Unsteady flow and contact coupling simulation method for separation process of aircraft and fairing

Abstract

The present invention discloses a method for simulating unsteady flow and contact coupling during the separation process of an aircraft and a fairing, including establishing a multi-body dynamics simulation model, an unsteady flow simulation model and a virtual deformation boundary grid adaptive model; performing unsteady flow simulation to determine the aerodynamic force and aerodynamic moment of the relative center of mass of the component; performing multi-body dynamics simulation to determine dynamic data; in the unsteady flow simulation model, the coordinates of the grid nodes are calculated according to the dynamic data, and if the virtual deformation surface is in contact with the adjacent solid wall, the coordinates of the virtual deformation boundary in the virtual deformation surface and the coordinates of the actual rigid body boundary are determined according to the virtual deformation boundary grid adaptive model, and then the positions of the spatial grid nodes in the unsteady flow simulation model are calculated. The simulation of aerodynamic separation with a contact process without manual processing is realized, the efficiency of simulation modeling is improved, and the needs of engineering research and development for separation scheme design, optimization and verification and assessment are supported.

Description

Technical Field

[0001] The invention relates to the technical field of computer-aided design, in particular to a method for simulating unsteady flow and contact coupling during separation of an aircraft and a fairing. Background Art

[0002] In the field of aerospace, there are unsteady flow processes under the condition of multiple objects contacting and colliding with each other. This process involves an important type of fluid-motion coupling problem, which is widely present in the process of fairing separation, mount separation, etc. However, the simulation of the contact and collision process belongs to the multi-body dynamics simulation problem, while the simulation of the unsteady flow process under the mutual motion of multiple objects belongs to the computational fluid dynamics problem, which generally requires the coupling simulation function of the flow field simulation tool and the multi-body simulation tool. The general coupling simulation function of the flow field and multi-body can be realized by most commercial software at present, but in the above scenario, although the contact and collision process does not need to be solved by flow field simulation, it is necessary to consider the reasonable modeling of contact and collision in the flow field simulation process to avoid the interference of the surface mesh of the object in the flow field, which leads to the exit of the simulation. The existing virtual baffle technology can solve the problem of the process from contact to separation of components, but because it is difficult to develop and integrate collision models and constraint models in single-discipline simulation tools, it is difficult to simulate the contact and collision process by relying solely on virtual baffle technology. Summary of the invention

[0003] Aiming at the contact and collision problem in the aerodynamic separation process of multiple components, the present invention provides a simulation method for unsteady flow and contact coupling in the separation process of an aircraft and a fairing.

[0004] In a first aspect, a method for simulating unsteady flow and contact coupling during separation of an aircraft and a fairing is provided, comprising:

[0005] A multi-body dynamics simulation model, an unsteady flow simulation model and a virtual deformation boundary mesh adaptive model are established, wherein a virtual deformation object surface is specified in the unsteady flow simulation model, and the virtual deformation object surface includes at least one of a virtual deformation boundary and an actual rigid body boundary. The virtual deformation boundary mesh adaptive model indicates the association relationship between the virtual deformation boundary and the actual rigid body boundary in the unsteady flow simulation model, and the simulation step length of the multi-body dynamics simulation model is consistent with the simulation step length of the unsteady flow simulation model;

[0006] The following steps are executed repeatedly until the simulation end condition is met:

[0007] Performing unsteady flow simulation according to the unsteady flow simulation model to determine the aerodynamic force and aerodynamic moment relative to the center of mass of the components in the unsteady flow simulation model;

[0008] Perform multi-body dynamics simulation according to the multi-body dynamics simulation model to determine dynamics data;

[0009] In the unsteady flow simulation model, the grid node coordinates are calculated based on the dynamic data. If the virtual deformation surface is in contact with the adjacent solid wall, the coordinates of the virtual deformation boundary in the virtual deformation surface are determined based on the virtual deformation boundary grid adaptive model. and the coordinates of the actual rigid body boundary ;

[0010] According to the coordinates of the virtual deformation boundary and the coordinates of the actual rigid body boundary , and the coordinates of the virtual deformation boundary at the previous time step and the coordinates of the actual rigid body boundary , calculate the positions of spatial grid nodes in the unsteady flow simulation model .

[0011] In conjunction with the first aspect, in certain implementations of the first aspect, determining the aerodynamic force and aerodynamic moment relative to the center of mass of a component in an unsteady flow simulation model includes:

[0012] Determine the pressure and shear stress on the grid nodes in the unsteady flow simulation model according to the position coordinates of the grid nodes in the unsteady flow simulation model and the boundary conditions set when establishing the unsteady flow simulation model;

[0013] The aerodynamic force and aerodynamic moment relative to the center of mass are obtained by performing area-weighted integration of the pressure, shear stress and relative center of mass moment on the grid nodes in the unsteady flow simulation model.

[0014] In conjunction with the first aspect, in certain implementations of the first aspect, performing a multi-body dynamics simulation according to a multi-body dynamics simulation model to determine dynamics data includes:

[0015] The unsteady flow simulation software sends the aerodynamic force on the component and the aerodynamic moment relative to the center of mass to the multi-body dynamics simulation software;

[0016] The multi-body dynamics simulation software performs a one-step dynamic equation solution based on the aerodynamic force and aerodynamic torque relative to the center of mass of the received components, obtains the center of mass position, center of mass translation velocity, angular velocity around the principal axis of inertia, and attitude angle of the principal axis of inertia of each component, and sends the calculation results to the unsteady flow simulation software.

[0017] In conjunction with the first aspect, in some implementations of the first aspect, before solving the kinetic equation, the method further includes:

[0018] Based on the aerodynamic force and aerodynamic moment relative to the center of mass of the components, as well as the relative positions and relative velocities of the components, it is calculated whether there is contact force between the components; if there is contact force, the dynamic equations are solved in combination with the contact force.

[0019] In combination with the first aspect, in some implementations of the first aspect, the coordinates of the virtual deformation boundary in the virtual deformation object plane are determined. and the coordinates of the actual rigid body boundary ,include:

[0020] Calculate the coordinates of the mesh nodes on the actual rigid body boundary The distance to the wall adjacent to the solid wall boundary ;

[0021] Determine the coordinates of the mesh nodes on the actual rigid body boundary And the distance near the solid wall boundary The nearest node coordinates ;

[0022] according to , determine the coordinates of the i-th grid node on the virtual deformation boundary , The distance to the wall function.

[0023] In combination with the first aspect, in some implementations of the first aspect, is a Wendland function, satisfying:

[0024]

[0025] Adjustment factor calculated for the virtual deformation boundary.

[0026] In combination with the first aspect, in some implementations of the first aspect, the wall distance The solution is obtained using the KD tree method.

[0027] In combination with the first aspect, in certain implementations of the first aspect, the position coordinates of the spatial grid node k at the nth step in the unsteady flow simulation model are , is the position coordinate of the spatial grid node k in the unsteady flow simulation model at step n-1, and the function satisfy:

[0028]

[0029] is the Wendland function or the Gauss function, is the number of nodes on the actual rigid body boundary, is the weight coefficient for the nth step calculation, Corresponding to the i-th node of the actual rigid body boundary, is the coordinate of the ith node of the actual rigid body boundary at the n-1th step, is the number of nodes on the virtual deformation boundary, is the weight coefficient for the nth step calculation, Corresponding to the i-th node of the virtual deformation boundary, is the coordinate of the i-th node of the virtual deformation boundary at the n-1th step.

[0030] In combination with the first aspect, in some implementations of the first aspect, The following conditions are met:

[0031] .

[0032] In combination with the first aspect, in some implementations of the first aspect, The following conditions are met:

[0033] .

[0034] The present invention aims at the simulation problem of unsteady process under the coupling of aerodynamic interference and multi-body contact during the separation process of an aircraft and its fairing, overcomes the bottleneck of the existing method that it is difficult to automatically process the geometric contact of objects and must rely on manual adjustment of the boundary grid of the object surface, and proposes a virtual deformation boundary grid processing technology based on the RBF grid deformation method, which realizes the aerodynamic separation simulation with contact process without manual processing, improves the efficiency of simulation modeling, and supports the needs of engineering research and development for separation scheme design, optimization and verification and assessment. Compared with the prior art, the scheme provided by the present invention includes at least the following beneficial technical effects:

[0035] (1) The present invention realizes the coupling simulation problem of unsteady flow simulation and multi-body dynamics simulation containing contact during the aerodynamic separation process of the aircraft and the fairing, so that the original method can be applied to the contact process, thus realizing the aerodynamic separation simulation with the contact process.

[0036] (2) This method can be combined with other existing wall distance calculation methods and dynamic mesh methods to form a new simulation method, such as the wall distance diffusion method and the spring dynamic mesh method. It can expand the contact and separation simulation capabilities of the existing dynamic mesh simulation tools at a relatively low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of virtual deformation boundary and mesh deformation. Left: When the two bodies are not in contact, the virtual deformation boundary (red) is consistent with the actual rigid body boundary; Right: When the two bodies are close or in contact, the virtual deformation boundary (red) produces displacement and deformation in a certain way to ensure that a certain quality of mesh units can be maintained between the two bodies. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] The present invention provides a method for simulating unsteady flow and contact coupling during the separation process of an aircraft and a fairing, and the specific steps are as follows.

[0040] Step 1: Establish a multi-body dynamics simulation model.

[0041] A multi-body dynamics simulation model with a contact model is established. In addition to the mass characteristics (such as mass size, center of mass position, moment of inertia, azimuth of the principal axis of inertia in the reference coordinate system), material properties, external loads and other model settings required for multi-body dynamics simulation, the model also includes a gap diagnosis model and a contact position diagnosis model. In this process, each component can use a three-dimensional solid model that is as realistic as possible as a geometric model. Generally, a triangular facet geometric model in STL format is used.

[0042] The multi-rigid body dynamics equations involved in the multi-body dynamics simulation model can be solved using the quaternion method in accordance with the existing technology. In a multi-body system, the motion of each rigid body can be described by the following equation:

[0043]

[0044] Where H is the inertia tensor, ω is the angular velocity and M is the external torque.

[0045] In multibody dynamics, using quaternions to describe the rotation of rigid bodies can avoid the universal joint lock problem and enable more efficient numerical calculations. The following are some basic mathematical formulas for solving multibody dynamics equations using quaternions: First, define quaternions q for:

[0046]

[0047] in, is the real part, ( q 1, q 2, q 3) is the imaginary part, they are all real numbers; (i, j, k) are all imaginary unit vectors. Combined with quaternions, the angular velocity can be ω With quaternions q The derivative of is connected and the rotation of the rigid body is updated, that is,

[0048]

[0049] In the above formula, is the quaternion corresponding to the angular velocity of rotation.

[0050] Step 2: Establish an unsteady flow simulation geometric model.

[0051] Establish an unsteady flow simulation geometry model with multiple components in motion. In this process, in order to facilitate the subsequent meshing, each component can use a properly simplified three-dimensional model. To ensure that there is no interference in the initial state of the calculation, it is necessary to manually perform local shaping at the contact and narrow gaps.

[0052] Step 3: Based on the unsteady flow simulation geometric model, establish the flow field calculation grid and flow field simulation parameter settings. The specific implementation method is as follows.

[0053] Step 3.1, based on the simplified three-dimensional model in step 2, establish the mesh in the unsteady flow simulation calculation domain. In order to allow the situation that the surface meshes interfere with each other due to the contact of objects during the simulation, that is, the simulation can still be executed in this case, the present invention adopts a virtual deformation object surface method and ensures that the surface meshes of the objects in the flow field calculation domain are advanced to the outer array surface by 3 layers (the number of layers can be customized through the configuration file).

[0054] Step 3.2, for the established grid in the computational domain, setting the unsteady flow simulation model mainly includes setting the thermophysical parameters of the gas, the far field and the boundary conditions of the object surface.

[0055] Step 4: Establish a virtual deformation boundary mesh adaptive model.

[0056] In order to solve the problem that the actual contact between objects in the flow field dynamic mesh calculation process causes the interference of the calculation domain boundary and makes the calculation unable to run, the present invention uses a method of replacing the actual model boundary with a virtual deformation boundary, so that in the flow field dynamic mesh calculation, there is always a certain distance between the virtual deformation boundary and the adjacent model boundary, thereby ensuring the quality of the flow field mesh. The specific steps are as follows.

[0057] Step 4.1, referring to the prior art, use the KD tree method to solve the wall distance from the grid node on the actual rigid body boundary to the adjacent solid wall boundary .

[0058] Step 4.2, calculate the displacement of the mapping point on the virtual deformation boundary.

[0059] Specifically, the position state of the grid nodes on the virtual deformation boundary is recorded as , the state of the closest distance from the corresponding grid node to the solid wall boundary of the adjacent object is recorded as ,in represents the coordinates of the ith grid node on the actual rigid body boundary at time n, Represents time n and The coordinates of the i-th grid node on the corresponding virtual deformation boundary, Represents the distance to the solid wall boundary The coordinates of the nearest node, express and Therefore, the present invention proposes to automatically correct a virtual deformation boundary according to the wall distance, that is,

[0060]

[0061] The present invention proposes to use the Wendland function as the functional expression for controlling the distance between the virtual deformation and the wall, that is,

[0062]

[0063] r0 is an artificially set parameter and is the adjustment coefficient for the virtual grid boundary calculation.

[0064] Step 5, according to the implicit coupling mode, start the multi-body dynamics simulation tool and the unsteady flow simulation tool. The coupling time step is consistent with the flow field simulation time step.

[0065] In step 5.1, the moving parts in the flow field simulation model are numbered, and the center of mass position, center of mass translation velocity, angular velocity around the principal axis of inertia, attitude angle of the principal axis of inertia, aerodynamic force, and aerodynamic torque relative to the center of mass of each component are registered as intermediate coupling variables of the coupling environment to automatically assign variable names and corresponding memory storage locations.

[0066] In step 5.2, an unsteady flow simulation is first performed to obtain the pressure and shear stress on the mesh nodes on the surface of each moving part. In step 5.2, the pressure and shear stress on the mesh nodes can be determined based on the known position coordinates of each node in the unsteady flow simulation and the boundary conditions set in step 3.2.

[0067] Step 5.3, in the unsteady flow simulation, perform area-weighted integration of pressure, shear stress and relative center-of-mass moment on the surface grid of each moving component to obtain the aerodynamic force and aerodynamic moment relative to the center of mass of the corresponding component. Then, the aerodynamic force and aerodynamic moment relative to the center of mass of each component are sent to the corresponding coupling variables of the multi-body dynamics simulation software through the network communication protocol.

[0068] Here, in order to ensure that the implicit iteration of multi-body simulation and flow field simulation can converge to the fixed point state more robustly, this method adopts the existing Aitken sub-relaxation method to correct the aerodynamic force and the aerodynamic moment relative to the center of mass at each iteration step.

[0069] Step 5.4, in the multi-body dynamics simulation, based on the received aerodynamic forces of each component and the aerodynamic moments relative to the center of mass, as well as the relative positions and relative velocities of each component, calculate whether there is contact between the components and calculate the corresponding interaction contact forces based on the model. If there is contact force, it is also necessary to perform the dynamic equation solution in combination with the contact force in step 5.5.

[0070] Step 5.5, in the multi-body dynamics simulation, perform one-step dynamic equation solving to obtain the center of mass position, center of mass translation velocity, angular velocity around the main axis of inertia, and attitude angle of the main axis of inertia of each component, and send the center of mass position, center of mass translation velocity, angular velocity around the main axis of inertia, and attitude angle of the main axis of inertia of each component to the corresponding coupling variables of the flow field simulation software through the network communication protocol.

[0071] Here, in order to ensure that the implicit iteration of multi-body simulation and flow field simulation can converge to the fixed point state more robustly, this method adopts the Aitken sub-relaxation method to correct the center of mass position, center of mass translation velocity, angular velocity around the principal axis of inertia, and attitude angle of the principal axis of inertia of each component in each iteration step.

[0072] Step 5.6: In the flow field simulation software, update the node positions of the component surface mesh according to the received center of mass position, center of mass translation velocity, angular velocity around the principal axis of inertia, and attitude angle of the principal axis of inertia of each component. and node movement speed.

[0073] Step 5.7: In the flow field simulation software, according to the node positions of the surface mesh of each component in the previous step , according to the virtual deformation boundary mesh adaptive model in step 4, update the coordinates of the virtual deformation boundary of each component Combined with the virtual deformation surface determined in step 3.1, on this virtual deformation surface, if the two bodies are not in contact, the virtual deformation boundary is consistent with the actual rigid body boundary; if the two bodies are close or in contact interference, the virtual deformation boundary produces displacement and deformation in a certain way to ensure that a certain quality of mesh units can be maintained between the two bodies, such as Figure 1 Step 5.7 determines the node coordinates on the virtual deformation object surface. The nodes on the virtual deformation object surface may include virtual nodes and real nodes. The virtual nodes indicate the virtual deformation boundaries, and the real nodes indicate the actual rigid body boundaries.

[0074] Specifically, according to step 4.1, the wall distance from the grid node on the actual rigid body boundary to the adjacent solid wall boundary can be calculated: , the coordinates of the grid nodes on the actual rigid body boundary can be determined by step 5.6 And the distance near the solid wall boundary The nearest node coordinates According to step 4.2, the coordinates of the i-th grid node on the virtual deformation boundary can be calculated .

[0075] Step 5.8, using the radial basis function (RBF) method to achieve the corresponding deformation of the spatial grid and update the grid in the calculation domain for the next time step.

[0076] Compared with the general RBF-based dynamic mesh method, the present invention needs to consider the boundary conditions as the superposition of two factors in the dynamic mesh coordinate calculation process, namely, the displacement of the surface mesh nodes caused by the actual rigid body motion of the object, and the relative displacement of the mesh nodes of the virtual deformation boundary considered to achieve non-interference of the surface mesh.

[0077] Specifically, consider a three-dimensional space function The radial basis function approximation of , where the radial basis function satisfy:

[0078]

[0079] in, is the weighting coefficient, is a radial basis function, and the Wendland or Gauss function can be used.

[0080] According to the position coordinates of the spatial grid node k in step n-1 , calculate the position coordinates of the spatial grid node k in the nth step , ,function satisfy:

[0081]

[0082] is the number of nodes on the actual rigid body boundary, is the weight coefficient for the nth step calculation, Corresponding to the i-th node of the actual rigid body boundary, is the coordinate of the ith node of the actual rigid body boundary at the n-1th step, is the number of nodes on the virtual deformation boundary, is the weight coefficient for the nth step calculation, Corresponding to the i-th node of the virtual deformation boundary, is the coordinate of the i-th node of the virtual deformation boundary at the n-1th step.

[0083] To solve the position of the spatial grid nodes, we need to solve the function The weight coefficient in and The following conditions should be met on the actual rigid body boundary:

[0084]

[0085] The following conditions should be met on the virtual deformation boundary:

[0086]

[0087] The weight coefficient can be solved by the above conditions and ,Will and Bring in the function The calculation formula is used to obtain the position of the spatial grid node .

[0088] Step 5.9, repeat steps 5.2 to 5.8 to complete the unsteady flow field simulation and multi-body dynamics coupling simulation, and then obtain the flow field changes in this process and the mutual movement of each component.

[0089] Although the present invention is disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope defined by the claims of the present invention.

Claims

1. A method for simulating unsteady flow and contact coupling during the separation process of an aircraft and a fairing, characterized in that: include: A multi-body dynamics simulation model, an unsteady flow simulation model and a virtual deformation boundary mesh adaptive model are established, wherein a virtual deformation object surface is specified in the unsteady flow simulation model, and the virtual deformation object surface includes at least one of a virtual deformation boundary and an actual rigid body boundary. The virtual deformation boundary mesh adaptive model indicates the association relationship between the virtual deformation boundary and the actual rigid body boundary in the unsteady flow simulation model, and the simulation step length of the multi-body dynamics simulation model is consistent with the simulation step length of the unsteady flow simulation model; The following steps are executed repeatedly until the simulation end condition is met: Performing unsteady flow simulation according to the unsteady flow simulation model to determine the aerodynamic force and aerodynamic moment relative to the center of mass of the components in the unsteady flow simulation model; Perform multi-body dynamics simulation according to the multi-body dynamics simulation model to determine dynamics data; In the unsteady flow simulation model, the grid node coordinates are calculated based on the dynamic data. If the virtual deformation surface is in contact with the adjacent solid wall, the coordinates of the virtual deformation boundary in the virtual deformation surface are determined based on the virtual deformation boundary grid adaptive model. and the coordinates of the actual rigid body boundary ; According to the coordinates of the virtual deformation boundary and the coordinates of the actual rigid body boundary , and the coordinates of the virtual deformation boundary at the previous time step and the coordinates of the actual rigid body boundary , calculate the positions of spatial grid nodes in the unsteady flow simulation model ; Determine the coordinates of the virtual deformation boundary in the virtual deformation object surface and the coordinates of the actual rigid body boundary ,include: Calculate the coordinates of the mesh nodes on the actual rigid body boundary The distance to the wall adjacent to the solid wall boundary , wall distance Solve using KD tree method; Determine the coordinates of the mesh nodes on the actual rigid body boundary And the distance near the solid wall boundary The nearest node coordinates , express and distance; according to , determine the coordinates of the i-th grid node on the virtual deformation boundary , The distance to the wall The function of is a Wendland function, satisfying: Adjustment factor calculated for the virtual deformation boundary.

2. The method according to claim 1, characterized in that: Determine the aerodynamic forces and moments about the center of mass of components in unsteady flow simulation models, including: Determine the pressure and shear stress on the grid nodes in the unsteady flow simulation model according to the position coordinates of the grid nodes in the unsteady flow simulation model and the boundary conditions set when establishing the unsteady flow simulation model; The aerodynamic force and aerodynamic moment relative to the center of mass are obtained by performing area-weighted integration of the pressure, shear stress and relative center of mass moment on the grid nodes in the unsteady flow simulation model.

3. The method according to claim 1, characterized in that Perform multi-body dynamics simulation based on the multi-body dynamics simulation model to determine the dynamics data, including: The unsteady flow simulation software sends the aerodynamic force on the component and the aerodynamic moment relative to the center of mass to the multi-body dynamics simulation software; The multi-body dynamics simulation software performs a one-step dynamic equation solution based on the aerodynamic force and aerodynamic torque relative to the center of mass of the received components, obtains the center of mass position, center of mass translation velocity, angular velocity around the principal axis of inertia, and attitude angle of the principal axis of inertia of each component, and sends the calculation results to the unsteady flow simulation software.

4. The method according to claim 3, characterized in that Before solving the dynamic equations, it also includes: Based on the aerodynamic force and aerodynamic moment relative to the center of mass of the components, as well as the relative positions and relative velocities of the components, it is calculated whether there is contact force between the components; if there is contact force, the dynamic equations are solved in combination with the contact force.

5. The method according to claim 1, characterized in that Position coordinates of spatial grid node k in the nth step of the unsteady flow simulation model , is the position coordinate of the spatial grid node k in the unsteady flow simulation model at step n-1, and the function satisfy: is the Wendland function or the Gauss function, is the number of nodes on the actual rigid body boundary, is the weight coefficient for the nth step calculation, Corresponding to the i-th node of the actual rigid body boundary, is the coordinate of the ith node of the actual rigid body boundary at the n-1th step, is the number of nodes on the virtual deformation boundary, is the weight coefficient for the nth step calculation, Corresponding to the i-th node of the virtual deformation boundary, is the coordinate of the i-th node of the virtual deformation boundary at the n-1th step.

6. The method according to claim 5, characterized in that The following conditions are met: 。 7. The method according to claim 5, characterized in that The following conditions are met: 。

Images