Flow field simulation method suitable for moving part contact separation problem

Abstract

The invention discloses a flow field simulation method suitable for a moving part contact and separation problem. The method comprises the following steps: obtaining separation surface positions between moving parts in a processed moving part geometric model; inputting the geometric file corresponding to each moving part into CFD grid generation software, and outputting a fluid calculation grid of each moving part by the CFD grid generation software; importing the fluid calculation grid of each moving part and a preset background grid into CFD simulation software, and performing cutting to obtain overlapped grids; in CFD simulation software, setting physical boundary conditions for the overlapped grids; iterative calculation is carried out on the overlapping grids with the physical boundary conditions in CFD simulation software; and when the total iteration time reaches the moment when each moving part needs to generate relative movement, stopping calculation, resetting the boundary condition of the curved surface corresponding to the gap as the boundary condition of the fluid penetrable interface, and restarting the iterative calculation. According to the invention, the problems of interpolation error, lap joint error and flow leakage are avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of aerospace systems, and in particular relates to a flow field simulation method suitable for the contact and separation problems of moving parts. Background Art

[0002] In the simulation of the interstage separation process, there is a problem called "contact separation". Before the detonating cord of the interstage shell section cuts the shell, the interstage section is a closed environment. After the upper stage engine is ignited and the plug is opened, the jet enters the closed interstage section, causing the pressure to rise rapidly. When the detonating cord is cut, a gap will appear between the ejection piece and the upper and lower stages. At this time, the ejection piece will fly away radially and the lower stage will be pushed backward. However, for the overlapping grid technology commonly used in current fluid simulation software, if the walls are tangent or intersecting, the wall boundary that was originally used as the retained boundary will be cut, which will affect the search for the mesh that needs to be retained; in addition, it will cause the retained mesh to have an internal overlap boundary, but there is no mesh around it.

[0003] If you choose to ignore the initial contact and keep the gap simulation in the simulation, gas will continue to leak out of the gap during the pressure holding process, resulting in the interstage pressure simulation being lower than the actual situation. The previous common method is to generate two sets of grids, the first set is seamless for pressure holding process calculation, and then the result is interpolated into the second set of gapped background + embedded grids when the cutting time is reached. This approach requires generating two sets of grids, which will produce interpolation errors and non-physical phenomena near the gap. Summary of the invention

[0004] The technical problem solved by the present invention is: to overcome the deficiencies of the prior art, to provide a flow field simulation method suitable for the contact and separation problems of moving parts, and to avoid the problems of interpolation error, overlap error and flow leakage.

[0005] The object of the present invention is achieved through the following technical scheme: a flow field simulation method suitable for the contact and separation problem of moving parts, comprising: processing a preset moving part geometric model through geometric modeling software to obtain the separation surface position between each moving part in the processed moving part geometric model; outputting each moving part in the processed moving part geometric model as a geometric file that can be recognized by CFD mesh generation software; inputting the geometric file corresponding to each moving part into the CFD mesh generation software, and the CFD mesh generation software outputs the fluid calculation grid of each moving part; importing the fluid calculation grid of each moving part and the preset background grid into the CFD simulation software, cutting them to obtain overlapping grids; setting physical boundary conditions for the overlapping grids in the CFD simulation software; iteratively calculating the overlapping grids with set physical boundary conditions in the CFD simulation software; when the total iteration time reaches the moment when each moving part should undergo relative motion, stopping the calculation, resetting the surface boundary conditions corresponding to the gap to the fluid penetrable interface boundary conditions, and restarting the iterative calculation.

[0006] In the above-mentioned flow field simulation method applicable to the contact and separation problems of moving parts, the separation surface positions between the moving parts in the processed moving part geometric model are obtained, including: if the separation surface between two adjacent moving parts of the moving part geometric model is a gap with a preset width, then a new surface is established for the gap through geometric modeling software, and the surface should not be merged with the two adjacent moving parts into one entity, but only as an independent surface; if the separation surface between two adjacent moving parts of the moving part geometric model itself has no width, the actual gap position and width that will be generated after the separation of the two adjacent moving parts of the moving part geometric model are clarified, and the two adjacent moving parts of the moving part geometric model are divided through geometric modeling software to separate the surface at the gap.

[0007] In the above-mentioned flow field simulation method applicable to the contact and separation problems of moving parts, in the processed geometric model of the moving parts, all gaps between the separation end faces have curved surfaces.

[0008] In the above-mentioned flow field simulation method applicable to the contact and separation problems of moving parts, when the geometry file can be output to be recognized by CFD mesh generation software, the surfaces corresponding to the gaps between all separation end faces involved in each moving part are output together.

[0009] In the above-mentioned flow field simulation method applicable to the contact and separation problems of moving parts, the fluid calculation grid of each moving part includes two parts of grids. The first part of the grid is the grid generated by the boundary of the moving part and the outer envelope of the gap, and the second part of the grid is the grid generated between the separation end face of the moving part and the gap.

[0010] In the above-mentioned flow field simulation method applicable to the contact and separation problems of moving parts, the curved surface of the gap is used as the internal boundary of the fluid calculation grid.

[0011] In the above-mentioned flow field simulation method applicable to the contact and separation problems of moving parts, the preset background grid is the grid corresponding to the environment space where all the moving parts are located.

[0012] In the above-mentioned flow field simulation method applicable to the contact and separation problem of moving parts, the curved surface corresponding to the gap does not participate in the overlapping grid cutting during the cutting process. At this time, the curved surfaces corresponding to the gaps of each moving part will overlap each other.

[0013] In the above-mentioned flow field simulation method applicable to the contact and separation problems of moving parts, the physical boundary conditions of the overlapping grids include: conventional boundary conditions of the overlapping grids and boundary conditions of the gap corresponding surface.

[0014] In the above-mentioned flow field simulation method applicable to the contact and separation problems of moving parts, the boundary condition of the curved surface corresponding to the gap is set to a solid wall. At this time, a closed space is formed inside the gap, and the flow cannot enter or exit the area, thereby achieving no flow leakage before the moving parts are separated.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention can realize the simulation before and after contact separation using only one set of grids, and avoids the problems of interpolation error, overlap error and flow leakage; (2) The present invention saves the time cost of generating a second set of computational grids, and flow leakage will not occur. The pressure prediction results at typical positions between stages in the pressure holding stage are improved by more than 20%. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] 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: Figure 1 is a flow chart of a flow field simulation method applicable to the contact and separation problem of moving parts provided by an embodiment of the present invention; FIG. 2 (a) is a schematic diagram of a grid generated in each gap before cutting provided by an embodiment of the present invention; FIG2( b ) is a schematic diagram of an embedded grid formed after cutting according to an embodiment of the present invention; FIG3 (a) is a diagram showing the application effect before cutting provided by an embodiment of the present invention; FIG. 3( b ) is a diagram showing the application effect after cutting provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0017] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although 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 in order to enable a more thorough understanding of the present disclosure and to be able to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0018] Figure 1 Flowchart of a flow field simulation method applicable to the contact and separation problem of moving parts provided by an embodiment of the present invention. Figure 1 As shown, the method comprises the following steps: The preset moving component geometric model is processed by geometric modeling software to obtain the separation surface positions between the moving components in the processed moving component geometric model; Output each moving part in the processed moving part geometric model as a geometric file that can be recognized by CFD mesh generation software; input the geometric file corresponding to each moving part into the CFD mesh generation software, and the CFD mesh generation software outputs the fluid calculation mesh of each moving part; Import the fluid calculation grid of each moving part and the preset background grid into the CFD simulation software and cut them to obtain overlapping grids; In CFD simulation software, set physical boundary conditions for overlapping grids; In the CFD simulation software, the overlapping grids with set physical boundary conditions are iteratively calculated; when the total iteration time reaches the moment when the moving parts should undergo relative motion, the calculation is stopped, and the boundary conditions of the surface corresponding to the gap are reset to the fluid penetrable interface boundary conditions, and then the iterative calculation is restarted.

[0019] Specifically, the method comprises the following steps: Step 1: According to the geometric model of the moving parts given by the party proposing the simulation task, it is processed in the geometric modeling software to identify the positions of the separation surfaces between the moving parts in the geometric model of the moving parts.

[0020] Judge all separation surfaces: if the separation surface of two adjacent moving parts in the moving part geometric model is a gap with a certain width, then a new surface is established for the gap through the geometric modeling software (the separation surfaces of the two adjacent moving parts are connected through this surface). This surface should not be merged with the two adjacent moving parts into one entity, but only serve as an independent surface; if the separation surface of two adjacent moving parts in the moving part geometric model itself has no width (that is, the separation end surfaces of the two adjacent moving parts overlap), it is necessary to contact the party proposing the simulation task to clarify the actual gap position and width that will be generated after the separation of the two adjacent moving parts of the moving part geometric model (for example, the actual gap measurement value generated after the detonating cord is cut to weaken the groove), and the two adjacent moving parts of the moving part geometric model are divided through the geometric modeling software to separate the surface at the gap.

[0021] Finally, the processed geometric model of the moving part is obtained, in which all gaps between the separated end faces have curved surfaces.

[0022] Step 2: Based on the processed moving component geometric model finally obtained in step 1, each moving component in the processed moving component geometric model is output as a geometric file that can be recognized by CFD (computational fluid dynamics) mesh generation software. When outputting each moving component in the processed moving component geometric model, it is necessary to output the curved surfaces corresponding to the gaps between all separation end faces involved in each moving component.

[0023] The geometry file corresponding to each moving part is input into the CFD mesh generation software, and the fluid calculation mesh of each moving part is output. The fluid calculation mesh of each moving part includes two parts of meshes. The first part of the mesh is the mesh generated by the boundary of the moving part and the outer envelope of the gap, and the second part of the mesh is the mesh generated between the separation end face of the moving part and the gap. The surface of the gap is used as the internal boundary of the fluid calculation mesh, as shown in Figure 2(a).

[0024] Step 3: Import the fluid calculation grid of each moving part generated in step 2 and the preset background grid (i.e., the grid corresponding to the environmental space where all moving parts are located) into the CFD simulation software, and cut them to obtain overlapping grids.

[0025] During the cutting process, the surfaces corresponding to the gaps do not participate in the overlapping mesh cutting (that is, when selecting the wall boundary, only the wall boundary of the moving component itself is selected). At this time, the surfaces corresponding to the gaps of each moving component will overlap each other, as shown in Figure 2(b).

[0026] Step 4: In the CFD simulation software, set physical boundary conditions for the overlapping grid generated in step 3.

[0027] The physical boundary conditions of the overlaid grid include: regular boundary conditions of the overlaid grid and boundary conditions of the gap corresponding surface.

[0028] The boundary condition of the surface corresponding to the gap is set to a solid wall. At this time, a closed space is formed inside the gap, and the flow cannot enter or exit the area, thereby achieving no flow leakage before the moving parts are separated.

[0029] Step 5: In the CFD simulation software, iterative calculations are performed on the overlapping grids with set physical boundary conditions; when the total iteration time reaches the moment when the moving parts should undergo relative motion, the calculation is stopped, and the boundary conditions of the surface corresponding to the gap are reset to the boundary conditions of the fluid-penetrable interface, and then the iterative calculation is restarted.

[0030] When processing the geometric model, an area with the same width as the gap is reserved on the upper stage wall and the interstage cast sheet; then when generating the mesh, a computational mesh is also generated between the wall and the gap area. At this time, the gap between the two sets of meshes becomes the internal boundary, as shown in Figure 2(a).

[0031] When cutting the mesh, the gaps in the mesh are neither used as cutting boundaries nor as retained boundaries, that is, these internal boundaries have no effect on the cutting process, and finally form an embedded mesh, as shown in Figure 2(b). After such processing, on the one hand, since the gaps on both sides are not involved in the cutting, there will be no cutting errors when the wall is tangent; on the other hand, the gap boundaries left by the two meshes form an overlap.

[0032] When calculating the pressure-blocking state, the gap boundary is set to the wall boundary. At this time, thanks to the complete overlap between the two residual boundaries, the internal flow cannot leak out of the interstage section. When it is necessary to calculate the state after cutting, the gap boundary is set to an interface that can be penetrated by flow (for example, ANSYS Fluent calls it Interface, and METACOMP CFD++ calls it Zonal - Simple Flow-through), and then the calculation can be resumed without regenerating the grid and interpolation.

[0033] Figures 3(a) and 3(b) show the flow field distribution comparison of the gap between the lower stage and the ejection disc before and after cutting in the actual interstage flow simulation. It can be seen that the interstage flow leakage to the outside is completely isolated before cutting (the results of the grid in the gap remain the results given by the initial conditions), and the interstage gas rushes out of the gap only after cutting, which proves the effectiveness of the method.

[0034] This embodiment uses only one set of grids to realize the simulation before and after contact separation, and avoids the problems of interpolation error, overlap error and flow leakage. This embodiment saves the time cost of generating a second set of calculation grids, and flow leakage will not occur. The pressure prediction results at typical positions between stages in the pressure holding stage are improved by more than 20%.

[0035] Although the present invention has been 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 to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A flow field simulation method suitable for the contact and separation problems of moving parts, characterized in that include: Processing the preset moving component geometric model to obtain the separation surface positions between the moving components in the processed moving component geometric model; Outputting each moving part in the processed moving part geometric model as a geometric file that can be recognized by CFD mesh generation software; Input the geometry file corresponding to each moving part into the CFD mesh generation software, and the CFD mesh generation software outputs the fluid calculation mesh of each moving part; Import the fluid calculation grid of each moving part and the preset background grid into the CFD simulation software and cut them to obtain overlapping grids; In CFD simulation software, set physical boundary conditions for overlapping grids; In the CFD simulation software, the overlapping grids with set physical boundary conditions are iteratively calculated; when the total iteration time reaches the moment when the moving parts should undergo relative motion, the calculation is stopped, and the boundary conditions of the surface corresponding to the gap are reset to the fluid penetrable interface boundary conditions, and then the iterative calculation is restarted.

2. The flow field simulation method applicable to the contact and separation problems of moving parts according to claim 1 is characterized in that: The separation surface positions between the moving parts in the processed moving part geometric model include: If the separation surface between two adjacent moving parts of the moving part geometric model is a gap with a preset width, a new surface is created for the gap through geometric modeling software. The new surface is not merged with the two adjacent moving parts into one entity, but is only an independent surface. If the separation surface between two adjacent moving parts of the moving part geometric model has no width, the actual gap position and width that will be generated after the two adjacent moving parts of the moving part geometric model are separated are clarified, and the two adjacent moving parts of the moving part geometric model are divided through geometric modeling software to separate the surface at the gap.

3. The flow field simulation method applicable to the contact and separation problems of moving parts according to claim 2 is characterized in that: In the processed geometric model of the moving part, there are curved surfaces in all gaps between the separated end faces.

4. The flow field simulation method applicable to the contact and separation problems of moving parts according to claim 1 is characterized in that: When the geometry file is output to be recognizable by CFD mesh generation software, the surfaces corresponding to the gaps between all separated end faces involved in each moving part are output together.

5. The flow field simulation method applicable to the contact and separation problems of moving parts according to claim 1 is characterized in that: The fluid calculation grid of each moving part includes two parts of grids. The first part of the grid is the grid generated by the boundary of the moving part and the outer envelope of the gap, and the second part of the grid is the grid generated between the separation end face of the moving part and the gap.

6. The flow field simulation method applicable to the contact and separation problems of moving parts according to claim 5 is characterized in that: The surface of the gap serves as the internal boundary of the fluid computational mesh.

7. The flow field simulation method applicable to the contact and separation problems of moving parts according to claim 1 is characterized in that: The preset background grid is the grid corresponding to the environment space where all moving parts are located.

8. The flow field simulation method applicable to the contact and separation problems of moving parts according to claim 1 is characterized in that: During the cutting process, the curved surfaces corresponding to the gaps do not participate in the overlapping grid cutting. At this time, the curved surfaces corresponding to the gaps of each moving part will overlap each other.

9. The flow field simulation method applicable to the contact and separation problems of moving parts according to claim 1, characterized in that: The physical boundary conditions of the overlaid grid include: regular boundary conditions of the overlaid grid and boundary conditions of the gap corresponding surface.

10. The flow field simulation method applicable to the contact and separation problems of moving parts according to claim 9, characterized in that: The boundary condition of the surface corresponding to the gap is set to a solid wall. At this time, a closed space is formed inside the gap, and the flow cannot enter or exit the area, thereby achieving no flow leakage before the moving parts are separated.

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