Methods for studying the interaction between AUV hull and propeller

Abstract

The present invention discloses a method for studying the interaction between an AUV hull and a propeller, including establishing a three-dimensional model of the AUV hull and the propeller; determining the grid structure, performing grid division and independence verification; selecting a turbulence model and setting boundary conditions; performing numerical simulation and steady-state solution, and post-processing the simulation results; analyzing the interaction law between the AUV hull and the propeller based on the solution results, and drawing research conclusions. First, the method of the present invention is used to carry out numerical simulation on the standard model, and the simulation data is compared with the measured data to verify the reliability of the method; then, based on the method, the independently developed AUV and propeller are studied, and the interaction between the hull and the propeller in direct flow and oblique flow is compared, and the influence of the appendage on the flow field distribution and the hydrodynamic characteristics of the AUV is analyzed, and the wake effect and thrust deduction effect are explored. The research results will be used to guide the design of AUVs and the optimization of the overall layout.

Description

Technical Field

[0001] The invention belongs to the field of ocean engineering and underwater robots, and in particular relates to a method for studying the interaction between an AUV hull and a propeller, and is suitable for hydrodynamic numerical simulation and overall design optimization of underwater vehicles. Background Art

[0002] Autonomous underwater vehicles (AUVs) play an increasingly important role in hydrological data collection, marine environment observation, and military applications. As the most important component of the drive system, the hydrodynamic performance of the propeller deeply affects the maneuverability, endurance, and operating efficiency of the AUV. The interaction between the AUV hull and the propeller affects the hull resistance and propeller thrust. With the development of computational fluid dynamics (CFD) and the improvement of computer performance, numerical simulation and prediction using CFD has become a mainstream method.

[0003] The invention patent with the authorization announcement number CN 112307559 A discloses an AUV shape optimization method based on the improved crow algorithm, which optimizes the AUV shape through fluid calculation, but only considers the AUV hull. The invention patent with the authorization announcement number CN110309573 A discloses a multidisciplinary proxy optimization method for underwater vehicles based on coupled adjointness, which solves the multidisciplinary coupling of shape and fluid dynamics, but also does not study the influence of appendages and propellers.

[0004] There is a strong interaction between the AUV hull and propeller. In the design stage, the optimization of a single component will produce a suboptimal solution, because the interaction between the components determines the actual application effect. Exploring the interaction between the AUV hull and propeller, studying the influence of the appendages on the hydrodynamic characteristics of the AUV, and analyzing the wake and thrust deduction effects are of positive significance to improving the design of the AUV and enhancing the performance of the AUV. Summary of the invention

[0005] Aiming at the shortcomings of traditional numerical methods, the present invention proposes a method for studying the interaction between the AUV hull and the propeller. Based on CFD and ANSYS Workbench, the interaction between the AUV hull and the propeller in direct and oblique flows is numerically simulated to understand the law of interaction between the two, analyze the influence of the appendages, and study the wake and thrust deduction effects, which are used to guide the AUV shape design and overall layout optimization.

[0006] The present invention is implemented by adopting the following technical scheme: a method for studying the interaction between an AUV hull and a propeller, which is divided into two stages: method verification and method application, and includes the following steps:

[0007] Step A, establish a three-dimensional geometric model: establish a three-dimensional model of the AUV and the B-3-50 propeller according to the parameters given in the literature; establish a three-dimensional model of the Sailfish AUV and the B-3-35 propeller according to the design parameters.

[0008] Furthermore, the step A specifically includes the following steps:

[0009] Step A1, model classification: The AUV model includes two types: with and without attachments, which are used to study the influence of attachments in step E;

[0010] Step A2, model fusion: fuse the propeller with the rotating domain to achieve the transformation of the propeller from volume to surface, which is convenient for meshing in step B;

[0011] Step A3, model combination: combine the AUV and propeller models, and set a gap between them.

[0012] Step B, determine the grid structure and size: according to the size and motion mode of the established 3D model, determine the grid type and size of each component, and select the parameters of the boundary layer grid, including the first layer height, number of layers, and growth rate.

[0013] Furthermore, the step B specifically includes the following steps:

[0014] Step B1, determine the grid structure: adopt a hybrid grid structure, use a coarse unstructured grid in the stationary domain, use a fine unstructured grid in the rotating domain, and add a boundary layer grid to the AUV hull, appendages and propeller;

[0015] Step B2: Calculate the boundary layer mesh parameters: The dimensions of the stationary domain, rotating domain, hull, appendage, and propeller are defined separately, and the Reynolds number Re and dimensionless wall distance y are calculated based on online tools and empirical formulas. + The value of determines the parameters of the boundary layer grid;

[0016]

[0017]

[0018]

[0019] Where ρ is the density of the fluid; v is the velocity of the fluid; l is the characteristic length; μ is the dynamic viscosity of the fluid; υ is the kinematic viscosity of the fluid; y is the vertical distance from the boundary; u τ is the friction velocity; τ w is the wall shear stress;

[0020] Step B3: Meshing: Automatically mesh the model based on ANSYS Meshing.

[0021] Step C, select boundary conditions and solution methods: Select appropriate boundary conditions and solution methods according to the problem being studied. The settings of the stationary domain and the rotating domain are determined based on the motion state of the component.

[0022] Furthermore, the step C specifically includes the following steps:

[0023] Step C1, constructing the computational domain: constructing a cylindrical computational domain and setting a large computational domain to reduce the influence of the wall boundary;

[0024] Step C2, set the calculation domain size: the calculation domain of the propeller in open water, the radius is 10D p , upstream extension length is 10D p , downstream extension length is 20D p (D p represents the diameter of the propeller); the calculation domain of the propeller behind the hull has a radius of 10D, an upstream extension length of L, and a downstream extension length of 3L (D represents the diameter of the AUV, and L represents the total length of the AUV);

[0025] Step C3, setting boundary conditions: setting the incoming flow to flow along the positive direction of the X-axis, the negative direction of the X-axis as the velocity inlet, the positive direction of the X-axis as the pressure outlet, and the no-slip wall boundary applied to the surface wall, AUV hull and propeller of the computational domain;

[0026] Step C4, select turbulence model: use MRF method and SST k-ω turbulence model for steady-state calculation, and set shared topology at the interface between rotating domain and stationary domain;

[0027] Step C5, select the solution method: the type of solver is pressure-based, the solution mode is velocity-pressure coupling based on SIMPLE algorithm, the gradient based on the least square unit is used for spatial discretization, and the pressure, momentum, turbulent kinetic energy and dissipation rate are all second-order upwind format;

[0028] Step C6, determine the control equation and initialization method: the Reynolds-averaged Navier-Stokes method is used to solve the control equation, and the hybrid method is used for initialization;

[0029]

[0030]

[0031] Where ρ is the density of the fluid, and the density of fresh water is 998.2 kg / m 3 ; is the average Cartesian component of the velocity vector; is the average pressure; μ is the dynamic viscosity of the fluid, and the dynamic viscosity of fresh water at 20°C is 0.001003 kg / (m·s); is the Reynolds stress.

[0032] Step D: Verification of independence of grid and iteration step: Perform simulation based on the divided grid and selected boundary conditions, compare the results of different grid sizes and iteration steps, and verify the independence of simulation results from grid size and iteration step.

[0033] Furthermore, the step D specifically includes the following steps:

[0034] Step D1, grid independence analysis: The grid is divided into three levels: coarse, medium and fine. The size of the static domain decreases arithmetic difference, and the size of the rotating domain changes proportionally. The grid refinement ratio R is calculated. 1 and R 2 , perform grid independence analysis based on simulation results;

[0035]

[0036]

[0037] In the formula, N is the total number of grids, and d represents the dimension of the problem being studied;

[0038] Step D2, iterative step independence analysis: perform steady-state calculations with different step lengths, compare the calculation results, perform iterative step independence analysis, and determine the appropriate number of iterative steps that can achieve a stable convergence state.

[0039] Step E: Numerical simulation and result analysis: Use the verified numerical method to conduct numerical research on the interaction between AUV and propeller in direct and oblique flow, and draw research conclusions based on the analysis of the results.

[0040] Step E1, numerical simulation: numerical simulation of the interaction between the AUV hull and propeller in direct and oblique flow is carried out based on ANSYS Workbench;

[0041] Step E2, study the influence of the appendage: study the influence of the appendage on the hydrodynamic characteristics and flow field distribution of the AUV;

[0042] Step E3, study wake and thrust deduction effects: compare the difference between propeller open water performance and after-boat performance, calculate the wake fraction and thrust deduction factor, and analyze the wake and thrust deduction effects.

[0043] Compared with the prior art, the advantages and positive effects of the present invention are:

[0044] This scheme emphasizes the importance of the interaction between the AUV hull and propeller, and conducts a coupling analysis of the hull and propeller, which is closer to the actual application situation; the models are merged and reorganized to facilitate meshing and simplify the pre-processing process; numerical simulation is performed based on ANSYS Workbench, and model processing, meshing, solution settings, and post-processing modules are integrated together to simplify the interaction process between modules and improve research efficiency; the model is automatically meshed based on ANSYS Meshing to reduce the complexity of meshing; this method is applicable to single models of the hull or propeller and the combined model of the two. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a general flow chart of the research method described in the embodiment of the present invention;

[0046] Figure 2 is a three-dimensional structure diagram of the reference model described in the embodiment of the present invention;

[0047] Figure 3 is a three-dimensional structural diagram of the research model described in the embodiment of the present invention;

[0048] Figure 4 is the open water performance calculation domain of the propeller according to the embodiment of the present invention;

[0049] Figure 5 is the calculation domain of the propeller's rear-boat performance according to the embodiment of the present invention;

[0050] Figure 6 is a surface mesh of the research model described in the embodiment of the present invention;

[0051] Figure 7 is a drag comparison bar graph of the Sailfish AUV according to an embodiment of the present invention;

[0052] Figure 8 It is a thrust comparison bar chart of the Sailfish AUV described in an embodiment of the present invention.

[0053] In the figure: 1. Suboff AUV; 2. 286AUV; 3. B-3-50 propeller; 4. Sailfish AUV; 5. B-3-35 propeller; 6. Rotating domain; 7. Stationary domain; 8. Velocity inlet; 9. Pressure outlet; 10. Wall; 11. Interface. DETAILED DESCRIPTION

[0054] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from this description. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0055] The present invention is implemented by adopting the following technical scheme: a method for studying the interaction between the AUV hull and the propeller, which is divided into two stages: method verification and method application, such as Figure 1 As shown, the following steps are included:

[0056] Step A, establishing a three-dimensional geometric model: establishing a three-dimensional model of the AUV and the B-3-50 propeller according to the parameters given in the literature, and establishing a three-dimensional model of the Sailfish AUV and the B-3-35 propeller according to the design parameters;

[0057] Step B, determine the grid structure and size: according to the size and motion mode of the established three-dimensional model, determine the grid type and size of each component, and select the parameters of the boundary layer grid, including the first layer height, number of layers, and growth rate;

[0058] Step C, select boundary conditions and solution methods: select appropriate boundary conditions and solution methods according to the problem being studied, and the setting of the stationary domain and the rotating domain is determined based on the motion state of the component;

[0059] Step D, grid and iteration step independence verification: perform simulation based on the divided grid and selected boundary conditions, compare the results of different grid sizes and iteration steps, and verify the independence of the simulation results from the grid size and iteration step;

[0060] Step E: Numerical simulation and result analysis: Use the verified numerical method to conduct numerical research on the interaction between AUV and propeller in direct and oblique flow, and draw research conclusions based on the analysis of the results.

[0061] Specifically, the research method of the present invention is described in detail below in conjunction with specific embodiments:

[0062] step A In this paper, the three-dimensional models of the reference object and the research object are established based on SolidWorks, and the individual parts and assemblies are saved in parasolid format. The modeling parameters of the reference object are from the reference literature. The research object is an independently developed product, and the design parameters have been mastered, as shown in Tables 1 and 2. The reference model is as follows Figure 2 As shown, the research model is Figure 3 As shown, specifically:

[0063] Step A1, model classification: Suboff AUV model has no appendages and is used to study the drag characteristics; 286AUV model has no appendages and is used to study the interaction with the B-3-50 propeller, 286 means the maximum outer diameter of the AUV is 286mm; Sailfish AUV model includes two types, with and without appendages, which are used to study the influence of appendages in step E;

[0064] Step A2, model fusion: Use the combined features to fuse the B-3-50 and B-3-35 propellers with the rotating domain respectively, realize the transformation of the propeller from volume to surface, and facilitate the meshing in step B;

[0065] Step A3, model combination: In SolidWorks, combine the 286AUV and B-3-50 propeller models, and combine the Sailfish AUV and B-3-35 propeller models. Set the interval between the AUV and the propeller to 5 mm to simulate the actual application distance.

[0066] Table 1 Sailfish AUV design parameters

[0067]

[0068] Table 2 Design parameters of B-3-35 propeller

[0069]

[0070] In step B, the pre-processing of numerical simulation is performed. The length of the Suboff AUV model is 4.356m, the length of the 286AUV model is 2.857m, the length of the Sailfish AUV model is 2.765m, the hull mesh size is 20mm, the appendage mesh size is 8mm, and the propeller mesh size is 2mm. Local encryption is performed to determine the parameters of the boundary layer mesh, including the first layer height, number of layers, and growth rate, which are as follows:

[0071] Step B1, determine the grid structure: the calculation domain adopts a hybrid grid structure, the static domain adopts a coarse unstructured grid with a size of 150 mm, and the rotating domain adopts a fine unstructured grid with a size of 8 mm; the AUV hull, appendages and propellers add boundary layer grids, the first layer height is calculated in B2, the number of layers is 10-15, and the growth rate is 1.2;

[0072] Step B2, calculate boundary layer mesh parameters: In the previous steps, the sizes of the stationary domain, rotating domain, hull, appendage and propeller are defined respectively, and the Reynolds number Re and dimensionless wall distance y are calculated based on online tools and empirical formulas. + The value of determines the first layer height of the boundary layer grid. The first layer height changes with the change of the inflow velocity. This method sets the expected y +is 30, the expected y of the propeller + is 40;

[0073]

[0074]

[0075]

[0076] Where ρ is the density of the fluid; v is the velocity of the fluid; l is the characteristic length; μ is the dynamic viscosity of the fluid; υ is the kinematic viscosity of the fluid; y is the vertical distance from the boundary; u τ is the friction velocity; τ w is the wall shear stress;

[0077] Step B3, meshing: Automatically mesh the model based on ANSYS Meshing, perform parametric global mesh control, and seamlessly connect with ANSYS Workbench.

[0078] In step C, appropriate boundary conditions and solution methods are selected according to the research problem. The setting of the stationary domain and the rotating domain is determined based on the motion state of the components. The hull and propeller have no axial motion in the calculation domain. The relative speed of the inflow and the hull is used to simulate the motion of the AUV. The propeller rotates clockwise in the rotating domain. The open water performance calculation domain is as follows: Figure 4 As shown in the figure, the calculation domain of the rear performance is as follows: Figure 5 As shown, specifically:

[0079] Step C1, constructing the computational domain: constructing a cylindrical computational domain, which mainly includes a stationary domain and a rotating domain. The computational domain is large enough to reduce the influence of the wall boundary;

[0080] Step C2, set the calculation domain size: the calculation domain of the propeller in open water, the radius is 10D p , upstream extension length is 10D p , downstream extension length is 20D p (D p represents the diameter of the propeller); the calculation domain of the propeller behind the hull has a radius of 10D, an upstream extension length of L, and a downstream extension length of 3L (D represents the diameter of the AUV, and L represents the total length of the AUV);

[0081] Step C3, setting boundary conditions: setting the incoming flow to flow along the positive direction of the X-axis, the negative direction of the X-axis as the velocity inlet, the positive direction of the X-axis as the pressure outlet, and the no-slip wall boundary applied to the surface wall, AUV hull and propeller of the computational domain;

[0082] Step C4, select turbulence model: use MRF method and SST k-ω turbulence model for steady-state calculation, and set shared topology at the interface between rotating domain and stationary domain;

[0083] Step C5, select the solution method: the type of solver is pressure-based, the solution mode is velocity-pressure coupling based on SIMPLE algorithm, the gradient based on the least square unit is used for spatial discretization, and the pressure, momentum, turbulent kinetic energy and dissipation rate are all second-order upwind format;

[0084] Step C6, determine the control equations and initialization method: the Reynolds-averaged Navier-Stokes method is used to solve the control equations, and the hybrid method is used for initialization; the mass and momentum conservation equations are solved by ANSYS Fluent 2020R2, and the Fluent solver uses the finite volume method to discretize the control equations;

[0085]

[0086]

[0087] Where ρ is the density of the fluid, and the density of fresh water is 998.2 kg / m 3 ; is the average Cartesian component of the velocity vector; is the average pressure; μ is the dynamic viscosity of the fluid, and the dynamic viscosity of fresh water at 20°C is 0.001003 kg / (m·s); is the Reynolds stress.

[0088] In step D, simulation is performed based on the divided grid and the selected boundary conditions, and the results of different grid sizes and iteration steps are compared to verify the independence of the simulation results with the grid size and iteration step. Figure 6 As shown, specifically:

[0089] Step D1, grid independence analysis: The grid is divided into three levels: coarse, medium and fine. The size of the stationary domain decreases from 200mm to 100mm, and the size of the rotating domain changes from 16mm to 4mm. The propeller sizes are 8mm, 2mm and 1mm respectively. Calculate the grid refinement ratio R 1 and R 2 They are 1.1 and 1.3 respectively. The independence analysis of the grid is carried out according to the simulation results, as shown in Table 3;

[0090]

[0091]

[0092] Wherein, N is the total number of grids, d represents the dimension of the problem being studied, and d=3 is taken in this embodiment.

[0093] Table 3 Grid independence verification

[0094]

[0095] Step D2, iterative step independence analysis: Compare the results after 500, 1000 and 1500 steps of calculation. For the calculation in direct current, there is almost no difference between the three, and 500 steps can reach a stable convergence state; however, for the calculation in oblique flow, data oscillation usually occurs during the calculation process, and more steps are required to achieve convergence; the results of 1000 and 1500 steps in direct current and oblique flow are consistent. In order to obtain accurate results, the number of iterative steps calculated in this embodiment is uniformly 1000 steps.

[0096] In step E, a numerical study of the interaction between the AUV and the propeller in direct and oblique flow was conducted using a validated numerical method. The results were analyzed and the research conclusions were drawn. The drag of the Sailfish AUV was compared with Figure 7 As shown, the reasoning pair is Figure 8 Specifically shown are:

[0097] Step E1, numerical simulation: Based on ANSYS Workbench, the interaction between the Sailfish AUV hull and propeller in direct and oblique flow was numerically simulated. The propeller speed was 1500 rpm, the inflow velocity increased from 0.5 m / s to 3.0 m / s, set to 6 levels, each increment was 0.5 m / s, and the angle of attack changed from 0° to 30°, each increase was 10°. The open water performance of the propeller was calculated by the following formula:

[0098]

[0099]

[0100]

[0101]

[0102] Where J is the dimensionless speed coefficient; V a is the average flow velocity in the propeller plane, m / s; n is the propeller speed, expressed in revolutions per second, rps; D p is the diameter of the propeller, m; K T is the dimensionless propulsion coefficient; T is the thrust generated by the propeller, N; ρ is the density of the fluid, kg / m 3 ; K Qis the dimensionless torque coefficient; Q is the torque generated by the propeller, Nm; η represents the propulsion efficiency of the propeller. In this embodiment, J is changed by changing the inflow speed to keep the rotation speed constant.

[0103] Conclusion: Hull resistance increases with increasing speed and angle of attack, especially at high speed and large angle of attack, the resistance increment is significant; since the propeller rotation changes the stern flow field and pressure distribution, the propeller rotation also causes an increase in hull resistance. At the same inflow speed, the thrust and torque of the propeller in open water increase slowly with the increase of angle of attack, which is more significant in the medium speed stage; under the same inflow conditions, the thrust and torque of the propeller behind the boat are generally greater than those in open water; the change of angle of attack has a greater impact on the open water performance of the propeller than the performance behind the boat.

[0104] Step E2, study the influence of the appendages: study the influence of the appendages on the hydrodynamic characteristics and flow field distribution of the AUV.

[0105] Conclusion: The appendages lead to a huge change in the resistance of the AUV, especially at high speeds, where the resistance increase is more obvious. Most of the increase in resistance comes from the pressure difference resistance. The appendages change the uniformity of the flow field and pressure distribution around the AUV, and the rudders in the appendages have a significant effect on the stern flow.

[0106] Step E3, study the wake and thrust deduction effects: compare the difference between the open water performance and the after-boat performance of the B-3-35 propeller. The open water characteristics are shown in Table 4, and the comparison between open water and after-boat is shown in Table 5. Calculate the wake fraction and thrust deduction factor, analyze the wake and thrust deduction effects, and use the following formula to complete the calculation:

[0107]

[0108]

[0109] Where: w is the wake fraction; V a represents the propeller speed; V is the AUV's headwind speed; t is the thrust deduction factor; R h is the hull resistance without propeller; T p It is the thrust generated by the propeller behind the boat.

[0110] Conclusion: With the increase of speed, the resistance increases and the thrust decreases. At the critical speed, the thrust and resistance are balanced and the self-propulsion point is reached. The calculated wake fraction w = 0.38 and the thrust deduction factor t = 0.16 are larger than the reference value, indicating the strong interaction between the hull and the propeller. The thrust deduction factor is within a reasonable range.

[0111] Table 4 Open water characteristics of B-3-35 propeller

[0112]

[0113] Table 5 Comparison of open water and rear water performance of B-3-35 propeller

[0114]

[0115] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for studying the interaction between an AUV hull and a propeller, characterized in that This method is divided into two stages: verification and application. Each stage includes the following steps: Step A, establishing a three-dimensional geometric model: establishing a separate three-dimensional model of the AUV and the propeller and a combined three-dimensional model of the two according to geometric parameters; Step B, determine the grid structure and size: according to the size and motion mode of the established three-dimensional model, determine the grid type and size of each component, and select the parameters of the boundary layer grid; Step C, select boundary conditions and solution method: set the boundary conditions of the cylindrical computational domain as velocity inlet and pressure outlet, use the multi-reference system method and SST k-ω turbulence model for steady-state calculation, and apply the Reynolds-averaged Navier-Stokes method and velocity-pressure coupling mode to solve the control equations; Step D, grid and iteration step independence verification: perform simulation based on the divided grid and selected boundary conditions, compare the results of different grid sizes and iteration steps, and verify the independence of the simulation results from the grid size and iteration step; Step E: Numerical simulation and result analysis: Use the verified numerical method to conduct numerical study on the interaction between AUV and propeller in direct and oblique flow, and draw conclusions based on the analysis of the results.

2. The method for studying the interaction between the AUV hull and the propeller according to claim 1, characterized in that In step A: (1) In order to obtain the influence of the appendage on the hydrodynamic characteristics of the AUV, the AUV model includes two types: with and without appendages; (2) The propeller is integrated with the rotating domain to achieve the transformation of the propeller from volume to surface, which facilitates the meshing in step B; (3) Combine the AUV and propeller models and set a gap between them.

3. The method for studying the interaction between the AUV hull and the propeller according to claim 1, characterized in that In the step B: (1) A hybrid grid structure is used, with a coarse unstructured grid in the stationary domain and a fine unstructured grid in the rotating domain. Boundary layer grids are added to the AUV hull, appendages, and propellers. (2) The dimensions of the stationary domain, rotating domain, AUV, and propeller are defined respectively, and the Reynolds number Re and the dimensionless wall distance y are calculated. + The value of determines the parameters of the boundary layer grid; Where ρ is the density of the fluid; v is the velocity of the fluid; l is the characteristic length; μ is the dynamic viscosity of the fluid; υ is the kinematic viscosity of the fluid; y is the vertical distance from the boundary; u τ is the friction velocity; τ w is the wall shear stress.

4. The method for studying the interaction between the AUV hull and the propeller according to claim 1, characterized in that In the step C: (1) Construct a cylindrical computational domain and set a large computational domain to reduce the influence of the wall boundary; (2) The computational domain of the propeller in open water has a radius of 10D p , upstream extension length is 10D p , downstream extension length is 20D p， D p Indicates the diameter of the propeller; The propeller is in the computational domain behind the hull, with a radius of 10D, an upstream extension length of L, and a downstream extension length of 3L. D represents the diameter of the AUV, and L represents the total length of the AUV; (3) The incoming flow is set to flow along the positive direction of the X-axis, the negative direction of the X-axis is the velocity inlet, the positive direction of the X-axis is the pressure outlet, and the no-slip wall boundary is applied to the surface wall, AUV hull and propeller of the computational domain; (4) Multiple reference frames (MRF) and shear stress transport (SST) k-ω turbulence model are used for steady-state calculations, and the interface between the rotating domain and the stationary domain is realized through shared topology; (5) The solver type is pressure-based, the solution mode is velocity-pressure coupling based on SIMPLE algorithm, the gradient based on the least squares unit is used for spatial discretization, and the pressure, momentum, turbulent kinetic energy and dissipation rate are all second-order upwind formats; (6) The Reynolds Averaged Navier-Stokes (RANS) method is used to solve the control equations, using a hybrid initialization method; Where ρ is the density of the fluid, and the density of fresh water is 998.2 kg / m 3 ; is the average Cartesian component of the velocity vector; is the average pressure; μ is the dynamic viscosity of the fluid, and the dynamic viscosity of fresh water at 20°C is 0.001003 kg / (m·s); is the Reynolds stress.

5. The method for studying the interaction between the AUV hull and the propeller according to claim 1, characterized in that In the step D: (1) The grid is divided into three levels: coarse, medium, and fine. The size of the stationary domain decreases arithmetic progression, and the size of the rotating domain changes proportionally. The grid refinement ratios R1 and R2 are calculated, and the independence analysis of the grid is performed based on the simulation results. In the formula, N is the total number of grids, and d represents the dimension of the problem being studied; (2) Perform steady-state calculations with different step sizes, compare the calculation results, conduct independence analysis of the iteration step size, and determine the appropriate number of iteration steps to achieve a stable convergence state.

6. The method for studying the interaction between the AUV hull and the propeller according to claim 1, characterized in that In the step E: (1) Numerical simulation of the interaction between the AUV hull and propeller in direct and oblique flow was carried out based on ANSYS Workbench; (2) Study the influence of the appendages on the hydrodynamic characteristics and flow field distribution of the AUV; (3) Compare the differences between the propeller open water performance and the aft performance, calculate the wake fraction and thrust deduction factor, and analyze the wake and thrust deduction effects.

Images