Pulsating pressure simulation calculation method
Through the three-dimensional grid model of the outflow field of high-precision rocket and the large vortex simulation turbulence model, the problem of long and large calculations of the launch vehicle pulsation pressure simulation is solved, and the rapid and accurate acquisition of pulsation pressure data is achieved, and the simulation results are improved consistency and feasibility of engineering design.
Patent Information
- Application Number
- CN202411211980.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-30
- Publication Date
- 2025-01-03
AI Technical Summary
In the prior art, the simulation calculation of the pulsation pressure of a carrier rocket takes a long time and is large in calculation, making it difficult to obtain accurate pulsation pressure data of the entire arrow in a short time, and there is a large difference between the simulation results and the test results, making it difficult to directly apply to engineering design. .
Using a high-precision three-dimensional grid model of rocket outflow field, combining large eddy simulation turbulence model and high-precision flow field solution method, the grid scale is controlled to be less than 2000W through non-stable simulation calculation, and the WALE model is used for eddy current separation, and through Low diffusion Roe-FDS method and second-order implicit transient expression method are calculated to monitor flow field convergence to obtain accurate pulsating pressure data.
It realizes the rapid acquisition of launch vehicle pulsation pressure data in a short time (within 2 weeks). The consistency between the simulation results and the wind tunnel test results is improved, reducing the cost and time of simulation calculations, and is suitable for engineering design.
Smart Images
Figure CN119249595A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a pulsation pressure simulation calculation method, belonging to the technical field of overall launch vehicle design. Background Art
[0002] When a launch vehicle is flying, shock wave oscillations and flow separation will occur at the parts where the cross section of the rocket changes sharply, thus generating pulsating pressure. Pulsating pressure will induce random vibrations in the structure of the launch vehicle, thereby arousing the rocket's buffeting response and severe noise environment. When the random vibration is severe, it may cause structural vibration damage to the launch vehicle. Therefore, during the rocket development stage, aerodynamic professional designers need to accurately predict the rocket's transonic pulsating pressure environment.
[0003] The traditional prediction method of rocket pulsating pressure environment is wind tunnel test method. By conducting pulsating pressure wind tunnel test of rocket rigid body model, the root mean square pulsating pressure coefficient, power spectrum density and coherence function between different sections at typical positions of rocket can be obtained. Since the traditional rocket pulsating pressure wind tunnel test requires more than one million yuan in funding and the test cycle is long, it takes more than 4 months from model design to test completion, which seriously restricts the prediction efficiency of rocket pulsating pressure environment. In recent years, with the rapid development of computer technology, some research institutions have begun to obtain the local pulsating pressure environment of launch vehicles through numerical simulation. For example, the articles "Research on the influence of fairing busbar shape on pulsating pressure environment [J]" and "Numerical simulation and optimization design of rocket fairing pulsating pressure environment [J]" both mentioned this technology. However, due to the huge calculation scale, the number of grids exceeds 3000W, and the small number of test data, there is a big difference between the rules of simulation results and test results. Therefore, it is still in the research stage and difficult to be directly applied to engineering design. Summary of the invention
[0004] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art and propose a pulsating pressure simulation calculation method, by establishing a high-precision rocket external flow field grid model and using a large eddy simulation turbulence model, the pulsating pressure characteristics of different rocket configurations can be quickly obtained while ensuring that the simulation results are consistent with the experimental laws.
[0005] The technical solution of the present invention is:
[0006] A pulsating pressure simulation calculation method, comprising:
[0007] Construct a rocket pulsating pressure wind tunnel test model and establish the model's external flow field area; divide the grids of the external flow field area and the model's boundary layer, fairing, and lower stage area to form a three-dimensional grid model of the rocket's external flow field; check the quality of the three-dimensional grid model of the rocket's external flow field through the Reynolds number of the first layer of the wall grid;
[0008] The three-dimensional grid model of the rocket's external flow field that has passed the inspection is loaded into the fluid mechanics simulation system to build a simulation model; the simulation model adopts the large eddy simulation model LES, the flow field medium adopts the ideal gas model, and the boundary conditions of the simulation model are defined according to the flow field information of the wind tunnel test section;
[0009] Unsteady simulation calculations are performed based on the simulation model to obtain the pulsating pressure data of the rocket body along the axial direction.
[0010] Furthermore, the meshes of the external flow field area, the model boundary layer, the fairing and the lower stage area are divided, and the height of the first layer of the wall mesh is no more than 1×10 -5 m, the grid size of the fairing and the lower stage area along the flow direction does not exceed 2mm, so that the overall grid scale is controlled below 2000W.
[0011] Furthermore, the simulation model adopts the large eddy simulation model LES and selects the WALE model to separate eddies of different scales by filtering the NS equations.
[0012] Furthermore, an unsteady simulation calculation is performed based on the simulation model, and the calculation time step is:
[0013]
[0014] Where L represents the height of the first layer of grid on the wall, V represents the incoming flow velocity, and the iteration is 20 steps per unit time step.
[0015] Furthermore, unsteady simulation calculations are performed based on the simulation model. The flux type adopts the low-diffusion Roe-FDS method, the flow adopts the second-order upwind scheme, and the transient expression method adopts the second-order implicit method.
[0016] Furthermore, the mesh quality generated by the three-dimensional mesh model of the rocket's external flow field is checked by the Reynolds number of the first layer of wall mesh. If the Reynolds number of the first layer of wall mesh is less than 2, it is considered to have passed the inspection and met the design requirements.
[0017] Furthermore, an external flow field region of the model is established, the length of the external flow field is not less than 10 times the length of the rocket pulsating pressure wind tunnel test model, and the diameter is not less than 10 times the envelope diameter of the rocket pulsating pressure wind tunnel test model.
[0018] Furthermore, unsteady simulation calculations were performed based on the simulation model. The flow field residuals were monitored during the simulation. If the residuals dropped to 10 -3 Below this value, the calculated flow field is considered to have converged, and the pulsating pressure data on the rocket body surface along the axial direction are counted. The statistical time is no less than 5×10 -3 s.
[0019] Furthermore, according to the pulsating pressure data of the rocket body along the axial direction, the pulsating pressure coefficient is calculated:
[0020]
[0021] In the formula, is the root mean square pulsating pressure, P LU is the local unsteady pressure, P LS is the time average of the local unsteady pressure, T is the sampling time, C p is the pulsation pressure coefficient.
[0022] Furthermore, a three-dimensional solid model of the rocket was established and reduced to 1:50 to form a rocket pulsating pressure wind tunnel test model.
[0023] The advantages of the present invention compared with the prior art are:
[0024] (1) The present invention adopts a high-precision three-dimensional grid model method for the rocket's external flow field to reduce the number of grids in non-key areas of concern, so that the overall grid scale is controlled below 2000W, thereby solving the problem in the prior art that the pulsating pressure simulation calculation is huge and it is impossible to obtain the pulsating pressure data of the entire rocket in a short time.
[0025] (2) The present invention comprehensively considers technical innovation and engineering feasibility, uses a large eddy simulation turbulence model, a high-precision flow field solution method, and a post-processing method based on computationally stable data to shorten the time for predicting the pulsating pressure of a launch vehicle to 2 weeks, thereby meeting the requirement of rapid data acquisition and achieving the goal of simulating and predicting the pulsating pressure of a launch vehicle. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:
[0027] Figure 1 A schematic diagram of a pulsating pressure simulation calculation method according to an embodiment of the present invention;
[0028] Figure 2 This is a numerical simulation flow chart of a pulsating pressure simulation calculation method according to an embodiment of the present invention;
[0029] Figure 3 Schematic diagram of the grid Reynolds number Y+ of an embodiment of the present invention;
[0030] Figure 4 The pulsating pressure distribution diagram of the rocket body surface and the flow field symmetry plane according to the embodiment of the present invention;
[0031] Figure 5 This is the entropy increase cloud diagram of the rocket body surface and the flow field symmetry surface according to the embodiment of the present invention;
[0032] Figure 6 It is a comparison chart of the pulsation pressure coefficient simulation results and the wind tunnel test values of the embodiment of the present invention. DETAILED DESCRIPTION
[0033] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.
[0034] In order to overcome the shortcomings of the existing pulsating pressure wind tunnel test, such as high funding requirements and long test cycle, the present invention proposes a pulsating pressure simulation calculation method, such as Figure 1 As shown, the method consists of three parts: rocket shape entity modeling, rocket flight external flow field mesh modeling, and rocket flight external flow field unsteady simulation calculation. It combines high-precision modeling methods, turbulence model selection methods, high-precision flow field solution methods, and post-processing methods based on stable calculation data. By carrying out large-scale numerical calculations, the simulation prediction results of the pulsating pressure of the launch vehicle are obtained.
[0035] The specific steps of this method are as follows Figure 1 As shown, including:
[0036] Step 110: Create a high-precision 3D mesh model of the rocket's external flow field
[0037] According to the theoretical diagram of the rocket, a three-dimensional solid model is established. Since the height of the new generation of rockets reaches 50m, and the pulsating pressure simulation belongs to the local mm-level small-scale flow field simulation of the rocket body, the designed solid model is reduced to the size of the pulsating pressure wind tunnel test model of about 1:50. Considering that the size of the flow field outside the rocket body is large enough, the boundary effect will not affect the flow field near the wall of the rocket body. The length of the flow field calculation domain is not less than 10 times the length of the wind tunnel model, and the diameter is not less than 10 times the diameter of the model envelope. In order to ensure the simulation accuracy, the hexahedral grid is used to divide the flow field calculation domain. The height of the first layer of the wall grid is not more than 1×10 -5 m, the mesh size of the fairing and the lower stage area along the flow direction does not exceed 2 mm, and the quality of the generated mesh is checked by the Reynolds number Y+ of the first layer of the wall mesh, Y+<2. The above step 110 may include:
[0038] Sub-step A1: Establish a physical model based on the rocket theoretical diagram;
[0039] Sub-step A2: scaling the physical model according to the size of the pulsating pressure wind tunnel test model;
[0040] Sub-step A3: Establishing the outer flow field region of the rocket model;
[0041] Sub-step A4: Perform hexahedral meshing on the rocket's external flow field, and mesh the boundary layer, fairing, and lower stage areas according to the design objectives;
[0042] Sub-step A5: Check the generated mesh with the Reynolds number Y+ of the first layer of the wall mesh, such as Figure 3 If the design requirements are not met, make local adjustments and recheck the mesh.
[0043] Step 120: Load the rocket external flow field three-dimensional mesh model that has passed the inspection into the fluid mechanics simulation system to build a simulation model
[0044] The commercial Fluent software is used as the fluid mechanics simulation system to establish a rocket pulsation pressure simulation model based on large eddy simulation. For the pulsation pressure in the transonic stage of the rocket, which is the focus of research, a density-based solver is used. For the simulation of turbulence, the large eddy simulation model LES (Large Eddy Simulation) is selected. By filtering the NS equation, large-scale and small-scale vortices are separated. The filtering process can effectively filter out vortices with a scale smaller than the filter width or grid spacing, and the WALE model is selected. This model produces almost no eddy viscosity in the wall laminar flow, so it can better capture the transition from laminar flow to turbulence. The ideal gas model is selected as the medium for calculating the flow field, and the boundary conditions are defined according to the flow field information such as the Ma number, static pressure, and static temperature of the wind tunnel test section.
[0045] Sub-step B1: Setting up the simulation-based solver;
[0046] Sub-step B2: Select the large eddy simulation (LES) turbulence model and select the WALE model;
[0047] Sub-step B3: the selected calculation flow field medium is an ideal gas;
[0048] Sub-step B4: select 0 as the reference pressure;
[0049] Sub-step B5: Select the pressure far field boundary as the calculation domain, and set the Ma, pressure, and temperature conditions according to the wind tunnel flow conditions.
[0050] Step 130: Calculate using high-precision flow field solution method
[0051] In order to reduce the dissipation of turbulent kinetic energy by viscosity and enable the unsteady simulation results to capture the development process of small-scale vortices, and then obtain the unsteady change process of local pressure, the flux type selects the low-diffusion Roe-FDS method, the flow selects the second-order upwind format, and the transient expression method selects the second-order implicit method. The order of magnitude of the calculation time step is close to that of formula (1), which is set to 5×10 -7 s.
[0052]
[0053] Where L represents the height of the first layer of grid on the wall, V represents the incoming flow velocity, and the iteration is 20 steps per unit time step.
[0054] Sub-step C1: Select explicit solution, select Roe-FDS method for flux type, select second-order upwind scheme for flow, and select second-order implicit for transient expression method;
[0055] Sub-step C2: Select the unsteady solver, the time step is 5×10-7s, and the iteration is 20 steps per unit time step.
[0056] Step 140: Post-processing method based on simulation convergence data
[0057] In order to ensure the reliability of the acquired flow field data, it is necessary to ensure the convergence of the calculated flow field and monitor the residual of the flow field. -3 Below, the flow field is considered to be convergent. In order to obtain a more reliable pulsating pressure coefficient of the rocket body along the axial direction, it is necessary to monitor and collect the pressure data on the third quadrant line of the rocket body. After the calculation is completed for 1000 time steps, if the flow field converges, the pressure data on the third quadrant line will be counted. In order to ensure the validity of the collected data, the statistical calculation time is 5×10 -3 s, the collected surface pressure data are processed according to equations (2) and (3) to obtain the root mean square pulsation pressure coefficient.
[0058]
[0059] In the formula, is the root mean square pulsating pressure; P LU is the local unsteady pressure; P LS is the time average of the local unsteady pressure; T is the sampling time; C p is the pulsation pressure coefficient.
[0060] Sub-step D1: judging the convergence of the simulated flow field;
[0061] Sub-step D2: Count 5×10 -3 s pressure data on the quadrant III line of the arrow body;
[0062] Sub-step D3: Post-process the pressure data.
[0063] The pulsating pressure on the rocket body surface and the symmetric surface of the flow field (6° attack angle) is calculated using this method as follows: Figure 4 As shown in the figure, it can be seen that the area with higher pulsating pressure in the rocket model is the interface between the front cone and the column section of the fairing. The entropy increase cloud diagram of the rocket body surface and the symmetric surface of the flow field (6° attack angle) is shown in the figure. Figure 5 As shown in the figure, at the interface of the cone and column of the fairing, there is a small-scale vortex structure that gradually develops backward into a large-scale vortex. The simulation results of the pulsating pressure coefficient are compared with the wind tunnel test values, as shown in the figure. Figure 6 As shown in the figure, it can be seen that the calculated law of the rocket surface pulsation pressure coefficient is consistent with the wind tunnel test results, and the deviation between the peak value of the pulsation pressure coefficient and the test results is within 30%.
[0064] The above-described embodiments are only preferred specific implementations of the present invention. Common changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.
Claims
1. A pulsating pressure simulation calculation method, characterized in that: include: Construct a rocket pulsating pressure wind tunnel test model and establish the model's external flow field area; divide the grids of the external flow field area and the model's boundary layer, fairing, and lower stage area to form a three-dimensional grid model of the rocket's external flow field; check the quality of the three-dimensional grid model of the rocket's external flow field through the Reynolds number of the first layer of the wall grid; The three-dimensional grid model of the rocket's external flow field that has passed the inspection is loaded into the fluid mechanics simulation system to build a simulation model; the simulation model adopts the large eddy simulation model LES, the flow field medium adopts the ideal gas model, and the boundary conditions of the simulation model are defined according to the flow field information of the wind tunnel test section; Unsteady simulation calculations are performed based on the simulation model to obtain the pulsating pressure data of the rocket body along the axial direction.
2. A pulsating pressure simulation calculation method according to claim 1, characterized in that: The meshes of the external flow field area, the model boundary layer, the fairing and the lower stage area are divided. The height of the first layer of the wall mesh is no more than 1×10 -5 m, the grid size of the fairing and the lower stage area along the flow direction shall not exceed 2mm.
3. A pulsating pressure simulation calculation method according to claim 1, characterized in that: The simulation model adopts the large eddy simulation model LES and selects the WALE model. By filtering the NS equations, eddies of different scales are separated.
4. A pulsating pressure simulation calculation method according to claim 1, characterized in that: Based on the simulation model, the unsteady simulation calculation is performed, and the calculation time step is: Where L represents the height of the first layer of grid on the wall, V represents the incoming flow velocity, and the iteration is 20 steps per unit time step.
5. The pulsating pressure simulation calculation method according to claim 1, characterized in that: Unsteady simulation calculations are performed based on the simulation model. The flux type adopts the low-diffusion Roe-FDS method, the flow adopts the second-order upwind format, and the transient expression method adopts the second-order implicit method.
6. A pulsating pressure simulation calculation method according to claim 1, characterized in that: The quality of the three-dimensional grid model of the rocket's external flow field is checked by the Reynolds number of the first layer of grid on the wall. If the Reynolds number of the first layer of grid on the wall is less than 2, it is considered to have passed the inspection and met the design requirements.
7. A pulsating pressure simulation calculation method according to claim 1, characterized in that: The external flow field area of the model is established, and the length of the external flow field is not less than 10 times the length of the rocket pulsating pressure wind tunnel test model, and the diameter is not less than 10 times the envelope diameter of the rocket pulsating pressure wind tunnel test model.
8. A pulsating pressure simulation calculation method according to claim 1, characterized in that: Based on the simulation model, unsteady simulation calculations are performed and the flow field residual is monitored during the simulation process. If the residual drops to 10 -3 Below this value, the calculated flow field is considered to have converged, and the pulsating pressure data on the rocket body surface along the axial direction are counted. The statistical time is no less than 5×10 -3 s.
9. The pulsating pressure simulation calculation method according to claim 1, characterized in that: According to the pulsating pressure data of the rocket body along the axis direction, the pulsating pressure coefficient is calculated: In the formula, is the root mean square pulsating pressure, P LU is the local unsteady pressure, P LS is the time average of the local unsteady pressure, T is the sampling time, C p is the pulsation pressure coefficient.
10. The pulsating pressure simulation calculation method according to claim 1, characterized in that: A three-dimensional solid model of the rocket is established and reduced to 1:50 level to form a three-dimensional solid model of the rocket pulsating pressure wind tunnel test model.