A method for rapid evaluation of engine vacuum plume impingement pressure and heat flux density

Abstract

A method for rapid evaluation of the impact pressure and heat flux density of the engine vacuum plume is provided. The method first analyzes the internal and external flow field of the engine by numerically solving the N-S equation and the point source method engineering empirical model. By traversing the local parameters of the engine external flow field, the maximum impact pressure and maximum heat flux density generated by the local flow on the equipment are given by using the momentum exchange principle and the one-dimensional adiabatic flow energy equation. The method solves the problem of multiple and incomplete coverage of the plume iterative analysis conditions caused by the uncertainty of the relative position of the release separation process load and the satellite platform. It can quickly evaluate the plume force and heat influence of the release separation process load and the satellite platform on each other when the engine is working. The evaluation results cover all relative positions of the load and the satellite platform, meet the needs of rapid iteration of release separation scheme demonstration and design, and provide analysis basis for plume force and heat influence avoidance and protection design.

Description

Technical Field

[0001] This invention relates to the field of engine vacuum plume force and heat effect analysis technology, and in particular to a rapid estimation method for plume impact pressure and heat flux density based on engine vacuum plume flow field energy theory. Background Technology

[0002] As spacecraft functional requirements become increasingly diverse and complex, on-orbit operations may involve docking, separation, and payload release. During these processes, the operation of the moving target (released payload) and the satellite platform's attitude and orbit control engines can generate significant plume force and thermal impacts on both. The design of the satellite platform payload release scheme must consider functional requirements and safety considerations, and is subject to numerous constraints. Furthermore, the design of parameters such as payload release speed, attitude, payload, and platform engine activation time significantly depends on the engine plume force and thermal analysis results. Because the moving target release scheme and motion path planning are subject to multiple possibilities during the feasibility study phase, and the payload's position relative to the spacecraft platform is uncertain, it is difficult to cover all relative positions of the moving payload and satellite platform during the separation and release process using a multi-condition firing method, and to capture the extreme conditions to provide the maximum force and thermal contamination impact of the plume. Multi-condition firing also suffers from the problem of excessive time consumption, making it difficult to meet the design requirements of rapid iteration during the feasibility study phase. Summary of the Invention

[0003] Based on the above background, this disclosure provides a conservative evaluation method for the mechanical and thermal effects based on the energy theory of engine vacuum plume flow field. It simplifies the multi-condition plume effect target analysis of the separation and release process into an evaluation based on the impact pressure and heat flux density of the local parameters of the plume flow field, thus solving the need for rapid and efficient plume analysis in the design and demonstration of separation and release schemes.

[0004] This method combines computational fluid dynamics (CFD) with engineering empirical models. First, it numerically simulates the continuous flow inside the engine and the external vacuum plume flow, obtaining flow parameters such as density, velocity, pressure, and temperature within a certain range from the engine nozzle exit. Then, assuming the presence of equipment in the flow field, based on the assumption of interaction between calorimetrically perfect gas and the equipment surface and the theory of one-dimensional steady adiabatic flow, it gives the maximum pressure and maximum heat flux density that the plume may generate on the equipment under local flow conditions. This method eliminates the need for three-dimensional modeling of the satellite platform and the equipment configuration on the release payload surface, and eliminates the need to set the relative positions and attitudes between them. It only requires numerical simulation of the engine flow field to provide an assessment of the maximum impact pressure and heat flux density of the plume within the motion envelope of the release payload, significantly saving computational and human resources and meeting the needs of rapid iteration in scheme demonstration and design. This technology is the first of its kind internationally and domestically, and it will provide key support for the rapid and efficient assessment of the mechanical and thermal effects of plumes.

[0005] Specifically, the rapid estimation method for plume impact pressure and heat flux density based on the energy theory of engine vacuum plume flow field provided in this disclosure mainly includes the following steps:

[0006] 1) Construct the internal and external flow field meshes based on the engine geometry. Set the inlet and boundary conditions of the computational domain according to the engine's operating parameters. Perform simulation analysis on the internal flow field region of the engine using numerical solutions to the Navier-Stokes equations.

[0007] 2) The flow parameters at the engine nozzle exit are used as input parameters for calculating the external flow field of the nozzle. The flow parameters of the external space of the engine, including flow density, velocity, pressure and temperature, are obtained by using the point source method based on engineering experience.

[0008] 3) Based on the flow parameters of the external flow field of the engine, assuming that the gas molecules undergo complete diffuse reflection with the surface of the equipment, the local flow field density, velocity and static pressure are extracted using the principle of momentum exchange to obtain the maximum pressure that the engine gas may generate on the surface of the equipment.

[0009] 4) Based on the flow parameters of the external flow field of the engine, a one-dimensional steady adiabatic flow energy model is used to extract parameters such as flow field density and velocity, ignoring the heating effect of the gas temperature on the surface of the equipment. The flow field energy is calculated, assuming that all of this energy can be transferred to the equipment, and the limiting conservative heat flux density per unit area of ​​the equipment in the local flow field is given.

[0010] Furthermore, the specific process of step 1) is as follows: Based on the geometric dimensions of the engine nozzle contraction and expansion sections and the defined influence area, a three-dimensional or two-dimensional axisymmetric grid of the internal and external flow fields of the engine is established. By setting the engine inlet gas parameters and adopting the assumption of frozen flow of gas components, the flow field inside the engine gas nozzle is numerically simulated using computational fluid dynamics (CFD) methods, providing flow field parameters including thermodynamic parameters of the mixed gas flow and flow field parameters such as density, velocity, pressure, and temperature.

[0011] The specific process of step 2) is as follows: Extract the engine nozzle outlet flow parameters calculated in step 1), and use them as input parameters for calculating the external flow field of the nozzle. The point source method, based on an engineering empirical model, is then used to calculate the external flow field of the engine. Specifically, a frozen surface is defined in the flow field, and a certain number of free molecular point sources are arranged on it. The flow parameters at any point in the flow field can be considered as the superposition of the flow fields generated by all free molecular point sources at that point. The flow field density ρ generated by the free molecular point sources follows the radiation attenuation law, i.e.

[0012]

[0013] In the formula: V is the plume expansion limiting velocity; s* is the flow rate at the nozzle throat; r is the distance from the nozzle exit; θ is the angle of deviation from the plume axis; θ Lθ is the PM expansion angle; f(θ) is a function of the angle of deviation from the plume axis.

[0014] Because the fundamental flow parameters differ, the expression for f(θ) differs between the plume core region and the boundary layer expansion region: the expression in the plume core region is...

[0015]

[0016] Where: γ is the specific heat ratio of the gas; θ0 is the flow limiting deflection angle in the core region of the plume; θ ∞ It is the nozzle flow limit deflection angle.

[0017] In the boundary layer expansion region, a coefficient β is introduced, and it is assumed that f(θ) decays exponentially in this region, with the expression being:

[0018] f(θ)=f(θ0)exp[-β(θ-θ0)],θ0≤θ≤θ ∞ (3)

[0019] Other physical quantities in the flow field, such as pressure P, temperature T, and limiting velocity V, can be calculated using a one-dimensional isentropic relationship.

[0020] The specific process of step 3) is as follows: traverse the local flow field parameter density ρ (kg / m³) corresponding to the flow field grid points in step 2). 3 The flow velocity V (m / s) and the plume disturbance force are mainly caused by the gas molecules hitting the equipment surface and exchanging momentum with the equipment. The change in momentum of the gas molecules can be expressed as:

[0021] P=mΔV

[0022] The mass m of the gas molecules acting on a unit surface of the equipment can be expressed as m = ρV, therefore

[0023] P=ρVΔV

[0024] Generally, gas molecules undergo perfect diffuse reflection with the surface of the equipment, therefore P = ρV 2 The unit is Pa. It can be seen that the pressure exerted by the gas molecules on the equipment surface is twice the dynamic pressure.

[0025] The specific process of step 4) is as follows: traverse the local flow field parameter density ρ (kg / m³) corresponding to the flow field grid points in step 2). 3 The flow velocity is V (m / s) and the gas temperature is T. Using the one-dimensional steady adiabatic flow energy equation, i.e.

[0026]

[0027] When the engine is running, the combustion chamber provides complete combustion, and the Laval nozzle design accelerates the gas inside the nozzle, resulting in a significantly lower outlet temperature compared to the combustion chamber temperature. Therefore, the heating of the equipment by the external gas plume is primarily due to the high-speed airflow.

[0028] For a specific engine plume flow field state, the limiting conservative heat flux density per unit area of ​​the equipment in the flow field is approximately:

[0029]

[0030] As can be seen from the above equation, the heat flux density q is related to the gas density ρ and the gas velocity V. 3 Proportional. Ignoring the heat transferred by the gas temperature gradient, the heat flux density formula can be written as:

[0031]

[0032] Compared with the prior art, the beneficial effects of this disclosure are:

[0033] (1) Compared with the previous method of conducting accurate evaluation of plume force and heat effects by establishing a three-dimensional model of the specific configuration of satellite platform and payload surface equipment, this method uses theoretical models to conservatively estimate plume impact pressure and heat flux density based on the calculated plume flow field parameters, which greatly saves the three-dimensional modeling time of complex configuration equipment and significantly improves the calculation efficiency.

[0034] (2) Compared with the previous approach of traversing all possible relative positions of satellite platform and release payload by working condition target shooting method, this method can give the plume force and heat effect of the entire flow field on local equipment by traversing the flow field parameters. That is, it can include the plume effect assessment work brought about by all possible flight paths of the release payload. It does not rely on random target shooting strategy, can accurately capture extreme working conditions and give the maximum impact pressure and heat flux density of the plume on the equipment.

[0035] (3) It can meet the engineering requirements for rapid iterative analysis of the thermal and mechanical effects of the plume after changes in the release and separation scheme. Attached Figure Description

[0036] The above and other objects, features and advantages of this disclosure will become more apparent from the more detailed description of exemplary embodiments of this disclosure taken in conjunction with the accompanying drawings, in which the same reference numerals generally represent the same components.

[0037] Figure 1 Here is a flowchart of an exemplary method for rapid evaluation of engine vacuum plume impact pressure and heat flux density according to this disclosure;

[0038] Figure 2 Flowchart for calculating the external flow field of an engine using the point source method;

[0039] Figure 3 This is a velocity distribution diagram of the external flow field of the 5000N engine plume.

[0040] Figure 4 This is a density distribution diagram of the external flow field of the 5000N engine plume.

[0041] Figure 5 This is a temperature distribution diagram of the external flow field of the plume from a 5000N engine.

[0042] Figure 6 This is a contour map of the impact pressure exerted by a 5000N engine on the surface of local equipment (the origin of the coordinate system is the center point of the engine nozzle exit, the horizontal axis is the axial distance of the engine, and the vertical axis is the distance perpendicular to the engine axis).

[0043] Figure 7 The graph shows the change in impact pressure on the surface of local equipment as a function of axial distance when the 5000N engine releases at a distance of 15m (the horizontal axis represents the axial distance from the center point of the engine nozzle exit).

[0044] Figure 8 A contour map of the heat flux density of a 5000N engine on the surface of local equipment (the origin of the coordinate system is the center point of the engine nozzle exit, the horizontal axis is the axial distance of the engine, and the vertical axis is the distance in the direction perpendicular to the engine axis).

[0045] Figure 9 The graph shows the change of heat flux density on the surface of local equipment as a function of axial distance when the release distance of the 5000N engine is 15m (the horizontal axis is the axial distance from the center point of the engine nozzle exit). Detailed Implementation

[0046] Preferred embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While preferred embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

[0047] This disclosure provides a rapid assessment method for the impact pressure and heat flux density of an engine vacuum plume. In one exemplary embodiment, the flowchart of the rapid assessment method for the force, heat, and contamination effects of an engine vacuum plume is attached. Figure 1 As shown, the main steps include the following:

[0048] 1) Based on the geometry of the 5000N engine, including parameters such as the engine throat diameter, nozzle diameter, and distance from the throat to the nozzle, the computational domain was determined, and a two-dimensional axisymmetric mesh was created for the engine. The inlet, outlet, and solid wall boundaries of the computational domain were set according to the engine's operating parameters (total temperature and total pressure). The flow field within the 5000N engine was numerically solved using the Navier-Stokes equations, providing the jet flow parameters within the computational domain.

[0049] 2) The calculated engine nozzle exit flow parameters (velocity, density, temperature, and pressure, etc.) are used as input parameters for calculating the external flow field of the nozzle. The point source method based on the engineering empirical model is employed to calculate the external flow field of the engine. The calculation process for the point source method of the engine external flow field is as follows: Figure 2 Using the engine nozzle exit parameters as the freezing surface, a certain number of point source molecules are arranged on the freezing surface. The external flow density is calculated using the radiation attenuation law and empirical formulas for the core region and limiting deflection angle. Other flow field parameters (velocity, temperature, and pressure, etc.) are calculated based on one-dimensional isentropic relationships. The velocity, density, and temperature distribution of the 5000N external flow are shown below. Figures 3-5 As shown.

[0050] 3) By traversing the external flow field parameters of the engine, assuming that the gas molecules undergo complete diffuse reflection with the equipment surface, and using the principle of momentum exchange, the pressure generated by the gas molecules on the equipment surface can be expressed as P = ρV. 2 By extracting the local flow field density and velocity parameters, the maximum pressure that the engine exhaust gas might generate on the equipment surface can be obtained. For example, at a distance of 3.6m from the engine nozzle outlet along the axial direction, ρ = 1.52e-4 kg / m². 2 The velocity V = 2940 m / s, p = ρV 2 =1310 Pa. If there is equipment at the location, the impact pressure of the plume gas molecules on the equipment will not exceed 1310 Pa. Using this method, the maximum possible impact pressure distribution of the plume gas molecules on local equipment within a 40 m axial direction and ±15 m vertical direction from the nozzle outlet of a 5000N engine is given, such as... Figure 6 As shown in the figure. At a distance of 15m from the vertical axis of the engine, the change in the impact pressure of the 5000N engine plume on local equipment during its release process with respect to the engine's axial distance is as follows: Figure 7 As shown.

[0051] Using a one-dimensional steady adiabatic flow energy model, neglecting the heating effect of gas temperature on the equipment surface, parameters such as flow field density and velocity are extracted to calculate the flow field energy. Assuming all this energy can be transferred to the equipment, give the limiting conservative heat flux density per unit area of ​​the equipment in the local flow field. For example, consider a location 3.6m from the engine nozzle exit along the axial direction: ρ = 1.52e-4 kg / m². 2Velocity V = 2940 m / s, q = 0.5ρV 3 =1931kW / m 2 If equipment is present at the location, the heat flux density of the plume gas molecules to the equipment shall not exceed 1931 kW / m³. 2 This method was applied to provide the maximum possible heat flux density distribution of plume gas molecules to local equipment within a 40m axial direction and ±15m vertical direction from the nozzle exit of a 5000N engine. Figure 8 As shown, at a distance of 15m from the vertical axis of the engine, the change in heat flux density of the plume released by the 5000N engine on local equipment as a function of the engine axial distance is as follows: Figure 9 As shown.

[0052] The above technical solutions are merely exemplary embodiments of the present invention. For those skilled in the art, based on the application methods and principles disclosed in the present invention, it is easy to make various types of improvements or modifications, and not limited to the methods described in the specific embodiments of the present invention. Therefore, the methods described above are only preferred and not restrictive.

Claims

1. A method for rapid estimation of the impact pressure and heat flux density of a vacuum plume in an engine, comprising the following steps: S1. Based on the engine geometry, construct the internal and external flow field grids of the engine, and obtain the flow parameters at the engine nozzle exit by numerically solving the Navier-Stokes equations. S2, using the engine nozzle outlet flow parameters as input parameters for calculating the external flow field of the nozzle, and employing the point source method based on engineering experience to obtain the flow parameters of the external flow field of the engine; S3. Based on the flow parameters of the external flow field of the engine, assuming that the gas molecules undergo complete diffuse reflection with the surface of the equipment, the maximum pressure generated by the engine gas on the surface of the equipment is obtained by using the principle of momentum exchange. S4. Based on the flow parameters of the external flow field of the engine, a one-dimensional steady adiabatic flow energy model is used to extract the flow field density and velocity parameters, neglecting the heating effect of the gas temperature on the equipment surface. The flow field energy is calculated, assuming that all of this energy can be transferred to the equipment, and the limiting conservative heat flux density per unit area of ​​the equipment in the local flow field is given.

2. The method according to claim 1, characterized in that, Step S1 specifically includes: Based on the geometric dimensions of the engine nozzle contraction and expansion sections and the defined influence area, a three-dimensional or two-dimensional axisymmetric mesh of the internal and external flow fields of the engine is established. By setting the engine inlet gas parameters and adopting the assumption of frozen flow of gas components, the flow field inside the engine gas nozzle is numerically simulated using computational fluid dynamics methods, and the thermodynamic parameters and flow field parameters of the mixed gas flow are given.

3. The method according to claim 1 or 2, characterized in that, Step S2 specifically includes: The engine nozzle exit flow parameters calculated in step S1 are extracted and used as input parameters for calculating the external flow field of the nozzle. The point source method, an engineering empirical model, is then used to calculate the external flow field of the engine. Define a frozen surface in the flow field and arrange a predetermined number of free molecular point sources on it. The flow parameters at any point in the flow field can be considered as the superposition of the flow fields generated by all the free molecular point sources at that point; the flow field density generated by the free molecular point sources... Follows the law of radiation attenuation, that is (1) In the formula: V m s* is the plume expansion limiting velocity; r is the nozzle throat flow rate; θ is the distance from the nozzle exit point; θ is the angle of deviation from the plume axis. L For PM extension angle; f(θ) It is a function of the angle of deviation from the plume axis; Due to the different fundamental parameters of the flow f(θ) The expressions differ between the plume core region and the boundary layer expansion region: the expression for the plume core region is... (2) in: θ is the specific heat ratio of the gas; θ0 is the flow limiting deflection angle in the core region of the plume; θ ∞ It is the nozzle flow limit deflection angle; In the boundary layer expansion region, a coefficient β is introduced and it is assumed that... f(θ) In this region, it decays exponentially, and its expression is: (3) The pressure, temperature, and limiting velocity in the flow field are calculated based on the one-dimensional isentropic relationship.

4. The method according to claim 3, characterized in that, Step S3 specifically includes: Assuming perfect diffuse reflection occurs between the gas molecules and the equipment surface, using the principle of momentum exchange, the pressure generated by the gas molecules on the equipment surface can be expressed as: ; Iterate through the local flow field parameter density corresponding to the grid points of the engine's external flow field. and flow velocity V This yields the maximum pressure generated by the local engine combustion gases on the equipment surface.

5. The method according to claim 4, characterized in that, The heat flux density q in step S4 is calculated using the following formula: in, These are the local flow field density parameters corresponding to the grid points of the engine's external flow field. V The velocity is the flow rate.

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