A quantitative calculation method for characteristics of composite combustion heat release patterns

Abstract

This invention discloses a method for quantitatively calculating composite combustion heat release pattern characteristics, relating to the technical field of combustion heat release pattern analysis. One specific embodiment of the invention includes determining supersonic and subsonic flow momentum, supersonic and subsonic combustion heat release rates, premixed and diffusion flame indices, and premixed and diffusion combustion heat release rates. The invention provides a visual post-processing calculation method capable of performing a relatively comprehensive quantification of combustion models, enabling rapid identification of the distribution of combustion heat release patterns in flow fields from numerical simulation results.

Description

Technical Field

[0001] The present invention relates to the technical field of combustion heat release pattern analysis, and in particular to a method for quantitatively calculating characteristics of a composite combustion heat release pattern. Background Art

[0002] Hypersonic vehicles, capable of reaching speeds exceeding Mach 5, hold significant potential for application in both civilian and military applications. Propulsion systems are key technologies for achieving hypersonic flight, with scramjets being hailed as the optimal air-breathing propulsion system for achieving these speeds. They offer advantages such as high specific impulse and high speed, and, due to their lack of internal rotating parts, high reliability.

[0003] In the scramjet combustion chamber, the combustion heat release state when the supersonic incoming flow reacts with the fuel can be divided into two categories. First, from the mixing perspective, the air flow and the fuel jet enter the flow channel in a diffused form. The combustion organization between the fuel and air first mainly exhibits diffusion combustion heat release. With the development and evolution of the large-scale vortex structure and the growth of the reaction mixing layer, the degree of mixing between the fuel and air gradually increases, forming a premixed combustion region. Diffusion combustion and premixed combustion exist simultaneously in the flow field. Second, from the flow perspective, due to the constraints of the combustion chamber, the wave system structure in the flow channel, and the influence of chemical reactions, although the fuel and air in the combustion chamber enter the flow channel at supersonic speed, there are still subsonic, transonic, and supersonic regions in the flow field, which indirectly reflects that subsonic and supersonic combustion heat release modes are occurring simultaneously in the flow field.

[0004] Because the combustion structure within a scramjet combustion chamber exhibits a complex heat release pattern, quantifying this heat release pattern from either the mixing or flow perspective alone is incomplete. Combining these two perspectives yields a comprehensive heat release pattern quantification mechanism, providing support for scramjet combustion chamber design. Summary of the Invention

[0005] This paper provides a visual post-processing calculation method that can comprehensively quantify the combustion model and quickly identify the distribution of combustion heat release patterns in the flow field in the numerical simulation results.

[0006] In view of this, according to one aspect of an embodiment of the present invention, a method for quantitatively calculating characteristics of a composite combustion heat release mode is provided, comprising:

[0007] According to formula (1), the supersonic flow and subsonic flow rate are determined.

[0008] (1)

[0009] in, sign(x)Represents a sign function. When x ≥ 0, the return value is 1, otherwise -1. Ma is the Mach number;

[0010] Use Equation (3) to determine the supersonic and subsonic combustion heat release rates,

[0011] (3)

[0012] hrrsup and hrrsub are the unlogarithmized supersonic and subsonic combustion heat release rates, respectively, and hrr is the total heat release rate;

[0013] According to formula (4), the premixed flame index and diffusion flame index are determined.

[0014] (4)

[0015] Where pre and dif are the premixed flame index and diffusion flame index identified by the flame index, ε is the correction value, sfi takes a value of 1 to represent premixed flame, -1 to represent diffusion flame, and 0 to represent no flame, max and min represent the maximum and minimum functions, respectively, and the fuel mass fraction Y F , oxidant mass fraction Y O ,

[0016] Use Equation (5) to determine the heat release rate for premixed and diffusion combustion,

[0017] (5)

[0018] Where log_hrrpre and log_hrrdif are the logarithms of the heat release rates of premixed and diffusion combustion, respectively.

[0019] Optionally, the proportion of supersonic and subsonic combustion heat release modes along the stream direction is determined according to formula (6):

[0020] (6)

[0021] Among them, hrr sup and hrr sub are the unlogarithmized supersonic and subsonic combustion heat release rates, respectively, determined by formula (3), η sub and η sub are the heat release contribution rates of supersonic and subsonic combustion, ds r is the infinitesimal area where chemical reaction occurs on the x-section.

[0022] Optionally, the proportion of the diffusion and premixed combustion heat release modes along the stream direction is determined according to formula (7):

[0023] (7)

[0024] Among them, η pre and η dif xq are the contribution rates of heat release from premixed and diffusion combustion, ds r is the infinitesimal area where chemical reaction occurs on the x-section.

[0025] Optionally, the heat release rate of subsonic premixed combustion, the heat release rate of supersonic premixed combustion, the heat release rate of subsonic diffusion combustion, and the heat release rate of supersonic diffusion combustion are determined according to formula (8).

[0026] (8)

[0027] Among them, hrr presub hrr presup hrr difsub and hrr difsup They represent the heat release rate of subsonic premixed combustion, the heat release rate of supersonic premixed combustion, the heat release rate of subsonic diffusion combustion and the heat release rate of supersonic diffusion combustion, respectively.

[0028] Alternatively, the total contribution rate of supersonic and subsonic combustion heat release in the entire flow field is determined according to formula (9):

[0029] (9)

[0030] Among them, Q sup and Q sub are ultrasonic and subsonic rapid heat release fluxes, η totalsup and η totalsub are the total contribution rates of supersonic and subsonic combustion heat release in the entire flow field, dA r is the area element where the chemical reaction occurs, that is, the area of ​​a single grid, Q represents the total heat flux of the entire flow field, and the area element dA where the chemical reaction occurs is determined according to formula (10): r The integral area of

[0031] (10)

[0032] A sup and A sub are the supersonic and subsonic combustion areas, respectively.

[0033] Alternatively, the total contribution rate of premixed and diffusion combustion heat release in the entire flow field is determined according to formula (11):

[0034] (11)

[0035] Among them, Q pre and Q dif are the heat release flux of premixed combustion and the heat release flux of diffusion combustion, η totalpre and ηtotaldif are the total contribution rates of premixed and diffusion combustion heat release in the entire flow field, respectively. The area element dA where the chemical reaction occurs is determined according to formula (12): r The integral area of

[0036] (12)

[0037] Among them, A pre and A dif are the areas of premixed and diffusion combustion zones, respectively.

[0038] Alternatively, the heat release of subsonic premixed combustion in the composite combustion flow field can be determined according to formula (13): , heat release of supersonic premixed combustion , Subsonic diffusion combustion heat release and supersonic diffusion combustion heat release ,

[0039] (13)

[0040] Among them, dA r is the infinitesimal area where the chemical reaction occurs.

[0041] Optionally, the supersonic and subsonic combustion heat release mode areas and their respective proportions are determined according to formula (10) and formula (10-1),

[0042] (10-1)

[0043] Among them, A sup and A sub are the supersonic and subsonic combustion area, ζ sup and ζ sub are the proportions of heat release areas for supersonic and subsonic combustion, respectively.

[0044] Optionally, the areas of the premixed and diffusion combustion zones and their respective proportions are determined according to formula (12):

[0045] (12)

[0046] Among them, A pre and A dif are the areas of premixed and diffusion combustion zones, ζ pre and ζ dif are the proportions of premixed and diffusion combustion zones, respectively.

[0047] Through integral calculation, the proportion of the overall composite combustion heat release mode in the combustion chamber can be quickly obtained, which improves the calculation efficiency and the efficiency of post-processing of simulation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 (a) Unidentified combustion heat release cloud diagram, (b) Supersonic combustion heat release cloud diagram, (c) Subsonic combustion heat release cloud diagram in the flow field;

[0049] Figure 2 (a) Unidentified combustion heat release cloud diagram, (b) Diffusion combustion heat release cloud diagram, (c) Premixed combustion heat release cloud diagram in the flow field;

[0050] Figure 3 is the distribution curve of the heat release contribution rate of supersonic and subsonic combustion along the flow direction in the flow field;

[0051] Figure 4 is the distribution curve of the heat release contribution rate of premixed combustion and diffusion combustion along the flow direction in the flow field;

[0052] Figure 5 The heat release distribution cloud diagrams of (a) subsonic premixed combustion, (b) subsonic diffusion combustion, (c) supersonic premixed combustion, and (d) supersonic diffusion combustion in the flow field are given. DETAILED DESCRIPTION

[0053] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0054] The present invention is based on the grid division and the Mach number Ma, heat release rate hrr, fuel mass fraction Y of each grid. F , oxidant mass fraction Y O ; Calculate the subsonic premixed combustion heat release rate, supersonic premixed combustion heat release rate, subsonic diffusion combustion heat release rate and supersonic diffusion combustion heat release rate in each grid, and the heat release rate distribution of all grids is the heat release rate cloud map.

[0055] Traditional flame models (premixed, diffusion; supersonic, and subsonic combustion) cannot identify cross-linked regions in a flow field where two different types of combustion models exist. For example, some areas may contain both supersonic and diffusion combustion. The calculation method provided by this patent can quickly determine the distribution of composite combustion heat release patterns in the flow field and their proportions across the entire flow field, improving computational efficiency and the efficiency of post-processing simulation results.

[0056] The present invention provides a method for quantitatively calculating characteristics of a composite combustion heat release mode, including:

[0057] According to formula (1), the supersonic flow and subsonic flow rate are determined.

[0058] (1)

[0059] in, sign(x) Represents a sign function. When x ≥ 0, the return value is 1, otherwise -1. Ma is the Mach number;

[0060] Since the magnitude of heat release rate in high-speed combustion flow field is large, it cannot well show the overall characteristics of the flow field. Usually, the heat release rate hrr is logarithmized according to formula (2).

[0061] (2)

[0062] Use Equation (3) to determine the supersonic and subsonic combustion heat release rates,

[0063] (3)

[0064] hrrsup and hrrsub are the unlogarithmized supersonic and subsonic combustion heat release rates, respectively, and hrr is the total heat release rate;

[0065] According to formula (4), the premixed flame index and diffusion flame index are determined.

[0066] (4)

[0067] Where pre and dif are the premixed flame index and diffusion flame index identified by the flame index, ε is the correction value, sfi takes a value of 1 to represent premixed flame, -1 to represent diffusion flame, and 0 to represent no flame, max and min represent the maximum and minimum functions, respectively, and the fuel mass fraction Y F , oxidant mass fraction Y O , ε can be a small positive value (for example, 10 -9 ), which is an empirical value. sfi essentially still reflects the directionality of the fuel mass fraction gradient vector and the oxidizer mass fraction gradient vector, and it avoids the difficulty of numerical calculation while retaining the three-valued properties.

[0068] Use Equation (5) to determine the heat release rate for premixed and diffusion combustion,

[0069] (5)

[0070] Where log_hrrpre and log_hrrdif are the logarithms of the heat release rates of premixed and diffusion combustion, respectively.

[0071] Furthermore, the proportion of supersonic and subsonic combustion heat release modes along the stream direction is determined according to formula (6):

[0072] (6)

[0073] Among them, hrr sup and hrr sub are the unlogarithmized supersonic and subsonic combustion heat release rates, respectively, determined by formula (3), η sub and η sub are the heat release contribution rates of supersonic and subsonic combustion, ds r is the area element where the chemical reaction occurs on the x-section. If it is a two-dimensional simulation, ds r It is the line segment element, that is, the length of a single grid in the y direction.

[0074] Furthermore, the proportion of the heat release modes of diffusion and premixed combustion along the stream direction is determined according to formula (7):

[0075] (7)

[0076] Among them, η pre and η dif are the heat release contribution rates of premixed and diffusion combustion, ds r is the infinitesimal area where chemical reaction occurs on the x-section.

[0077] Furthermore, the heat release rate of subsonic premixed combustion, the heat release rate of supersonic premixed combustion, the heat release rate of subsonic diffusion combustion, and the heat release rate of supersonic diffusion combustion are determined according to formula (8).

[0078] (8)

[0079] Among them, hrr presub hrr presup hrr difsub and hrr difsup Respectively represent the heat release rate of subsonic premixed combustion, the heat release rate of supersonic premixed combustion, the heat release rate of subsonic diffusion combustion and the heat release rate of supersonic diffusion combustion. A self-written Fortran program is used to read the existing Ma, heat release rate hrr, calculation model grid distribution, fuel mass fraction Y F , oxidant mass fraction Y O , and then outputs the identified supersonic combustion heat release, subsonic combustion heat release, diffusion combustion heat release, premixed combustion heat release, subsonic premixed combustion heat release rate, supersonic premixed combustion heat release rate, subsonic diffusion combustion heat release rate and supersonic diffusion combustion heat release rate cloud map.

[0080] Furthermore, the total contribution rate of supersonic and subsonic combustion heat release in the entire flow field is determined according to formula (9):

[0081] (9)

[0082] Among them, Q sup and Q sub are ultrasonic and subsonic rapid heat release fluxes, η totalsup and η totalsub are the total contribution rates of supersonic and subsonic combustion heat release in the entire flow field, dA r is the area element where the chemical reaction occurs, that is, the area of ​​a single grid, Q represents the total heat flux of the entire flow field, and the area element dA where the chemical reaction occurs is determined according to formula (10): r The integral area of

[0083] (10)

[0084] A sup and A sub are the supersonic and subsonic combustion areas, respectively.

[0085] Alternatively, the total contribution rate of premixed and diffusion combustion heat release in the entire flow field is determined according to formula (11):

[0086] (11)

[0087] Among them, Q pre and Q dif are the heat release flux of premixed combustion and the heat release flux of diffusion combustion, η totalpre and η totaldif are the total contribution rates of premixed and diffusion combustion heat release in the entire flow field, respectively. The area element dA where the chemical reaction occurs is determined according to formula (12): r The integral area of

[0088] (12)

[0089] Among them, A pre and A dif are the areas of premixed and diffusion combustion zones, respectively.

[0090] Furthermore, the heat release of subsonic premixed combustion in the composite combustion flow field is determined according to formula (13): , heat release of supersonic premixed combustion , Subsonic diffusion combustion heat release and supersonic diffusion combustion heat release ,

[0091] (13)

[0092] Among them, dA ris the area element where the chemical reaction occurs. Use Fortran to compile the above formula into a program, and then read the existing Ma, heat release rate hrr, calculation model grid distribution, fuel mass fraction Y F , oxidant mass fraction Y O , the quantitative proportion of each combustion mode in the entire flow field is obtained through program integration for subsequent comparative analysis.

[0093] Furthermore, according to formula (10) and formula (10-1), the supersonic and subsonic combustion heat release mode areas and their respective proportions are determined.

[0094] (10-1)

[0095] Among them, A sup and A sub are the supersonic and subsonic combustion area, ζ sup and ζ sub are the proportions of heat release areas for supersonic and subsonic combustion, respectively.

[0096] Furthermore, the areas of the premixed and diffusion combustion zones and their respective proportions are determined according to formula (12):

[0097] (12)

[0098] Among them, A pre and A dif are the areas of premixed and diffusion combustion zones, ζ pre and ζ dif are the proportions of premixed and diffusion combustion zones, respectively.

[0099] Example

[0100] Attachment Figure 1 Figures 1 and 2 show heat release clouds for (a) unidentified combustion, (b) supersonic combustion, and (c) subsonic combustion in the flow field. The black dashed lines represent the Zst contours for the appropriate equivalence ratio. The figures clearly show the differences between the different combustion heat release models, with both supersonic and subsonic regions coexisting in the flow field. The subsonic combustion heat release region is generally located below Zst. Supersonic combustion is observed across most of the flow field, with subsonic combustion occurring only in smaller localized areas and the recirculation zone behind the baffle.

[0101] Attachment Figure 2 The heat release cloud diagrams of (a) unidentified combustion, (b) diffusion combustion, and (c) premixed combustion in the flow field are shown. The difference between different combustion heat release models can be seen from the figure. The heat release of premixed combustion mainly occurs in the large-scale structure area of ​​the mixing layer and the area close to the fuel side. Both areas are below the appropriate equivalent mixture fraction isoline Zst. Figure 1Analysis shows that heat release in premixed combustion occurs in relatively low-velocity regions, while heat release in diffusion combustion occurs primarily in the high-velocity air-side mixing layer and adjacent regions of the mixing layer's large-scale structure. The premixed flame serves as the foundation for the overall flame, promoting the diffusion flame's own stable propagation and anchoring. Overall, the flow field is dominated by the diffusion combustion mode.

[0102] Attachment Figure 3 Figure 2 shows the distribution of the contribution of supersonic and subsonic combustion heat release along the flow direction. In the initial stage (0 ≤ x ≤ 45 mm), subsonic combustion dominates the heat release, playing a crucial role in overall flame stability and propagation. From x = 45 mm to x = 300 mm, supersonic combustion heat release remains firmly dominant. From x = 300 mm up to the exit, supersonic combustion heat release exhibits an oscillating downward trend, but remains dominant in this region.

[0103] Attachment Figure 4 The figure shows the distribution of the heat release contributions of premixed combustion and diffusion combustion along the flow direction. Initially, the contributions of premixed and diffusion combustion are comparable, exhibiting a large oscillation trend with alternating increases. From the aft of the baffle to x = 100 mm, the premixed combustion contribution clearly dominates. Beyond x = 100 mm, although the premixed and diffusion combustion contributions continue to oscillate, diffusion combustion clearly dominates.

[0104] Attachment Figure 5 The heat release distribution cloud diagrams for (a) subsonic premixed combustion, (b) subsonic diffusion combustion, (c) supersonic premixed combustion, and (d) supersonic diffusion combustion are shown in the flow field. The solid black line represents the contour line for the proper equivalence ratio mixture fraction, Zst. As can be seen from the figure, the supersonic diffusion heat release rate accounts for the highest proportion in the flow field, followed by the supersonic premixed combustion heat release rate. Both the subsonic premixed combustion heat release and the subsonic diffusion combustion heat release rate are located below the contour line for the proper equivalence ratio mixture fraction, i.e., in the rich fuel region. Furthermore, the majority of supersonic diffusion combustion is also in the rich fuel region, with only a small portion remaining in the lean fuel region.

[0105] Appendix 1 provides evaluation parameters for the combustion heat release pattern in the flow field, which are used to determine the dominant combustion mode in the flow channel. Clearly, the flow field is dominated by supersonic diffusion combustion heat release. The data in this table facilitates quantitative analysis of the flow field.

[0106]

[0107] The above description is merely a detailed description of specific embodiments of the present invention. Any unspecified portions are conventional techniques. However, the scope of the present invention is not limited thereto. Any changes or substitutions that can be readily conceived by a person skilled in the art within the technical scope disclosed in the present invention are intended to be encompassed within the scope of the present invention. The scope of the present invention shall be determined by the scope of the claims.

Claims

1. A method for quantitatively calculating characteristics of a composite combustion heat release pattern, characterized in that: include: According to formula (1), the supersonic flow and subsonic flow rate are determined. (1) in, sign(x) Represents a sign function. When x ≥ 0, the return value is 1, otherwise -1. Ma is the Mach number; Use Equation (3) to determine the supersonic and subsonic combustion heat release rates, (3) hrrsup and hrrsub are the unlogarithmized supersonic and subsonic combustion heat release rates, respectively, and hrr is the total heat release rate; According to formula (4), the premixed flame index and diffusion flame index are determined. (4) Where pre and dif are the premixed flame index and diffusion flame index identified by the flame index, ε is the correction value, sfi takes a value of 1 to represent premixed flame, -1 to represent diffusion flame, and 0 to represent no flame, max and min represent the maximum and minimum functions, respectively, and the fuel mass fraction Y F , oxidant mass fraction Y O , Use Equation (5) to determine the heat release rate for premixed and diffusion combustion, (5) Wherein, log_hrrpre and log_hrrdif are the logarithms of the heat release rates of premixed and diffusion combustion, respectively; According to formula (8), the heat release rate of subsonic premixed combustion, the heat release rate of supersonic premixed combustion, the heat release rate of subsonic diffusion combustion and the heat release rate of supersonic diffusion combustion are determined. （8） Among them, hrr presub hrr presup hrr difsub and hrr difsup They represent the heat release rate of subsonic premixed combustion, the heat release rate of supersonic premixed combustion, the heat release rate of subsonic diffusion combustion and the heat release rate of supersonic diffusion combustion, respectively.

2. The method according to claim 1, characterized in that According to formula (6), the proportion of supersonic and subsonic combustion heat release modes along the stream direction is determined. （6） Among them, hrr sup and hrr sub are the unlogarithmized supersonic and subsonic combustion heat release rates, respectively, determined by formula (3), η sub and η sub are the heat release contribution rates of supersonic and subsonic combustion, ds r is the infinitesimal area where chemical reaction occurs on the x-section.

3. The method according to claim 1, characterized in that According to formula (7), the proportion of diffusion and premixed combustion heat release modes along the stream direction is determined. （7） Among them, η pre and η dif are the heat release contribution rates of premixed and diffusion combustion, ds r is the infinitesimal area where chemical reaction occurs on the x-section.

4. The method according to claim 1, wherein According to formula (9), the total contribution rate of supersonic and subsonic combustion heat release in the entire flow field is determined as follows: （9） Among them, Q sup and Q sub are ultrasonic and subsonic rapid heat release fluxes, η totalsup and η totalsub are the total contribution rates of supersonic and subsonic combustion heat release in the entire flow field, dA r is the area element where the chemical reaction occurs, that is, the area of ​​a single grid, Q represents the total heat flux of the entire flow field, and the area element dA where the chemical reaction occurs is determined according to formula (10): r The integral area of （10） A sup and A sub are the supersonic and subsonic combustion areas, respectively.

5. The method according to claim 1, wherein According to formula (11), the total contribution rate of premixed and diffusion combustion heat release in the entire flow field is determined as follows: （11） Among them, Q pre and Q dif are the heat release flux of premixed combustion and the heat release flux of diffusion combustion, η totalpre and η totaldif are the total contribution rates of premixed and diffusion combustion heat release in the entire flow field, respectively. The area element dA where the chemical reaction occurs is determined according to formula (12): r The integral area of （12） Among them, A pre and A dif are the areas of premixed and diffusion combustion zones, respectively.

6. The method according to claim 4, characterized in that According to formula (13), the heat release of subsonic premixed combustion in the composite combustion flow field is determined as follows: , heat release of supersonic premixed combustion , Subsonic diffusion combustion heat release and supersonic diffusion combustion heat release , （13） Among them, dA r is the infinitesimal area where the chemical reaction occurs.

7. The method according to claim 5, characterized in that According to formula (10) and formula (10-1), the supersonic and subsonic combustion heat release mode areas and their respective proportions are determined. （10-1） Among them, A sup and A sub are the supersonic and subsonic combustion area, ζ sup and ζ sub are the proportions of heat release areas for supersonic and subsonic combustion, respectively.

8. The method according to claim 1, characterized in that According to formula (12), the area of ​​premixed and diffusion combustion zones and their respective proportions are determined. （12） Among them, A pre and A dif are the areas of premixed and diffusion combustion zones, ζ pre and ζ dif are the proportions of premixed and diffusion combustion zones, respectively.

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