CN115081347A - Statistical evaluation method for combustion air proportion in air intake at different positions of flame tube - Google Patents

Statistical evaluation method for combustion air proportion in air intake at different positions of flame tube Download PDF

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CN115081347A
CN115081347A CN202210053768.XA CN202210053768A CN115081347A CN 115081347 A CN115081347 A CN 115081347A CN 202210053768 A CN202210053768 A CN 202210053768A CN 115081347 A CN115081347 A CN 115081347A
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combustion
inlet
mass fraction
flame tube
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龚诚
黄序
郝颜
赵姝帆
阳杰
邱名
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Institute of Aerospace Technology of China Aerodynamics Research and Development Center
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Abstract

The invention discloses a statistical evaluation method for combustion air proportion in air intake at different positions of a flame tube, which relates to the technical field of aviation gas turbine combustion chamber design and adopts the technical scheme that: based on the idea of calculating Euler transport equation in fluid mechanics, a corresponding transport equation is established, and the mass fraction of the intake air and the mass fraction of the carried oxygen at the concerned position are tracked. In order to mark the air flowing into the flame tube at different air inlet positions, the air flow path in the combustion chamber is simplified and dispersed in a separated air inlet mode in the calculation. The proportion of the air participating in combustion in the marked air can be obtained by integrating the marked air mixing fraction and the mass fraction of the oxygen carried by the air mixing fraction at the outlet of the combustion chamber. The method can be used for the combustion air source tracing analysis and the air flow distribution optimization design in the design process of the aviation air-fuel gas turbine combustor.

Description

Statistical evaluation method for combustion air proportion in air intake at different positions of flame tube
Technical Field
The invention relates to the technical field of aviation gas turbine combustor design, in particular to a statistical evaluation method for combustion air proportion in air inlet at different positions of a flame tube.
Background
Due to the limitation of materials and cooling technology, the total oil-gas ratio of a combustion chamber in an aviation gas turbine is far lower than the chemically correct ratio, and the mixed gas of fuel and air can perform combustion chemical reaction only in a narrow oil-gas ratio range (the equivalence ratio alpha is approximately equal to 0.5-2.5). To achieve stable operation of the engine and combustion chamber within the broad disclosure, a zoned flow organization as shown in fig. 1 is typically employed in the combustor basket design. The basic principle is that air entering a combustion chamber flows into a flame tube through air inlets at different positions on the flame tube, so that different functional areas are formed in the flame tube, including a main combustion area, a middle area (also called a post-combustion area) and a blending area. The air flowing into the flame tube is mainly divided into head air inlet, main combustion hole air inlet, middle hole air inlet, mixing hole air inlet and cooling air (divided into front section cooling air, middle section cooling air and rear section cooling air). The relative proportion of air with different air inlet flows is the air flow distribution design of the combustion chamber, and is an important link in the design process of the combustion chamber.
The main purpose of air flow distribution is divided into two: firstly, ensuring that proper air flows into a combustion area (a main combustion area and a supplementary combustion area) to ensure stable and efficient combustion under different working conditions; secondly, the high-efficiency mixing of cold/hot air flow is realized in the mixing area, thereby ensuring the temperature uniformity of the outlet of the combustion chamber. To achieve the first objective, the concept of "combustion air", i.e. the relative flow of air involved in the combustion reaction within the liner, needs to be introduced in the air flow distribution. It is considered that the combustion air contains head intake air flowing from the swirler (2), main combustion hole intake air flowing from the main combustion holes (3), and cooling air (front-stage and middle-stage cooling air) flowing from the cooling holes. The proportions of the air flowing in from different positions participating in combustion are different. Taking the air intake of the main combustion hole (3) as an example, at present, only 40% -50% of the air flowing through the main combustion hole (3) enters the combustion zone through backflow to participate in combustion. However, this ratio is only an empirical value, and it is obvious that the actual backflow ratio is different for different combustion chambers affected by the intake momentum ratio of the main combustion hole.
At present, the statistical analysis method for the combustion air is too empirical, and the development of a combustion chamber design method system is limited. Particularly, an objective combustion air statistical analysis method is urgently needed for the positive design of a novel combustion chamber. Therefore, the present invention is directed to provide a statistical evaluation method for the ratio of combustion air in the intake air at different positions of the liner to solve the above problems.
Disclosure of Invention
The invention aims to provide a statistical evaluation method for the proportion of combustion air in air intake at different positions of a flame tube based on solving the problems, the method of the invention is based on the computational fluid mechanics numerical simulation technology, marks the air inflow at different positions of the flame tube, and establishes a mixing fraction and an oxygen mass fraction to establish a transport equation based on an Euler field; synchronously solving the established transport equation and conventional combustion simulation software of the combustion chamber; the mass percentage of air in the air that participates in combustion can be obtained by integrating the mass of oxygen in the air flowing into the combustion chamber at the outlet of the combustion chamber at the marked response position during the post-treatment.
The technical purpose of the invention is realized by the following technical scheme: a statistical evaluation method for combustion air proportion in air intake at different positions of a flame tube comprises the following steps:
s1, dispersing the inner and outer calculation domains of the flame tube by adopting a multi-inlet separated air inlet method, wherein the whole calculation domain has one outlet and a plurality of air inlets;
s2, establishing a corresponding transport equation based on the calculation domain in the step S1, and tracking the mixed fraction of the air flowing in from the specific inlet i of the flame tube and the mass fraction of the oxygen carried by the air, namely:
Figure BDA0003475378900000031
Figure BDA0003475378900000032
wherein rho is the density of local gas in the flow field, U is the velocity vector, D is the component diffusion coefficient, t is the physical time corresponding to the flow field simulation, z is air,i Characterizing the local mass fraction of air, Y, flowing in at a particular inlet to be traced O2,i And
Figure BDA0003475378900000033
respectively the mass fraction of oxygen in local gas carried by the air flowing in from the tracked specific inlet and the chemical reaction rate thereof;
wherein the content of the first and second substances,
Figure BDA0003475378900000034
is defined as:
Figure BDA0003475378900000035
wherein, Y O2 And
Figure BDA0003475378900000036
respectively the total oxygen mass fraction in the local gas mixture and its chemical reaction rate, Y O2 And
Figure BDA0003475378900000037
provided by a combustion model in a combustion chamber numerical simulation;
s3, solving the two transport equations (1) and (2) in the step S based on the dispersion and the value, namely obtaining the mixing fraction z of the air flowing into the specific inlet i of the concerned flame tube in the flow field air,i And the mass fraction Y of oxygen carried thereby O2,i The spatial distribution of (a);
then to z air,i And Y O2,i Two physical quantities are integrated at the combustion chamber outlet, i.e. the percentage of combustion air in the incoming air at the specific inlet of the flame tube in question is obtained:
Figure BDA0003475378900000041
wherein the content of the first and second substances,
Figure BDA0003475378900000042
is the integral of the point multiplication of the vector of the infinitesimal area on the section A;
Figure BDA0003475378900000043
is the mass fraction of oxygen in pure air.
Further, one outlet in the step S1 is a flame tube outlet; the plurality of air inlets include a head inlet, a main combustion bore inlet, a dilution bore inlet, and a cooling bore inlet.
Further, the transport equation (2) in step S2 is composed of a time partial derivative term, a spatial convection term, a diffusion term, and a source term.
Further, the source item in the oxygen mass fraction transport equation carried by the specific inlet air is determined based on the local total oxygen mass fraction calculated in the region, the reaction source item and the oxygen mass fraction carried by the specific inlet air.
In conclusion, the invention has the following beneficial effects:
the method is based on the idea of calculating Euler transport equation in fluid mechanics, establishes corresponding transport equation, and tracks the mixture fraction of the air intake at the concerned position and the mass fraction of the carried oxygen; meanwhile, in order to mark the air flowing into the flame tube at different air inlet positions, a separate air inlet mode is adopted in calculation to simplify and disperse the air flow path in the combustion chamber; the proportion of the marked air to the air for combustion can be obtained by integral processing of the marked air mixing fraction and the oxygen mass fraction carried by the air mixing fraction at the outlet of the combustion chamber, and the problems that the current statistical analysis method for the combustion air is too high in experience and limits the development of a combustion chamber design method system are solved; the method can be used for the combustion air source tracing analysis and the air flow distribution optimization design in the aviation gas turbine combustor design process.
Drawings
FIG. 1 is a schematic view of a combustion chamber;
FIG. 2 is a schematic diagram of a numerical simulation computational domain based on split charge.
In the figure: 1. a diffuser; 2. a swirler; 3. a main burning hole; 4. a mixing hole; 5. a front section cooling hole; 6. a middle section cooling hole; 7 rear section cooling holes; 8. a head air inlet; 9; a front section cooling gas inlet; 10. a main burner air inlet; 11. a middle section cooling gas inlet; 12. an aeration gas inlet; 13. a rear section cooling gas inlet; 14. an outlet of the combustion chamber.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example (b): a statistical evaluation method for combustion air proportion in air intake at different positions of a flame tube is based on a combustion chamber shown in figure 1, taking air flowing into a main combustion hole (3) of the combustion chamber as an example, a main combustion hole inlet (10) is marked as an inlet 1, and corresponding air mixing fraction and oxygen mass fraction are marked as z air,1 And Y O2,1 The method comprises the following steps:
the method comprises the following steps: simplifying the structure of the conventional combustion chamber shown in FIG. 1 to obtain a calculated area of the multi-inlet liner as shown in FIG. 2;
step two: adding the aim in the pretreatment of the flow combustion simulation of the combustion chamber
Figure BDA0003475378900000061
Figure BDA0003475378900000062
The initial condition and the boundary condition of (1); wherein z is air,1 And Y O2,1 All the initial values of the whole field are set to be 0; in the setting of boundary conditions, z is set at the entrance of the main burning hole air,1 1 and
Figure BDA0003475378900000063
at other inlets set to z air,1 0 and Y O2,1 ＝0；
Step three: performing numerical simulation calculation on the flow field structure in the combustion chamber to obtain a steady-state flow field structure of the combustion chamber; based on the simulation result, the statistics defined by the equation are carried out at the outlet (14) of the combustion chamber, and the percentage of the air flowing into the main combustion hole and participating in the combustion chemical reaction in the flame tube can be obtained.
The present embodiment is only for explaining the present invention, and it is not limited to the present invention, and those skilled in the art can make modifications without inventive contribution to the present embodiment as required after reading the present specification, but all of them are protected by patent law within the scope of the claims of the present invention; for example, the percentage of the combustion air in the intake air at the head of the flame tube can be obtained by replacing the main combustion hole inlet in the above step with the head intake inlet. Therefore, any technical changes made in the technical scheme according to the technical idea provided by the invention fall into the protection scope of the claims of the invention.

Claims (4)

1. A statistical evaluation method for combustion air proportion in air intake at different positions of a flame tube is characterized by comprising the following steps: the method comprises the following steps:
s1, dispersing the inner and outer calculation domains of the flame tube by adopting a multi-inlet separated air inlet method, wherein the whole calculation domain has one outlet and a plurality of air inlets;
s2, based on the calculation domain described in step S1, establishing a corresponding transport equation for tracking the mixture fraction of air flowing in from a specific inlet i of the liner and the mass fraction of oxygen carried by the air, namely:
Figure FDA0003475378890000011
Figure FDA0003475378890000012
wherein rho is the density of local gas in the flow field, U is the velocity vector, D is the component diffusion coefficient, t is the physical time corresponding to the flow field simulation, z is air,i Characterizing the local mass fraction of air, Y, flowing in at a particular inlet to be traced O2,i And
Figure FDA0003475378890000013
respectively the mass fraction of oxygen in local gas carried by the air flowing in from the tracked specific inlet and the chemical reaction rate thereof;
wherein, the first and the second end of the pipe are connected with each other,
Figure FDA0003475378890000014
is defined as:
Figure FDA0003475378890000015
wherein, Y O2 And
Figure FDA0003475378890000016
respectively the total oxygen mass fraction in the local gas mixture and its chemical reaction rate, Y O2 And
Figure FDA0003475378890000017
provided by combustion models in combustion chamber numerical simulation；
S3, solving the two transport equations (1) and (2) in the step S based on the dispersion and the value, namely obtaining the mixing fraction z of the air flowing into the specific inlet i of the concerned flame tube in the flow field air,i And the mass fraction Y of oxygen carried thereby O2,i The spatial distribution of (a);
then to z air,i And Y O2,i Two physical quantities are integrated at the combustion chamber outlet, i.e. the percentage of combustion air in the incoming air at the specific inlet of the flame tube in question is obtained:
Figure FDA0003475378890000021
wherein the content of the first and second substances,
Figure FDA0003475378890000022
is the integral of the point multiplication of the vector of the infinitesimal area on the section A;
Figure FDA0003475378890000023
is the mass fraction of oxygen in pure air.
2. The method as claimed in claim 1, wherein the statistical evaluation of the ratio of combustion air in the intake air at different positions of the liner comprises: one outlet in the step S1 is a flame tube outlet; the plurality of air inlets include a head inlet, a main combustion bore inlet, a dilution bore inlet, and a cooling bore inlet.
3. The method as claimed in claim 1, wherein the statistical evaluation of the ratio of combustion air in the intake air at different positions of the liner comprises: the transport equation (2) in step S2 is composed of a time partial derivative term, a spatial convection term, a diffusion term, and a source term.
4. The method as claimed in claim 3, wherein the statistical evaluation of the ratio of combustion air in the intake air at different positions of the liner comprises: and determining the source item in the mass fraction transport equation of the oxygen carried by the specific inlet air based on the local total mass fraction of the oxygen in the calculated region, the reaction source item and the mass fraction of the oxygen carried by the specific inlet air.
CN202210053768.XA 2022-01-18 2022-01-18 Statistical evaluation method for combustion air proportion in air intake at different positions of flame tube Pending CN115081347A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116522046A (en) * 2023-07-04 2023-08-01 中国航发四川燃气涡轮研究院 Method for analyzing smoke number of main combustion chamber of engine based on axial partition

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116522046A (en) * 2023-07-04 2023-08-01 中国航发四川燃气涡轮研究院 Method for analyzing smoke number of main combustion chamber of engine based on axial partition
CN116522046B (en) * 2023-07-04 2023-09-15 中国航发四川燃气涡轮研究院 Method for analyzing smoke number of main combustion chamber of engine based on axial partition

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