Flow channel configuration optimization design method for combustion chamber of powder scramjet engine

Abstract

The invention discloses a flow channel configuration optimization design method of a powder scramjet engine combustion chamber, and belongs to the field of powder scramjet engine optimization, and the method comprises the following steps: S1, based on a particle orbit model, obtaining a motion state of particles; s2, decomposing a momentum equation, a motion equation and a drag equation of the particles; s3, deducing a differential equation of particle velocity on-way distribution; s4, the residence time and the penetration depth of the particles in different positions in a combustion chamber of the powder scramjet engine are solved; s5, correcting the cross sectional area of the combustion chamber runner in the quasi one-dimensional calculation; and S6, iterating the steps S1 to S5 until an end condition is met, and outputting the optimal combustion chamber runner configuration. By adopting the runner configuration optimization design method of the powder scramjet engine combustion chamber, the time required by simulation calculation is reduced through mathematical modeling, so that the calculation cost and the calculation time are reduced, and the design of the engine combustion chamber runner is facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of powder scramjet engine optimization, and in particular to a flow channel configuration optimization design method for a powder scramjet engine combustion chamber. Background Art

[0002] Hypersonic vehicles have broad application prospects in the fields of national defense and space transportation. In recent years, high Mach number and wide range have become the main research directions for the development of hypersonic vehicles. As the main component of hypersonic vehicles, the power unit is the key technology that determines the development of hypersonic vehicles.

[0003] At present, liquid fuel ramjet engines are the main form of hypersonic vehicle power plant. They have a high specific impulse and can use a control device to adjust the fuel supply speed. Therefore, the engine thrust can be freely changed, or even the engine can be shut down to control the speed and direction. However, since liquid fuel cannot be stored in the missile body and can only be filled before launch, it often has disadvantages such as difficult storage, complex structure, and poor reliability. Problems such as low density of liquid fuel, easy dissociation of liquid fuel at high Mach numbers, poor combustion stability, and complex engine structure have greatly limited the application of this type of power plant.

[0004] Solid fuel ramjet engines, which use solid propellants as fuel, are a new type of ramjet engine. Compared with liquid fuel ramjet engines, they have the advantages of relatively simple structure, light weight, high density specific impulse, low cost, good safety, and short combat response time. However, they also have the problem of low specific impulse and inability to accurately control thrust during flight. Therefore, the research on solid fuel ramjet engines has attracted much attention in recent years.

[0005] In order to make up for the shortcomings of the two fuel forms of engines and provide ideas for the research of the power system of the new generation of hypersonic weapons, some scholars have proposed the idea of ​​using high-energy metals (aluminum, magnesium, boron, etc.) as ramjet fuel, that is, powder fuel ramjet. Powder fuel (Al, Mg, B) has high energy calorific value and volume calorific value, and there is no storage aging problem, so the fuel cost is greatly reduced; at the same time, powder fuel has higher anti-sensitivity than solid propellant, which greatly improves the safety of powder fuel during manufacturing, storage and use, and has good safety even in high overload environment.

[0006] However, there is a lack of scientific basis for the flow path design of the engine combustion chamber, which greatly limits the performance optimization of powder fuel ramjet engines. Summary of the invention

[0007] The purpose of the present invention is to provide a method for optimizing the flow path configuration of a powder scramjet combustion chamber to solve the above technical problems.

[0008] To achieve the above object, the present invention provides a method for optimizing the flow path configuration of a powder scramjet combustion chamber, comprising the following steps:

[0009] S1. Based on the particle trajectory model, combined with quasi-one-dimensional thermodynamic calculations, the Mach number and static temperature distribution along the path are obtained to obtain the motion state of the particle;

[0010] S2. Based on the particle trajectory model, the particle motion is decomposed into the x-direction and the y-direction, and the momentum equation, motion equation and drag equation of the particle are decomposed;

[0011] S3, combining the Mach number and static temperature distribution solutions along the path described in step S1 with the momentum equation, motion equation and drag equation described in step S2 to derive a differential equation for the particle velocity distribution along the path;

[0012] S4, integrating the differential equation described in step S3 in combination with the equation of motion, and solving the residence time and penetration depth of the particles at different positions in the combustion chamber of the powder scramjet engine;

[0013] S5, estimating the height and length of the combustion chamber flow channel by the penetration depth, and correcting the cross-sectional area of ​​the combustion chamber flow channel in the quasi-one-dimensional calculation described in step S1 based on the estimation result;

[0014] S6. Iterate step S1 to step S5 until the end condition is met, and output the optimal combustion chamber flow channel configuration.

[0015] Preferably, in step S1, the particle trajectory model expression is as follows:

[0016]

[0017] Where V x is the velocity of the particle in the x direction; M is the Mach number; k is the Boltzmann constant; R is the gas constant;

[0018] The differential equation expression of Mach number along the path is as follows:

[0019]

[0020] In the formula, is the rate of change of Mach number M along the x direction; γ is the specific heat ratio; T t is the temperature; C f is the friction coefficient; D is the diameter of the combustion chamber flow channel; A is the cross-sectional area of ​​the combustion chamber flow channel;

[0021] The differential equation for static temperature is as follows:

[0022]

[0023] In the formula, is the rate of change of static temperature T along the x direction; c p is the specific heat capacity at constant pressure; h t is the enthalpy of the fluid.

[0024] Preferably, in step S2, in a Cartesian coordinate system, Lagrangian is used to construct the particle dynamics equation:

[0025]

[0026] In the formula, X p is the particle position vector; V p is the velocity vector of the particle; F p is the resistance force on the particle per unit mass; F is the gravity on the particle;

[0027] Momentum equation:

[0028]

[0029] In the formula, v px and v py Represent the speed of the particle in the x direction and y direction respectively; F px and F py represent the drag force of the particle in the x and y directions respectively; f py represents mass force;

[0030] Equations of motion:

[0031]

[0032] Assuming that the incoming flow has only velocity in the x direction, the drag equation is as follows:

[0033]

[0034] In the formula, C Dx and C Dy represent the drag forces in the x and y directions respectively; ρ represents the density of the fluid; ρ p represents the particle density; d p Indicates particle size; V x represents the velocity of the fluid in the x direction.

[0035] Preferably, in step S3, it is set that:

[0036] f py = -g (12);

[0037] Combining (10), (11), (12), (6) and (7), we obtain:

[0038]

[0039] Substituting formula (1) into formula (13), we obtain:

[0040]

[0041] Divide formula (15) by formula (8) to obtain V px The solution in the x direction is:

[0042]

[0043] Preferably, in step S4, formula (8) is rewritten in inverse form and combined with formula (16) to calculate the time t required for the particles to pass through the combustion chamber:

[0044]

[0045] Decompose the integral x into multiple x i The time t required for the particles to reach any position in the combustion chamber is obtained. i ;

[0046] At the same time, the velocity solution V of the particle in the y direction is obtained by formula (14): py =V py (t), perform piecewise integration to obtain different x values ​​for the combustion chamber. i Position and corresponding time t i The penetration depth h i :

[0047]

[0048] Where V Py (t) represents the velocity of the particle in the y direction as a function of time;

[0049] Then, assuming that x is the dimensionless distance along the way, all time points t i The corresponding penetration depth h i Adding this up, calculate the penetration depth of the entire combustion chamber:

[0050]

[0051] Where L is the length from the injection inlet to the outlet of the burner; t(x) is the dimensionless time corresponding to the distance x along the burner.

[0052] Preferably, in step S5, the length L from the injection inlet to the outlet of the burner is regarded as the combustion chamber flow path length L f :

[0053] L f =L (19);

[0054] Assuming that the cross section of the combustion chamber flow channel is rectangular, the particle is placed at position x. i The maximum offset at position x is considered i The height of the flow channel H f :

[0055] H f =max(h i ) (20);

[0056] Calculate the cross-sectional area A' of the modified flow channel:

[0057] A'=W×h i (twenty one);

[0058] Where W is the designed flow channel width.

[0059] Preferably, in step S6, the cross-sectional area A' of the corrected flow channel is substituted for A in formulas (2) and (3) for iteration.

[0060] Therefore, the present invention adopts the above-mentioned flow channel configuration optimization design method for a powder scramjet engine combustion chamber, which has the following beneficial effects:

[0061] By optimizing the flow channel configuration of the combustion chamber, the overall performance of the engine can be further improved. It can be used to explore the laws between different incoming flows, different particle sizes, different injection angles and penetration depths, and residence times, for example:

[0062] Improve combustion efficiency: The optimized flow channel configuration helps to better control the trajectory of particles and improve fuel mixing and combustion efficiency;

[0063] Enhanced thrust output: A better combustion chamber design can improve airflow organization, thereby increasing the engine's thrust output.

[0064] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 A flowchart of a method for optimizing the flow channel configuration of a powder scramjet combustion chamber according to the present invention;

[0066] Figure 2 This is the distribution diagram of the penetration depth of particles with different particle sizes (2-6μm) during 90° vertical injection as described in the simulation experiment;

[0067] Figure 3 This is a graph showing the change in y-direction velocity of particles of different particle sizes (2-6 μm) over time during 90° vertical injection as described in the simulation experiment;

[0068] Figure 4This is a graph showing the change in x-direction velocity of particles of different sizes (2-6 μm) during 90° vertical injection as described in the simulation experiment;

[0069] Figure 5 This is the distribution diagram of the penetration depth of particles with different particle sizes (20-60μm) during 90° vertical injection as described in the simulation experiment;

[0070] Figure 6 This is a graph showing the change in y-direction velocity of particles of different particle sizes (20-60 μm) over time during 90° vertical injection as described in the simulation experiment;

[0071] Figure 7 This is a graph showing the change in velocity of particles of different diameters (20-60 μm) along the x-direction during 90° vertical injection as described in the simulation experiment;

[0072] Figure 8 This is the distribution diagram of the penetration depth of particles with different particle sizes (2-6μm) along the way during 120° reverse injection as described in the simulation experiment. DETAILED DESCRIPTION

[0073] In order to make the purpose, technical solution and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention are further described in detail in combination with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not used to limit the embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, where the same or similar numbers throughout are the same or similar elements or elements with the same or similar functions.

[0074] It should be noted that the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or inherent to these processes, methods, products or devices.

[0075] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0076] like Figure 1 As shown, a flow path configuration optimization design method for a powder scramjet combustion chamber comprises the following steps:

[0077] S1. Based on the particle trajectory model, combined with quasi-one-dimensional thermodynamic calculations, the Mach number and static temperature distribution along the path are obtained to obtain the motion state of the particle;

[0078] In step S1, the particle trajectory model expression is as follows:

[0079]

[0080] Where V x is the velocity of the particle in the x direction; M is the Mach number; k is the Boltzmann constant; R is the gas constant;

[0081] The differential equation expression of Mach number along the path is as follows:

[0082]

[0083] In the formula, is the rate of change of Mach number M along the x direction; γ is the specific heat ratio; T t is the temperature; C f is the friction coefficient; D is the diameter of the combustion chamber flow channel; A is the cross-sectional area of ​​the combustion chamber flow channel;

[0084] The differential equation for static temperature is as follows:

[0085]

[0086] In the formula, is the rate of change of static temperature T along the x direction; c p is the specific heat capacity at constant pressure; h t is the enthalpy of the fluid.

[0087] S2. Based on the particle trajectory model, the particle motion is decomposed into the x-direction and the y-direction, and the momentum equation, motion equation and drag equation of the particle are decomposed;

[0088] In step S2, the particle dynamics equation is constructed using Lagrangian in the Cartesian coordinate system:

[0089]

[0090] In the formula, X p is the particle position vector; V p is the velocity vector of the particle; F p is the resistance force on the particle per unit mass; F is the gravity on the particle;

[0091] The resistance F of the particle per unit mass is p The expression is as follows:

[0092]

[0093] Where V is the velocity vector of the gas phase; C D is the drag coefficient; d p is the particle size;

[0094] Drag coefficient C D The expression is as follows:

[0095]

[0096] In the formula, Re p is the particle Reynolds number;

[0097] Particle Reynolds number Re p The expression is as follows:

[0098]

[0099] Where μ is the dynamic viscosity of the fluid;

[0100] Momentum equation:

[0101]

[0102] In the formula, v px and v py Represent the speed of the particle in the x direction and y direction respectively; F px and F py represent the drag force of the particle in the x and y directions respectively; f py represents mass force;

[0103] Equations of motion:

[0104]

[0105] Assuming that the incoming flow has only velocity in the x direction, the drag equation is as follows:

[0106]

[0107]

[0108] In the formula, C Dx and C Dy represent the drag forces in the x and y directions respectively; ρ represents the density of the fluid; ρ p represents the particle density; d p Indicates particle size; V x represents the velocity of the fluid in the x direction;

[0109] S3, combining the Mach number and static temperature distribution solutions along the path described in step S1 with the momentum equation, motion equation and drag equation described in step S2 to derive a differential equation for the particle velocity distribution along the path;

[0110] In step S3, set:

[0111] f py = -g (12);

[0112] Combining (10), (11), (12), (6) and (7), we obtain:

[0113]

[0114] Substituting formula (1) into formula (13), we obtain:

[0115]

[0116] Divide formula (15) by formula (8) to obtain V px The solution in the x direction is:

[0117]

[0118] S4, integrating the differential equation described in step S3 in combination with the equation of motion, and solving the residence time and penetration depth of the particles at different positions in the combustion chamber of the powder scramjet engine;

[0119] In step S4, formula (8) is rewritten into an inverse form and combined with formula (16) to calculate the time t required for the particles to pass through the combustion chamber:

[0120]

[0121] Decompose the integral x into multiple x i The time t required for the particles to reach any position in the combustion chamber is obtained. i ;

[0122] At the same time, the velocity solution V of the particle in the y direction is obtained by formula (14): py =V py (t), perform piecewise integration (the step length along the path selected for integration is less than 10 -6 Level), get different x in the combustion chamber i Position and corresponding time t i The penetration depth h i :

[0123]

[0124] Where V Py (t) represents the velocity of the particle in the y direction as a function of time;

[0125] Then, assuming that x is the dimensionless distance along the way, all time points t i The corresponding penetration depth h i Adding this up, calculate the penetration depth of the entire combustion chamber:

[0126]

[0127] Where L is the length from the injection inlet to the outlet of the burner; t(x) is the dimensionless time corresponding to the distance x along the burner.

[0128] In this embodiment, particles with large diameters (e.g., diameters greater than 20 μm) or large radial velocities (greater than 200 m / s) will have a high penetration depth and thus hit the engine wall. Therefore, the x and y direction velocities after reflection can be calculated by the velocity attenuation coefficient.

[0129] S5, estimating the height and length of the combustion chamber flow channel by the penetration depth, and correcting the cross-sectional area of ​​the combustion chamber flow channel in the quasi-one-dimensional calculation described in step S1 based on the estimation result;

[0130] In step S5, the length L from the injection inlet to the outlet of the burner is regarded as the combustion chamber flow path length L f :

[0131] L f =L (19);

[0132] Assuming that the cross section of the combustion chamber flow channel is rectangular, the particle is placed at position x. i The maximum offset at position x is considered i The height of the flow channel H f :

[0133] H f =max(h i ) (20);

[0134] Calculate the cross-sectional area A' of the modified flow channel:

[0135] A'=W×h i (twenty one);

[0136] Where W is the designed flow channel width.

[0137] S6. Iterate step S1 to step S5 until the end condition is met, and output the optimal combustion chamber flow channel configuration.

[0138] In step S6, the corrected cross-sectional area A' of the flow channel is substituted for A in formulas (2) and (3) for iteration.

[0139] Simulation experiment:

[0140] like Figure 2 As shown, the horizontal axis X is the axial distance of the combustion chamber. It can be known that when the particle size is 2μm to 6μm, the time the particles stay in the combustion chamber and the penetration depth after leaving the combustion chamber.

[0141] like Figure 3As shown, the horizontal axis t is time (s). It can be seen that the y-direction velocity of small-size particles will quickly approach the mainstream y-direction velocity, which has a greater impact on the penetration depth.

[0142] like Figure 4 As shown, the horizontal axis x is the axial distance of the combustion chamber, and the vertical axis is the particle x-direction velocity.

[0143] like Figure 5 As shown, it can be seen that when the particle size is 20μm to 60μm, the time the particles stay in the combustion chamber and the penetration depth after leaving the combustion chamber. It can be clearly seen that the penetration depth of large-size particles in the combustion chamber cannot be stable in a short period of time, and there is wall reflection phenomenon.

[0144] like Figure 6 As shown in the figure, it can be seen that the y-direction velocity of large-size particles is less likely to be affected by the mainstream than that of small-size particles. Figure 7 As shown, it can be seen that the x-direction velocity of large-diameter particles is less likely to be affected by the mainstream than that of small-diameter particles.

[0145] like Figure 8 As shown in Figure 2, it can be seen that when the particle size is 2μm to 6μm, the time the particles stay in the combustion chamber and the penetration depth after leaving the combustion chamber are Figure 8 As can be seen from the sub-graph, the larger the particle size, the farther it sprays in the reverse direction.

[0146] This proves that the present invention can explore the rules between different incoming flows, different particle sizes, different injection angles and penetration depths, and residence times.

[0147] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for optimizing the flow channel configuration of a powder scramjet combustion chamber, characterized in that: The following steps are involved: S1. Based on the particle trajectory model, combined with quasi-one-dimensional thermodynamic calculations, the Mach number and static temperature distribution along the path are obtained to obtain the motion state of the particle; S2. Based on the particle trajectory model, the particle motion is decomposed into the x-direction and the y-direction, and the momentum equation, motion equation and drag equation of the particle are decomposed; S3, combining the Mach number and static temperature distribution solutions along the path described in step S1 with the momentum equation, motion equation and drag equation described in step S2 to derive a differential equation for the particle velocity distribution along the path; S4, integrating the differential equation described in step S3 in combination with the equation of motion to solve the residence time and penetration depth of the particles at different positions in the combustion chamber of the powder scramjet engine; S5, estimating the height and length of the combustion chamber flow channel by the penetration depth, and correcting the cross-sectional area of ​​the combustion chamber flow channel in the quasi-one-dimensional calculation described in step S1 based on the estimation result; S6. Iterate step S1 to step S5 until the end condition is met, and output the optimal combustion chamber flow channel configuration.

2. The method for optimizing the flow path configuration of a powder scramjet combustion chamber according to claim 1, characterized in that: In step S1, the particle trajectory model expression is as follows: Where V x is the velocity of the particle in the x direction; M is the Mach number; k is the Boltzmann constant; R is the gas constant; The differential equation expression of Mach number along the path is as follows: In the formula, is the rate of change of Mach number M along the x direction; γ is the specific heat ratio; T t is the temperature; C f is the friction coefficient; D is the diameter of the combustion chamber flow channel; A is the cross-sectional area of ​​the combustion chamber flow channel; The differential equation for static temperature is as follows: In the formula, is the rate of change of static temperature T along the x direction; c p is the specific heat capacity at constant pressure; h t is the enthalpy of the fluid.

3. The method for optimizing the flow path configuration of a powder scramjet combustion chamber according to claim 2, characterized in that: In step S2, the particle dynamics equation is constructed using Lagrangian in the Cartesian coordinate system: Where, X p is the particle position vector; V p is the velocity vector of the particle; F p is the resistance force on the particle per unit mass; F is the gravity on the particle; Momentum equation: In the formula, v px and v py Represent the speed of the particle in the x direction and y direction respectively; F px and F py represent the drag force of the particle in the x and y directions respectively; f py represents mass force; Equations of motion: Assuming that the incoming flow has only velocity in the x direction, the drag equation is as follows: In the formula, C Dx and C Dy represent the drag forces in the x and y directions respectively; ρ represents the density of the fluid; ρ p represents the particle density; d p Indicates particle size; V x represents the velocity of the fluid in the x direction.

4. The method for optimizing the flow path configuration of a powder scramjet combustion chamber according to claim 3, characterized in that: In step S3, set: f py =-g (12); Combining (10), (11), (12), (6) and (7), we obtain: Substituting formula (1) into formula (13), we obtain: Divide formula (15) by formula (8) to obtain V px The solution in the x direction is:

5. The method for optimizing the flow path configuration of a powder scramjet combustion chamber according to claim 4, characterized in that: In step S4, formula (8) is rewritten into an inverse form and combined with formula (16) to calculate the time t required for the particles to pass through the combustion chamber: Decompose the integral x into multiple x i The time t required for the particles to reach any position in the combustion chamber is obtained. i ; At the same time, the velocity solution V of the particle in the y direction is obtained by formula (14): py =V py (t), perform piecewise integration to obtain different x values ​​for the combustion chamber. i Position and corresponding time t i The penetration depth h i : Where V Py (t) represents the velocity of the particle in the y direction as a function of time; Then, assuming that x is the dimensionless distance along the way, all time points t i The corresponding penetration depth h i Adding this up, calculate the penetration depth of the entire combustion chamber: Where L is the length from the injection inlet to the outlet of the burner; t(x) is the dimensionless time corresponding to the distance x along the burner.

6. The method for optimizing the flow path configuration of a powder scramjet combustion chamber according to claim 5, characterized in that: In step S5, the length L from the injection inlet to the outlet of the burner is regarded as the combustion chamber flow path length L f : L f =L (19); Assuming that the cross section of the combustion chamber flow channel is rectangular, the particle is placed at position x. i The maximum offset at position x is considered i The height of the flow channel H f : H f =max(h i ) (20); Calculate the cross-sectional area A' of the modified flow channel: A'=W×h i (21); Where W is the designed flow channel width.

7. The method for optimizing the flow path configuration of a powder scramjet combustion chamber according to claim 6, characterized in that: In step S6, the corrected cross-sectional area A' of the flow channel is substituted for A in formulas (2) and (3) for iteration.

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