Construction method of rudder wing structure wake vortex pattern and fluid force prediction model

Abstract

The present invention discloses a method for constructing a rudder wing structure wake vortex pattern and fluid force prediction model. The method includes establishing a two-dimensional rudder wing physical model; clarifying the model's external flow field boundary conditions, determining the grid size, and performing grid division; setting fluid parameters, boundary conditions, and solution parameters, wherein the solution parameters include the turbulence model, solution accuracy, time step, and total number of grids; selecting an optimal turbulence model through comparative analysis, and performing time step independence verification and grid independence check on the selected values; calculating the optimal turbulence model, plotting cloud maps of rudder wing wake vortex shedding and fluid force coefficient curves under multiple different conditions, analyzing the wake vortex shedding structure, defining the vortex shedding pattern of the wake vortex structure, calculating the root mean square value of the lift and drag coefficient at different incoming flow velocities and angles of attack, and establishing a rudder wing wake vortex shedding pattern prediction model and a fluid force prediction model. The method can quickly predict the rudder wing wake vortex shedding pattern and fluid force magnitude at different incoming flow velocities and angles of attack.

Description

Technical Field

[0001] The present invention relates to the technical field of rudder wing structure model prediction, and in particular to a method for constructing a rudder wing structure wake vortex pattern and fluid force prediction model. Background Art

[0002] When fluid flows around a rudder, a slight difference in fluid velocity on either side of the rudder creates a pressure differential on both sides of the rudder's tail, causing the rudder to shed a pair of periodic, linear vortices with opposite rotational directions. Different incoming flow velocities and rudder angles of attack affect the frequency and intensity of rudder wake vortex shedding. Currently, research on rudder wake vortex shedding and fluid force prediction is limited and complex. To rapidly predict complex rudder wake vortex shedding and fluid force magnitude under varying incoming flow velocities and angles of attack, a method for constructing a rudder wake vortex pattern and fluid force prediction model is needed. Summary of the Invention

[0003] The main purpose of the present invention is to propose a method for constructing a rudder wing structure wake vortex pattern and fluid force prediction model. By establishing a two-dimensional rudder wing physical model, then comparing and analyzing the selected turbulence model, time step value and grid independence, and analyzing the laws of rudder wing wake vortex shedding and lift and drag coefficients under different working conditions through simulation calculation, the model prediction of rudder wing structure wake vortex shedding and fluid force (including lift and drag) is finally obtained, so as to quickly predict the rudder wing wake vortex shedding pattern and fluid force size under different incoming flow velocities and different attack angles.

[0004] The technical solution adopted in the present invention is:

[0005] A method for constructing a rudder wing structure wake vortex pattern and fluid force prediction model, comprising:

[0006] S1. Establishing a two-dimensional rudder wing physical model to be calculated;

[0007] S2. Define the external flow field boundary conditions of the calculation model, determine the grid size and perform grid division; generate a grid file and import the grid into the fluid calculation software;

[0008] S3. Setting fluid parameters, boundary conditions, and solution parameters in the fluid calculation software. The solution parameters include turbulence model, solution accuracy, time step, and total number of grids. To ensure the accuracy of the calculation results, multiple different turbulence models are set.

[0009] S4. Solve the flow field, draw the vortex shedding cloud diagram of the rudder wing and the lift and drag coefficient curve of the rudder wing under different turbulence models, and select the most suitable turbulence model through comparative analysis;

[0010] S5. Perform time step independence verification and grid independence check on the selected time step and total number of grids, respectively. If the results meet the calculation requirements, proceed to the next step of calculation; otherwise, return to step S3 and select an appropriate time step or total number of grids to recalculate;

[0011] S6. Calculate the vortex shedding data and lift-drag coefficient data of the rudder wing at different incoming flow velocities and different angles of attack in the fluid calculation software, and draw a vortex shedding cloud diagram and a lift-drag coefficient curve diagram of the rudder wing;

[0012] S7. In the wake vortex shedding cloud map, a wake vortex shedding pattern is defined based on the wake vortex shedding structure of the rudder at different attack angles at various incoming flow velocities. The wake vortex shedding pattern of the rudder at different attack angles at various incoming flow velocities is synthesized to establish a rudder wake vortex shedding prediction model with the attack angle as the x-axis and the incoming flow velocity as the y-axis.

[0013] The lift and drag coefficients of a stable wake of the rudder at different attack angles at various incoming flow velocities were selected, the root mean square values ​​of the lift and drag coefficients at various incoming flow velocities were calculated, and a fluid force prediction model was established with the attack angle as the x-axis and the root mean square value of the lift and drag coefficient as the y-axis.

[0014] In the above scheme, ICEM CFD software is used to establish a two-dimensional rudder wing physical model to be calculated and to divide the mesh; a rudder wing with a chord length of b is placed in the incoming flow, and its surface is set as a no-slip wall; the left side of the rudder wing is the incoming flow boundary, the upper and lower boundaries of the flow field are symmetrical walls, and the right side of the rudder wing is the outlet boundary; the body-fitting mesh part is generated using the "O-block" strategy in the ICEM software, and the outer flow field area adopts a quadrilateral structured mesh setting.

[0015] In the above scheme, in step S3, four turbulence models are selected, namely the LES model, the DES model, the Realizable ke model and the SST k-Ω model, and the boundary conditions set for each turbulence model are the same.

[0016] In the above scheme, in step S4, a curve diagram of the change of the lift and drag coefficient over time under different turbulence models is obtained by calculation, and the change of the lift and drag coefficient curves of each turbulence model is compared and analyzed, and a turbulence model with obvious periodic changes in the lift and drag coefficient is selected; then, a cloud diagram of the rudder vortex shedding of the turbulence model is calculated and drawn, and the vortex shedding pattern is compared and analyzed, and the vortex with regular and alternating arrangement at the wake shedding point is selected as the most suitable turbulence model.

[0017] In the above scheme, in step S5, the time step independence of the selected time step is verified. The specific method is: multiple time steps under the same incoming flow velocity and angle of attack are selected for verification, and the vortex shedding frequency of the rudder at each time step is extracted. If the vortex shedding frequency shows a stable trend, the calculation requirements are met.

[0018] In the above scheme, in step S5, a grid independence check is performed on the total number of grids. The specific method is: calculations are performed using multiple rudder wing models with the same total number of grids under the same incoming flow velocity and angle of attack, and the relative errors between the Strouhal numbers St or the drag mean Cd of different rudder wing grid models are analyzed. If the relative errors between the results of adjacent total number of grids are within 4%, the calculation requirements are met.

[0019] In the above solution, in step S6, the vortex shedding data is plotted using Tecplot software to plot vortex shedding cloud diagrams at different incoming flow velocities at different angles of attack.

[0020] In the above solution, in step S6, Origin software is used to draw a lift-drag coefficient curve graph for the lift-drag coefficient data.

[0021] In the above scheme, in step S7, the defined wake vortex shedding modes include 2S mode, 2S+U mode, U+2S mode, T+S mode and 2P mode; the 2S mode is a wake flow that presents a periodic, alternating positive and negative vortex structure; the 2S+U mode is a wake flow that first alternates between positive and negative vortices, and as the vortices continue to develop, it finally transforms into a stable wake structure; the U+2S mode is a wake flow that first maintains a stable wake structure, and then alternates between positive and negative vortex structures; the T+S mode is a wake flow that sheds three vortices on the upper side of the rudder, which are respectively negative positive and negative vortices, and then an alternating positive and negative vortex structure appears; the 2P mode is a wake flow that sheds two pairs of positive and negative vortices on the upper side of the rudder.

[0022] The beneficial effects produced by the present invention are:

[0023] The present invention is based on the commercial software Ansys / Fluent, and takes the wake vortex shedding and fluid force size of the rudder wing at different incoming flow velocities and different angles of attack as the research background, and constructs the wake vortex shedding pattern and fluid force prediction model of the rudder wing. A more suitable turbulence model is selected through comparative analysis, and the selected numerical value is verified for time step independence and grid independence to ensure the accuracy and reliability of the subsequent calculation results. Then the most suitable turbulence model is calculated, and cloud maps of the wake vortex shedding and fluid force coefficient curves of the rudder wing under multiple different conditions are drawn, the wake vortex shedding structure under different conditions is analyzed, and the vortex shedding pattern is defined for the wake vortex structure. Then, the root mean square value of the lift and drag coefficient at different incoming flow velocities is calculated, and finally, the wake vortex shedding pattern prediction model and fluid force prediction model of the rudder wing are established. Compared with the existing technology, the method for constructing a rudder wing structure wake vortex pattern and fluid force prediction model provided by the present invention can quickly and accurately predict the rudder wing wake vortex shedding and lift and drag coefficient under different incoming flow velocities and different attack angles, providing a guiding basis for the analysis of the rudder wing structure's wake vortex shedding and fluid force size under different conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 Flowchart of the method for constructing the rudder wing structure wake vortex pattern and fluid force prediction model of the present invention;

[0026] Figure 2 Schematic diagram of the calculation domain and boundary conditions of a two-dimensional rudder wing in an embodiment of the present invention;

[0027] Figure 3 This is a cloud diagram of the vortex shedding of the rudder blade at different attack angles and different incoming flow velocities in an embodiment of the present invention;

[0028] Figure 4 Graph showing lift and drag coefficients of the rudder wing at different flow velocities at different attack angles in an embodiment of the present invention;

[0029] Figure 5 The vortex shedding modes of the rudder blade at different attack angles when U=1m / s in an embodiment of the present invention are shown;

[0030] Figure 6 This is a diagram showing the prediction of the vortex shedding mode of the rudder blade at different attack angles and different incoming flow velocities in an embodiment of the present invention;

[0031] Figure 7 This is a prediction diagram of the lift and drag coefficient root mean square of the rudder wing at different attack angles and different incoming flow velocities in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0033] It should be noted that the illustrations provided in the embodiments of the present invention are only schematic illustrations of the basic concept of the present invention. Therefore, the drawings only show components related to the present invention and are not drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component can be changed at will, and the component layout type may also be more complicated.

[0034] In the present invention, it should also be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" and the like are used to indicate positions or locations based on those shown in the accompanying drawings. These terms are intended solely to facilitate the description of the present application and to simplify the description. They are not intended to indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting the present application. Furthermore, the terms "first" and "second" are used solely for descriptive and distinguishing purposes and should not be construed as indicating or implying relative importance.

[0035] like Figure 1 The figure shows a flow chart of the method for constructing the vortex pattern and fluid force prediction model of the rudder wing structure proposed by the present invention. The specific implementation method of the present invention is described below using the two-dimensional flow around the rudder wing in a turbulent flow field as an example, which includes the following steps:

[0036] S1. Establish a two-dimensional rudder-wing physical model. Use ICEM CFD software to establish a two-dimensional numerical model of the rudder wing at different attack angles α (0°, 0.5°, 1°, 1.5°, 2°), namely, the near-wall rudder-wing flow model.

[0037] S2. Set the external flow field boundary conditions: Figure 2 As shown, the rudder surface is set as a no-slip wall. The left side of the rudder (Inlet) serves as the incoming flow boundary, with a radius of 14b, where b is the chord length of the rudder. The upper and lower flow boundaries (Wall) are symmetrical walls, each spaced 14b apart from the rudder. The right side of the rudder (Outlet) serves as the outlet boundary, spaced 21b apart from the rudder. The body-fitting mesh is generated using the "O-block" strategy in ICEM software. A quadrilateral structured mesh is used in the outer flow region. The mesh size is determined and meshing is performed. A boundary layer mesh is generated on the rudder wall. The generated mesh file is then imported into Fluent software.

[0038] S3. In Fluent software, set each boundary condition as follows: the left boundary condition is velocity inlet (velocity-inlet); the right boundary condition is pressure outlet (pressure-out); the upper and lower side (wall) boundary conditions are symmetry boundaries (symmetry); the rudder surface is a no-slip wall (no-slip wall). The fluid medium in the flow field is water. At room temperature, the density of water is ρ = 998.2 kg / m3, and the kinematic viscosity of water is υ = 1.004 × 10-6 m2 / s. In order to ensure the accuracy of the calculation results, a more appropriate turbulence model needs to be selected. This embodiment sets four turbulence models, namely LES model, DES model, Realizable ke model and SST k-Ω model. The boundary conditions set for each turbulence model are the same. The solution accuracy is set to 0.00001; the time step is set to 0.0005s; and the total number of grids is set to 150,000.

[0039] S4. In order to obtain a more appropriate turbulence model, a comparative analysis is conducted by numerical simulation calculations of four models, namely, the LES model, the DES model, the Realizable ke model, and the SST k-Ω model. The incoming flow velocity of the four turbulence models is uniformly set to U=1m / s, and the angle of attack is set to α=0°. In this embodiment, the lift coefficient curve time history diagrams of different turbulence models are first calculated. It is found that the lift coefficient calculated by the rudder using the SST k-Ω model and the Realizable ke model does not change significantly, so it does not meet the calculation requirements. When the DES model and the LES model are used for calculation, the lift coefficient has obvious periodic changes. Then, the wake vortex shedding cloud diagrams of the DES model and the LES model are calculated. It is found that the DES model sheds regular, alternating vortices in the wake, while the LES model sheds complex, fine vortices. Therefore, the DES model is the most suitable turbulence model.

[0040] S5. In order to determine a more appropriate time step, the incoming flow velocity is set to 1m / s, the angle of attack is set to α=0°, and four time steps of 0.005s, 0.001s, 0.0005s, and 0.0002s are selected for verification. The vortex shedding frequency of the rudder at each time step is extracted for comparison. The results show that starting from the time step of 0.001s, the vortex shedding frequency gradually becomes stable. To ensure the accuracy of the results, 0.0005s is finally selected as the time step for this calculation.

[0041] In order to verify the rationality of the total number of grids, multiple first-layer grid heights were selected near the first-layer boundary layer grid height of 0.02mm, namely (0.005mm, 0.01mm, 0.02mm, 0.03mm, 0.035mm), thus obtaining rudder wing grid models with different total number of grids. The incoming flow velocity was set to 1m / s and the angle of attack was set to α=0°. The difference between the Strouhal number St or the drag mean Cd of different rudder wing grid models was calculated and analyzed. The relative errors of the Strouhal number St and the drag mean Cd between the adjacent grid total number results of 0.02mm and 0.03mm in the first-layer boundary layer grid were 1% and 2%, respectively. Therefore, the rudder wing grid model with a first-layer boundary layer grid height of 0.02mm and a total number of 150,000 grids meets the calculation requirements.

[0042] S6. In order to study the vortex shedding of the rudder wake under different incoming flow velocities U and different angles of attack α, this embodiment sets four incoming flow velocities U (0.5m / s, 1m / s, 1.5m / s, 2m / s) and five angles of attack α (0°, 0.5°, 1°, 1.5°, 2°) for calculation. Then, based on the vortex shedding data calculated for the rudder under various conditions, the vortex shedding cloud diagram of each incoming flow velocity at different angles of attack is drawn using Tecplot software, as shown in FIG. Figure 3 As shown in the tail vortex shedding cloud map, the blue vortex is a positive vortex and the red vortex is a negative vortex.

[0043] In order to study the magnitude of the fluid force on the rudder under different incoming flow velocities U and different angles of attack α, the lift and drag coefficient curves were drawn using Origin software based on the lift and drag coefficient data obtained under various conditions, as shown in Figure 2. Figure 4 As shown in the figure, Cl is the lift coefficient and Cd is the drag coefficient.

[0044] S7. In the wake vortex shedding cloud diagram, the wake vortex shedding pattern is defined according to the wake vortex shedding structure of the rudder blade at different incoming flow speeds and different angles of attack, such as Figure 5 As shown in the figure, the blue is the positive vortex, the red is the negative vortex, and the defined wake vortex shedding modes include 2S mode, 2S+U mode, U+2S mode, T+S mode and 2P mode. Among them: 2S mode is a wake flow that presents a positive and negative vortex structure that sheds periodically and alternately; 2S+U mode is a wake flow that first alternates between positive and negative vortices, and as the vortex continues to develop, it finally transforms into a stable wake structure; U+2S mode is a wake flow that first maintains a stable wake structure, and then alternates between positive and negative vortex structures; T+S mode is a wake flow that sheds three vortices on the upper side of the rudder, which are negative positive and negative vortices, and then an alternating positive and negative vortex structure appears; 2P mode is a wake flow that sheds two pairs of positive and negative vortices on the upper side of the rudder. Based on the wake vortex shedding modes of the rudder at different angles of attack at various incoming flow velocities, a rudder wake vortex shedding prediction model is established with the angle of attack as the x-axis and the incoming flow velocity as the y-axis, as shown below: Figure 6As shown in Figure 1, the wake vortex shedding pattern of the rudder wing is predicted when the incoming flow velocity is 0-2 m / s and the attack angle is 0-20°.

[0045] The lift and drag coefficients of a stable wake of the rudder wing at different attack angles at various incoming flow speeds are selected, the root mean square value of the lift and drag coefficients at various incoming flow speeds is calculated, and a fluid force prediction model is established with the attack angle as the x-axis and the root mean square value of the lift and drag coefficient as the y-axis, as shown in the following example: Figure 7 As shown in the figure, Cl RMS is the root mean square of the lift coefficient, Cd RMS The root mean square value of the lift and drag coefficient of the rudder is predicted when the incoming flow velocity is 0-2m / s and the angle of attack is 0-20°.

[0046] In this embodiment, a comparative analysis is performed on four turbulence models. To ensure the accuracy and reliability of the calculation results, the time step and the total number of grids are verified and checked. Then, a more appropriate turbulence model is selected from the four turbulence models for calculation. Cloud maps of rudder vortex shedding and fluid force coefficient curves under multiple different conditions are plotted. The vortex shedding structure under different conditions is analyzed, and the vortex shedding pattern of the vortex structure is defined. Then, the root mean square value of the lift and drag coefficient of each incoming flow velocity at different angles of attack is calculated. Finally, a rudder vortex shedding pattern prediction model and a fluid force prediction model are established.

[0047] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, or two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0048] The size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0049] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all such improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A method for constructing a rudder wing structure wake vortex pattern and fluid force prediction model, characterized in that: include: S1. Establishing a two-dimensional rudder wing physical model to be calculated; S2. Define the external flow field boundary conditions of the calculation model, determine the grid size and perform grid division; Generate a grid file and import the grid into the fluid calculation software; S3. Setting fluid parameters, boundary conditions, and solution parameters in the fluid calculation software. The solution parameters include turbulence model, solution accuracy, time step, and total number of grids. To ensure the accuracy of the calculation results, multiple different turbulence models are set. S4. Solve the flow field, draw cloud maps of rudder wing wake vortex shedding and curve maps of rudder wing lift and drag coefficient under different turbulence models, compare and analyze to select the most suitable turbulence model, the specific method is: obtain curve maps of lift and drag coefficient variation over time under different turbulence models by calculation, compare and analyze the variation of lift and drag coefficient curves of various turbulence models, select a turbulence model with obvious periodic variation of lift and drag coefficient, then calculate and draw cloud maps of rudder wing wake vortex shedding for the turbulence model, compare and analyze the wake vortex shedding patterns, and select the one with regular and alternating arrangement of vortices at the wake shedding as the most suitable turbulence model; S5. Perform time step independence verification and grid independence check on the selected time step and total number of grids, respectively. If the results meet the calculation requirements, proceed to the next step of calculation; otherwise, return to step S3 and select an appropriate time step or total number of grids to recalculate; S6. Calculate the vortex shedding data and lift-drag coefficient data of the rudder wing at different incoming flow velocities and different angles of attack in the fluid calculation software, and draw a vortex shedding cloud diagram and a lift-drag coefficient curve diagram of the rudder wing; S7. In the wake vortex shedding cloud map, a wake vortex shedding pattern is defined based on the wake vortex shedding structure of the rudder at different attack angles at various incoming flow velocities. The wake vortex shedding pattern of the rudder at different attack angles at various incoming flow velocities is synthesized to establish a rudder wake vortex shedding prediction model with the attack angle as the x-axis and the incoming flow velocity as the y-axis. The lift and drag coefficients of a stable wake of the rudder at different attack angles at various incoming flow velocities were selected, the root mean square values ​​of the lift and drag coefficients at various incoming flow velocities were calculated, and a fluid force prediction model was established with the attack angle as the x-axis and the root mean square value of the lift and drag coefficient as the y-axis.

2. The method for constructing a rudder wing structure wake vortex pattern and fluid force prediction model according to claim 1, characterized in that: The ICEM CFD software was used to establish a two-dimensional rudder wing physical model to be calculated and to divide the mesh. A rudder wing with a chord length of b was placed in the incoming flow, and its surface was set as a no-slip wall. The left side of the rudder wing was the incoming flow boundary, the upper and lower boundaries of the flow field were symmetrical walls, and the right side of the rudder wing was the outlet boundary. The body-fitting mesh was generated using the O-type segmentation strategy in the ICEM software, and the outer flow field region was set with a quadrilateral structured mesh.

3. The method for constructing a rudder wing structure wake vortex pattern and fluid force prediction model according to claim 1, characterized in that: In step S3, four turbulence models are selected, namely the LES model, the DES model, the Realizable ke model and the SSTk-Ω model, and the boundary conditions set for each turbulence model are the same.

4. The method for constructing a rudder wing structure wake vortex pattern and fluid force prediction model according to claim 1, characterized in that: In step S5, the time step independence of the selected time step is verified. The specific method is: multiple time steps under the same incoming flow velocity and angle of attack are selected for verification, and the vortex shedding frequency of the rudder at each time step is extracted. If the vortex shedding frequency shows a stable trend, the calculation requirements are met.

5. The method for constructing a rudder wing structure wake vortex pattern and fluid force prediction model according to claim 1, characterized in that: In step S5, a grid independence check is performed on the total number of grids. The specific method is: calculations are performed using multiple rudder models with the same total number of grids under the same incoming flow velocity and angle of attack, and the relative errors between the Strouhal numbers St or the drag mean Cd of different rudder grid models are analyzed. If the relative errors between the results of adjacent grid numbers are within 4%, the calculation requirements are met.

6. The method for constructing a rudder wing structure wake vortex pattern and fluid force prediction model according to claim 1, characterized in that: In step S6, the vortex shedding data is plotted using Tecplot software to generate vortex shedding cloud diagrams at different incoming flow velocities and angles of attack.

7. The method for constructing a rudder wing structure wake vortex pattern and fluid force prediction model according to claim 1, characterized in that: In step S6, a lift-drag coefficient curve is drawn based on the lift-drag coefficient data using Origin software.

8. The method for constructing a rudder wing structure wake vortex pattern and fluid force prediction model according to claim 1, characterized in that: In step S7, the defined wake vortex shedding modes include 2S mode, 2S+U mode, U+2S mode, T+S mode and 2P mode; the 2S mode is a wake flow that presents a periodic, alternating positive and negative vortex structure; the 2S+U mode is a wake flow that first alternates between positive and negative vortices, and as the vortices continue to develop, it finally transforms into a stable wake structure; the U+2S mode is a wake flow that first maintains a stable wake structure for a period of time, and then alternates between positive and negative vortex structures; the T+S mode is a wake flow that sheds three vortices on the upper side of the rudder wing, which are respectively negative positive and negative vortices, and then an alternating positive and negative vortex structure appears; the 2P mode is a wake flow that sheds two pairs of positive and negative vortices on the upper side of the rudder wing.

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