Standard cfd calculation method for aerodynamic characteristics of transport helicopter fuselage

Abstract

The application belongs to the field of helicopter aerodynamic design, and relates to a standardization CFD calculation method for fuselage aerodynamic characteristics of a transport type helicopter. The method measures the upper reverse angle of the inclined wall plate of the transition section between the fuselage and the tail beam, then sets the grid parameters of the fuselage surface and the fluid domain according to the standardization method, then performs grid division and imports into the solver, sets the corresponding fuselage calculation model size according to the measured upper reverse angle, and performs fuselage aerodynamic characteristic flow field solving calculation to obtain the fuselage aerodynamic characteristic result. The calculation method can set the size of the fuselage surface grid and the fluid domain space grid according to the standardization method, and can save 18% to 25% of the time in the whole CFD calculation process. In the whole helicopter development process, the standardization fuselage CFD calculation method can save 4% to 5% of the time and reduce 1.5% to 2% of the development cost in the whole helicopter type development cycle.

Description

Technical Field

[0001] This invention belongs to the field of helicopter aerodynamic design and relates to a standardized CFD calculation method for the aerodynamic characteristics of a transport helicopter fuselage. Background Technology

[0002] In recent years, CFD calculation methods have been increasingly widely used in the calculation of helicopter fuselage aerodynamic characteristics, accelerating the development of helicopter models, saving development time and reducing development costs to some extent. Currently, in the CFD calculation process of helicopter fuselage aerodynamic characteristics, after receiving the helicopter fuselage shape, technicians first perform geometric model repair, filling in surface holes and other defects to form a closed geometry. Then, they set the surface mesh size for each component, including the fuselage, and simultaneously set the fluid domain space volume mesh size. Next, they perform mesh generation, and finally import the results into the solver for flow field calculation to obtain the fuselage aerodynamic characteristics calculation results. Literature such as "Research on the Influencing Factors of DLR-F6 Shape Calculation Mesh and Turbulence Model" (Sun Yue et al., 2017) analyzes the influence of mesh type and turbulence model on the CFD calculation results of aircraft fuselage aerodynamic characteristics for standard aircraft calculation models. Literature such as "Research on Flow Control and Drag Reduction Calculation of Helicopter Tail" (Mao Xu et al., 2019) and "Research on Aerodynamic Shape Design of Long-Endurance Unmanned Helicopters" (Li Jie, 2014) have performed CFD calculations on the aerodynamic characteristics of helicopter fuselages, but they have not proposed a standardized CFD calculation process and method for fuselage aerodynamic characteristics. Therefore, there are significant differences among technicians in the CFD calculation of helicopter fuselage aerodynamic characteristics regarding the parameter settings of surface meshes and spatial volume meshes for fuselage components, mesh generation and transformation, and the selection of calculation model dimensions. This is largely influenced by individual technicians' subjective factors, and a unified method for mesh generation and calculation model size selection has not been established. Furthermore, in actual calculations, technicians tend to perform detailed mesh generation on the surfaces and spatial volume of fuselage components, resulting in a large number of meshes in current fuselage aerodynamic characteristic CFD calculations, leading to slow CFD calculation speeds and high computational resource consumption. Summary of the Invention

[0003] The purpose of this invention is to effectively reduce the impact of human factors on the CFD calculation results of helicopter fuselage aerodynamic characteristics, while improving the CFD calculation speed of helicopter fuselage aerodynamic characteristics to a certain extent. This invention designs a standard CFD calculation method for the aerodynamic characteristics of transport helicopter fuselage.

[0004] Technical Solution: A standard CFD calculation method for the aerodynamic characteristics of a transport helicopter fuselage. The method involves measuring the upward reflection angle of the inclined wall panel at the transition section between the fuselage and the tail boom, then setting the mesh parameters for the fuselage surface and the fluid domain, followed by mesh generation and importing the mesh into the solver. Based on the measured upward reflection angle, the corresponding fuselage calculation model size is set; and the aerodynamic characteristics flow field of the fuselage is calculated to obtain the aerodynamic characteristics results.

[0005] Furthermore, select the midpoint between the front and rear of the transition section between the fuselage and the tail boom, draw a tangent line tangent to the surface of the transition section, and then measure the angle θ between the tangent line and the horizontal line to obtain the upper angle of the inclined wall of the transition section between the fuselage and the tail boom.

[0006] Furthermore, when setting the size of the computational model, based on the measured angle θ value, if the measured angle θ is greater than 15°, the next step is to perform flow field calculation; if the measured angle θ is equal to or less than 15°, all the obtained polyhedral meshes are enlarged by 18 to 22 times, and then the flow field calculation is performed.

[0007] Furthermore, when the measured included angle θ is less than 15°, the smaller the included angle, the greater the magnification.

[0008] Furthermore, when measuring the upper reversal angle, select the midpoint between the front and rear of the transition section between the fuselage and the tail boom, draw a tangent line tangent to the surface of the transition section, and then measure the angle θ between the tangent line and the horizontal line, which is the upper reversal angle.

[0009] Furthermore, the mesh generation process is as follows: First, the scale of the fuselage is selected; then, the surface mesh generation parameters are set for the scaled-down fuselage surface, and the volume mesh generation parameters are set for the defined space region between the fuselage and the far field; based on the set surface and volume mesh generation parameters, the octree method is used to generate tetrahedral meshes for the fluid domain around the fuselage.

[0010] Furthermore, during tetrahedral mesh generation, a cube is first used to cover the entire computational domain. Then, the cube obtained in the previous round is continuously subdivided into eight smaller cubes until the corresponding spatial volume mesh and surface mesh size requirements are met. Finally, each cube is divided into tetrahedrons to obtain a tetrahedral mesh.

[0011] Furthermore, the tetrahedral mesh is further converted into a polyhedral mesh. The resulting tetrahedral mesh is then imported into the solver and converted into a polyhedral mesh. The method involves decomposing the non-hexahedral mesh into multiple sub-regions; each sub-region is associated with a node of the original mesh; these sub-regions combine around the original node to form polygons; the set of all sub-regions sharing a special node constitutes each polyhedral mesh.

[0012] Furthermore, when calculating the aerodynamic characteristics of the fuselage, the flow field is first solved at 0° angle of attack and 0° sideslip angle, which yields convergence results relatively quickly. Afterward, the angle of attack or sideslip angle is changed by approximately 2° each time.

[0013] Furthermore, the aerodynamic characteristics of the fuselage include at least the drag coefficient, lift coefficient, lateral force coefficient, pitching moment coefficient, rolling moment coefficient, and yaw moment coefficient.

[0014] Advantages and beneficial technical effects of this invention: Using the standardized CFD calculation method for fuselage aerodynamic characteristics, there is no need to spend time specifically verifying the accuracy and reliability of the CFD calculations, saving 9% to 12% of the total CFD calculation time. Due to the standardized method for setting the dimensions of the fuselage surface mesh and fluid domain space mesh, especially the mesh generation and transformation approach used in the solution process, 18% to 25% of the total CFD calculation time can be saved. Throughout the helicopter development process, using the standardized fuselage CFD calculation method can save 4% to 5% of the development time and reduce development costs by 1.5% to 2%. Attached Figure Description

[0015] Figure 1 This is a flowchart of the present invention;

[0016] Figure 2 This is a diagram showing the upward angle.

[0017] Figure 3 This is a schematic diagram of the mesh division of components such as the fuselage from the left-side view.

[0018] Figure 4 A schematic diagram of the mesh division of the fuselage and other components from a backward tilting view;

[0019] Figure 5 A schematic diagram of the mesh division on the main rotor hub surface of a helicopter;

[0020] Figure 6 A schematic diagram of the grid division for a helicopter's horizontal stabilizer;

[0021] Figure 7 A schematic diagram of the grid division for the helicopter's vertical tail surface;

[0022] Figure 8 A schematic diagram showing the grid division of the helicopter tail rotor hub and tail rotor blades. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] The present invention proposes a standard CFD calculation method for the aerodynamic characteristics of a transport helicopter fuselage, the specific implementation process of which includes the following steps;

[0025] Step 1: Measure the upward angle of the inclined wall panel of the transition section between the fuselage and the tail boom. Select the midpoint between the front and rear ends of the transition section between the fuselage and the tail boom, and draw a tangent line tangent to the surface of the transition section. Then measure the angle θ between the tangent line and the horizontal line; this is the upward angle of the inclined wall panel of the transition section between the fuselage and the tail boom. Figure 1 As shown, the upward reversal angle of the inclined wall panel at the transition section between the fuselage and the tail boom can be easily obtained by drawing two straight lines and then measuring them.

[0026] Step 2: Select the fuselage scaling ratio. First, measure the total length of the helicopter fuselage, that is, the horizontal length from the nose to the tail. Then, shorten the fuselage length to about 2 meters, within the range of 1.8 meters to 2.3 meters. Divide the fuselage length by 2 to obtain the initial scaling ratio. Then, round the scaling ratio to one decimal place, close to 0 or 0.5. For example, if the result is 5.2, then take the scaling ratio as 5; if the result is 6.7, then take the scaling ratio as 6.5. This step ensures that the CFD calculation of the fuselage aerodynamic characteristics yields a standardized calculation model size, providing a better foundation for subsequent comparison of calculation results.

[0027] Step 3: Select the computational domain for the fuselage aerodynamic characteristics. Draw a sphere with the geometric center of the helicopter fuselage as the origin. The radius of the sphere is 30-40 times the fuselage length. The computational domain outside the fuselage is a sphere. At any angle of attack and sideslip angle, the distance from the far-field boundary to the fuselage surface is essentially the same, which can effectively eliminate the influence of the far-field boundary on the calculation results.

[0028] Step 4: Set surface and volume mesh generation parameters. Set the surface mesh generation parameters for the scaled-down fuselage surface. The general principle for surface mesh setting is: the resulting mesh surface should have a shape that is basically consistent with the original aerodynamic surface, and the surface mesh size should be selected as large as possible to reduce the number of meshes obtained later. Selecting standardized surface mesh generation parameters for each fuselage component can effectively reduce the interference of human factors during mesh generation, laying the foundation for subsequent standardized CFD calculations of the fuselage aerodynamic characteristics.

[0029] The surface grid parameter settings for the nose, fuselage, main rotor hub, landing gear, transition section, tail boom, horizontal stabilizer, and vertical stabilizer are as follows: Figure 3-8 As shown, the specific settings and corresponding parameters are shown in Tables 1-5.

[0030] Table 1. Parameter Setting Table for Mesh Generation of Components such as the Fuselage

[0031] Component Name Surface mesh size machine head 18-22 fuselage belly and left and right sides 36-44 Fuselage and tail boom transition section 27-33 Main reducer fairing (except trailing edge) 30-38 Trailing edge of main reducer fairing 20-26 Main propeller hub tower 28-36 Tail boom 25-31

[0032] Table 2. Main propeller hub surface mesh generation parameter settings.

[0033] Component Name Surface mesh size Hub fairing 13-17 propeller hub center component 9-13 propeller hub support 8-12 upper and lower surfaces of the blade root 11-15 Leading edge of blade root 5-8 blade root end face 7-11 Trailing edge of blade root 5-8 propeller hub shaft 7-11

[0034] Table 3. Parameter settings for horizontal tail plane mesh generation

[0035] Component Name Surface mesh size Flat tail leading edge 6-8 upper and lower surfaces of the flat tail 20-24 Tail tail trailing edge 5-7 Left and right end faces of the flat tail 9-13 Flat tail edge 4-6

[0036] Table 4. Mesh Generation Parameter Settings for Vertical Tail Surface

[0037] Component Name Surface mesh size Leading edge of the tail 8-10 Left and right sides of the vertical tail 20-24 Trailing edge of tail 7-9 Top end face of the vertical tail 13-15 Tail edge 6-8

[0038] Table 5. Parameter settings for tail rotor hub and tail rotor blade mesh generation.

[0039] Component Name Surface mesh size Tail rotor shaft 6-10 Tail rotor hub 6-10 Tail rotor hub tie rod 4-7 Tail rotor blade support arm 4-7 Tail rotor blade surface 6-10 Tail blade leading edge 3-5 Tail rotor blade end face 2-3 Trailing edge of tail rotor blade 2-2.5

[0040] Step 5: Set the volumetric meshing parameters. For the spatial region between the fuselage and the far field defined in Step 3, the volumetric meshing parameters are set to 20000-30000, and the growth rate between adjacent spatial meshes is set to 0. Using standardized parameter settings for the fluid computational domain volumetric meshing can effectively reduce interference from human factors during the meshing process and control the number of tetrahedral meshes obtained later.

[0041] Step 6: Generate the tetrahedral mesh. Following the parameter settings in Steps 4 and 5, use the octree method to generate a tetrahedral mesh for the fluid domain surrounding the fuselage. This method first covers the entire computational domain with a cube, then continuously subdivides the previously obtained cube into eight smaller cubes until the required spatial and surface mesh sizes are met. Finally, each cube is divided into tetrahedrons, resulting in the tetrahedral mesh. Using the octree method to generate the tetrahedral mesh can adapt to complex object surface shapes and yields relatively good meshes even for components with complex surfaces such as propeller hubs.

[0042] Step 7: Convert to a polyhedral mesh. Import the resulting tetrahedral mesh into the solver, and then convert it to a polyhedral mesh. This is done by decomposing the non-hexahedral mesh into multiple sub-regions. Each sub-region is associated with a node in the original mesh. These sub-regions combine around the original node to form polygons. The set of all sub-regions sharing a single node constitutes each polyhedral mesh. Converting to a polyhedral mesh reduces the number of meshes, speeds up computation, and improves the accuracy of the results due to increased information exchange between meshes.

[0043] Step 8: Set the dimensions of the computational model. Based on the included angle θ value measured in Step 1, if the measured included angle θ is equal to or greater than 15°, proceed to the next step for flow field calculation. If the measured included angle θ is less than 15°, enlarge all obtained polyhedral meshes (i.e., all meshes of the fuselage surface, fluid domain, and far field) by a factor of 20 before performing flow field calculation. Enlarging all obtained polyhedral meshes is a relatively simple operation. This ensures that the turbulence intensity of the flow field near the fuselage is basically the same, thus obtaining more consistent CFD calculation results for the fuselage aerodynamic characteristics.

[0044] Step 9: Calculate the aerodynamic characteristics of the fuselage flow field. In the solver, set the turbulence mode for the flow field solution to SA turbulence mode, the far-field boundary condition to pressure, the fuselage surface boundary condition to no-slip wall boundary condition, the inflow velocity to 60 m / s, and the temperature to 288 K. Then perform the flow field calculation. First, solve the flow field at 0° angle of attack and 0° sideslip. Then, keeping the 0° sideslip constant, solve the flow field at angles of attack from -2° to -24° (set the minimum angle of attack value as needed), with a 2° interval between each step. Then, solve the flow field at angles of attack from 2° to 28° (set the maximum angle of attack value as needed), with a 2° interval between each step. The sideslip angle is then gradually decreased from 0° to -32° (the minimum sideslip angle value is set as needed). For each sideslip angle state, the angle of attack from 0° to -24° (the minimum angle of attack value is set as needed) is solved sequentially, with a 2° interval between each step. Then, the angle of attack from 2° to 28° (the maximum angle of attack value is set as needed) is solved, with a 2° interval between each step. Finally, the sideslip angle is changed from 2° to 32° (the maximum sideslip angle value is set as needed), with the angle of attack variation range and steps remaining the same. After each step of the calculation is completed, aerodynamic characteristics such as fuselage drag coefficient, lift coefficient, lateral force coefficient, pitch moment coefficient, roll moment coefficient, and yaw moment coefficient are obtained.

[0045] In the above implementation process, the flow field is first solved at 0° angle of attack and 0° sideslip angle, which can yield convergence results relatively quickly. Afterwards, the angle of attack or sideslip angle is changed by approximately 2° each time, and the difference between the two calculations is relatively small, allowing for relatively quick convergence results. This accelerates the entire fuselage aerodynamic characteristic CFD calculation process and saves computation time.

[0046] By adopting the standardized CFD calculation method for fuselage aerodynamic characteristics described above, it is no longer necessary to spend time specifically verifying the accuracy and reliability of the fuselage aerodynamic characteristic CFD calculations, saving 9% to 12% of the time in the entire CFD calculation process. Because the fuselage surface mesh and fluid domain space mesh are sized according to standardized methods, 18% to 25% of the time in the entire CFD calculation process can be saved. Throughout the helicopter development process, adopting the standardized fuselage CFD calculation method can save 4% to 5% of the development time and reduce development costs by 1.5% to 2%.

[0047] The above description is merely a specific embodiment of the present invention, providing a detailed description of the invention. Parts not covered herein are conventional techniques. However, the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A standard CFD calculation method for the aerodynamic characteristics of a transport helicopter fuselage, characterized in that, The method involves measuring the upward reflection angle of the inclined wall plate of the transition section between the fuselage and the tail boom, setting mesh parameters for the fuselage surface and fluid domain, then generating the mesh and importing it into the solver. Based on the measured upward reflection angle, the corresponding fuselage calculation model size is set. The aerodynamic characteristics of the fuselage are then calculated to obtain the aerodynamic characteristics. A tangent line tangent to the surface of the transition section is drawn at the midpoint between the front and rear ends of the transition section between the fuselage and the tail boom. The angle θ between the tangent line and the horizontal line is then measured, which is the upward reflection angle of the inclined wall plate of the transition section between the fuselage and the tail boom. When setting the size of the calculation model, based on the measured angle θ, if the measured angle θ is greater than 15°, the next step is to calculate the flow field. If the measured angle θ is equal to or less than 15°, the entire polyhedral mesh is enlarged by 18 to 22 times before the flow field calculation is performed.

2. The standard CFD calculation method for the aerodynamic characteristics of a transport helicopter fuselage as described in claim 1, characterized in that, When the measured included angle θ is less than 15°, the smaller the included angle, the greater the magnification.

3. The standard CFD calculation method for the aerodynamic characteristics of a transport helicopter fuselage as described in claim 1, characterized in that, The mesh generation process is as follows: First, select the scale of the fuselage; then set the surface mesh generation parameters for the scaled-down fuselage surface, and set the volume mesh generation parameters for the defined space region between the fuselage and the far field; based on the set surface and volume mesh generation parameters, use the octree method to generate tetrahedral meshes for the fluid domain around the fuselage.

4. The standard CFD calculation method for the aerodynamic characteristics of a transport helicopter fuselage as described in claim 3, characterized in that, When generating a tetrahedral mesh, the entire computational domain is first covered by a cube. Then, the cube obtained in the previous round is continuously subdivided into eight smaller cubes until the corresponding spatial volume mesh and surface mesh size requirements are met. Finally, each cube is divided into tetrahedrons to obtain a tetrahedral mesh.

5. The standard CFD calculation method for the aerodynamic characteristics of a transport helicopter fuselage as described in claim 4, characterized in that, After the tetrahedral mesh is generated, it is imported into the solver and further converted into a polyhedral mesh.

6. The standard CFD calculation method for the aerodynamic characteristics of a transport helicopter fuselage as described in claim 5, characterized in that, The transformation method decomposes the non-hexahedral mesh into multiple sub-regions, each of which is associated with a node of the original mesh. These sub-regions combine to form polygons around the original node, and the set of all sub-regions sharing a special node constitutes each polyhedral mesh.

7. The standard CFD calculation method for the aerodynamic characteristics of a transport helicopter fuselage as described in claim 1, characterized in that, When calculating the aerodynamic characteristics of the fuselage flow field, the flow field is first solved at 0° angle of attack and 0° sideslip angle, and the convergence result is obtained relatively quickly; thereafter, the angle of attack or sideslip angle is changed by 2° each time.

8. The standard CFD calculation method for the aerodynamic characteristics of a transport helicopter fuselage as described in claim 1, characterized in that, The results of the fuselage aerodynamic characteristics include at least the drag coefficient, lift coefficient, lateral force coefficient, pitching moment coefficient, rolling moment coefficient, and yaw moment coefficient.

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