A method for dividing a structure grid of an internal and external flow field of an aircraft based on a non-matching interface

Abstract

The application belongs to the field of aerospace and fluid mechanics, and discloses an aircraft internal and external flow field structure grid division method based on a non-matching interface, which comprises the following steps: decomposing the aircraft shape into two topological subdomains of an external flow field, an inlet duct and an internal flow field of a tail nozzle, and connecting each subdomain through a pair of completely coinciding interfaces; wherein the internal flow field of the inlet duct and the tail nozzle adopts an O-type topological structured grid, the external flow field adopts a C-type topological structured grid, and the nodes of the O-type topological structured grid and the C-type topological structured grid can slide on the interface. The problems that the adaptability of the non-structured grid is poor in the near-wall boundary layer region, the calculation amount is large, and the mixed grid is difficult to maintain the overall field conservation and high precision in the current numerical simulation of the internal and external flow coupling of the complex aircraft shape are solved.

Description

Technical Field

[0001] This application belongs to the fields of aerospace and fluid mechanics, and in particular relates to a method for mesh generation of the internal and external flow field structure of an aircraft based on a non-matching interface. Background Technology

[0002] With the development of computer technology, computational fluid dynamics (CFD) methods have been widely applied in aerospace and aerodynamics. This method can obtain the global flow field structure of an aircraft, which is crucial for aerodynamic performance analysis and optimization design. The principle of this method is to discretize the continuous external flow field of the aircraft into a grid, and then numerically discretize and solve the Navier-Stokes equations to obtain an approximate solution for the flow field. Therefore, mesh generation is indispensable when using this method. Currently, the most common methods are unstructured meshing and structured meshing. Unstructured meshes are suitable for complex surfaces, are easy to generate, and have strong adaptability, but they have low computational efficiency, poor boundary handling capabilities, and require a large number of meshes to fill the flow field. Structured meshes, on the other hand, have high computational efficiency, easily generate high-quality boundary layer meshes, and have a small number of meshes with high accuracy, but they are less adaptable to complex geometries, require more manual intervention, and need to be divided into blocks, which makes mesh generation difficult.

[0003] Currently, most studies on the coupling of internal and external flows in integrated internal and external flow aircraft use unstructured meshes to divide the flow field. For more complex geometries, the mesh size increases dramatically, leading to low computational efficiency. Furthermore, when using unstructured meshes, the boundary layer mesh is generally set as a prismatic layer. However, at the junction of the air intake and the fuselage, there are usually large curvatures and corners, making it easy for prismatic layer meshes to fail when generated in such locations.

[0004] When using structured meshes to divide the internal and external flow fields, the air intake and nozzle are generally cylindrical in shape. To ensure that there are boundary layer meshes on the upper and lower walls, O-type meshes are generally chosen for this type of shape. However, the external flow field of an aircraft is generally divided into C-type meshes, and the mesh growth directions of these two regions are perpendicular to each other. This makes it difficult to use the same topology structure for the internal and external flow field meshes, thus preventing the internal and external flow fields from being directly connected. Summary of the Invention

[0005] The purpose of this application is to overcome the problems of the prior art by disclosing a method for mesh generation of the internal and external flow fields of an aircraft based on a non-matching interface. This method aims to solve the problems of poor adaptability of unstructured meshes in the near-wall boundary layer region, large computational load, and difficulty in maintaining the overall conservation and high accuracy of hybrid meshes in the numerical simulation of the internal and external flow coupling of complex aircraft shapes.

[0006] The objective of this application is achieved through the following technical solution:

[0007] A method for mesh generation of the internal and external flow field structure of an aircraft based on a non-matching interface surface, the method comprising:

[0008] The aircraft's shape is decomposed into two topological subdomains: the external flow field and the internal flow field of the air intake and tail nozzle. Each subdomain is connected by a pair of completely overlapping interfaces.

[0009] The internal flow field of the air intake and tail nozzle adopts an O-type topological structured grid, while the external flow field adopts a C-type topological structured grid. The nodes of the O-type and C-type topological structured grids can slide relative to each other at the interface.

[0010] That is, due to the different topologies, the nodes of the O-type and C-type topological structured meshes do not need to correspond one-to-one at the interface, allowing arbitrary sliding and completely eliminating the mesh quality degradation caused by the traditional "node matching".

[0011] According to a preferred embodiment, the O-type topological structured grid corresponding to the flow field inside the air intake and exhaust nozzle is designed and divided according to the following structure:

[0012] Using the inlet section of the air intake as the "source surface", the geometric construction lines along the air intake and nozzle are first obtained. Then, an internal O-type block topology is set on the section with curvature greater than the preset value. Finally, O-type grid blocks are generated along the flow direction using polar coordinate transformation.

[0013] According to a preferred embodiment, in the O-type topological structured mesh, a single O-type mesh is used for circular / elliptical cross-sections; for rectangular cross-sections, an "OH" combined topology is adopted, that is, H-grid transition blocks are added at the four corners so that there are no singular lines at the mesh corners.

[0014] According to a preferred embodiment, the grid nodes of the O-type topologically structured grid adopt an exponentially growing distribution in the normal direction of the grid wall. Specifically, the height Δy1 of the first layer grid is calculated by inversely using y+≈1, the growth factor R=1.08~1.12, and the total number of layers N≥100.

[0015] According to a preferred embodiment, the C-type topologically structured grid corresponding to the external flow field is designed and divided according to the following structure: the external flow field is divided into a boundary layer region, a wake region, and a far-field region.

[0016] Specifically, a C-shaped body-fitted mesh is generated around the aircraft surface in the boundary layer region, and the aircraft surface is divided into several regular quadrilateral blocks in the three-dimensional spanwise direction to generate the structural mesh; and each mesh node adopts an exponential growth distribution in the normal direction of the mesh wall. Specifically, in terms of boundary layer settings, the first normal layer Δy1 is also set according to y+≈1, with a growth factor of 1.1.

[0017] According to a preferred embodiment, the wake region is generated into a three-dimensional volume mesh using a square-structured mesh surface.

[0018] According to a preferred embodiment, the size of the wake region extends rearward from the tail edge of the aircraft by ≥20 times the body length to capture the flow structure generated by the tail jet.

[0019] According to a preferred embodiment, the far-field region is generated into a three-dimensional volume mesh using a square-structured mesh surface.

[0020] According to a preferred embodiment, the far-field region corresponds to a rectangle with a radius 100 times the feature length centered on the body, and the grid grows geometrically at a rate of 1.3 times. This minimizes far-field boundary reflections.

[0021] According to a preferred embodiment, for the docking region of the O-type topological structured grid and the C-type topological structured grid, two sets of construction lines with completely consistent spatial position and geometric length are used to construct the interface adapted to the O-type topological structured grid of the internal flow field and the interface adapted to the C-type topological structured grid, respectively.

[0022] The aforementioned main solution and its various further alternative solutions can be freely combined to form multiple solutions, all of which are solutions that can be adopted and are claimed in this application. Those skilled in the art, after understanding the solution of this application, will realize that there are many combinations based on the prior art and common general knowledge, all of which are technical solutions to be protected in this application, and will not be exhaustively listed here.

[0023] The beneficial effects of this application are:

[0024] The method described in this application effectively eliminates the geometric gaps between the internal and external flow fields without requiring the mesh nodes of the two interfaces to overlap one by one. During numerical calculations, it ensures stable interaction and accurate transmission of flow field data at the interface. At the same time, it ensures that both the internal and external flow fields maintain the topological form of the structured mesh, meeting the requirements for continuity and reasonable distribution of the boundary layer meshes on each wall. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the grid of the outer and inner boundaries of the external flow field;

[0026] Figure 2 This is a schematic diagram of the two-dimensional C-shaped mesh topology of the external flow field of an aircraft.

[0027] Figure 3 This is a schematic diagram of the three-dimensional structure of the external flow field;

[0028] Figure 4 This is a schematic diagram of the flow field geometry and O-shaped structure lines inside the air intake;

[0029] Figure 5 This is a schematic diagram of the three-dimensional O-shaped body mesh and cross-sectional mesh of the flow field inside the air intake;

[0030] Figure 6 This is a schematic diagram showing the location of the interface between the internal and external flow fields;

[0031] Figure 7 This is a schematic diagram of the three-dimensional mesh surfaces and positions of interface 1 and interface 2;

[0032] Figure 8 It is a three-dimensional mesh diagram using the interface connecting the internal and external flow fields;

[0033] Wherein, 1 is the far-field outer boundary, 2 is the inner boundary of the aircraft's outline, 3 is the grid at the junction surface, 4 is the C-shaped radial and circumferential construction lines of the aircraft's leading edge, 5 is the three-dimensional volume grid construction line, 6 is the geometric shape construction line of the air intake and nozzle, 7 is the O-shaped topological construction line of each section, 8 is the three-dimensional O-shaped grid of the air intake, 9 is the O-shaped grid of different sections, 10 is the C-shaped grid of the external flow field on the two-dimensional section, 11 is the O-shaped grid of the internal flow field on the two-dimensional section, 12 is the junction surface of the internal and external flow fields, 13 is the three-dimensional junction surface 1 of the external flow field, 14 is the three-dimensional junction surface 2 of the internal flow field, 15 is the display of the internal and external junction surfaces in the same three-dimensional coordinates, 16 is the three-dimensional C-shaped grid of the external flow field (green area), 17 is the junction surface (yellow area), 18 is the three-dimensional O-shaped grid of the internal flow field (red area), and 19 is the aircraft surface grid (purple area). Detailed Implementation

[0034] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, unless otherwise specified, the following embodiments and features in the embodiments can be combined with each other.

[0035] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0036] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this application is in use. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0037] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0038] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0039] Furthermore, it should be noted that unless otherwise specified in this application, the specific structures, connections, positions, power sources, etc. involved are all things that a person skilled in the art can know without creative effort based on the prior art.

[0040] Example 1

[0041] refer to Figures 1 to 8As shown in the figure, this embodiment discloses a method for mesh generation of the internal and external flow field structure of an aircraft based on a non-matching interface. The method includes: decomposing the aircraft shape into two topological subdomains: the external flow field and the flow field inside the air intake and tail nozzle. Each subdomain is connected by a pair of completely overlapping interfaces. The flow field inside the air intake and tail nozzle uses an O-type topological structured mesh, while the external flow field uses a C-type topological structured mesh. The nodes of the O-type and C-type topological structured meshes can slide relative to each other at the interface. That is, due to the different topological structures, the nodes of the O-type and C-type topological structured meshes do not need to correspond one-to-one at the interface, allowing arbitrary sliding and completely eliminating the mesh quality degradation caused by traditional "node matching".

[0042] Preferably, the C-shaped topological structured mesh corresponding to the external flow field is designed and divided according to the following structure: the external flow field is divided into a boundary layer region, a wake region, and a far-field region; wherein, a C-shaped body-fitting mesh is generated around the aircraft surface in the boundary layer region, and the aircraft surface is divided into several regular quadrilateral blocks in the three-dimensional spanwise direction to generate the structured mesh; and each mesh node adopts an exponential growth distribution in the normal direction of the mesh wall. Specifically, in terms of boundary layer settings, the first normal layer Δy1 is set as y+≈1, with a growth factor of 1.1. The wake region uses a square-constructed mesh surface to generate a three-dimensional volume mesh; the size of the wake region extends backward from the tail edge of the aircraft by ≥20 times the body length to capture the flow structure generated by the tail jet. The far-field region uses a square-constructed mesh surface to generate a three-dimensional volume mesh; the mesh size corresponding to the far-field region is a rectangle with a radius of 100 times the characteristic length centered on the aircraft, and the mesh grows geometrically at a rate of 1.3 times. This minimizes far-field boundary reflection.

[0043] Specifically, the C-type topology structured mesh generation process for the external flow field includes:

[0044] (1) First, extract the geometric contour of the aircraft shape as the inner boundary wall, and select a far-field closed curve that sufficiently covers the core calculation area as the far-field outer boundary 1 to construct a C-shaped topological boundary surrounding the aircraft contour. It should be noted that when extracting the inner boundary 2 of the aircraft shape contour, at the junction of the inner and outer flow fields, the inlet lip contour is regarded as the wall of the inner boundary.

[0045] (2) Then, radial construction lines are generated uniformly from the inner boundary wall to the outer boundary, and circumferential construction lines orthogonal to the radial construction lines are generated simultaneously to form a grid skeleton.

[0046] (3) Then, based on the orthogonal construction lines, the algebraic grid generation method is used to generate a structured quadrilateral grid.

[0047] (4) Finally, the first layer mesh height, growth rate and total number of growth layers are set for the surface mesh boundary of the aircraft to generate the boundary layer mesh.

[0048] Preferably, the O-type topological structured grid corresponding to the flow field inside the air intake and tail nozzle is designed and divided according to the following structure: taking the inlet section of the air intake as the "source surface", firstly obtain the geometric construction lines along the air intake and nozzle, then set the internal O-type block topological structure on the section with curvature greater than the preset value, and finally generate O-type grid blocks by polar coordinate transformation along the flow direction.

[0049] In the O-type topologically structured mesh, a single O-type mesh is used for circular / elliptical cross-sections; for rectangular cross-sections, an "OH" combined topology is adopted, that is, H-grid transition blocks are added at the four corners to ensure that there are no singular lines at the mesh corners. The mesh nodes in the O-type topologically structured mesh exhibit an exponential growth distribution along the mesh wall normal. Specifically, the height Δy1 of the first layer mesh is calculated by inversely using y+≈1, with a growth factor R=1.08~1.12, and the total number of layers N≥100.

[0050] Specifically, since the air intake and nozzle resemble a closed cylinder, this type of shape requires boundary layer meshes on all circumferential walls; therefore, an O-type mesh is used. The O-type topological mesh generation process for the internal flow field includes:

[0051] (1) First, extract the geometric shape construction lines based on the geometric shape of the air intake and nozzle, and set the number of nodes for each of the several shape construction lines.

[0052] (2) Set up an O-type topology on the cross-section with large geometric curvature, and set the first layer mesh height parameters, growth rate and number of nodes on each construction line. Then generate a surface mesh based on the area enclosed by each construction line. It should be noted that when setting up an O-type topology at the junction of the internal and external flow fields and at the lip position, it is necessary not only to extract the outer contour of the lip as the construction line, but also to set the O-type topology construction line.

[0053] (3) Select the generated surface mesh to encapsulate it into a volume mesh.

[0054] Preferably, the interface mesh construction method includes: since the topological structures of the interface constructed by the C-type mesh of the outer flow field and the interface constructed by the O-type mesh of the inner flow field are inconsistent at the interface location, it is not necessary to ensure a one-to-one correspondence between nodes; only data exchange needs to be set during calculation. Although the nodes do not need to correspond one-to-one, it is necessary to ensure that the two interface surfaces completely overlap to guarantee accurate data interaction. This requires the two interface surfaces to share the same spatial location. In addition, to ensure that the two interface surfaces completely overlap, it is preferable to use a plane to construct the interface surface. If the geometry of the inlet lip is relatively complex, the outer contour of the inlet is divided into multiple planes for construction.

[0055] Specifically, addressing the problem of adapting the interface between the C-type grid of the external flow field and the O-type grid of the internal flow field in the inlet, this application discloses a construction method that achieves accurate data interaction without requiring a one-to-one correspondence of nodes, solely through spatial overlap. The specific implementation steps are as follows:

[0056] (1) Topology adaptation design of the interface: In the process of meshing the flow field of the inlet, the outer flow field adopts a C-type mesh to form interface 1, and the inner flow field adopts an O-type mesh to form interface 2. Since the topology of the two is different, it is not necessary to match the nodes of interface 1 and interface 2 one by one. It is only necessary to set the data exchange rules between the two interfaces through the solver in the subsequent CFD calculation process to realize the transfer of flow field parameters.

[0057] (2) Spatial overlap control of the interface: In order to ensure the accuracy of data interaction, the interface 1 and the interface 2 need to be completely overlapped. Specifically, this is achieved by making the two interface surfaces share the same geometric surface in the same spatial position. This geometric surface needs to be defined in advance in the three-dimensional model of the air intake as the boundary reference point, reference line and reference surface of the external flow field C-type grid and the internal flow field O-type grid. Finally, two interface surfaces that are completely overlapped in planar form are constructed.

[0058] (3) Segmented construction scheme under complex geometry: When the geometry of the intake lip is complex and it is difficult to achieve the overlap of the interface through a single plane, a segmented construction strategy is adopted: along the curvature change node of the lip contour, the outer contour of the intake is divided into multiple continuous sub-planes. Each sub-plane serves as the shared interface between the O-type grid of the flow field and the C-type grid of the external flow field in the corresponding region. The sub-interfaces are connected in sequence to form a complete boundary, ensuring the spatial overlap of the overall interface and the continuity of the flow field.

[0059] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for mesh generation of the internal and external flow field structure of an aircraft based on a non-matching interface, characterized in that, The method for mesh generation of the internal and external flow field structure of the aircraft includes: The aircraft's shape is decomposed into two topological subdomains: the external flow field and the internal flow field of the air intake and tail nozzle. Each subdomain is connected by a pair of completely overlapping interfaces. The internal flow field of the air intake and tail nozzle adopts an O-type topological structured grid, while the external flow field adopts a C-type topological structured grid. The nodes of the O-type and C-type topological structured grids can slide relative to each other at the interface. The O-type topological structured grid corresponding to the flow field inside the air intake and tail nozzle is designed and divided according to the following structure, including: Using the inlet section of the air intake as the "source surface", the geometric construction lines along the air intake and nozzle are first obtained. Then, an internal O-type block topology structure is set on the section with curvature greater than the preset value. Finally, O-type grid blocks are generated along the flow direction using polar coordinate transformation. In the O-type topological structured mesh, a single O-type mesh is used for circular / elliptical cross sections; for rectangular cross sections, an "OH" combined topology is used, which adds H-grid transition blocks at the four corners to ensure that there are no singular lines at the mesh corners. The C-type topological structured grid corresponding to the external flow field is designed and divided according to the following structure: the external flow field is divided into boundary layer region, wake region and far field region. Specifically, a C-shaped body-fitted mesh is generated around the surface of the aircraft in the boundary layer region, and the surface of the aircraft is divided into several regular quadrilateral blocks in the three-dimensional spanwise direction to generate the structural mesh; and each mesh node adopts an exponential growth distribution in the normal direction of the mesh wall.

2. The method for mesh generation of the internal and external flow field structure of an aircraft as described in claim 1, characterized in that, In an O-type topologically structured mesh, each mesh node adopts an exponentially growing distribution along the mesh wall normal.

3. The method for mesh generation of the internal and external flow field structure of an aircraft as described in claim 1, characterized in that, The wake region is generated into a three-dimensional volume mesh using square grid surfaces.

4. The method for mesh generation of the internal and external flow field structure of an aircraft as described in claim 3, characterized in that, The size of the wake region extends backward from the tail edge of the aircraft by ≥20 times the body length, capturing the flow structure generated by the tail jet.

5. The method for mesh generation of the internal and external flow field structure of an aircraft as described in claim 1, characterized in that, The far-field region uses a square-structured mesh surface to generate a three-dimensional volume mesh.

6. The method for mesh generation of the internal and external flow field structure of an aircraft as described in claim 5, characterized in that, The far-field region corresponds to a rectangle with a radius of 100 times the feature length centered on the machine body, and the mesh grows geometrically at a rate of 1.3 times.

7. The method for mesh generation of the internal and external flow field structure of an aircraft as described in claim 1, characterized in that, For the interface region between O-type and C-type topologically structured grids, two sets of construction lines with identical spatial position and geometric length are used to construct the interface adapted to the O-type topologically structured grid and the interface adapted to the C-type topologically structured grid for the internal flow field, respectively.

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