DSMC method coupled with surface catalytic reaction

Abstract

The invention discloses a DSMC method for coupling a surface catalytic reaction, which is characterized in that on the architecture of a basic DSMC method, a limited reaction rate model of the surface catalytic reaction is constructed by coupling physical adsorption, chemical adsorption, E-R composite reaction and L-H composite reaction; the method is used for considering heat flow contribution brought by surface reaction in prediction of the strength of an aircraft surface thermal protection system and characterization of a thermochemical unbalanced surface effect under a hypersonic flight condition. According to the DSMC method coupled with the surface catalytic reaction, compared with a traditional surface reflection and diffuse reflection gas-surface action model, a limited reaction rate model provides a gas-solid chemical reaction model based on multidisciplinary intersection of chemical kinetics, statistical mechanics and the like, heat flow contribution brought by the surface reaction can be further considered, and the method has the advantages that the method is simple and convenient to operate. The problem of inaccurate prediction of the heat flow intensity of the aircraft surface thermal protection system is effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of hypersonic wind tunnel tests. More specifically, the present invention relates to a DSMC method coupled with surface catalytic reactions. Background Art

[0002] In June 2024, the Chang'e-6 probe embarked on its journey to the moon. After orbiting and landing, it landed in the South Pole-Aitken Basin (SPA) on the moon, mainly completing the "first lunar backside sampling and return mission for humanity". The spacecraft will return at a reentry speed close to the second cosmic velocity (about 11.2 km / s), and the gradually denser atmosphere will pose a huge challenge to the thermal protection of the spacecraft. During the hypersonic reentry process, the high-temperature real gas effect becomes prominent. Simply considering the excitation of rotational energy, vibrational energy, and gas-phase chemical reactions is no longer sufficient to accurately solve the aerodynamic heat of the return capsule. The high-enthalpy dissociating gas will interact with the surface of aerospace vehicles made of materials such as carbon-based materials, and surface chemical reactions will occur, further increasing the surface heat flux. At the initial stage of the design of the spacecraft shell structure, it is necessary to accurately predict the aerodynamic and thermodynamic characteristics of the spacecraft along the reentry trajectory. It is very difficult to reproduce and simulate the ground experiment of the high-altitude and high-temperature non-equilibrium flight environment. Therefore, numerical methods are the main research means. In previous numerical method studies, there are few extensions of complex physical and chemical processes based on the DSMC method, mainly focusing on typical gas-phase chemical reactions.

[0003] Among current numerical methods, the DSMC method is the most popular, but this method does not consider the gas-solid chemical reactions that occur between the gas and the matrix material on the surface of the spacecraft. Existing experiments have verified the importance of surface catalytic reactions in a hypersonic environment with high temperature, high pressure, and non-equilibrium. Specifically, the current DSMC method is applied to the problem of difficult characterization of the thermochemical non-equilibrium surface effect under hypersonic flight conditions and the prediction of the heat flux intensity of the thermal protection system on the surface of the spacecraft. Its research mainly focuses on gas-phase chemical reactions and energy exchange. Gas-phase chemical reactions include dissociation chemical reactions, recombination chemical reactions, exchange chemical reactions, and ionization chemical reactions that have emerged in recent years. The gas components mainly involved in this part include molecular gases such as nitrogen, oxygen, nitric oxide, and carbon dioxide, as well as atomic gas components such as nitrogen and oxygen. Considering gas-phase chemical reactions alone, the main purpose is to explore the reentry process of the spacecraft, especially within the near space (100 km), in the high-temperature viscous shock layer on the surface of the spacecraft, where free gas molecules decompose into atoms, ions, and even smaller electrons through chemical reactions such as dissociation and ionization. The chemical reactions caused by the collision of these gas-phase particles will cool or heat the oncoming flow. In recent years, there has also been a "simplified" version of surface catalytic reaction technology. Delving into its principle will reveal that the realization of surface catalytic reactions is only to fix the surface catalytic adsorption index, that is, the adsorption and settlement of surface particles.

[0004] For gas-phase chemical reactions, its main function is to explore the interaction laws within the gas. The impact on the surface of the aircraft belongs to an external effect, that is, an external factor that causes substantial changes on the surface or even inside the aircraft. However, there is no research considering surface catalytic reactions on the process that truly leads to the catastrophic problems of ablation, softening, and melting on the aircraft surface. That is, in the existing DSMC method, there are problems such as the difficulty in reproducing the high-altitude high-temperature non-equilibrium flight environment on the ground, the difficulty in characterizing the thermochemical non-equilibrium surface effect under hypersonic flight conditions, and the inaccurate prediction of the heat flux intensity of the thermal protection system on the aircraft surface, which in turn leads to the catastrophic problems of surface ablation, softening, and melting. Therefore, there is an urgent need for a method for predicting the heat flux intensity of the aircraft surface considering surface catalytic reactions. Summary of the Invention

[0005] An object of the present invention is to solve at least the above problems and / or deficiencies and provide at least the advantages described hereinafter.

[0006] To achieve these objects and other advantages of the present invention, a DSMC method coupled with surface catalytic reactions is provided. Based on the architecture of the basic DSMC method, a finite reaction rate model of surface catalytic reactions is constructed by coupling physical adsorption, chemical adsorption, E-R recombination reaction, and L-H recombination reaction, so as to consider the heat flux contribution brought by surface reactions in the prediction of the strength of the thermal protection system on the aircraft surface and the characterization of thermochemical non-equilibrium surface effects under hypersonic flight conditions.

[0007] Preferably, the construction process of the finite reaction rate model includes:

[0008] S1. Based on the particle motion in the simulation domain of the basic DSMC method, when the moving particles approach the wall surface, the particles actually reaching the aircraft surface are calculated by using the particle-wall collision method and the sign of the dot product of the velocity vector of molecular motion and the outer normal vector of the triangular surface element.

[0009] S2. Based on the macroscopic finite rate method, the desorption operation is performed on the particles reaching the aircraft surface, and it is judged whether the number of iterations reaches a predetermined threshold. If not, return to S1; otherwise, the macroscopic quantities are statistically analyzed for the prediction of the strength of the thermal protection system on the aircraft surface and the characterization of thermochemical non-equilibrium surface effects under hypersonic flight conditions.

[0010] Preferably, in S1, during the process of particles actually reaching the aircraft surface, the establishment of the linked list relationship between each wall boundary grid and its related triangular surface element is also included.

[0011] Preferably, the construction process of the linked list relationship includes:

[0012] Based on the maximum and minimum values of the corner coordinates of each triangular surface element, the background grid belonging to the wall boundary grid is determined.

[0013] When a triangular surface element S is entirely or partially located within the boundary grid S' of the object surface, S is considered an element in the linked list relationship of S'. If S also partially enters the adjacent boundary grid S'' at the same time, S is also considered an element in the linked list relationship of S''.

[0014] Preferably, in the particle-object surface collision method, the position of the collision point is determined by the condition P = R, where P is the position equation of any point on the triangular surface element, and R is the motion trajectory equation of the particle, which are respectively represented by the following formulas:

[0015] R = x 0 +τ·c

[0016]

[0017] In the above formula, x 0 is the starting position of the particle motion located within the boundary grid of the object surface, c is the motion speed of the particle, τ is the motion time of the molecule, a i is a real number of the equation, r i is the angular coordinate of the triangular surface element.

[0018] Preferably, the desorption operation includes:

[0019] S20. Determine the physical adsorption and chemical adsorption coefficients of the hardened glass based on experiments;

[0020] S21. Determine the probability P of the E-R recombination reaction on the aircraft surface of the hardened glass composition at each temperature based on the macroscopic finite rate method using the Arrhenius equation ER ;

[0021] S22. Determine the physical, chemical, and L-H desorption processes by the existence time of the particle on the aircraft surface.

[0022] Preferably, the surface adsorption coefficients of the physical adsorption and chemical adsorption are both 0.1.

[0023] Preferably, the acquisition process of the probability P of the E-R recombination reaction on the aircraft surface ER is as follows:

[0024] S210. Determine the surface catalytic reaction rate coefficient k based on the following formula:

[0025]

[0026] In the above formula, C r is the Arrhenius constant, R is the molar gas constant, E a is the reaction activation energy;

[0027] S211. Based on the E-R composite reaction equation and the k obtained in S210, the change in the density of adsorbed atoms on the object surface is characterized by the following formula:

[0028]

[0029] In the above formula, M represents a kind of particle, M S is the surface-adsorbed particle, M 2 is the particle generated by the E-R composite reaction, S V is the chemical adsorption site, n M is the number density of the particles, is the density of the particles already adsorbed on the surface;

[0030] S212. Based on n M and the obtained in S211, then P ER is characterized by the following formula:

[0031]

[0032] In the above formula, T is the temperature of the oncoming gas, m is the particle mass, N M is the number of physical adsorption vacant sites of the surface element with an area of A S , F N is the number of real particles represented by the simulated particles in the DSMC method, is the proportion of the chemical adsorption sites.

[0033] Preferably, the determination method of the physical desorption process is as follows:

[0034] S220. Based on the surface catalytic reaction rate coefficient k, the characteristic frequency v of the physical desorption process F is characterized by the following formula:

[0035]

[0036] In the above formula, is the number of surface physically adsorbed particles;

[0037] S221. If the desorption process follows the Poisson distribution, then the physical desorption τ F is characterized by the following formula:

[0038]

[0039] In the above formula, Ra is a random number from 0 to 1.

[0040] The present invention has at least the following beneficial effects: Aiming at the problems that it is difficult to reproduce the high-altitude high-temperature non-equilibrium flight environment on the ground, it is difficult to characterize the thermochemical non-equilibrium surface effect under hypersonic flight conditions, and the inaccurate prediction of the heat flux intensity of the thermal protection system on the aircraft surface, which leads to catastrophic problems such as surface ablation, softening, and melting. Based on the framework of the basic DSMC method, the present invention constructs a finite reaction rate model of surface catalytic reaction by coupling physical adsorption, chemical adsorption, E-R recombination reaction, and L-H recombination reaction. Compared with the traditional surface reflection and diffuse reflection gas-surface interaction models, the finite reaction rate model provides a gas-solid chemical reaction model based on the interdisciplinary of chemical kinetics, statistical mechanics, etc., which can further consider the heat flux contribution brought by surface reactions and effectively improve the problem of inaccurate prediction of the heat flux intensity of the thermal protection system on the aircraft surface.

[0041] Other advantages, objectives, and features of the present invention will be partially reflected by the following description and partially understood by those skilled in the art through the research and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Schematic flow chart of the DSMC method coupling surface catalytic reaction of the present invention

[0043] Figure 2 Triangular unstructured grid diagram of the aircraft surface of the present invention;

[0044] Figure 3 Flow chart of the surface catalytic reaction of the present invention;

[0045] Figure 4 Schematic flow chart of desorption and L-H recombination reaction of the present invention;

[0046] Figure 5 Temperature cloud map of the flow field of the aircraft return capsule when comparing NS-DSMC and the method SC-DSMC of the present invention (it should be noted that NS-DSMC mentioned in this figure and the subsequent figures represents the traditional basic DSMC method, while SC-DSMC represents the improved DSMC method based on coupling surface catalytic reaction in the present invention);

[0047] Figure 6 Pressure cloud map of the flow field of the aircraft return capsule when comparing the two methods of NS-DSMC and the present invention;

[0048] Figure 7 Particle number density cloud map of the flow field of the aircraft return capsule when comparing the two methods of NS-DSMC and the present invention;

[0049] Figure 8 Curve graph of the temperature change along the stagnation line of the flow field of the aircraft return capsule when comparing NS-DSMC and the method SC-DSMC of the present invention;

[0050] Figure 9 To compare NS-DSMC with the SC-DSMC method of the present invention, a curve graph showing the variation of pressure along the stagnation line in the flow field of the aircraft return capsule;

[0051] Figure 10 To compare NS-DSMC with the SC-DSMC method of the present invention, a curve graph showing the variation of particle number density along the stagnation line in the flow field of the aircraft return capsule;

[0052] Figure 11 For the proportion cloud map of N in the flow field of the aircraft return capsule 2 ;

[0053] Figure 12 For the proportion cloud map of O in the flow field of the aircraft return capsule 2 ;

[0054] Figure 13 For the proportion cloud map of NO in the flow field of the aircraft return capsule;

[0055] Figure 14 For the proportion cloud map of N in the flow field of the aircraft return capsule;

[0056] Figure 15 For the proportion cloud map of O in the flow field of the aircraft return capsule;

[0057] Figure 16 To compare NS-DSMC with the SC-DSMC method of the present invention, the heat flux distribution of the aircraft return capsule. Detailed implementation manner

[0058] The following further elaborates on the present invention with reference to the accompanying drawings, enabling those skilled in the art to implement it according to the description in the specification.

[0059] To overcome the deficiencies of the prior art, the main core idea of this patent is different from traditional gas-phase chemical reactions and the "simplified" version of surface catalytic reactions, that is, using surface catalytic reactions to consider the physical and chemical processes of the interaction between gas molecules, atoms and the surface material matrix.

[0060] The present invention proposes a DSMC method coupled with surface catalytic reactions. Based on the basic DSMC method framework, by coupling physical adsorption, chemical adsorption, E-R recombination reaction and L-H recombination reaction, a limited reaction rate model of surface catalytic reactions is constructed. It is a limited surface catalytic reaction considering the actual matrix composition of the aircraft surface and the physical and chemical processes of the reentry velocity and environmental temperature, which can further consider the heat flux contribution brought by surface reactions and effectively improve the inaccurate prediction problem of the heat flux intensity of the aircraft surface thermal protection system. Its specific operation process includes:

[0061] S1. Initialize the velocity and direction of each particle in the computational domain according to the Maxwell - Boltzmann distribution function;

[0062] S2. Execute particle motion within a specified time step. During this period, two situations will occur. If the moving particles meet, execute the particle collision process. If the moving particles move near the surface of the aircraft, execute the gas - surface interaction process;

[0063] S3. Update the gas components in the computational domain through the TCE gas - phase chemical reaction method;

[0064] S4. If the moving particles approach the wall, use the particle - surface interaction method to calculate the particles actually reaching the surface by the sign of the dot product of the velocity vector of molecular motion and the outer normal vector of the triangular surface element;

[0065] S5. Determine the surface adsorption coefficients of physical adsorption and chemical adsorption by referring to experimental data;

[0066] S6. Determine the probability of E - R recombination reaction on the surface of the aircraft at each temperature of the hardened glass composition based on the Arrhenius equation;

[0067] S7. Determine the physical, chemical, and L - H desorption processes by the existence time (lifetime) of particles on the surface of the aircraft;

[0068] Embodiment

[0069] As Figure 1 shown, a DSMC method coupling surface catalytic reaction of the present invention includes the following steps:

[0070] S1. Initialize the velocity and direction of each particle in the computational domain according to the Maxwell - Boltzmann distribution function, which is the basis for subsequent particle motion, particle - particle interaction, and particle - surface interaction;

[0071] S2. Execute particle motion within a specified time step. During this period, two situations will occur. If the moving particles meet, execute the particle collision process. If the moving particles move near the surface of the aircraft, execute the gas - surface interaction process;

[0072] S3. Update the gas components in the computational domain through the TCE gas - phase chemical reaction method. In the particle collision process executed in S2 and the TCE gas - phase chemical reaction method described in S3, when the re - entry velocity of the aircraft exceeds the first cosmic velocity, a large amount of energy is released during the collision of gas particles. When the energy exceeds a certain threshold, a chemical reaction will be induced, and the chemical reaction will cause changes in the gas components and the energy distribution state. With the addition of new gas components, the types of reactions will also increase. This patent only considers dissociation reactions, exchange reactions, and recombination reactions.

[0073] a) The dissociation reaction refers to a chemical reaction that occurs when the total energy of the collision between a conventional diatomic molecule AB (oxygen, nitrogen, nitric oxide) and a particle (commonly known as a catalyst, such as oxygen, nitrogen, nitric oxide, nitrogen atoms, oxygen atoms) exceeds the activation energy for the dissociation of molecule AB. The dissociation reaction equation is:

[0074] AB + M → A + B + M (1)

[0075] b) The exchange reaction involved in the reentry process refers to the replacement of another atom in the diatomic molecule AB after the collision between the diatomic molecule AB and a single-atom particle such as N or O. The exchange reaction equation is:

[0076] AB + C → AC + B (2)

[0077] c) The recombination reaction can be understood as the reverse process of the dissociation reaction, and its reaction formula is:

[0078] A + B + M → AB + M (3)

[0079] Referring to Gupta's gas-phase chemical reaction model, it contains a total of 19 reactions, including 15 dissociation reactions, 4 exchange reactions, and the recombination reaction refers to the reverse reaction of the dissociation reaction. The specific chemical reaction parameters refer to Table 1 (chemical reaction-related constants for 5 components of air):

[0080] Table 1

[0081]

[0082]

[0083] S4. If the moving particle approaches the wall surface, using the method of particle-wall interaction, by the sign of the dot product of the velocity vector of molecular motion and the outer normal vector of the triangular surface element, calculate the particles that actually reach the surface. The process of performing gas-surface interaction in S2 and the method of judging particle-wall collision in S4 stipulate that within a time step, the moving particle moves near the surface of the aircraft. Using the method of particle-wall interaction, by the sign of the dot product of the velocity vector of molecular motion and the outer normal vector of the triangular surface element, calculate the particles that actually reach the surface. The triangular unstructured grid on the surface of the aircraft is as Figure 2 shown.

[0084] In order to accurately calculate the position of the collision point when a particle collides with the object surface and determine the triangular surface element to which the collision point belongs, it is necessary to establish the linked list relationship between each object surface boundary grid and its related triangular surface elements. The method is as follows: First, according to the maximum and minimum values of the corner point coordinates of each triangular surface element, determine which background grids belong to the object surface boundary grids. In this process, the linked list relationship between each object surface boundary grid and all its related triangular surface elements is also established simultaneously. When a triangular surface element is entirely or partially located within a certain object surface boundary grid, this surface element constitutes an element in the linked list relationship of this boundary grid. If this surface element also partially enters the adjacent boundary grid at the same time, it also becomes an element in the linked list relationship of the adjacent boundary grid.

[0085] The motion trajectory equation R of the particle and the position equation P of any point on the triangular surface element are respectively:

[0086]

[0087] where x 0 is the starting position of the particle's motion (located within the object surface boundary grid), c is the particle's motion speed, τ is the motion time of the molecule, a i is a real number of the equation, r i is the angular coordinate of the triangular surface element, and the position of the collision point is determined by the condition P = R;

[0088] S5. Determine that the surface adsorption coefficients of physical adsorption and chemical adsorption are both 0.1 by referring to experimental data;

[0089] S6. Determine the probability of the E-R recombination reaction on the surface of the aircraft at each temperature of the hardened glass composition based on the Arrhenius equation;

[0090] Based on the DSMC method program framework developed by Bird, the main idea of the surface catalytic reaction model constructed in this paper is based on the macroscopic finite rate method, which is an extension of the traditional TCE chemical reaction model. The surface catalytic reaction rate coefficient is determined by the Arrhenius equation:

[0091]

[0092] where, C r is the Arrhenius constant, R is the molar gas constant, E a is the reaction activation energy.

[0093] According to the E-R recombination reaction equation As the particle continuously collides with the surface, the change in the adsorbed atom density on the object surface is expressed as:

[0094]

[0095] In the above formula, k is determined by the Arrhenius equation, and n M is the number density of atoms, is the particles already adsorbed on the surface, and the probability P of the E-R recombination reaction ER can be obtained from the ratio of the particle flux physically adsorbed after the particles collide with the surface to the total collision particle flux:

[0096]

[0097] where, T is the temperature of the oncoming gas, m is the particle mass; N M is the number of physically adsorbed vacant site positions of the surface element with an area of A S , F N is the number of real particles represented by the simulated particles in the DSMC method, is the proportion of chemisorbed sites

[0098] such as Figure 3 shown, after the particles reach the surface, a preliminary judgment is made on whether the surface positions are occupied. If the judgment result is occupied, then based on whether Ra (Ra is a random number between 0 and 1) is less than P ER judge whether the E-R recombination reaction occurs. If it occurs, E-R recombination is carried out, otherwise reflection is carried out;

[0099] while if the judgment result is not, then based on whether Ra is less than P 1 or P 2 determine whether to choose chemisorption or physisorption, otherwise reflection is carried out. It should be noted that P 1 is the physisorption probability, and P 2 is the chemisorption probability.

[0100] S7. Determine the physical, chemical, and L-H desorption processes through the residence time (lifetime) of the particles on the aircraft surface. After the particles are adsorbed on the physical surface positions, there is a certain adaptation time (referred to as the lifetime). During the lifetime, the adsorbed particles gradually adapt to the surface temperature, and the potential kinetic energy of the particles gradually increases. When the kinetic energy of the particles exceeds the van der Waals force of physisorption, the particles will spontaneously desorb physically and escape from the surface, releasing the physically adsorbed site positions. Here, the physisorption frequency v F is introduced, that is, the number of physisorption desorptions occurring per unit time;

[0101]

[0102] where, k 2 is still the rate coefficient obtained from formula (5). To distinguish its application in physisorption desorption, it is set as k 2 , and in chemisorption desorption, it is represented by k 4 , and in the L-H recombination reaction, it is represented by k 6It is shown that the characteristic frequency of the physical desorption process is:

[0103]

[0104] Among them, is the number of physically adsorbed particles on the surface. Assuming that the desorption process follows the Poisson distribution, the physical desorption τ F is:

[0105]

[0106] Among them, Ra is a random number between 0 and 1. Calculate within a simulated time step t, loop through the list of physically adsorbed particles on the cyclic object surface, and successively perform the desorption process of physically adsorbed particles. Accumulate the desorption time of adsorbed particles Until End.

[0107] As Figure 4 shown, the chemical desorption τ S and the L-H composite reaction τ LH are the same in principle.

[0108] S8. Judge whether the cumulative iteration step number Δt is greater than the total iteration step number t. If it is satisfied, go to step 9; otherwise, loop through steps 1-8;

[0109] S9. Statistically analyze macroscopic quantities such as the heat flux density on the aircraft surface and flow field parameters.

[0110] Compare the DSMC method with coupled surface catalytic reactions of the present invention with the existing NS method to obtain a comparison schematic diagram as Figures 5 - 16 . Further, from Figures 5 - 7 it can be seen that: compared with the NS-DSMC program results, for the method SC-DSMC of the present invention, after adding the surface catalytic reaction model, the thickness of the high-temperature region in the detached shock layer increases significantly.

[0111] From Figures 8 - 10 it can be seen that: the compression behind the detached shock wave is extremely severe. Compared with the oncoming flow, the particle number density increases by about 500 times, resulting in a sharp increase in pressure along the stagnation line.

[0112] From Figures 11 - 15 it can be seen that: the initial flow components are only N 2 and O 2 . The increase in temperature in the detached shock layer activates the dissociation reaction, and N 2 and O 2 decompose into O and N atoms and gather in the shock layer. The proportion of O and N atom components increases along the stagnation line direction. The generated NO molecules are limited by the number of N 2 , O 2 , O, and N components, and the proportion of NO molecule components along the stagnation line direction is the lowest.

[0113] From Figure 16 It can be seen that the extremely high oncoming flow velocity compresses the shock wave, resulting in a "ring-shaped" distribution structure of the heat flux on the return capsule surface, and the pressure at the leading edge of the aircraft head is the highest. Compared with the results of the NS-DSMC program, the maximum value of the surface heat flux of the SC-DSMC method of the present invention is 30% higher. This is because a part of the particles are adsorbed on the surface of the aircraft head, and the kinetic energy of the high-speed particles and the activation energy of some surface catalytic reactions are absorbed by the surface and converted into heat energy.

[0114] The present invention studies the DSMC method coupled with surface catalytic reactions, which can predict the heat flux of typical blunted-body aircraft. Compared with the calculation results of the DSMC method program that does not consider surface catalytic reactions in heat transfer, the surface heat flux calculated in this patent is nearly 30% higher than that of the NS-DSMC method that does not consider surface catalytic reactions. It further solves the problem of difficult characterization of the surface effect of thermochemical non-equilibrium under hypersonic flight conditions, and predicts the impact of hypersonic aerodynamic heating of the aircraft reentry on the thermal protection system with higher accuracy.

[0115] The above solution is only an illustration of a preferred example, but is not limited thereto. When implementing the present invention, appropriate substitutions and / or modifications can be made according to the needs of users.

[0116] Although the embodiments of the present invention have been disclosed as above, it is not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the illustrated examples described herein.

Claims

1. A DSMC method for coupled surface catalytic reaction, characterized in that: Based on the framework of the basic DSMC method, a finite reaction rate model of surface catalytic reaction is constructed by coupling physical adsorption, chemical adsorption, ER composite reaction and LH composite reaction, so as to consider the heat flux contribution brought by surface reaction in the prediction of the strength of aircraft surface thermal protection system and the characterization of thermochemical non-equilibrium surface effects under hypersonic flight conditions.

2. The DSMC method for coupled surface catalytic reaction according to claim 1, characterized in that: The construction process of the finite reaction rate model includes: S1. Based on the basic DSMC method, the particle motion in the simulation domain is used to calculate the particles that actually reach the surface of the aircraft by using the particle-surface collision method when the moving particles approach the wall through the positive and negative dot product of the velocity vector of the molecular motion and the external normal vector of the triangular surface element; S2. Based on the macroscopic finite rate method, desorption operation is performed on the particles reaching the surface of the aircraft, and it is determined whether the number of iterations reaches the predetermined threshold. If not, it returns to S1. Otherwise, the statistical macroscopic quantity is used to predict the strength of the thermal protection system of the aircraft surface and characterize the thermochemical non-equilibrium surface effect under hypersonic flight conditions.

3. The DSMC method for coupled surface catalytic reaction as claimed in claim 2, characterized in that: In S1, in the process of actually reaching the particles on the surface of the aircraft, it also includes establishing a linked list relationship between each object surface boundary mesh and its related triangular face elements.

4. The DSMC method for coupled surface catalytic reaction according to claim 3, characterized in that: The construction process of the linked list relationship includes: Based on the maximum and minimum values ​​of the coordinates of the corner points of each triangular facet, a background grid belonging to the boundary grid of the object surface is determined; When a triangular face element S is completely or partially located in the object surface boundary grid S′, S is deemed to be an element in the S′ linked list relationship. If S also partially enters the adjacent boundary grid S″, S is deemed to be an element in the S″ linked list relationship.

5. The DSMC method for coupled surface catalytic reaction as claimed in claim 3, characterized in that: In the particle-surface collision method, the position of the collision point is determined by the condition P=R, where P is the position equation of any point on the triangular surface element, and R is the motion trajectory equation of the particle, which are respectively represented by the following formulas: R=x0+τ·c In the above formula, x0 is the starting position of the particle movement within the boundary grid of the object surface, c is the movement speed of the particle, τ is the movement time of the molecule, and a i is the real number of the equation, r i are the angular coordinates of the triangle face.

6. The DSMC method for coupled surface catalytic reaction according to claim 2, characterized in that: The desorption operation comprises: S20, determining the physical adsorption and chemical adsorption coefficients of hardened glass based on experiments; S21. Based on the macroscopic finite rate method, the Arrhenius equation is used to determine the probability P of ER complex reaction on the aircraft surface of hardened glass components at various temperatures. ER ; S22. Determine the physical, chemical and LH desorption process by the presence time of the particles on the aircraft surface.

7. The DSMC method for coupled surface catalytic reaction according to claim 6, characterized in that: The surface adsorption coefficients of the physical adsorption and chemical adsorption are both 0.

1.

8. The DSMC method for coupled surface catalytic reaction according to claim 6, characterized in that: The probability of ER complex reaction on the aircraft surface P ER The acquisition process is: S210, determining the surface catalytic reaction rate coefficient k based on the following formula: In the above formula, C r is the Arrhenius constant, R is the molar gas constant, E a is the activation energy of the reaction; S211, based on the ER complex reaction equation And k is obtained in S210, and the change of the density of adsorbed atoms on the surface of the object is characterized by the following formula: In the above formula, M represents a particle, M S are surface adsorbed particles, M2 are particles generated by ER complex reaction, S V is the chemical adsorption site, n M is the number density of particles, is the density of particles adsorbed on the surface; S212, based on n M And obtained in S211 Then P ER It is characterized by the following formula: In the above formula, T is the incoming gas temperature, m is the particle mass, N M The area is A S The number of surface element physical adsorption vacant sites, F N is the real number of particles represented by the simulated particles in the DSMC method, is the percentage of chemical adsorption sites.

9. The DSMC method for coupled surface catalytic reaction according to claim 8, characterized in that: The physical desorption process is determined as follows: S220, based on the surface catalytic reaction rate coefficient k, the characteristic frequency v of the physical desorption process F It is characterized by the following formula: In the above formula, is the number of particles physically adsorbed on the surface; S221. If the desorption process follows a Poisson distribution, then the physical desorption τ F It is characterized by the following formula: In the above formula, Ra is a random number between 0 and 1.

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