A FLUENT-based method for predicting the high-Mach aerodynamic characteristics of Mars orbiters

Abstract

This invention discloses a method for predicting the high-Mach aerodynamic characteristics of a Mars orbiter based on FLUENT, belonging to the aerospace field. This invention establishes a symmetrical geometric model of the Mars orbiter and uses a dual-temperature model based on FLUENT to achieve numerical simulation of the Mars orbiter under high-Mach conditions in CO2 medium. By setting a boundary layer based on O-Block mesh coupling, it achieves unified simulation prediction for different velocities and angles of attack, reducing the computational burden of re-partitioning the mesh for different conditions, thereby improving the efficiency of aerodynamic characteristic prediction. Simultaneously, it can accurately simulate and analyze the aerodynamic characteristics of the Mars orbiter under different conditions, enabling the corresponding aerodynamic performance evaluation of the Mars orbiter. This invention can analyze and construct the hypersonic aerodynamic characteristics of the Mars orbiter under different high-Mach conditions upon entering the Martian atmosphere, assisting in the optimization of the Mars orbiter and guidance and control commands.

Description

Technical Field

[0001] This invention relates to a method for predicting the high Mach aerodynamic characteristics of a Mars orbiter based on FLUENT, and more particularly to a method applicable to analyzing the high Mach aerodynamic characteristics of a Mars orbiter during its aerodynamically assisted descent into the Martian atmosphere, belonging to the field of aerospace. Background Technology

[0002] Mars is the closest terrestrial planet to Earth, and Mars exploration is a primary goal of human deep space exploration. Landing exploration is currently the main approach for comprehensive Mars exploration. Compared to Earth's atmosphere, Mars' atmosphere is mainly composed of CO2 and is extremely thin, with a surface pressure equivalent to the atmospheric pressure at an altitude of 35 km on Earth. Furthermore, Mars has a complex and varied climate, with low temperatures and large diurnal temperature variations. This causes discrepancies between the atmospheric environmental parameters encountered by the Mars orbiter during landing and existing data. These complex and variable environments pose a significant challenge to predicting the orbiter's aerodynamic characteristics. The Mars orbiter enters the Martian atmosphere at hypersonic speeds, and the surrounding flow field exhibits characteristics of low Reynolds numbers and high Mach numbers. To ensure the accuracy of the Mars orbiter's aerodynamic-assisted orbit descent and landing design, it is necessary to establish appropriate aerodynamic prediction methods tailored to the unique medium environment and high Mach flow characteristics of the Martian atmosphere, thereby accurately and effectively predicting the aerodynamic characteristics of the Mars orbiter.

[0003] Finite element method (FEM) numerical simulations for predicting the aerodynamic properties of the Martian atmosphere can generally be divided into two categories: one is the Monte Carlo method (DSMC), used for direct numerical simulation of rarefied flows; the other is the traditional Navier-Stokes (NS) equations solution method, which considers thermodynamic and chemical nonequilibrium. Existing analytical methods often utilize FLUENT to analyze the aerodynamic characteristics of Mars orbiters in continuous flow regions at low Mach, while the DSMC method is more commonly used in high Mach regions. However, when dealing with various high Mach conditions, the DSMC method requires the creation of corresponding discrete meshes for conditions with significant velocity variations. Since the Martian atmosphere is primarily composed of CO2, has a low density, and is relatively rarefied, Mars orbiters are often designed in a conical shape to stabilize their attitude by using centroid shift or finite thrust upon entering the Martian atmosphere. Simulating flight into the Martian atmosphere requires appropriate mesh discretization methods to effectively handle multiple ring-shaped structures, making the computation process cumbersome and complex.

[0004] Currently, there are no convenient and accurate analysis methods and numerical prediction methods for using FLUENT to simulate the flow of a Mars orbiter under different operating conditions in the high Mach flow region during its flight, especially a unified simulation numerical prediction method for the Mars orbiter under different operating conditions such as different speeds or angles of attack at high Mach. Summary of the Invention

[0005] The main objective of this invention is to provide a method for predicting the high-Mach aerodynamic characteristics of a Mars orbiter based on FLUENT. This method utilizes a dual-temperature model based on FLUENT to achieve numerical simulation of a Mars orbiter under high-Mach conditions in a CO2 medium. By using O-Block mesh coupling to set boundary layers, it achieves unified simulation prediction for different velocities and angles of attack, reducing the computational burden of re-meshing the mesh under different conditions and thus improving the efficiency of aerodynamic characteristic prediction. Simultaneously, it can accurately simulate and analyze the aerodynamic characteristics of the Mars orbiter under different conditions, enabling the corresponding aerodynamic performance evaluation of the Mars orbiter. This invention can analyze and construct the hypersonic aerodynamic characteristics of a Mars orbiter under different high-Mach conditions upon entering the Martian atmosphere, assisting in the optimization of Mars orbiter design and guidance and control command design.

[0006] The objective of this invention is achieved through the following technical solution.

[0007] This invention discloses a method for predicting the high Mach aerodynamic characteristics of a Mars orbiter based on FLUENT. It establishes a symmetrical model of the Mars orbiter based on its external structure and appropriately adjusts the center-of-mass offset position based on the characteristic that the orbiter generates aerodynamic forces due to its center of mass being off-center during entry. Considering the compositional distribution of the Martian atmosphere, the computational domain medium for the external flow field of the Mars orbiter is set to CO2, and the relevant turbulence parameters are set according to the Martian environment, improving the accuracy of the prediction and analysis of the high Mach aerodynamic characteristics of the Mars orbiter. Furthermore, considering that Mars orbiters often operate in high Mach hypersonic flows, which easily generate thermal imbalances, a dual-temperature model is used to simulate the energy relaxation process in the flow. Compared to single-temperature models, this invention improves the prediction accuracy of flow fields in high Mach regions. Considering the large-scale rigid-body motion required for the Mars orbiter, the displacement of the moving boundary needs to be much larger than the mesh size to better simulate flow field changes. Traditional unstructured meshes result in uneven mesh transitions and long computation times, affecting aerodynamic prediction efficiency and potentially leading to non-convergence. Therefore, a structured mesh is used. Furthermore, given the predominantly circular shape of the Mars orbiter, a local O-Block remodeling model is employed. This ensures the remodeled mesh meets the slope and size requirements of the circular transition zone, improving prediction efficiency while maintaining the accuracy of high Mach aerodynamic characteristic simulation. This invention can analyze and construct the hypersonic aerodynamic characteristics of the Mars orbiter under different high Mach conditions upon entering the Martian atmosphere, enabling corresponding aerodynamic performance evaluation. This invention can also analyze and construct the hypersonic aerodynamic characteristics of the Mars orbiter under different high Mach conditions upon entering the Martian atmosphere, assisting in optimizing the Mars orbiter design and guidance and control command design.

[0008] The high Mach aerodynamic characteristics prediction method for Mars orbiters based on FLUENT disclosed in this invention includes the following steps:

[0009] Step 1: The Mars orbiter adopts a symmetrical configuration, with its forebody primarily consisting of a circular heat-resistant base made of high-temperature resistant materials. Because the Mars orbiter relies on its irregular mass for attitude adjustment, its center of mass is not entirely at the orbiter's geometric center. Therefore, when initially establishing the symmetrical geometric model of the Mars orbiter, the center of mass offset position is appropriately adjusted based on the characteristic that the Mars orbiter generates corresponding aerodynamic forces during entry due to its center of mass not being at the geometric center. Considering the compositional distribution of the Martian atmosphere, the computational domain medium for the external flow field of the Mars orbiter is set to CO2, and the relevant turbulence parameters are set according to the Martian environment, improving the accuracy of the symmetrical geometric model's prediction and analysis of the Mars orbiter's high-Mach aerodynamic characteristics.

[0010] Step Two: Based on the required simulated atmospheric flow field region around the Mars orbiter, establish a three-dimensional fluid computational domain for the symmetrical geometric model of the Mars orbiter established in Step One. Considering the orbiter's symmetrical cabin configuration, to reduce computational load and improve aerodynamic characteristic prediction efficiency, a half-field approach is used for fluid computational domain modeling. Therefore, the computational domain mainly includes the following parts: inlet section, outlet section, pressure far-field (required for the external flow field), and symmetry plane. Furthermore, considering the Mars orbiter's need to undergo large-scale rigid body motion during descent, the fluid computational domain is set as a cylinder to ensure a relatively uniform aerodynamic environment for the Mars orbiter. The size of the three-dimensional fluid computational domain is also set to be sufficiently large to reflect the actual situation of a large-scale descent.

[0011] Step 3: Mesh the three-dimensional fluid computational domain established in Step 2 to obtain the computational mesh for the high Mach external flow field of the Mars orbiter.

[0012] To improve numerical computation efficiency and accuracy, structured meshes are preferred for the computational domain. Since the fluid in the turbulent boundary layer is simultaneously subjected to viscous shear stress and turbulent additional shear stress, the boundary layer configuration significantly impacts the simulation predictions of the external flow field to ensure the accuracy of the solution. Furthermore, because the cross-section of the computational domain for the flow field outside the Mars orbiter and the cylinder is arc-shaped, an O-block meshing method suitable for curved geometric models is employed to improve mesh quality and ensure a uniform transition in the arc region. The outer O-block of the O-block method is used to refine the boundary layer mesh at the Mars orbiter wall, ensuring that the boundary layer mesh satisfies the y-axis. + To ensure a reasonable range, so as to better capture the parameters near the nozzle wall and improve the accuracy of the calculation.

[0013] The height Δs of the first mesh layer of the boundary layer is set as follows:

[0014]

[0015]

[0016]

[0017]

[0018] Where Re represents the Reynolds number of the free flow, ρ ∞ For the incoming flow density, U ∞ For the incoming flow velocity, C f The wall friction resistance is given by μ, where L is the characteristic length of the surround. ∞ The viscosity coefficient of the incoming flow, y as described in step three + The metric for measuring grid accuracy is related to the selected turbulence model; as an optimal choice, y + The aforementioned reasonable range is 0.1 ≤ y for high Mach flow of Mars orbiters. + ≤5.

[0019] Step 4: Based on Steps 1 to 3, conduct numerical calculations of the Mars orbiter under high Mach conditions. Use a turbulence model to establish and determine boundary conditions, and use a function that conforms to the CO2 variation law of the Martian atmosphere to improve the simulation accuracy and efficiency of the aerodynamic characteristics of the Mars orbiter under high Mach flow conditions. That is, make high-precision predictions of the aerodynamic characteristics of the Mars orbiter at different speeds or angles of attack in a fluid environment with CO2 as the medium, and obtain the aerodynamic characteristics of the Mars orbiter under high Mach flow.

[0020] As a preferred option, the viscosity term, Viscosity, is expressed using the Sutherland formula:

[0021]

[0022] Where μ0 is the reference viscosity, T0 is the reference temperature, and C is the Sutherland constant. For the Martian atmospheric model, μ0 is taken as 1.48 × 10⁻⁶. -5 kg / (m·s), T0=293.15K, C=240K.

[0023] To ensure the rationality of the computational model and improve prediction efficiency and computational accuracy, the SST k-omega model is preferred as the turbulence model. The boundary conditions are pressure far-field conditions, and the implicit algorithm is used for the solution. The convection term is discretized using the AUSM scheme. The SST k-omega two-equation model formula is as follows:

[0024]

[0025]

[0026]

[0027] In the formula, Ω represents vorticity. and These are mixed functions, all related to the distance from the point to the wall, where...

[0028]

[0029]

[0030]

[0031] In the formula, y is the distance from the wall. In the SST k-omega two-equation model, the parameter value is ψ = F1ψ1 + (1-F1)ψ2, where ψ1 and ψ2 are two sets of set parameters. Since F1 can complete the transition of the model from the near-wall k-ω model to the far-wall k-ε model, this equation has relatively small requirements for the wall function and high calculation accuracy. The target y + As long as the variation is consistent within a predetermined range, the adaptability requirements of the turbulence model are met. The SST k-omega two-equation model shown by formulas (6)(7)(8) can reduce the number of times the height of the first layer of the wall boundary layer is modified under different working conditions. It can simultaneously calculate a single grid at different hypersonic Mach levels, thereby improving the prediction efficiency for different working conditions.

[0032] Furthermore, considering the high-Mach operating environment of the Mars orbiter and the complex flow, as a preferred approach, a high-speed numerical format is enabled using TUI (Text User Interface) during initialization, and the calculation conditions are initialized using FMG (Full Multigrid Initialization) to obtain better initial values ​​with minimal computational cost, thereby improving computational efficiency and facilitating computational convergence.

[0033] The process also includes step five: based on the aerodynamic characteristics of the Mars orbiter under high Mach flow simulated in step four, numerical simulation analysis and post-processing are performed on the results to obtain the temperature changes, Mach number cloud map, and pressure distribution of the surrounding flow field under different high Mach conditions of the Mars orbiter. Additionally, the lift and drag coefficients and wall y-values ​​under the corresponding high Mach conditions of the Mars orbiter are obtained. + The distribution of the data is analyzed, and the results are visualized. The aerodynamic characteristics of the Mars orbiter in the high Mach flow region are analyzed to evaluate the corresponding aerodynamic performance of the Mars orbiter and assist in optimizing the design of the Mars orbiter and the design of guidance and control commands.

[0034] The wall surface y +The distribution pattern only shows parameter variations on the surface of the surround, which can be used to determine the accuracy of calculation results under the turbulence model.

[0035] The lift-drag coefficient mentioned in step five is calculated using the following formula:

[0036]

[0037]

[0038] p = 0.5ρV 2 (14)

[0039] In the formula, C l C d Here, L represents the lift coefficient, D represents the drag coefficient (in the same direction as the incoming flow velocity), A represents the reference area (for a Mars orbiter, the forebody area can be used), p represents the dynamic pressure, ρ represents the incoming flow density, and V represents the airflow velocity relative to the object.

[0040] Beneficial effects:

[0041] 1. The FLUENT-based method for predicting the high-Mach aerodynamic characteristics of a Mars orbiter disclosed in this invention uses the visualization software FLUENT for simulation. When initially establishing the symmetrical geometric model of the Mars orbiter, the center of mass offset position is appropriately adjusted based on the characteristic that the Mars orbiter generates corresponding aerodynamic forces by relying on its own center of mass not being at the geometric center during entry. Considering the characteristics of the composition distribution of the Martian atmosphere, the computational domain medium of the external flow field of the Mars orbiter is set to CO2. By establishing a landing model of the orbiter under CO2 environment and using a turbulence model to establish accurate boundary conditions, the actual changes of the orbiter in the Martian atmospheric flow field can be effectively simulated. The hypersonic aerodynamic characteristics of the Mars orbiter under different high-Mach conditions when entering the Martian atmosphere can be analyzed, and the corresponding aerodynamic performance of the Mars orbiter can be evaluated, which can help optimize the design of the Mars orbiter and the design of guidance and control commands.

[0042] 2. The FLUENT-based method for predicting the high Mach aerodynamic characteristics of Mars orbiters disclosed in this invention, considering the circular cabin structure of Mars orbiters, adopts a local O-Block remodeling model based on a structured mesh, so that the remodeled mesh meets the requirements of the slope and size of the circular transition zone, thereby improving the accuracy and efficiency of predicting the high Mach aerodynamic characteristics of Mars orbiters.

[0043] 3. The FLUENT-based method for predicting the high Mach aerodynamic characteristics of a Mars orbiter disclosed in this invention adopts a half-field processing approach for fluid computational domain modeling, which reduces the amount of computation and improves the efficiency of aerodynamic characteristic prediction, taking into account the characteristic that the Mars orbiter needs to perform rigid body motion with a large range of descent. At the same time, considering the characteristic that the Mars orbiter needs to perform rigid body motion with a large range of descent, the fluid computational domain is set as a cylinder to meet the aerodynamic environment where the direction of the aerodynamic force on the Mars orbiter is relatively uniform. At the same time, the size of the three-dimensional fluid computational domain is set to be large enough to meet the actual situation of large-range descent.

[0044] 4. In view of the fact that Mars orbiters often operate in high Mach hypersonic flows and are prone to thermal imbalance, the present invention discloses a FLUENT-based method for predicting the high Mach aerodynamic characteristics of Mars orbiters. This method uses a dual-temperature model to simulate the energy relaxation process in the flow, thereby improving the prediction accuracy of the flow field in the high Mach region.

[0045] 5. The FLUENT-based method for predicting the high Mach aerodynamic characteristics of a Mars orbiter disclosed in this invention establishes accurate boundary conditions by applying the SST k-omega turbulence model, enabling the high-speed numerical format through TUI settings, and performing FMG initialization settings. This method can obtain good initial values ​​with minimal computational cost, effectively handle simulations under various conditions such as different speeds or angles of attack at high Mach, reduce the number of times the mesh needs to be re-divided, and improve the efficiency of predicting the high Mach aerodynamic characteristics of a Mars orbiter. Attached Figure Description

[0046] Figure 1 This is a flowchart of the FLUENT-based method for predicting the high Mach aerodynamic characteristics of a Mars orbiter, as presented in this invention.

[0047] Figure 2 This is a schematic diagram of the geometric model structure of the Mars orbiter in an example of the present invention.

[0048] Figure 3 This is a schematic diagram of the external flow field of the Mars orbiter established in the example of this invention.

[0049] Figure 4 This is a schematic diagram of the Mars orbiter structural mesh adopted by the present invention based on the wall function theory.

[0050] Figure 5 This is a cloud map showing the Mach number variation around the orbiter under simulated Mars conditions in this embodiment.

[0051] Figure 6 This is the y-axis of the orbiter surface under the simulated Mars conditions in this embodiment. + Distribution map. Detailed Implementation

[0052] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0053] Example 1

[0054] like Figure 1 As shown in the figure, the specific implementation steps of the FLUENT-based method for predicting the high Mach aerodynamic characteristics of a Mars orbiter disclosed in this embodiment are as follows:

[0055] Step 1: Establish a symmetrical model of the Mars orbiter's hull configuration.

[0056] Using the Mars Science Laboratory (MSL) as the verification object, the geometric parameters of the symmetrical configuration of the Mars orbiter cabin were determined. As the preferred design, geometric modeling was performed using SolidWorks software, such as... Figure 2 The diagram shown is a schematic diagram of the geometric model structure of the Mars orbiter in an example of the present invention.

[0057] Step 2: Model the three-dimensional fluid computational domain of the Mars orbiter based on the atmospheric flow field region around the Mars orbiter to be simulated.

[0058] A three-dimensional fluid computational domain for the Mars orbiter was established using the shell manipulation function of ANSYS's SpaceClaim modeling software. Since the orbiter has a symmetrical structure, a half-field approach was adopted for modeling to reduce computational load and improve efficiency. Therefore, the computational domain mainly includes the following parts: inlet section, outlet section, pressure far-field (required for the external flow field), and symmetry plane. To ensure the realism of the flow field simulation, the computational domain was set as a cylinder with sufficiently large dimensions, such as... Figure 3 The figure shows a schematic diagram of the external flow field of the Mars orbiter established in the example of the present invention. Let the characteristic length of the orbiter be d, then the distance from the inlet of the computational domain to the orbiter is set to 3d, the distance from the outlet to the orbiter is set to 10d, and the distance from the far field to the orbiter is set to 3d.

[0059] Step 3: Mesh the three-dimensional fluid computational domain from Step 2 to generate a discrete form of the computational domain and perform mesh correlation and quality verification.

[0060] The three-dimensional fluid computational domain was imported into the mesh generation software ICEM, and the various surfaces of the fluid computational domain were defined: inlet, outlet, pressure far field, and symmetry plane. Furthermore, the shape of the Mars orbiter was defined as a wall form. Then, a high-quality mesh was generated, and a discrete form of the three-dimensional fluid computational domain was produced. Since the fluid in the turbulent boundary layer is simultaneously subjected to viscous shear stress and turbulent additional shear stress, the boundary layer setting has a significant impact on the simulation results of the external flow field to ensure the accuracy of the solution. Because the cross-section of the flow field computational domain outside the Mars orbiter and the cylinder is semi-circular, an O-type mesh cutting method suitable for curved geometric models is required. This invention uses the outer O-Block of the O-type mesh cutting method to refine the boundary layer mesh, where the height of the first layer mesh is set to 10. -5 m. For example Figure 4 The diagram shown is a schematic of the Mars orbiter structural mesh adopted by this invention based on the wall function theory.

[0061] Step 4: Based on the characteristics of the Martian atmospheric parameters and the orbiter's operating conditions, import the three-dimensional fluid computational domain mesh of the orbiter into the FLUENT software, set the solver model, boundary conditions, and initial conditions, that is, use the turbulence model to establish accurate boundary conditions, and use a function that conforms to the CO2 variation law of the Martian atmosphere to improve the simulation accuracy and efficiency of the aerodynamic characteristics of the Mars orbiter under high Mach flow conditions. In other words, based on the fluid environment with CO2 as the medium, perform high-precision prediction of the aerodynamic characteristics of the Mars orbiter at different speeds or angles of attack at high Mach, and obtain the aerodynamic characteristics of the Mars orbiter under high Mach flow.

[0062] Step four includes the following specific steps:

[0063] Step 4.1: Using FLUENT software, select Density-Based in the Type box under the Solver column of General.

[0064] Step 4.2: Under Models, open the Energy Equation section and check the Two-Temperature Model. Under Models, select the SST k-omega two-equation model in the Viscous section, and check the Compressibility Effects section in the Options section.

[0065] Step 4.3: Under Materials, select Fluid and add the CO2 phase. Since this is a far-field simulation, set the density to ideal gas and use the Sutherland formula for the viscosity term Viscosity.

[0066] Step 4.4: When performing external flow field calculations, the operating pressure is often specified as 0 Pa, so the pressure in the computational domain is the absolute pressure. Under the volume mesh Cell Zone Conditions, set the computational domain to the desired fluid. In Boundary Conditions, set the boundary conditions: the inlet, outlet, and upper, lower, and one side boundaries of the computational domain are set as pressure far-fields; the other side of the computational domain is set as a symmetric boundary; the surface of the surround model is a no-slip wall, and the temperature is set.

[0067] Step 4.5: In the Solver settings, select the Implicit algorithm in the Solution Methods section; discretize the convection term using the AUSM scheme; and check all panel options to facilitate convergence of the results.

[0068] Step 4.6: Adjust the Courant number by assigning a small initial value to reduce the calculation step size and increase convergence.

[0069] Step 4.7: Since the simulation is under high Mach conditions, the TUI settings are enabled to enable the high-speed numerical format.

[0070] Step 4.8: In the Solver settings, select Standard Initialization under Solvency and initialize at the entry point.

[0071] Step 4.9: Perform FMG initialization settings, set the number of grid layers to 4, the minimum grid size of each layer to 0.001, the convergence count for the first layer to 100, the second layer to 200, the third layer to 400, and the fourth layer to 1000, and improve the convergence of the results by relaxing the grid.

[0072] Step 4.10: Finally, set the number of calculation steps in Run Calculation, start the calculation, and obtain the convergence file of the relevant parameters.

[0073] Step 5: Perform numerical simulation prediction analysis and post-processing on the Mars orbiter's entry process under high Mach conditions.

[0074] Numerical simulation analysis and post-processing were performed on the results to obtain the temperature changes, Mach number cloud map, pressure distribution, etc. of the surrounding flow field under different high Mach conditions of the Mars orbiter, as well as its lift and drag coefficients under these conditions, and the wall y + Visualization results, such as distribution patterns, are used to analyze the aerodynamic characteristics of the Mars orbiter in the high Mach flow region, providing a reference for designing guidance and control laws. (Wall surface y) +The distribution pattern, with parameter variations only occurring on the surface of the surround, can be used to assess the accuracy of calculation results under turbulence models. For example... Figure 5 As shown, this is a cloud map illustrating the Mach number variation around the orbiter under simulated Mars conditions in this embodiment. Figure 6 As shown, the y-axis of the orbiter surface under simulated Mars conditions in this embodiment is... + Distribution map.

[0075] In the simulation prediction and verification process, taking the US Mars Science Laboratory (MSL) as an example, the entry altitude was selected as 44km, and the specific calculation parameters were: T = 140K, Ma = 22.2. The orbiter wall was subjected to a no-slip isothermal condition, and the wall temperature was set as T. W =1500K, characteristic length is taken as the forebody diameter of 4.5m, entry angle of attack is α = 0°, reference area is the forebody area, FLUENT simulation is performed through the above steps, and compared with reference 3:

[0076]

[0077] This indicates that the error between the method used in this invention based on FLUENT and the data in the literature is within a reasonable range, thus verifying the accuracy of the simulation prediction data of this invention.

[0078] In summary, the FLUENT-based method for predicting the high Mach aerodynamic characteristics of Mars orbiters disclosed in this example establishes a symmetrical model based on the common external structure of Mars orbiters and appropriately adjusts the position of the center of mass offset based on the characteristic that the orbiter generates corresponding aerodynamic forces by relying on its own center of mass not being at the geometric center during entry. Considering the characteristics of the atmospheric composition distribution on the Martian surface, the computational domain medium for the external flow field of the Mars orbiter is set to CO2, and the relevant turbulence parameters are set according to the Martian environment to improve the accuracy of the analysis. Furthermore, considering that Mars orbiters often operate in high Mach hypersonic flows, which easily generate thermal imbalances, a dual-temperature model can simulate the energy relaxation process in the flow. Compared to single-temperature models, this invention provides more accurate predictions of flow fields in high-Mach regions. Considering the large-scale rigid-body motion required for the Mars orbiter, to better simulate flow field changes, the displacement of the moving boundary needs to be much larger than the mesh size. Traditional unstructured meshes result in uneven mesh transitions, long computation times, and reduced computational efficiency, potentially leading to non-convergence. Therefore, a structured mesh is employed. Furthermore, given the predominantly circular shape of the Mars orbiter, a local O-Block remodeling model is used. This ensures the remodeled mesh meets the slope and size requirements of the circular transition zone, improving simulation prediction efficiency and accuracy. This invention can analyze and construct the hypersonic aerodynamic characteristics of the Mars orbiter under different high-Mach conditions upon entering the Martian atmosphere, enabling corresponding aerodynamic performance evaluation. This invention can also analyze and construct the hypersonic aerodynamic characteristics of the Mars orbiter under different high-Mach conditions upon entering the Martian atmosphere, assisting in optimizing the Mars orbiter design and guidance and control command design.

[0079] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for predicting the high Mach aerodynamic characteristics of Mars orbiters based on FLUENT, characterized in that: Includes the following steps, Step 1: The Mars orbiter adopts a symmetrical configuration. The forebody of the Mars orbiter is mainly a circular heat-resistant base made of high-temperature resistant materials. Because the Mars orbiter needs to adjust its attitude by relying on the irregularity of its own mass, its center of mass is not completely at the geometric center of the orbiter. Therefore, when initially establishing the symmetrical geometric model of the Mars orbiter, the position of the center of mass offset is appropriately adjusted according to the characteristic that the Mars orbiter generates corresponding aerodynamic forces by relying on its own center of mass not being at the geometric center when entering. Considering the characteristics of the composition distribution of the Martian atmosphere, the computational domain medium of the external flow field of the Mars orbiter is set to CO2, and the relevant turbulence parameters are set according to the Martian environment to improve the accuracy of the symmetrical geometric model of the Mars orbiter in predicting and analyzing the high Mach aerodynamic characteristics of the Mars orbiter. Step 2: Based on the atmospheric flow field region around the Mars orbiter to be simulated, establish a three-dimensional fluid computational domain for the symmetrical geometric model of the Mars orbiter established in Step 1. Considering the symmetrical configuration of the orbiter, to reduce the amount of computation and improve the efficiency of aerodynamic characteristic prediction, a half-field processing method is adopted for fluid computational domain modeling. Therefore, the computational domain mainly includes the following parts: inlet section, outlet section, pressure far field, and symmetry plane. At the same time, considering the rigid body motion of the Mars orbiter that needs to perform large-scale descent, the fluid computational domain is set as a cylinder to meet the aerodynamic environment where the direction of the aerodynamic force on the Mars orbiter is relatively uniform. The size of the three-dimensional fluid computational domain is set to be large enough to match the actual situation of large-scale descent. Step 3: Mesh the three-dimensional fluid computational domain established in Step 2 to obtain the computational mesh for the high Mach external flow field of the Mars orbiter; In step three, The structured grid is used in the calculation domain. In the turbulent boundary layer, the fluid is subjected to the viscous shear stress and the turbulent additional shear stress. Because the cross section of the outer flow field of the Mars orbiter and the cylinder presents a circular arc shape, the O-type grid cutting method suitable for the arc line of the geometric model is used. The outer O-Block of the O-type grid cutting method is used to encrypt the boundary layer grid at the wall surface of the Mars orbiter, so that the boundary layer grid meets the reasonable range of y + , so as to better capture the near-wall parameters of the nozzle and improve the calculation accuracy. Height of the first mesh layer of the boundary layer Set to: in, The Reynolds number represents the free flow. For the incoming flow density, For the incoming flow velocity, For wall friction resistance, The characteristic length of the surround, The viscosity coefficient of the incoming flow; Step 4: Based on Steps 1 to 3, conduct numerical calculations of the Mars orbiter under high Mach conditions. Use a turbulence model to establish and determine boundary conditions, and use a function that conforms to the CO2 variation law of the Martian atmosphere to improve the simulation accuracy and efficiency of the aerodynamic characteristics of the Mars orbiter under high Mach flow conditions. That is, make high-precision predictions of the aerodynamic characteristics of the Mars orbiter at different speeds or angles of attack in a fluid environment with CO2 as the medium, and obtain the aerodynamic characteristics of the Mars orbiter under high Mach flow.

2. The method for predicting high Mach aerodynamic characteristics of Mars orbiters based on FLUENT as described in claim 1, characterized in that: The process also includes step five, which involves performing numerical simulation analysis and post-processing on the aerodynamic characteristics of the Mars orbiter under high Mach flow, based on the simulation results obtained in step four. This yields the temperature changes, Mach number cloud maps, and pressure distribution of the surrounding flow field under different high Mach conditions of the Mars orbiter. Additionally, the lift and drag coefficients and wall y-values ​​under the corresponding high Mach conditions of the Mars orbiter are obtained. + The distribution of the data is analyzed, and the results are visualized. The aerodynamic characteristics of the Mars orbiter in the high Mach flow region are analyzed to evaluate the corresponding aerodynamic performance of the Mars orbiter. This will help optimize the Mars orbiter and its guidance and control commands, and further optimize the design of the Mars orbiter and its guidance and control commands.

3. The method for predicting high Mach aerodynamic characteristics of Mars orbiters based on FLUENT as described in claim 2, characterized in that: In step four, the viscosity term, Viscosity, is calculated using the Sutherland formula: in, For reference viscosity coefficient, For reference temperature, It is Sutherland's constant; The turbulence model adopted is the SST k-omega model, the boundary conditions are pressure far-field conditions, the solution method is the implicit algorithm, and the convection term is discretized using the AUSM scheme; the SST k-omega two-equation model formula is as follows: In the formula, vorticity, and These are mixed functions, all related to the distance from the point to the wall, where... In the formula, The distance from the wall is given by the parameter values ​​in the SST k-omega two-equation model. , and Set parameters for two sets, because Able to complete the model from near the wall To get away from the wall The model transition, therefore, the equation has relatively low requirements for the wall function and high computational accuracy, the objective y + As long as the variation is consistent within a predetermined range, the adaptability requirements of the turbulence model are met. The SST k-omega two-equation model shown by formulas (6)(7)(8) can reduce the number of times the height of the first layer of the wall boundary layer is modified under different working conditions. It can simultaneously calculate a single grid at different hypersonic Mach levels, thereby improving the prediction efficiency for different working conditions.

4. The method for predicting high Mach aerodynamic characteristics of Mars orbiters based on FLUENT as described in claim 3, characterized in that: During initialization, TUI settings are used to enable high-speed numerical formats, and FMG is used to initialize the calculation conditions. This allows for obtaining better initial values ​​with minimal computational cost, thereby improving computational efficiency and facilitating computational convergence.

5. The method for predicting high Mach aerodynamic characteristics of Mars orbiters based on FLUENT as described in claim 4, characterized in that: The lift-drag coefficient mentioned in step five is calculated using the following formula: In the formula, , These are the lift and drag coefficients, For lift, As resistance, For reference area, the area of ​​the forebody can be used for the Mars orbiter. For dynamic pressure, For the incoming flow density, The velocity of the airflow relative to the object.

6. The method for predicting high Mach aerodynamic characteristics of Mars orbiters based on FLUENT as described in claim 5, characterized in that: The wall surface y + The distribution pattern only shows parameter variations on the surface of the surround, which is used to determine the accuracy of the calculation results under the turbulence model.

7. The method for predicting high Mach aerodynamic characteristics of Mars orbiters based on FLUENT as described in claim 6, characterized in that: y + The aforementioned reasonable range is 0.1 ≤ y for high Mach flow of Mars orbiters. + ≤5.

8. The method for predicting high Mach aerodynamic characteristics of Mars orbiters based on FLUENT as described in claim 7, characterized in that: For the Martian atmosphere model, take , , .

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