Method for turbulent combustion simulation for temperature and pressure adaptation of a scramjet engine

Abstract

This invention relates to a turbulent combustion simulation method for temperature and pressure adaptation in scramjet engines, comprising: constructing a flame front database; estimating the base temperature and pressure range of the target combustion flow field, wherein the base temperature includes: estimating the minimum and maximum temperatures at the oxidizer end and the minimum and maximum temperatures at the fuel end; determining four sets of estimated operating conditions; solving the flame front equations to obtain four sets of laminar flame front solutions; using a predefined PDF function to perform ensemble averaging on the four sets of laminar flame front solutions to obtain four sets of ensemble average solutions for the laminar flame front solutions; selecting a reference flame front database based on each set of ensemble average solutions, and obtaining the scaling factor of each database within the group relative to each reference flame front database; constructing a flame front database using the reference flame front database and the scaling factor; performing CFD calculations on the flow field of the scramjet engine, and updating the local flame front database with the flame front database after each calculation.

Description

Technical Field

[0001] This invention relates to the field of computational fluid dynamics (CFD), and more particularly to a method for temperature and pressure adaptive turbulent combustion simulation of scramjet engines. Background Technology

[0002] In recent years, hypersonic vehicle technology has become a research hotspot and focus of major aerospace powers worldwide. However, due to limitations in experimental techniques and the rapid development of large-scale computing power, computational combustion has become an effective means of studying the internal flow and combustion of scramjet engines. A key technology in the numerical simulation of scramjet engines is the simulation of turbulent combustion processes. Currently, there are two main types of combustion models: PDF-type models and flame-surface-type models. The former is characterized by its complete theoretical methods, but it is difficult to process numerically and has a large computational load. The latter, flame-surface-type models, are physically intuitive and computationally efficient and accurate, and therefore have been widely used.

[0003] However, since the flamefront model is derived from low-speed diffusion flames, despite the compressibility correction by Oevermann et al., it still uses the solution of the flamefront equation under a single, fixed temperature and pressure condition to describe the entire supersonic flow field. This approximation is clearly coarse for the combustion flow field of scramjet engines, which experience drastic temperature and pressure variations. Therefore, existing flamefront-based methods cannot adaptively select the build-up temperature and cannot handle the effects of non-uniform pressure, thus exhibiting significant limitations in simulating the turbulent combustion process within scramjet engines. Figure 1 As shown, after the supersonic flow enters the isolation section, its temperature and pressure gradually increase under the action of the oblique shock wave or pre-burning shock wave train. Figure 1 The average temperature in the extremely lean combustion zone can be approximated as the temperature of the incoming stream before it enters the reaction zone. However, the temperature of the underexpanded fuel jet quickly deviates from the injection temperature after it is injected into the combustion chamber and mixed with part of the incoming stream. Figure 1 The average temperature within the highly fuel-rich region can be approximated as the temperature before the fuel flow enters the reaction zone. Furthermore, the pressure varies at different locations within the combustion chamber, leading to different chemical reaction rates. To accurately and adaptively describe such a supersonic combustion flow field, pressure- and temperature-dependent corrections to the flame front model are urgently needed. Summary of the Invention

[0004] The purpose of this invention is to provide a turbulent combustion simulation method for temperature and pressure adaptation in scramjet engines.

[0005] To achieve the above-mentioned objectives, this invention provides a turbulent combustion simulation method for temperature and pressure adaptation in scramjet engines, comprising the following steps:

[0006] S1. Construct a flame surface database;

[0007] The build-up temperature and pressure range of the target combustion flow field are estimated, wherein the build-up temperature includes: the estimated minimum temperature T at the oxidant end. ox1 and maximum temperature T ox2 Predict the minimum temperature T at the fuel end. fuel1 and maximum temperature T fuel2 Within the pressure range, n pressure values ​​are uniformly discrete, and are P1, P2, ..., Pn. n ;

[0008] Based on the aforementioned temperature and pressure range for reservoir construction, four sets of estimated operating conditions were determined.

[0009] Solve the flame surface equations under the four sets of predicted operating conditions to obtain four sets of laminar flame surface solutions;

[0010] The four sets of laminar flame surface solutions are obtained by ensemble averaging using a predefined PDF function.

[0011] A reference flame surface database is selected based on the ensemble average solution of each group, and the scaling factor of each database in the group relative to each reference flame surface database is obtained respectively.

[0012] The flame surface database is constructed based on the reference flame surface database and the scaling factor;

[0013] S2. Perform CFD calculations on the flow field of the scramjet engine, and update the local flame surface database based on the flame surface database after each calculation.

[0014] According to one aspect of the invention, in step S1, in the step of determining four sets of estimated operating conditions based on the reservoir construction temperature and pressure range, the four sets of estimated operating conditions are based on the minimum temperature T at the estimated oxidant end. ox1 and maximum temperature T ox2 The estimated minimum temperature T at the fuel end fuel1 and maximum temperature T fuel2 The pressure range contains n pressures P1, P2, ..., P n Combining and constructing, respectively represented as: (T ox1 T fuel1 P i ), (T ox1 T fuel2 P i ), (T ox2 T fuel1 P i ) and (T ox2 T fuel2 P i ),in,

[0015] According to one aspect of the present invention, in step S1, the step of solving the flame surface equations under the four sets of predicted operating conditions to obtain four sets of laminar flame surface solutions is performed using FlameMaster; the four sets of laminar flame surface solutions are respectively expressed as:

[0016] φ 1,i (Z,C),φ 2,i (Z,C),φ 3,i (Z,C),φ 4,i (Z,C)

[0017] Where Z represents the mixed fraction and C represents the schedule variable;

[0018] In the step of obtaining four ensemble average solutions for the laminar flame surface solutions by using a predefined PDF function to perform ensemble averaging on the four sets of laminar flame surface solutions, the beta PDF function is used for the mixing fraction, and the delta PDF function is used for the progress variable. The four sets of ensemble average solutions obtained are expressed as follows:

[0019]

[0020] The superscript “~” indicates the result after ensemble averaging.

[0021] According to one aspect of the present invention, in step S1, in the step of selecting a reference flame surface database based on the average solution of each group of ensembles, and obtaining the scaling factor of each database within the group relative to each reference flame surface database, the reference flame surface databases are respectively:

[0022]

[0023] The scaling factors are as follows:

[0024] α 1,i ,α 2,i ,α 3,i ,α 4,i

[0025] The scaling factor satisfies the following condition with the reference flame surface database:

[0026]

[0027] According to one aspect of the present invention, step S2, which involves performing CFD calculations on the flow field of the scramjet engine and updating the local flamefront database based on the flamefront database after each calculation, includes:

[0028] After each step of CFD calculation, the average temperature in the extremely lean combustion region is statistically calculated as the approximate temperature at the oxidizer end, denoted as T ox_count , and the average temperature in the extremely rich combustion region is statistically calculated as the approximate temperature at the fuel end, denoted as T fuel_count ; Among them, the region where the mixture fraction is in the range of 1E-5 < Z < 1E-4 is used as the extremely lean combustion region, and the region where the mixture fraction is in the range of Z > 0.25 is used as the extremely rich combustion region;

[0029] Based on the flamelet database and linearly interpolated according to the local pressure, four flamelet matching databases matching the local pressure are obtained;

[0030] Based on the obtained approximate temperature at the oxidizer end and the approximate temperature at the fuel end, weight factors for the four flamelet matching databases are constructed, which are respectively expressed as:

[0031]

[0032]

[0033]

[0034]

[0035] Among them, T ox1 < T ox_count < T ox2 And T fuel1 < T fuel_count < T fuel2 ;

[0036] Based on the weight factors and the flamelet matching databases, linear weighting is performed to obtain the local flamelet database, which is expressed as:

[0037]

[0038] Among them, represents the local flamelet database, respectively represent four flamelet matching databases.

[0039] According to one scheme of the present invention, the adaptive library building temperature is realized by statistically calculating temperature information and interpolating multiple groups of databases, and the database pressure is scaled according to the local pressure of the flow field, so that the change of the engine inlet temperature and the non-uniformity of the flow field pressure are adaptively considered simultaneously, and the accuracy of the supersonic turbulent combustion flamelet model is improved.

[0040] According to one aspect of the present invention, the physical effects of the present invention are considered realistically and completely. Compared with traditional flame surface databases, it can take into account the non-uniformity of flow field pressure, and can adaptively modify the oxidizer end temperature and fuel end temperature of the database based on statistical temperature.

[0041] According to one aspect of the present invention, the numerical implementation and program design of the present invention are clear and feasible. Compared with the traditional flame surface model, although the database dimension is expanded, the database construction temperature can be adaptively considered according to the actual flow field, thereby improving the accuracy of the model. Attached Figure Description

[0042] Figure 1 This is a schematic diagram illustrating the combustion flow inside an existing scramjet engine;

[0043] Figure 2 This is a schematic diagram illustrating the steps of a turbulent combustion simulation method according to an embodiment of the present invention;

[0044] Figure 3 This is a flowchart schematically illustrating a turbulent combustion simulation method according to an embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram illustrating the database interpolation topology in a turbulent combustion simulation method according to an embodiment of the present invention;

[0046] Figure 5 This is a schematic representation comparing the OH distribution at high and low total temperatures in the Micka experiment with the calculation results of the turbulent combustion simulation method in this scheme. Detailed Implementation

[0047] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The embodiments cannot be described in detail here, but the embodiments of the present invention are not limited to the following embodiments.

[0048] Combination Figure 2 and Figure 3 As shown, according to one embodiment of the present invention, a turbulent combustion simulation method for temperature and pressure adaptation in a scramjet engine includes the following steps:

[0049] S1. Construct a flame surface database;

[0050] The predicted build-up temperature and pressure range of the target combustion flow field are determined, where the build-up temperature includes: the predicted minimum temperature T at the oxidant end. ox1 and maximum temperature T ox2 Predict the minimum temperature T at the fuel end. fuel1 and maximum temperature T fuel2 Within a pressure range, n pressure values ​​are uniformly discrete, and are P1, P2, ..., Pn.n In this embodiment, the pressure range is determined based on the pressure that may occur in the flow field to be calculated, and the subsequent calculation process is performed by discretizing the pressure range into multiple pressure values. For example, the possible pressure range in the target combustion flow field is estimated to be 1 to 4 bar. The pressure values ​​that can be discretized based on the estimated pressure range can be 1 bar, 2 bar, 3 bar, 4 bar, etc. Of course, other discretization precision can also be used to obtain pressure values, for example, discretizing a value every 0.5 bar.

[0051] Four sets of predicted operating conditions were determined based on the temperature and pressure range of the reservoir construction; among them, the four sets of predicted operating conditions were based on the predicted minimum temperature T at the oxidant end. ox1 and maximum temperature T ox2 Predict the minimum temperature T at the fuel end. fuel1 and maximum temperature T fuel2 n pressures P1, P2, ..., P within the pressure range n Combining and constructing, respectively represented as: (T ox1 T fuel1 P i ), (T ox1 T fuel2 P i ), (T ox2 T fuel1 P i ) and (T ox2 T fuel2 P i ),in, Among them, P i This represents a discrete value within a pressure range, i.e., n pressures P1, P2, ..., P n one of the.

[0052] Solving the flame surface equations under four sets of predicted operating conditions yields four sets of laminar flame surface solutions. FlameMaster was used to solve the flame surface equations. The four sets of laminar flame surface solutions are expressed as follows:

[0053] φ 1,i (Z,C),φ 2,i (Z,C),φ 3,i (Z,C),φ 4,i (Z,C)

[0054] Where Z represents the mixed fraction and C represents the schedule variable;

[0055] Four ensemble average solutions for the laminar flame surface were obtained by using a predefined PDF function to perform ensemble averaging on the four sets of laminar flame surface solutions. Specifically, a beta PDF function was used for the mixing fraction, and a delta PDF function was used for the schedule variable. The four ensemble average solutions are expressed as follows:

[0056]

[0057] The superscript “~” indicates the result after ensemble averaging.

[0058] Based on the ensemble average solution of each group, a reference flame surface database is selected, and the scaling factor of each database within the group (i.e., the four predicted operating conditions) relative to each reference flame surface database is obtained; wherein, the reference flame surface databases are as follows:

[0059]

[0060] The scaling factors are as follows:

[0061] α 1,i ,α 2,i ,α 3,i ,α 4,i

[0062] The scaling factor satisfies the following conditions with the reference flame surface database:

[0063]

[0064]

[0065]

[0066]

[0067] in, These are the average solutions of the four ensembles mentioned above.

[0068] A flame surface database is constructed based on the baseline flame surface database and scaling factors; the baseline flame surface databases of each group and the solved scaling factors are saved as a database, thus completing the preprocessing database construction process.

[0069] S2. Perform CFD calculations on the flow field of the scramjet engine and update the local flame front database based on the flame front database after each calculation.

[0070] Combination Figure 2 and Figure 3 As shown, according to one embodiment of the present invention, step S2, which involves performing CFD calculations on the flow field of the scramjet engine and updating the local flame front database based on the flame front database after each calculation, includes:

[0071] After each step of CFD calculation is completed, the average temperature in the extremely lean combustion region is statistically obtained as the approximate temperature at the oxidizer end, denoted as T ox_count , and the average temperature in the extremely rich combustion region is statistically obtained as the approximate temperature at the fuel end, denoted as T fuel_count ; among them, the region with a mixture fraction within the range of 1E-5 < Z < 1E-4 is used as the extremely lean combustion region, and the region with a mixture fraction in the range of Z > 0.25 is used as the extremely rich combustion region;

[0072] Based on the flamelet database and linearly interpolated according to the local pressure, four flamelet matching databases matching the local pressure are obtained; in this embodiment, when querying the aforementioned constructed flamelet database in the CFD calculation, this process is executed, where it is assumed that the local pressure P local ∈(P i , P i+1 ), then the four flamelet matching databases obtained by linear interpolation are respectively denoted as: Among them, taking the interpolation of the first group as an example, it can be expressed as:

[0073]

[0074] The remaining interpolation results are similar to the above results and will not be elaborated here.

[0075] Based on the obtained approximate temperature at the oxidizer end and the approximate temperature at the fuel end, weight factors for the four flamelet matching databases are constructed, which are respectively expressed as:

[0076]

[0077]

[0078]

[0079]

[0080] Among them, T ox1 < T ox_count < T ox2 And T fuel1 < T fuel_count < T fuel2 ;

[0081] Based on the weight factors and the flamelet matching databases, linear weighting is performed to obtain the local flamelet database, which is expressed as:

[0082]

[0083] Among them, represents the local flamelet database, as shown in Figure 4 .

[0084] like Figure 5 As shown, the present invention has been verified through simulation, and the results have achieved the expected goals. Specifically, taking the experiments of Micka et al. as an example, the turbulent combustion simulation method of the present invention can adaptively cope with high and low total temperatures, and the calculation results show the different calculated flame stability modes.

[0085] The above description is merely an example of a specific solution of the present invention. For any devices and structures not described in detail herein, it should be understood that they are implemented using common devices and methods already available in the art.

[0086] The above description is merely one embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A turbulent combustion simulation method for temperature and pressure adaptation in scramjet engines, characterized in that, Includes the following steps: S1. Construct a flame surface database; The build-up temperature and pressure range of the target combustion flow field are estimated, wherein the build-up temperature includes: the estimated minimum temperature at the oxidant end. T ox1 and maximum temperature T ox2 Predict the minimum temperature at the fuel end. T fuel1 and maximum temperature T fuel2 Uniformly discrete within the pressure range n There are several pressure values, and they are respectively P 1 ，P 2 ，…，P n ; Based on the aforementioned storage temperature and pressure range, four sets of estimated operating conditions were determined; wherein, the four sets of estimated operating conditions are based on the estimated minimum temperature at the oxidant end. T ox1 and maximum temperature T ox2 The estimated minimum temperature at the fuel end T fuel1 and maximum temperature T fuel2 The pressure range n individual pressure P 1 ，P 2 ，…，P n Combining and constructing, respectively represented as: , , and ,in, ; Solve the flame surface equations under the four sets of predicted operating conditions to obtain four sets of laminar flame surface solutions; The four sets of laminar flame surface solutions are obtained by ensemble averaging using a predefined PDF function. A reference flame surface database is selected based on the ensemble average solution of each group, and the scaling factor of each database in the group relative to each reference flame surface database is obtained respectively. The flame surface database is constructed based on the reference flame surface database and the scaling factor; S2. Perform CFD calculations on the flow field of the scramjet engine, and update the local flamefront database based on the flamefront database after each calculation, including: After each step of CFD calculation, the average temperature in the extremely lean combustion region is statistically calculated as the approximate temperature at the oxidizer end, denoted as T ox_count , and the average temperature in the extremely rich combustion region is statistically calculated as the approximate temperature at the fuel end, denoted as T fuel_count ; among which, the region with the mixture fraction within the range of 1E-5 < Z < 1E-4 is taken as the extremely lean combustion region, and the region with the mixture fraction within the range of Z > 0.25 is taken as the extremely rich combustion region; Based on the flame face database and by linear interpolation according to the local pressure, four flame face matching databases are obtained that match the local pressure. Weighting factors for the four flame-face matching databases are constructed based on the obtained approximate oxidizer end temperature and approximate fuel end temperature, and are respectively expressed as: in, T ox1 < T ox_count <T ox2 and T fuel1 < T fuel_count <T fuel2 ; The local flame surface database is obtained by linearly weighting the weighting factors and the flame surface matching database, and is expressed as follows: in, This refers to the local flame surface database. These represent four flame surface matching databases.

2. The turbulent combustion simulation method according to claim 1, characterized in that, In step S1, the flame surface equations under the four sets of predicted operating conditions are solved to obtain four sets of laminar flame surface solutions. FlameMaster is used to solve the flame surface equations; the four sets of laminar flame surface solutions are expressed as follows: Where Z represents the mixed fraction and C represents the schedule variable; In the step of obtaining four ensemble average solutions for the laminar flame surface solutions by using a predefined PDF function to perform ensemble averaging on the four sets of laminar flame surface solutions, the beta PDF function is used for the mixing fraction, and the delta PDF function is used for the progress variable. The four sets of ensemble average solutions obtained are expressed as follows: ； The superscript "~" indicates the result after ensemble averaging.

3. The turbulent combustion simulation method according to claim 2, characterized in that, In step S1, the step of selecting a reference flame surface database based on the ensemble average solution of each group, and obtaining the scaling factor of each database within the group relative to each reference flame surface database, wherein the reference flame surface databases are: The scaling factors are as follows: The scaling factor satisfies the following condition with the reference flame surface database: 。

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