A numerical calculation method for unsteady force of underwater vehicle propulsion system

Abstract

The present invention discloses a method for numerically calculating the unsteady force of an underwater vehicle thruster, the method comprising: S1: creating a geometric model of an underwater vehicle and a thruster; S2: creating a calculation domain for simulation calculation of the underwater vehicle and the thruster; S3: setting boundary conditions, establishing a fluid dynamics analysis model and carrying out simulation calculation of the steady flow field of the entire calculation domain until the flow field is fully converged; S4: extracting the flow field data of the interface between the head calculation domain and the tail calculation domain; S5: deleting the grid and data of the head calculation domain, and setting the boundary of the interface between the tail calculation domain and the head calculation domain as the flow inlet boundary; S6: carrying out calculation of unsteady flow. The present invention obtains accurate unsteady force values ​​of the vehicle thruster by simulating only the flow of the tail vehicle and the thruster, thereby reducing the amount of calculation while ensuring the accuracy of the calculation results, and solving the problems of large amount of calculation and inaccurate calculation results in the existing calculation methods.

Description

Technical Field

[0001] The present invention relates to the technical field of underwater vehicles, and in particular to a numerical calculation method for an unsteady force of an underwater vehicle thruster. Background Art

[0002] Since the propellers and other thrusters working at the tail of underwater vehicles encounter uneven turbulent inflows during rotation, the rotor blades of the propellers generate unsteady thrust and then radiate line spectrum noise outward. Propeller noise is an important noise source for underwater vehicles and is the key control object in propeller research and design. Therefore, the amplitude of the unsteady force of the rotor blades of underwater vehicle propellers is an important characteristic parameter in the design and research of underwater vehicle propellers.

[0003] In the prior art, the methods for obtaining the unsteady excitation force of the rotor blades of the underwater vehicle propeller include model test method, potential flow theory calculation method, and CFD simulation calculation method. Among them, the CFD simulation calculation method takes into account the viscosity of the fluid and can directly simulate the effect of the underwater vehicle on the propeller, so the calculation result is better than the potential flow theory method. However, since the unsteady force of the propeller is closely related to the characteristics of the wake field generated by the underwater vehicle, it is often necessary to bring the underwater vehicle as a whole into the simulation calculation of the unsteady force of the propeller using the CFD method, which brings about the problem of a significant increase in the amount of calculation. If the characteristics of the wake field generated by the underwater vehicle are not considered, the amount of calculation can be greatly reduced, but it will cause a large deviation in the calculation result of the unsteady force of the propeller.

[0004] Therefore, it is urgent to design a numerical calculation method for the unsteady force of the underwater vehicle thruster to solve the problems existing in the above-mentioned prior art. Summary of the invention

[0005] In view of the above defects or improvement needs of the prior art, the present invention provides a numerical calculation method for the unsteady force of an underwater vehicle thruster, the purpose of which is to obtain accurate unsteady force data of the thruster by constructing a calculation domain that only includes the tail control surface and the thruster that have a greater impact on the wake field, and setting the boundary of the interface between the tail calculation domain and the bow calculation domain as the flow inlet boundary, thereby reducing the amount of calculation while ensuring the accuracy of the calculation results.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A first aspect of the present invention provides a method for numerically calculating an unsteady force of an underwater vehicle thruster, the method comprising the following steps:

[0008] S1: creating a geometric model of an underwater vehicle and a propeller, dividing the model into three parts: a bow vehicle body, a tail vehicle body, and a propeller, wherein the tail vehicle body includes a stern control surface of the underwater vehicle;

[0009] S2: Create a computational domain for underwater vehicle and propeller simulation calculation. Create the bow computational domain, tail computational domain, and propeller rotation computational domain according to the bow vehicle body, tail vehicle body, and propeller. Use meshing software to mesh the computational domains of each part and create a fluid computational grid model.

[0010] S3: Set boundary conditions, establish a fluid dynamics analysis model, and carry out simulation calculations of the steady flow field in the entire computational domain until the flow field is fully converged. The rotation of the propeller is simulated using the rotating coordinate system method.

[0011] S4: extracting flow field data at the interface between the head calculation domain and the tail calculation domain, wherein the flow field data includes three-dimensional velocity field, pressure field, turbulent kinetic energy, and specific dissipation rate;

[0012] S5: deleting the grid and data of the head calculation domain, setting the boundary of the interface between the tail calculation domain and the head calculation domain as the flow inlet boundary, using the flow field data extracted in step S4 as the flow inlet data, simulating the rotation of the propeller by the rotating grid method, and keeping other boundary conditions unchanged, finally forming a fluid dynamics analysis model for unsteady calculation;

[0013] S6: Carry out unsteady flow calculation for the fluid dynamics analysis model of the unsteady calculation finally formed in step S5, and monitor and output the unsteady force of the thruster.

[0014] As an embodiment of the present application, the grid of the interface between the head calculation domain and the tail calculation domain in step S2 is completely the same.

[0015] As an embodiment of the present application, in step S2, the bow calculation domain and the tail calculation domain use a full hexahedral structured grid, and the thruster calculation domain uses a tetrahedral unstructured grid.

[0016] As an embodiment of the present application, setting boundary conditions in step S3, establishing a fluid dynamics analysis model, and carrying out simulation calculation of a steady flow field in the entire computational domain until the flow field fully converges specifically includes:

[0017] S31: Set physical boundary conditions and establish a fluid dynamics analysis model for the steady-state solution of the underwater vehicle propulsion system based on the Navier-Stokes equations;

[0018] S32: After the fluid dynamics analysis model is established, the Reynolds time-averaged simulation method is used to steadily solve the NS equations and perform grid sensitivity analysis;

[0019] S33: The above fluid dynamics analysis model is set in the fluid simulation software. After the setting is completed, it is initialized with the flow inlet and the calculation is carried out until convergence.

[0020] As an embodiment of the present application, setting the physical boundary conditions in step S31 specifically includes:

[0021] The interface between the head calculation domain and the tail calculation domain is set as an internal surface;

[0022] The far-field incoming flow is set as the velocity inlet boundary condition;

[0023] The far-field outflow is set as the pressure outlet boundary condition;

[0024] The surrounding far fields are set as wall boundary conditions or velocity inlet boundary conditions;

[0025] No-slip wall boundary conditions are used on the walls of underwater vehicles and thrusters.

[0026] As an embodiment of the present application, the steady-state solution of the NS equations using the Reynolds time-averaged simulation method in step S32 is expressed as follows:

[0027]

[0028] in, is the fluid density in kg / m 3 ; is the speed, the unit is m / s; is pressure, the unit is Pa; is the dynamic viscosity coefficient, the unit is N·s / ㎡; is the Reynolds stress term, and the SST turbulence model is selected to close the equation; the pressure term , momentum term Selects the second-order discretization format.

[0029] As an embodiment of the present application, the flow field data extracted in step S4 in step S5 is used as the data of the flow inlet, specifically including: respectively selecting the pressure field, three-dimensional velocity field, turbulent kinetic energy, and specific dissipation rate in the flow field data to assign values ​​to the pressure field, three-dimensional velocity field, turbulent kinetic energy, and specific dissipation rate in the flow inlet boundary.

[0030] As an embodiment of the present application, the step S5 further includes:

[0031] After setting the boundary conditions, change the fluid dynamics analysis model to the unsteady calculation fluid dynamics analysis model, select the second-order format for the time format, and the iteration time step is ,The time step is selected as one propeller rotation per 200 steps, and the calculation formula is as follows:

[0032]

[0033] in, is the propeller speed in r / s.

[0034] As an embodiment of the present application, monitoring the change of thrust and torque of the propeller over time in step S6 to obtain the unsteady excitation force coefficient specifically includes:

[0035] S61: After the calculation is stable, monitor and record the axial force of the thruster at each time step , lateral force and vertical force ;

[0036] S62: After the calculation is completed, the full cycle data of the rotor time domain curve is intercepted and Fourier transform is performed to obtain the unsteady pulsating force at the rotor characteristic frequency , , .

[0037] The beneficial effects of the present invention are:

[0038] The present invention first divides the fluid calculation grid of the underwater vehicle and the propeller according to the bow calculation domain, the tail calculation domain, and the propeller rotation calculation domain, and performs steady-state iterative calculation, wherein the grid of the interface between the bow calculation domain and the tail calculation domain is completely consistent; then the wake field data of the interface between the bow calculation domain and the tail calculation domain are extracted; next, the bow calculation domain is deleted to reduce the amount of calculation, and the interface wake field data is used as the flow inlet boundary condition to achieve high-fidelity simulation of the working state of the propeller behind the vehicle, and carry out unsteady calculation; finally, the thrust and torque of the propeller rotor in the unsteady calculation are extracted for analysis to obtain the unsteady excitation force coefficient. Compared with the prior art, the present method reduces the amount of calculation while ensuring the accuracy of the calculation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A technical solution flow chart of a method for numerically calculating an unsteady force of an underwater vehicle thruster provided in an embodiment of the present invention;

[0040] Figure 2 A schematic diagram of the division of the underwater vehicle geometric model provided in an embodiment of the present invention;

[0041] Figure 3 A schematic diagram of the calculation domain setting for steady calculation of an underwater vehicle propeller provided in an embodiment of the present invention;

[0042] Figure 4A schematic diagram of the calculation domain setting for the unsteady calculation of an underwater vehicle provided in an embodiment of the present invention;

[0043] Figure 5 A comparison diagram of the thruster axial force calculation results provided in an embodiment of the present invention and the calculation results of a traditional method;

[0044] Figure 6 A comparison diagram of the thruster lateral force calculation results provided in an embodiment of the present invention and the calculation results of a traditional method;

[0045] Figure 7 It is a comparison chart of the thruster vertical force calculation results provided in the embodiment of the present invention and the calculation results of the traditional method. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0048] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0049] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in the field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0050] Reference Figures 1 to 7 The first aspect of the present invention provides a method for numerically calculating the unsteady force of an underwater vehicle thruster, the method comprising the following steps:

[0051] S1: Create a geometric model of the underwater vehicle and the propeller, and divide the model into three parts: the bow vehicle body, the tail vehicle body, and the propeller. The tail vehicle body includes the stern control surface of the underwater vehicle; establish a coordinate system, with the stern of the rotation axis of the propeller as the x-axis, assuming that the positive x direction is downstream and the negative x direction is upstream; Figure 2 The longitudinal section of the geometric model used in this embodiment and the schematic diagram of the division of the model area are shown.

[0052] S2: Import the geometric model created in step S1 into the dedicated meshing software for computational fluid dynamics analysis to create a computational domain for underwater vehicle and propeller simulation calculations, and create a bow calculation domain, a tail calculation domain, and a propeller rotation calculation domain according to the three parts of the bow vehicle body, the tail vehicle body, and the propeller. Use the meshing software to mesh the calculation domains of each part to create a fluid calculation grid model; wherein the mesh at the interface between the bow calculation domain and the tail calculation domain is exactly the same.

[0053] Preferably, in this embodiment, the bow calculation domain and the tail calculation domain use a full hexahedral structured grid, and the thruster calculation domain uses a tetrahedral unstructured grid. In practical applications, a hybrid grid model such as a combination of tetrahedral and triangular prism grids can also be used, and the grid scale can be set according to the principles of ordinary fluid simulation calculations.

[0054] S3: Set boundary conditions, establish a fluid dynamics analysis model, and carry out simulation calculations of the steady flow field in the entire computational domain until the flow field is fully converged. The rotation of the propeller is simulated using the rotating coordinate system method. Specifically, there are generally two ways to handle the rotation of the propeller, one is to simulate it using the rotating coordinate system method (Frame Motion), and the other is to simulate it using the rotating mesh method (Mesh Motion). Since the main purpose of the steady flow field calculation at this stage is to obtain the flow field information at the interface between the bow computational domain and the tail computational domain, the simulation method of the propeller rotation effect has basically no effect on the calculation results of the interface flow field, and the rotating coordinate system method has a small amount of calculation, so the rotation of the propeller at this stage is simulated using the rotating coordinate system method.

[0055] Among them, setting boundary conditions, establishing a fluid dynamics analysis model and carrying out simulation calculations of the steady flow field in the entire computational domain until the flow field fully converges specifically includes:

[0056] S31: Set physical boundary conditions and establish a fluid dynamics analysis model for the steady-state solution of the underwater vehicle propulsion system based on the Navier-Stokes equations;

[0057] The physical boundary conditions are specifically set as follows:

[0058] The interface between the head calculation domain and the tail calculation domain is set as an internal surface;

[0059] The far-field incoming flow is set as the velocity inlet boundary condition;

[0060] The far-field outflow is set as the pressure outlet boundary condition;

[0061] The surrounding far fields are set as wall boundary conditions or velocity inlet boundary conditions;

[0062] No-slip wall boundary conditions are used on the walls of underwater vehicles and thrusters.

[0063] S32: After the fluid dynamics analysis model is established, the Reynolds time-averaged simulation method is used to steadily solve the NS equations and perform grid sensitivity analysis;

[0064] Specifically, the steady-state solution of the NS equation using the Reynolds time-averaged simulation method is expressed as follows:

[0065]

[0066] in, is the fluid density in kg / m 3 ; is the speed, the unit is m / s; is pressure, the unit is Pa; is the dynamic viscosity coefficient, the unit is N·s / ㎡; is the Reynolds stress term, and the SST turbulence model is selected to close the equation; the pressure term , momentum term Selects the second-order discretization format.

[0067] S33: The above fluid dynamics analysis model is set in the fluid simulation software. After the setting is completed, it is initialized with the flow inlet and the calculation is carried out until convergence.

[0068] S4: Extract the flow field data of the interface between the head calculation domain and the tail calculation domain, wherein the flow field data includes the pressure field (P), three-dimensional velocity field (Vx, Vy, Vz), turbulent kinetic energy (k), specific dissipation rate (w), etc.; in the fluid simulation calculation software, save the interface data as a Profile file.

[0069] S5: Delete the grid and data of the head calculation domain, and only retain the tail calculation domain and the propeller rotation calculation domain, set the boundary of the interface between the tail calculation domain and the head calculation domain as the flow inlet boundary, and use the flow field data extracted in step S4 as the flow inlet data. Specifically, read the flow field data in the Profile file output by step S4, and select the pressure field (P), three-dimensional velocity field (Vx, Vy, Vz), turbulent kinetic energy (k), and specific dissipation rate (w) in the flow field data as the pressure field, three-dimensional velocity field, turbulent kinetic energy, and specific dissipation rate in the flow inlet boundary.

[0070] Specifically, after setting the boundary conditions, change the fluid dynamics analysis model to the fluid dynamics analysis model for unsteady calculation, select the second-order format for the time format, and the iterative time step is ,The time step is generally selected as one propeller rotation per 200 steps, and the calculation formula is as follows:

[0071]

[0072] in, is the propeller speed in r / s.

[0073] As a preferred embodiment of the present application, the rotation simulation method of the propeller is changed from the rotating coordinate system method (FrameMotion) to the rotating mesh method (Mesh Motion), and the other boundary conditions of the tail calculation domain and the propeller rotation calculation domain remain unchanged. Specifically, other discrete formats are consistent with step S3; after the above-mentioned boundary conditions are set, a fluid dynamics analysis model for unsteady calculation is finally formed.

[0074] S6: Carry out unsteady flow calculation for the fluid dynamics analysis model of the unsteady calculation finally formed in step S5, wherein the number of iterations for each time step in the calculation is m, and specifically, different numbers of iterations are selected according to different calculation software; monitor and output the unsteady force of the thruster, specifically monitor the changes of the axial force, lateral force and vertical force of the thruster with time.

[0075] As an embodiment of the present application, monitoring and outputting the unsteady force of the thruster in step S6 specifically includes:

[0076] S61: After the calculation is stable, monitor and record the axial force of the thruster at each time step , lateral force and vertical force ;

[0077] S62: After the calculation is completed, the full cycle data of the rotor time domain curve is intercepted and Fourier transform is performed to obtain the unsteady pulsating force at the rotor characteristic frequency , , .

[0078] Combination Figure 5 , Figure 6 , Figure 7 As shown, for the Suboff+E1619 propeller calculation model in this embodiment, the calculation method provided by the present invention is compared with the results of the conventional direct CFD simulation Suboff+E1619 overall calculation method. It can be seen that the calculation results provided by the present invention are basically consistent with the original calculation results; at the same time, the calculation amount of the calculation method provided by the present invention is greatly shortened; the calculation time of the entire example is reduced from 24h of the original model to 12h, and the calculation efficiency is improved by 50%. Therefore, compared with the traditional calculation method, the numerical calculation method for unsteady forces of underwater vehicle propellers proposed in the present invention has the characteristics of small calculation amount, fast calculation speed and good calculation accuracy, and can be used for the numerical calculation of unsteady forces of various propellers such as underwater vehicles, UUVs and other underwater vehicle propeller propellers.

[0079] The above descriptions are only some preferred embodiments of the present disclosure and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the embodiments of the present disclosure is not limited to the technical solutions formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the above inventive concept. For example, the above features are replaced with (but not limited to) technical features with similar functions disclosed in the embodiments of the present disclosure.

Claims

1. A method for numerically calculating the unsteady force of an underwater vehicle thruster, characterized in that: The method comprises the following steps: S1: creating a geometric model of an underwater vehicle and a propeller, dividing the model into three parts: a bow vehicle body, a tail vehicle body, and a propeller, wherein the tail vehicle body includes a stern control surface of the underwater vehicle; S2: Create a computational domain for underwater vehicle and propeller simulation calculation. Create the bow computational domain, tail computational domain, and propeller rotation computational domain according to the bow vehicle body, tail vehicle body, and propeller. Use meshing software to mesh the computational domains of each part and create a fluid computational grid model. S3: Set boundary conditions, establish a fluid dynamics analysis model, and carry out simulation calculations of the steady flow field in the entire computational domain until the flow field is fully converged. The rotation of the propeller is simulated using the rotating coordinate system method. S4: extracting flow field data at the interface between the head calculation domain and the tail calculation domain, wherein the flow field data includes pressure field, three-dimensional velocity field, turbulent kinetic energy, and specific dissipation rate; S5: deleting the grid and data of the head calculation domain, setting the boundary of the interface between the tail calculation domain and the head calculation domain as the flow inlet boundary, using the flow field data extracted in step S4 as the flow inlet data, simulating the rotation of the propeller by the rotating grid method, and keeping other boundary conditions unchanged, finally forming a fluid dynamics analysis model for unsteady calculation; S6: performing unsteady flow calculation on the fluid dynamics analysis model of the unsteady calculation finally formed in step S5, and monitoring and outputting the unsteady force of the thruster; The step S5 uses the flow field data extracted in step S4 as the flow inlet data, specifically including: respectively selecting the pressure field, three-dimensional velocity field, turbulent kinetic energy, and specific dissipation rate in the flow field data as the pressure field, three-dimensional velocity field, turbulent kinetic energy, and specific dissipation rate in the flow inlet boundary; The step S5 further comprises: After setting the boundary conditions, change the fluid dynamics analysis model to the fluid dynamics analysis model for unsteady calculation, select the second-order format for the time format, the iterative time step is Δt, and the time step is one propeller rotation per 200 steps. The calculation formula is as follows: Where N is the rotation speed of the propeller in r / s.

2. The method for numerically calculating the unsteady force of an underwater vehicle thruster according to claim 1, characterized in that: The grids at the interface between the head calculation domain and the tail calculation domain in step S2 are completely the same.

3. The method for numerically calculating the unsteady force of an underwater vehicle thruster according to claim 1, characterized in that: In the step S2, the bow calculation domain and the tail calculation domain use full hexahedral structured grids, and the thruster calculation domain uses tetrahedral unstructured grids.

4. The method for numerically calculating the unsteady force of an underwater vehicle thruster according to claim 1, characterized in that: The step S3 of setting boundary conditions, establishing a fluid dynamics analysis model, and carrying out simulation calculation of the steady flow field in the entire computational domain until the flow field is fully converged specifically includes: S31: Set physical boundary conditions and establish a fluid dynamics analysis model for the steady-state solution of the underwater vehicle propulsion system based on the Navier-Stokes equations; S32: After the fluid dynamics analysis model is established, the Reynolds time-averaged simulation method is used to steadily solve the NS equations and perform grid sensitivity analysis; S33: The above fluid dynamics analysis model is set in the fluid simulation software. After the setting is completed, it is initialized with the flow inlet and the calculation is carried out until convergence.

5. The method for numerically calculating the unsteady force of an underwater vehicle thruster according to claim 4, characterized in that: The physical boundary conditions set in step S31 specifically include: The interface between the head calculation domain and the tail calculation domain is set as an internal surface; The far-field incoming flow is set as the velocity inlet boundary condition; The far-field outflow is set as the pressure outlet boundary condition; The surrounding far fields are set as wall boundary conditions or velocity inlet boundary conditions; No-slip wall boundary conditions are used on the walls of underwater vehicles and thrusters.

6. The method for numerically calculating the unsteady force of an underwater vehicle thruster according to claim 4, characterized in that: The steady-state solution of the NS equations using the Reynolds time-averaged simulation method in step S32 is expressed as follows: Where ρ is the fluid density in kg / m 3 ; is the speed, the unit is m / s; is the pressure, the unit is Pa; μ is the dynamic viscosity coefficient, the unit is N·s / ㎡; is the Reynolds stress term, and the SST turbulence model is selected to close the equation; the pressure term Momentum term Selects the second-order discretization format.

7. The method for numerically calculating the unsteady force of an underwater vehicle thruster according to claim 1, characterized in that: The monitoring and outputting of the thruster unsteady force in step S6 specifically includes: S61: After the calculation is stable, monitor and record the axial force F of the thruster at each time step xt , lateral force F yt and vertical force F zt ; S62: After the calculation is completed, the full cycle data of the rotor time domain curve is intercepted and Fourier transform is performed to obtain the unsteady pulsating force at the rotor characteristic frequency

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