A surface source loading method for simulating fuel injection in aerospace engine combustion chamber

Abstract

The present invention belongs to the field of engines and computational fluid dynamics, and discloses a surface source loading method for simulating fuel injection in aerospace engine combustion chambers. The surface source loading method for simulating fuel injection in aerospace engine combustion chambers proposed by the present invention is aimed at the requirements of fast, efficient and accurate numerical simulation of fuel injection in aerospace engine combustion chambers. Without reducing the accuracy of numerical simulation of the combustion chamber, the nozzle is set as a surface source, and the mass source term, momentum source term, energy source term and mixed fraction source term are added to the control equation group, which reduces the difficulty of complex engineering configuration combustion chamber grid modeling and the number of overall combustion chamber grids, better describes the near-field physical characteristics of the nozzle, makes the flow field converge faster, improves the efficiency of combustion chamber design evaluation, and has good engineering practical value.

Description

Technical Field

[0001] The invention belongs to the field of engines and computational fluid dynamics, and in particular relates to a surface source loading method for simulating fuel injection in a combustion chamber of an aerospace engine. Background Art

[0002] In the numerical simulation of the combustion chamber of aerospace engines, it is necessary to solve the Navier-Stokes equations and the component continuity equations or the conservation scalar transport equations to characterize the conservation of mass, momentum, and energy. For compressible flow, the specific control equations are as follows:

[0003] .

[0004] by Figure 1a Taking the concave cavity combustion chamber shown in the figure as an example, kerosene and hydrogen are sprayed into the combustion chamber through dozens or even hundreds of kerosene nozzles and hydrogen nozzles respectively to achieve rapid mixing and organize efficient combustion. In order to simulate the fuel injection, mixing and combustion process of the concave cavity combustion chamber, the traditional combustion chamber numerical simulation method needs to divide all the nozzles into Figure 1b The grid shown.

[0005] Due to the large number of nozzles and their small size, this method of directly dividing the nozzles into grids is time-consuming and labor-intensive, which brings great difficulties to the generation of combustion chamber grids. Especially in the preliminary design stage of the combustion chamber, it is necessary to optimize the selection from hundreds of combustion chamber configurations, which greatly delays the combustion chamber design process.

[0006] At present, a "point source" loading mode has been developed to replace the direct simulation of the nozzle, and good results have been achieved. However, the defect of the "point source" loading mode is that the prediction effect of the flow field near the nozzle is not good. At present, it is urgent to develop a surface source loading method for simulating the fuel injection of the combustion chamber of an aerospace engine. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a surface source loading method for simulating fuel injection in a combustion chamber of an aerospace engine.

[0008] The surface source loading method for simulating fuel injection in a combustion chamber of an aerospace engine of the present invention comprises the following steps:

[0009] S10. Establishing a control equation group for combustion chamber numerical simulation and a CFD program for combustion chamber numerical simulation;

[0010] The control equations for the numerical simulation of the combustion chamber are as follows:

[0011] ;

[0012] in, is the fluid density, For pressure, is the total energy, is a mixed fraction, is the diffusion coefficient, is the enthalpy, for Direction speed, for Direction speed, is the energy flux, is the shear stress, is the Dirichilet constant, For time, for Direction and location;

[0013] S20. Using the surface source loading method to simulate the fuel injection combustion process, determine the combustion chamber numerical simulation control equations with surface source loading, and establish a surface source loading calculation module;

[0014] The nozzle is equivalent to the wall surface, and the mass source term is added to the mesh surface intersecting with the nozzle. , momentum source term , Energy source term and the mixed fraction source term To characterize the effect of fuel injection on the combustion chamber, the mass, momentum and energy conservation of the entire system are guaranteed, the mesh modeling of many nozzles is omitted, and the efficiency of numerical simulation is improved; the control equations for the numerical simulation of the combustion chamber with surface source loading are as follows:

[0015] ;

[0016] S30. Start numerical simulation of the combustion chamber without surface source, calculate to step N, and determine whether to inject fuel;

[0017] S40. If no fuel is injected, the calculation continues until convergence, and the combustion chamber numerical simulation calculation ends;

[0018] S50. If fuel is injected, source item information is determined based on the fuel injection information; the injection information includes injection position, component, and flow rate; the source item information includes mass source item , momentum source term , Energy source term and the mixed fraction source term ;

[0019] S60. According to the injection position, the relative relationship between the injection hole and the grid unit is determined. If the injection hole and the grid unit have an intersection, the intersecting grid surface and grid unit are marked to determine that they are the injection surface and the injection unit;

[0020] S70. Collect all the injection surfaces and injection units, calculate the injection flow of each injection surface according to the fuel injection flow, and then calculate the source items that need to be loaded in the grid unit where the injection surface is located, and update the right-hand side of the control equation group of the combustion chamber numerical simulation in the N+1 step;

[0021] S80. Calling the surface source loading calculation module to simulate the fuel injection combustion process;

[0022] S90. Update the flow field information and return to S50 until convergence. The numerical simulation calculation of the combustion chamber with surface source loading is completed.

[0023] The surface source loading method for simulating fuel injection in an aerospace engine combustion chamber of the present invention aims at the demand for fast, efficient and accurate numerical simulation of fuel injection in an aerospace engine combustion chamber. Without reducing the numerical simulation accuracy of the combustion chamber, the nozzle is set as a surface source, and the mass source term, momentum source term, energy source term and mixed fraction source term are added to the control equation group, thereby reducing the difficulty of mesh modeling of a complex engineering configuration combustion chamber and the number of overall meshes in the combustion chamber, better characterizing the near-field physical characteristics of the nozzle, faster convergence of the flow field, and improving the efficiency of combustion chamber design evaluation, which has practical engineering value. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1a It is a schematic diagram of the structure of the concave cavity combustion chamber model;

[0025] Figure 1b Compute mesh for nozzles of the cavity combustion chamber model;

[0026] Figure 2 This is a flow chart of a surface source loading method for simulating fuel injection in a combustion chamber of an aerospace engine according to the present invention;

[0027] Figure 3 This is a schematic diagram of the combustion chamber configuration of the DLR engine;

[0028] Figure 4a Loading diagram for point source (2D);

[0029] Figure 4b Schematic diagram of point source loading (3D);

[0030] Figure 5a Schematic diagram for area source loading (2D);

[0031] Figure 5b Schematic diagram for area source loading (three-dimensional);

[0032] Figure 6a is the mixture fraction distribution in the unburned case (point source simulated injection);

[0033] Figure 6b is the mixture fraction distribution in the unburned case (surface source simulated injection);

[0034] Figure 6c is the mixture fraction distribution in the unburned case (real physical nozzle);

[0035] Figure 7 It is a schematic diagram of the cavity injection combustion chamber configuration;

[0036] Figure 8a The fuel distribution in the center section of the fuel injection hole (point source simulation injection);

[0037] Figure 8b The fuel distribution in the center section of the fuel injection hole (surface source simulation injection);

[0038] Figure 8c It is the fuel distribution in the center section of the fuel injection hole (real physical injection hole). DETAILED DESCRIPTION

[0039] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0040] like Figure 2 As shown, the surface source loading method for simulating fuel injection in the combustion chamber of an aerospace engine of the present invention comprises the following steps:

[0041] S10. Establishing a control equation group for combustion chamber numerical simulation and a CFD program for combustion chamber numerical simulation;

[0042] The control equations for the numerical simulation of the combustion chamber are as follows:

[0043] ;

[0044] in, is the fluid density, For pressure, is the total energy, is a mixed fraction, is the diffusion coefficient, is the enthalpy, for Direction speed, for Direction speed, is the energy flux, is the shear stress, is the Dirichilet constant, For time, for Direction and location;

[0045] S20. Using the surface source loading method to simulate the fuel injection combustion process, determine the combustion chamber numerical simulation control equations with surface source loading, and establish a surface source loading calculation module;

[0046] The nozzle is equivalent to the wall surface, and the mass source term is added to the mesh surface intersecting with the nozzle. , momentum source term , Energy source term and the mixed fraction source term To characterize the effect of fuel injection on the combustion chamber, the mass, momentum and energy conservation of the entire system are guaranteed, the mesh modeling of many nozzles is omitted, and the efficiency of numerical simulation is improved; the control equations for the numerical simulation of the combustion chamber with surface source loading are as follows:

[0047] ;

[0048] S30. Start numerical simulation of the combustion chamber without surface source, calculate to step N, and determine whether to inject fuel;

[0049] S40. If no fuel is injected, the calculation continues until convergence, and the combustion chamber numerical simulation calculation ends;

[0050] S50. If fuel is injected, source item information is determined based on the fuel injection information; the injection information includes injection position, component, and flow rate; the source item information includes mass source item , momentum source term , Energy source term and the mixed fraction source term ;

[0051] S60. According to the injection position, the relative relationship between the injection hole and the grid unit is determined. If the injection hole and the grid unit have an intersection, the intersecting grid surface and grid unit are marked to determine that they are the injection surface and the injection unit;

[0052] S70. Collect all the injection surfaces and injection units, calculate the injection flow of each injection surface according to the fuel injection flow, and then calculate the source items that need to be loaded in the grid unit where the injection surface is located, and update the right-hand side of the control equation group of the combustion chamber numerical simulation in the N+1 step;

[0053] S80. Calling the surface source loading calculation module to simulate the fuel injection combustion process;

[0054] S90. Update the flow field information and return to S50 until convergence. The numerical simulation calculation of the combustion chamber with surface source loading is completed.

[0055] Embodiment 1: This embodiment is a combustion chamber of a DLR engine. The configuration of the combustion chamber of a DLR engine is shown in Figure 3 The DLR engine combustion chamber inlet is 50mm high and 40mm wide, and the combustion chamber support plate is 32mm long and 6mm high. Hydrogen is sprayed into the combustion chamber through 15 nozzles on the bottom of the support plate. The nozzle diameter is 1mm, the nozzle spacing is 2.4mm, the incoming flow Mach number Ma=2, and the jet flow Mach number Ma=1.

[0056] The schematic diagram of point source loading in this embodiment is shown in Figure 4a , Figure 4b , the schematic diagram of surface source loading is shown in Figure 5a , Figure 5b .

[0057] For the convenience of comparison, three methods are used to carry out calculations: real physical nozzle, point source loading and surface source loading. Figure 6a The distribution of the mixture fraction in the unburned case (point source simulation injection) is given. Figure 6b The distribution of the mixture fraction under unburned conditions (surface source simulated injection) is given. Figure 6c The distribution of the mixture fraction under unburned conditions (real physical nozzle) is given. It can be seen that in the flow field near the nozzle, the results of the injection simulation using a point source are somewhat different from those of the real physical nozzle, while the results of the simulation using a surface source are closer to the real physical nozzle.

[0058] Embodiment 2: This embodiment is a concave cavity injection combustion chamber, and the configuration of the concave cavity injection combustion chamber is shown in Figure 7 The inlet of the cavity injection combustion chamber is 50mm high and 40mm wide; hydrogen is injected from the CU2 position, and 3 nozzles are set in each row, with a nozzle diameter of 1.5mm.

[0059] Figure 8a The fuel distribution in the center section of the fuel injection hole is given (point source simulation injection). Figure 8b The fuel distribution in the center section of the fuel injection hole is given (surface source simulation injection). Figure 8c The fuel distribution in the cross section through the center of the fuel nozzle hole (real physical nozzle hole) is given. It can be seen that near the fuel nozzle hole, there is a large gap between the fuel jet injection height predicted by the point source simulation injection and the real physical nozzle hole, while the fuel jet injection height predicted by the surface source simulation injection is consistent with the real physical nozzle hole.

[0060] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and the embodiments, and can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional improvements and modifications can be easily realized without departing from the principles of the present invention. Therefore, without departing from the general concept defined by the claims and equivalent scope, the present invention is not limited to the specific details and the illustrations shown and described here.

Claims

1. A surface source loading method for simulating fuel injection in a combustion chamber of an aerospace engine, characterized in that: The following steps are involved: S10. Establishing a control equation group for combustion chamber numerical simulation and a CFD program for combustion chamber numerical simulation; The control equations for the combustion chamber numerical simulation are as follows: ； in, is the fluid density, For pressure, is the total energy, is a mixed fraction, is the diffusion coefficient, is the enthalpy, for Direction speed, for Direction speed, is the energy flux, is the shear stress, is the Dirichilet constant, For time, for Direction and location; S20. Using the surface source loading method to simulate the fuel injection combustion process, determine the combustion chamber numerical simulation control equations with surface source loading, and establish a surface source loading calculation module; The nozzle is equivalent to the wall surface, and the mass source term is added to the mesh surface intersecting with the nozzle. , momentum source term , Energy source term and the mixed fraction source term To characterize the effect of fuel injection on the combustion chamber, it ensures the conservation of mass, momentum, and energy of the entire system, saves the mesh modeling of numerous nozzles, and improves the efficiency of numerical simulation; The control equations for the numerical simulation of the combustion chamber with surface source loading are as follows: ； S30. Start numerical simulation of the combustion chamber without surface source, calculate to step N, and determine whether to inject fuel; S40. If no fuel is injected, the calculation continues until convergence, and the combustion chamber numerical simulation calculation ends; S50. If fuel is injected, source item information is determined based on the fuel injection information; the injection information includes injection position, component, and flow rate; the source item information includes mass source item , momentum source term , Energy source term and the mixed fraction source term ; S60. According to the injection position, the relative relationship between the injection hole and the grid unit is determined. If the injection hole and the grid unit have an intersection, the intersecting grid surface and grid unit are marked to determine that they are the injection surface and the injection unit; S70. Collect all the injection surfaces and injection units, calculate the injection flow of each injection surface according to the fuel injection flow, and then calculate the source items that need to be loaded in the grid unit where the injection surface is located, and update the right-hand side of the control equation group of the combustion chamber numerical simulation in the N+1 step; S80. Calling the surface source loading calculation module to simulate the fuel injection combustion process; S90. Update the flow field information and return to S50 until convergence. The numerical simulation calculation of the combustion chamber with surface source loading is completed.

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