (PDF) method, it is usually coupled with the large eddy simulation (LES) to solve it, which is called the LES-PDF method. This method has been widely used in turbulent combustion.

[0005] In addition, an important model in large eddy simulation of compressible turbulent combustion is the filtered pressure model. The filtered pressure is obtained by filtering the multi-component ideal gas state equation, which includes the sub-grid temperature component correlation term. However, the existing filtered pressure calculation method often directly ignores the sub-grid temperature component correlation term.

[0006] In existing large eddy simulations (LES), the filtered pressure is usually directly calculated from the filtered components, temperature, and density based on the ideal gas state equation, and the sub-grid temperature component correlation term is generally ignored. Studies have shown that for cases with weak combustion heat release, the sub-grid temperature component correlation term has little effect and can be ignored; however, for strong heat release, ignoring this term will lead to significant errors. At the same time, for traditional large eddy simulations (LES), there are theoretical difficulties in directly and accurately closing the filtered pressure. Summary of the invention

[0007] For multi-component ideal gas, pressure is a nonlinear function of temperature, composition and density, so it is difficult to directly close the filtered pressure in large eddy simulation. In view of this technical problem, the present invention proposes a method and system for calculating filtered pressure in large eddy simulation of compressible turbulent combustion.

[0008] In order to achieve the above technical objectives, the technical solution proposed by the present invention is:

[0009] In one aspect, the present invention provides a method for calculating filtered pressure in large eddy simulation of compressible turbulent combustion, comprising:

[0010] A multi-component ideal gas model for large eddy simulation is established for the flow combustion process, the grids and particles in the area where the multi-component ideal gas model is located are initialized, and the filter density, filter temperature, number of multi-component gas components, filter mass fraction of each component, and particle position, particle temperature, and particle mass fraction of each grid are obtained;

[0011] Based on the filter density of each grid, the filter temperature, the number of components of the multi-component gas, and the filter mass fraction of each component, the large eddy simulation solvable pressure is calculated;

[0012] Based on the filter density of each grid and the temperature and mass fraction of the particles in the current grid, the particle solvable pressure and the average pressure of the particles are calculated;

[0013] Based on the LES solvable pressure, the particle average pressure and the particle solvable pressure, the filtered pressure in LES is calculated.

[0014] In another aspect, the present invention provides a system for calculating filtered pressure in large eddy simulation of compressible turbulent combustion, comprising:

[0015] The first module is used to establish a multi-component ideal gas model for large eddy simulation of the flow combustion process, initialize the grid and particles in the area where the multi-component ideal gas model is located, and obtain the filter density, filter temperature, number of components of the multi-component gas, filter mass fraction of each component, and particle position, particle temperature, and particle mass fraction of each grid;

[0016] The second module is used to calculate the large eddy simulation solvable pressure based on the filter density of each grid, the filter temperature, the number of components of the multi-component gas, and the filter mass fraction of each component;

[0017] The third module is used to calculate the particle solvable pressure and particle average pressure based on the filter density of each grid and the temperature and particle mass fraction of the particle itself in the current grid;

[0018] The fourth module is used to calculate the filtered pressure in the large eddy simulation based on the large eddy simulation solvable pressure, the particle average pressure and the particle solvable pressure.

[0019] On the other hand, the present invention provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps in the method for calculating filtered pressure in large eddy simulation of compressible turbulent combustion are implemented.

[0020] On the other hand, the present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps in the method for calculating filtered pressure in large eddy simulation of compressible turbulent combustion.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] The present invention effectively combines the advantages of the strong robustness of the large eddy simulation (LES) numerical solution and the ability of the probability density function (PDF) method to accurately close the single-point physical process, while reasonably considering the sub-grid temperature component correlation terms, reducing the negative impact of statistical noise and enhancing the robustness of the numerical solution.

[0023] The traditional LES filter pressure model ignores the sub-grid temperature component correlation term, while the present invention better considers the influence of the sub-grid temperature component correlation term, and the simulation effect of the combustion flow field is better than that of the traditional LES.

[0024] The present invention is based on the large eddy simulation solvable pressure, and the relationship between the particle average pressure and the particle solvable pressure obtains the filtered pressure in the large eddy simulation. On the one hand, with the help of the numerical stability of the large eddy simulation solvable pressure, the robustness of the numerical calculation can be effectively improved. On the other hand, the temperature component correlation item information contained in the particle average pressure and the particle solvable pressure is also considered, and a high accuracy is still maintained when the combustion heat release is strong. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a flow chart of an embodiment of the present invention; it includes the following steps:

[0026] Figure 2 1 is a schematic diagram of the comparison of statistical results of the fully developed stage of an embodiment of the present invention, wherein (a) gives the average distribution of hydroxyl groups OH, and (b) gives the average distribution of peroxide groups (HO2).

[0027] Figure 3 Isosurfaces of vorticity ω=0.1 colored by dimensionless subgrid pressure and heat release rate for an embodiment of the present invention, where (a) gives the distribution of dimensionless subgrid pressure and (b) gives the distribution of dimensionless heat release rate. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention more clearly understood, the following will be used with drawings and detailed descriptions to clearly illustrate the spirit of the contents disclosed by the present invention. After understanding the embodiments of the contents of the present invention, any person skilled in the art can change and modify the techniques taught by the contents of the present invention without departing from the spirit and scope of the contents of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0029] For multi-component ideal gases, pressure is a nonlinear function of temperature, components and density, so it is difficult to directly close the filtered pressure in large eddy simulation. In terms of its own physical meaning, pressure is a single-point physical quantity (i.e., a function of a single point in space), so the probability density function (PDF) method is expected to directly close the filtered pressure. However, the probability density function (PDF) method can theoretically accurately close the filtered pressure, but the numerical calculation contains serious statistical noise, and the numerical solution results are not ideal. Based on the scale similarity assumption, the present invention proposes a method and system for calculating the filtered pressure in large eddy simulation of compressible turbulent combustion, which can make full use of the respective advantages of large eddy simulation and probability density function (PDF) method.

[0030] Reference Figure 1 In one embodiment of the present invention, a method for calculating filtered pressure in large eddy simulation of compressible turbulent combustion is provided, comprising:

[0031] A multi-component ideal gas model for large eddy simulation is established for the flow combustion process, the grids and particles in the area where the multi-component ideal gas model is located are initialized, and the filter density, filter temperature, number of multi-component gas components, filter mass fraction of each component, and particle position, particle temperature, and particle mass fraction of each grid are obtained;

[0032] Based on the filter density of each grid, the filter temperature, the number of components of the multi-component gas, and the filter mass fraction of each component, the large eddy simulation solvable pressure is calculated;

[0033] Based on the filter density of each grid and the temperature and mass fraction of the particles in the current grid, the particle solvable pressure and the average pressure of the particles are calculated;

[0034] Based on the LES solvable pressure, the particle average pressure and the particle solvable pressure, the filtered pressure in LES is calculated.

[0035] The present invention is aimed at flow combustion problems in engineering practice, such as fuel injection, mixing, ignition, flame stabilization, combustion oscillation, flameout re-ignition and other flow combustion processes in scramjet engines, and establishes a corresponding multi-component ideal gas model for large eddy simulation, and obtains the filter pressure in the large eddy simulation of compressible turbulent combustion based on the filter pressure calculation method in the large eddy simulation of compressible turbulent combustion proposed by the present invention. Based on the method provided by the present invention, a given flow combustion problem is simulated, the instantaneous structure and key statistics of the flow field are obtained, and the internal mechanisms such as ignition, flame stabilization, and combustion oscillation in the engine are analyzed, so as to display the real flow combustion process, reveal the key physical phenomena and mechanism problems of concern, and provide a basis for better understanding of the physical process, thereby improving the design capabilities of scramjet engines, etc.

[0036] The pressure of the multi-component ideal gas in the present invention can be determined by the following formula:

[0037]

[0038] Where p is pressure, ρ is density, T is temperature, Y α is the mass fraction of component α, N s is the number of components in the multi-component ideal gas, all of which are given by initialization; R u is the universal gas constant, which is a constant and remains unchanged at 8.3145.

[0039] By performing spatial filtering on equation (1), we can obtain:

[0040]

[0041] The overline indicates the amount of filtering for that quantity, and the wavy line indicates the amount of quality-weighted filtering for that quantity. is the filter density, is the filtered mass fraction of component α, is the filtering temperature. u is the universal gas constant, which is a constant and remains constant at 8.3145. α is the molecular weight of component α, which is directly determined by component α; N s is the number of components in a multicomponent ideal gas.

[0042] The second term in the brackets of formula (2) is called the temperature component correlation term. It is generally believed that when the combustion heat release is weak, the influence of the temperature component correlation term is small and can be ignored; when the combustion heat release is strong, it cannot be ignored. However, due to the difficulty of closure, it is usually ignored in large eddy simulation.

[0043] Therefore, the large eddy simulation solvable pressure of the present invention is calculated by the following formula:

[0044]

[0045] in, It is called the large eddy simulation solvable pressure. Indicates definition.

[0046] For the PDF method, some people have proposed to use the following model to calculate the filter pressure:

[0047]

[0048] In the above formula, the superscript (n) represents the parameter of the nth particle in the current grid of the ensemble domain. p is the number of particles in a single grid, obtained by counting the particles; m (n) , T (n) , represent the mass, temperature and component mass fraction of the nth particle respectively.

[0049] Due to the limited number of particles in actual calculations, the PDF filter pressure contains statistical noise when it is solved by Lagrangian random particles, which introduces random errors. If this result is directly fed back to the large eddy simulation (LES) for iterative calculations, the quality of the numerical solution will be reduced and may even lead to calculation divergence.

[0050] Considering the PDF solvable pressure, the particle solvable pressure in the present invention is calculated by the following formula:

[0051]

[0052] in is the average mass fraction of particles of component α, is the average particle temperature, which is obtained by weighted average of the particle mass fraction and particle temperature of the current grid.

[0053] The average particle pressure is calculated by the following formula:

[0054]

[0055] in is the particle average component temperature product term, which is obtained by weighted averaging the particle mass fraction of the current grid multiplied by the particle temperature. The superscript (w) indicates the result of particle averaging in the current grid.

[0056] The filtered pressure in the large eddy simulation is calculated by the following formula:

[0057]

[0058] in is the average particle pressure, is the solvable pressure of the LES, is the average particle pressure.

[0059] It can be seen that the filter pressure in the large eddy simulation of the present invention includes the traditional large eddy simulation solvable pressure. With the numerical stability of the large eddy simulation solvable pressure, the robustness of the numerical calculation can be effectively improved. In addition, the temperature component correlation information contained in the PDF filter pressure is also considered, and a high accuracy is still maintained when the combustion heat release is strong.

[0060] In another embodiment of the present invention, a method for numerical simulation of a combustion flow field is provided, comprising:

[0061] The filter pressure in the large eddy simulation is obtained by using the method for calculating the filter pressure in the large eddy simulation of compressible turbulent combustion provided in any of the above embodiments;

[0062] Based on the filter pressure, filter density, filter temperature and filter component in the large eddy simulation, other parameters of the combustion flow field are solved to realize the numerical simulation of the combustion flow field.

[0063] It can be understood that those skilled in the art can, according to currently available methods and means, solve other parameters of the combustion flow field based on the filter pressure, filter density, filter temperature, and filter components in the large eddy simulation to achieve numerical simulation of the combustion flow field. Other parameters of the combustion flow field include but are not limited to the average distribution of each component in the combustion flow field, the distribution of dimensionless sub-grid pressure, the distribution of dimensionless heat release rate, etc.

[0064] Reference Figure 1 In one embodiment of the present invention, a numerical simulation method of a combustion flow field is provided, comprising:

[0065] 1) Given a combustion flow field, a multi-component ideal gas model for large eddy simulation is established, the grids and particles in the area where the multi-component ideal gas model is located are initialized, and the filter density, filter temperature, number of multi-component gas components, filter mass fraction of each component, and particle position, particle temperature, and particle mass fraction of each grid are obtained;

[0066] 2) Calculate the large eddy simulation solvable pressure based on the filter density, filter temperature, number of components of the multi-component gas, and filter mass fraction of each component of the current grid;

[0067] 3) Based on the filter density of the current grid, the temperature of the particles themselves in the current grid, and the particle mass fraction, calculate the particle solvable pressure and the particle average pressure;

[0068] 4) Based on the LES solvable pressure, the particle average pressure and the particle solvable pressure, the filtered pressure in the LES is calculated.

[0069] 5) Based on the filter pressure, filter density, filter temperature and filter component in the large eddy simulation, other parameters of the combustion flow field are solved;

[0070] 6) Set the iteration termination condition to determine whether to terminate the iteration. If so, end the calculation. If not, return to step 2) to continue the iteration.

[0071] Those skilled in the art can understand that the iteration termination condition refers to a pre-set model calculation constraint condition, which is used to constrain the entire model to converge in the process of performance calculation so that the model can output a result that meets the condition. For example, the iteration convergence condition can be set to whether the maximum number of iterations is met. When the iteration convergence condition is met, the iteration stops. Of course, in practical applications, those skilled in the art can also set different iteration termination conditions based on the prior art, conventional technical means in this field, or common knowledge.

[0072] Another specific embodiment is provided below to test the accuracy and efficiency of the filtered pressure calculation method in the large eddy simulation of compressible turbulent combustion provided by the present invention.

[0073] This embodiment takes the supersonic hydrogen / air reaction time development mixing layer as an example to introduce the use effect of the invention. The example configuration and boundary conditions are relatively simple, the calculation amount is small, and it also includes typical characteristics of supersonic combustion flow fields such as shock waves, large gradients, and turbulence-chemical reaction interactions.

[0074] The filter pressure calculation method in the large eddy simulation of compressible turbulent combustion provided by the present invention is defined as LESPDF-P3, the traditional large eddy simulation uniformly stirred reactor model is defined as LES-WSR, and the LES-PDF method of the traditional filter pressure model is defined as LESPDF-P1. These three methods are compared. In order to make a quantitative comparison, the results at the full development stage t = 800 are selected for statistics. The average results obtained by different methods are shown in the figure below. Figure 2 shown. Figure 2 : It is a schematic diagram of the comparison of statistical results of the full development stage of an embodiment of the present invention. Among them, (a) gives the average distribution of hydroxyl groups OH, and (b) gives the average distribution of peroxide groups (HO2). From (a), it can be seen that the overall effect of LESPDF-P3 is better than LES-WSR and LESPDF-P1. Especially on the high-temperature oxidant side, the advantage is more obvious. (b) gives the average distribution of peroxide groups (HO2). Similarly, the overall effect of LESPDF-P3 is better than LES-WSR. In numerical calculations, HO2 is generally used as a marker of the self-ignition process. On the oxidant side, the mixed gas is under the action of high temperature, and the related chain reaction of generating HO2 proceeds at a relatively fast speed, so that HO2 accumulates rapidly and reaches a peak value.

[0075] It can be seen that in the fully developed turbulent stage, the turbulent pulsation is very strong, and the turbulence-chemical reaction interaction cannot be ignored. The LES-WSR method has a large error due to the neglect of the turbulence-chemical reaction interaction, especially on the high-temperature oxidant side. The temperature of the mixing layer on the oxidant side is higher, and the self-ignition effect becomes significant at this time. Hydrogen peroxide (HO2) is generally used as a marker of the self-ignition process in numerical calculations. It can be seen that on the oxidant side, the related chain reaction of the mixed gas to generate HO2 proceeds at a faster speed under the action of high temperature, causing HO2 to accumulate rapidly and reach a peak value. Even on the fuel flow side, the HO2 obtained by the LES-WSR method has a certain error. In general, the LES-WSR method cannot accurately describe the turbulent combustion process containing self-ignition characteristics due to the neglect of the turbulence-chemical reaction interaction at the sub-grid scale. At the same time, the LESPDF-P3 method is better than the LES-PDF method based on the traditional filter pressure model (ie, LESPDF-P1) in simulating the supersonic combustion flow field.

[0076] Figure 3 The vorticity isosurfaces at t=800 are given and colored by the dimensionless subgrid pressure and the dimensionless combustion heat release rate. Figure 3 Vorticity |ω|=0.1 isosurfaces colored by dimensionless subgrid pressure and heat release rate, respectively, for one embodiment of the present invention, where (a) gives the distribution of dimensionless subgrid pressure, and (b) gives the distribution of dimensionless heat release rate. In (a), on the oxidant side, the influence of the subgrid pressure term becomes important, with a maximum value of about 0.014. It can be seen in (b) that the combustion heat release reaction mainly takes place on the oxidant side, and at the same time, the enhancement of combustion heat release increases the influence of the subgrid temperature component correlation term. The subgrid component temperature correlation term is 2-3 orders of magnitude smaller than the solvable pressure. Although the relative amount is very small, it will still have a greater impact on the overall reaction flow field through the time accumulation effect.

[0077] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0078] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. Filter pressure calculation method in large eddy simulation of compressible turbulent combustion, It is characterized in that include: A multi-component ideal gas model for large eddy simulation is established for the flow combustion process, the grids and particles in the area where the multi-component ideal gas model is located are initialized, and the filter density, filter temperature, number of multi-component gas components, filter mass fraction of each component, and particle position, particle temperature, and particle mass fraction of each grid are obtained; Based on the filter density of each grid, the filter temperature, the number of components of the multi-component gas, and the filter mass fraction of each component, the large eddy simulation solvable pressure is calculated; Based on the filter density of each grid and the temperature and mass fraction of the particles in the current grid, the particle solvable pressure and the average pressure of the particles are calculated; Based on the LES solvable pressure, the particle average pressure and the particle solvable pressure, the filtered pressure in LES is calculated.

2. The method for calculating filtered pressure in large eddy simulation of compressible turbulent combustion according to claim 1, It is characterized in that The large eddy simulation solvable pressure is calculated by the following formula: in is the filter density, is the filtered mass fraction of component α in the multi-component gas, is the filtering temperature, R u is the universal gas constant, which is a constant, M α is the molecular weight of component α, which is directly determined by component α; N s is the number of components in a multi-component gas.

3. The method for calculating filtered pressure in large eddy simulation of compressible turbulent combustion according to claim 2, It is characterized in that The particle solvable pressure is calculated by the following formula: in is the average mass fraction of particles of component α, is the average particle temperature, which is obtained by weighted average of the particle mass fraction and particle temperature of the current grid.

4. The method for calculating filtered pressure in large eddy simulation of compressible turbulent combustion according to claim 3, It is characterized in that The average particle pressure is calculated by the following formula: in It is the particle average component temperature product term, which is obtained by weighted averaging the particle mass fraction of the current grid multiplied by the particle temperature.

5. The method for calculating filtered pressure in large eddy simulation of compressible turbulent combustion according to any one of claims 1 to 4, It is characterized in that The filtered pressure in the large eddy simulation is calculated by the following formula: in is the average particle pressure, is the solvable pressure of the LES, is the average particle pressure.

6. A numerical simulation method for combustion flow field, It is characterized in that include: The filtered pressure in the large eddy simulation is obtained by using the steps in the method for calculating the filtered pressure in the large eddy simulation of compressible turbulent combustion as described in any one of claims 1 to 4; Based on the filter pressure, filter density, filter temperature and filter component in the large eddy simulation, other parameters of the combustion flow field are solved to realize the numerical simulation of the combustion flow field.

7. Filter pressure calculation system in large eddy simulation of compressible turbulent combustion, It is characterized in that include: The first module is used to establish a multi-component ideal gas model for large eddy simulation of the flow combustion process, initialize the grid and particles in the area where the multi-component ideal gas model is located, and obtain the filter density, filter temperature, number of components of the multi-component gas, filter mass fraction of each component, and particle position, particle temperature, and particle mass fraction of each grid; The second module is used to calculate the large eddy simulation solvable pressure based on the filter density of each grid, the filter temperature, the number of components of the multi-component gas, and the filter mass fraction of each component; The third module is used to calculate the particle solvable pressure and particle average pressure based on the filter density of each grid and the temperature and particle mass fraction of the particle itself in the current grid; The fourth module is used to calculate the filtered pressure in the large eddy simulation based on the large eddy simulation solvable pressure, the particle average pressure and the particle solvable pressure.

8. A computer device comprising a memory and a processor, the memory storing a computer program, Features: When the processor executes the computer program, the steps in the method for calculating filtered pressure in large eddy simulation of compressible turbulent combustion described in any one of claims 1 to 4 are implemented.

9. A computer-readable storage medium having a computer program stored thereon, Features: When the computer program is executed by a processor, the steps of the method for calculating filtered pressure in large eddy simulation of compressible turbulent combustion described in any one of claims 1 to 4 are implemented.

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