Rudder design method for avoiding cavitation denudation

Abstract

The invention belongs to the technical field of ship design, and particularly discloses a rudder design method for avoiding cavitation denudation, which comprises the following steps: step S1, analyzing and evaluating the assembly mode of a false rudder and a rudder blade based on CFD simulation data, and determining that the top of the rudder blade is designed to be step-shaped; s2, performing memory comparative analysis on the flow data corresponding to the real ship with the same step and the CFD simulation data, and determining the size of a matched gap between a propeller and a rudder; rudder cavitation bubbles are avoided, and it is guaranteed that in the operation process of the ship, the using performance cannot be affected by the rudder cavitation bubbles.

Description

Technical Field

[0001] The invention relates to the technical field of ship design, and in particular to a rudder design method for avoiding cavitation erosion. Background Art

[0002] The rudder is currently the most commonly used ship heading control device and is generally arranged behind the propeller. It is mainly used to meet the requirements of ship turning and heading stability. However, in addition to meeting the ship's maneuverability and recovering energy in the propeller wake field, it also requires certain anti-cavitation performance to avoid the risk of cavitation erosion.

[0003] There are many types of rudders at present, including flat rudders, twisted rudders, flap rudders, etc. A good rudder design has good heading maneuverability, hydrodynamic performance and anti-cavitation performance. In ship design, conventional optimization methods are to optimize the hull, propeller, rudder and hydrodynamic energy-saving device individually. For example, Chinese patent application No. CN107264763A discloses an anti-cavitation twisted rudder and a design method thereof. On the basis of fully considering the influence of various factors such as the rotation speed in the wake of the ship's propeller on the rudder, the purpose is to improve the stress state of the rudder blade, enhance the rudder efficiency, and reduce the load on the steering gear.

[0004] For example, Chinese patent application number CN210338261U discloses a twisted flap rudder, which reduces the negative pressure caused by the propeller water flowing into the rudder blade through the curved shell, thereby effectively avoiding the generation of cavitation.

[0005] The above-mentioned comparative documents are all based on single optimized ship type, optimized propeller, optimized rudder and hydrodynamic energy-saving device, etc., and the optimization process is carried out separately for each component. The disadvantage is that there is no communication and coordination during the design. Each of the line type, propeller, rudder and hydrodynamic energy-saving device may be optimized to the extreme, but combining them together may cause the propeller's wake field to rotate to the gap between the rudder blade and the false rudder, causing cavitation erosion, resulting in one or two of the rudder's heading maneuverability, hydrodynamic performance and anti-cavitation performance, or even three of them cannot meet the requirements, affecting the performance of the rudder.

[0006] In view of this, the present invention provides a rudder design method for avoiding cavitation erosion. Summary of the invention

[0007] The purpose of the present invention is to provide a rudder design method for avoiding cavitation erosion, so as to solve the above-mentioned problem.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] In a first aspect, the present invention provides a rudder design method for avoiding cavitation erosion, comprising the following steps:

[0010] Step S1: analyzing and evaluating the assembly method of the dummy rudder and the rudder blade based on the CFD simulation data, and determining that the top of the rudder blade is designed to be stepped;

[0011] Step S2: Compare and analyze the flow data corresponding to the actual ship with the same steps with the CFD simulation data to determine the size of the gap between the propeller and the rudder.

[0012] As a preferred technical solution of the present invention, the rotating wake of the propeller enters the gap between the dummy rudder and the rudder blade to produce cavitation erosion. CFD is used to numerically analyze the cavitation between the dummy rudder and the rudder blade to predict the occurrence of cavitation erosion.

[0013] As a preferred technical solution of the present invention, CFD simulation data analysis based on computational fluid dynamics includes the following steps:

[0014] A three-dimensional motion model is established based on the assembly method of the dummy rudder and the rudder blade; the three-dimensional motion model is divided into N grid units, and the flow velocity of the rotating wake of the propeller entering the gap between the dummy rudder and the rudder blade is obtained based on the grid units;

[0015] Based on prior knowledge, the boundary conditions of the dummy rudder and rudder blade assembly and the initial state of the rotating wake are obtained;

[0016] Analyze the simulation results based on the dynamic equations of computational fluid dynamics to evaluate the flow data corresponding to the assembly method of the dummy rudder and the rudder blade;

[0017] Based on the size of the flow data, the assembly method of the dummy rudder and the rudder blade that meets the design requirements is obtained, and based on the assembly method of the dummy rudder and the rudder blade, it is determined that the top of the rudder blade is designed to be stepped.

[0018] As a preferred technical solution of the present invention, the step of comparing and analyzing the flow data corresponding to the actual ship of the same level with the CFD simulation data includes:

[0019] The flow data corresponding to the actual ship include water velocity data, pressure data and cavitation data; at the same time, based on CFD simulation to simulate the flow between the propeller and the rudder, it is set according to the geometry of the actual ship, operating conditions and fluid characteristics;

[0020] Compare and analyze the flow data of the actual ship with the CFD simulation data to determine the optimal gap size between the propeller and the rudder;

[0021] If there is a significant difference between the simulation data and the actual ship data, the CFD model is adjusted, and multiple iterations of adjustment and verification are carried out until the CFD simulation results match the actual ship data;

[0022] According to CFD numerical analysis, cavitation occurs between the dummy rudder and the rudder blade. The cavitation erodes the rudder blade top plate and the dummy rudder bottom plate, causing damage to the rudder body and the dummy rudder.

[0023] As a preferred technical solution of the present invention, the CFD model is adjusted, and the adjustment direction includes improving grid division, adjusting boundary conditions and modifying fluid model parameters.

[0024] As a preferred technical solution of the present invention, the adjustment logic of the gap size between the propeller and the rudder includes:

[0025] Raise the gap between the dummy rudder and the rudder blade, raise the top plate of the leading edge of the rudder blade by 410mm, so that the gap between the rudder blade and the dummy rudder is about 400mm higher than the propeller, which can avoid the influence of the propeller wake. The raised part is made into a stepped structure at 840mm from the center of the rudder stock, and the gap between the raised top plate and the bottom plate of the dummy rudder is reduced to 40mm to prevent the propeller's rotating wake from entering the gap;

[0026] A spoiler with a width of about 150 mm is added to the upper edge of the slot rudder blade. The spoiler is flush with the rudder blade top plate, and its line shape is the rudder blade top plate line shape offset 150 mm outward, which can further block the propeller's rotating wake from entering the gap.

[0027] In a second aspect, the present invention provides a rudder design device for avoiding cavitation erosion, based on the implementation of the first aspect, comprising a simulation design module and a comparison analysis module, wherein the modules are connected via wired or wireless connections;

[0028] The simulation design module analyzes and evaluates the assembly method of the dummy rudder and the rudder blade based on CFD simulation data, and determines that the top of the rudder blade should be designed to be stepped;

[0029] The comparison and analysis module compares and analyzes the flow data corresponding to the actual ship with the same steps with the CFD simulation data to determine the size of the gap between the propeller and the rudder.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention is based on the optimization and improvement of the matching problem between the propeller and the rudder, designs a stepped gap, and reduces the propeller wake from entering the gap between the rudder blade and the dummy rudder; adding a baffle of a certain width is also to further strengthen the prevention of the propeller wake from entering the gap between the rudder blade and the dummy rudder, avoiding the occurrence of rudder cavitation. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a flow chart of the rudder design method of the present invention;

[0033] Figure 2 This is a framework diagram of the rudder design system of the present invention. DETAILED DESCRIPTION

[0034] 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.

[0035] In the description of the present invention, it should be noted that the terms "vertical", "up", "down", "horizontal", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0036] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it 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 it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] Example 1

[0038] See also Figure 1 The present invention provides a technical solution: a rudder design method for avoiding cavitation erosion, comprising the following steps:

[0039] Step S1: analyzing and evaluating the assembly method of the dummy rudder and the rudder blade based on the CFD simulation data, and determining that the top of the rudder blade is designed to be stepped;

[0040] Specifically, when an ordinary flap rudder is sailing in the water, after a long period of accumulation, serious cavitation erosion occurs between the dummy rudder and the rudder blade, which directly affects the performance of the rudder. Before redesigning the rudder, CFD simulation was used for numerical analysis, and cavitation was also found between the dummy rudder and the rudder blade. It can be predicted that cavitation erosion will definitely occur. It can be seen from this that the rotating wake of the propeller just enters the gap between the dummy rudder and the rudder blade, which is prone to cavitation erosion. Therefore, it can be found from the actual ship and CFD simulation that there are certain problems in the rudder design and it needs to be improved.

[0041] More specifically, the CFD simulation data analysis based on computational fluid dynamics includes the following steps:

[0042] A three-dimensional motion model is established based on the assembly method of the dummy rudder and the rudder blade; the three-dimensional motion model is divided into N grid units, and the flow velocity of the rotating wake of the propeller entering the gap between the dummy rudder and the rudder blade is obtained based on the grid units;

[0043] Based on prior knowledge, the boundary conditions of the dummy rudder and rudder blade assembly and the initial state of the rotating wake are obtained;

[0044] Analyze the simulation results based on the dynamic equations of computational fluid dynamics to evaluate the flow data corresponding to the assembly method of the dummy rudder and the rudder blade;

[0045] Based on the size of the flow data, the assembly method of the dummy rudder and the rudder blade that meets the design requirements is obtained. Based on the assembly method of the dummy rudder and the rudder blade, it is determined that the top of the rudder blade is designed to be stepped, thereby reducing the risk of cavitation.

[0046] Step S2: Compare and analyze the flow data corresponding to the actual ship with the same steps with the CFD simulation data to determine the size of the gap between the propeller and the rudder;

[0047] Specifically, the equal-step real ship aims to ensure the consistency between the flow data of the real ship and the CFD simulation data, thereby providing an accurate reference for ship design.

[0048] The flow data corresponding to the actual ship include water velocity data, pressure data and cavitation data. At the same time, CFD simulation is used to simulate the flow between the propeller and the rudder, which is set according to the geometry of the actual ship, operating conditions (such as speed, rudder angle, etc.) and fluid properties (such as water density and viscosity). The flow data of the actual ship is compared and analyzed with the CFD simulation data, and key parameters such as velocity distribution, pressure distribution, cavitation formation area and size are specifically compared. In this way, the optimal gap size for mutual cooperation between the propeller and the rudder is determined. The gap size is crucial to preventing cavitation erosion and improving ship maneuverability.

[0049] If there are significant differences between the simulation data and the actual ship data, the CFD model needs to be adjusted. The adjustment direction includes improving the grid division, adjusting the boundary conditions and modifying the fluid model parameters. Through multiple iterative adjustments and verifications, the CFD simulation results will match the actual ship data.

[0050] According to CFD numerical analysis, cavitation occurs between the dummy rudder and the rudder blade, and the cavitation erodes the rudder blade top plate and the dummy rudder bottom plate, causing damage to the rudder body and the dummy rudder. Adjustments were made from the following two aspects:

[0051] Raise the position of the gap between the dummy rudder and the rudder blade, lift the top plate of the leading edge of the rudder blade upward by 410mm, so that the position of the gap between the rudder blade and the dummy rudder is about 400mm higher than the propeller, which can avoid the influence of the propeller wake. The raised part is made into a stepped structure at a distance of 840mm from the center of the rudder stock, and the gap between the raised top plate and the bottom plate of the dummy rudder is reduced to 40mm to prevent the rotating wake of the propeller from entering the gap.

[0052] A spoiler with a width of about 150 mm is added to the upper edge of the slot rudder blade. The spoiler is flush with the rudder blade top plate, and its line shape is the rudder blade top plate line shape offset 150 mm outward, which can further block the propeller's rotating wake from entering the gap.

[0053] Specifically, a stepped gap is designed between the propeller and the rudder to reduce the propeller wake from entering the gap between the rudder blade and the dummy rudder; a baffle of a certain width is added to further prevent the propeller wake from entering the gap between the rudder blade and the dummy rudder, thereby avoiding the occurrence of rudder cavitation. In order to verify the reliability of the designed rudder, a cavitation test was conducted in a cavitation circulation water tank. The test results show that the design method corresponding to this embodiment can prevent the propeller water flow from entering the gap between the dummy rudder and the rudder blade, thereby avoiding the risk of cavitation erosion.

[0054] Example 2

[0055] like Figure 2 As shown, the undisclosed part of this embodiment is detailed in Example 1. This embodiment provides a rudder design device for avoiding cavitation erosion, including a simulation design module and a comparison analysis module, and each module is connected by wire or wirelessly;

[0056] The simulation design module analyzes and evaluates the assembly method of the dummy rudder and the rudder blade based on CFD simulation data, and determines that the top of the rudder blade should be designed to be stepped;

[0057] The comparison and analysis module compares and analyzes the flow data corresponding to the actual ship with the same steps with the CFD simulation data to determine the size of the gap between the propeller and the rudder.

[0058] As a preferred technical solution of the present invention, the rotating wake of the propeller enters the gap between the dummy rudder and the rudder blade to produce cavitation erosion. CFD is used to numerically analyze the cavitation between the dummy rudder and the rudder blade to predict the occurrence of cavitation erosion.

[0059] As a preferred technical solution of the present invention, CFD simulation data analysis based on computational fluid dynamics includes the following steps:

[0060] A three-dimensional motion model is established based on the assembly method of the dummy rudder and the rudder blade; the three-dimensional motion model is divided into N grid units, and the flow velocity of the rotating wake of the propeller entering the gap between the dummy rudder and the rudder blade is obtained based on the grid units;

[0061] Based on prior knowledge, the boundary conditions of the dummy rudder and rudder blade assembly and the initial state of the rotating wake are obtained;

[0062] Analyze the simulation results based on the dynamic equations of computational fluid dynamics to evaluate the flow data corresponding to the assembly method of the dummy rudder and the rudder blade;

[0063] Based on the size of the flow data, the assembly method of the dummy rudder and the rudder blade that meets the design requirements is obtained, and based on the assembly method of the dummy rudder and the rudder blade, it is determined that the top of the rudder blade is designed to be stepped.

[0064] As a preferred technical solution of the present invention, the step of comparing and analyzing the flow data corresponding to the actual ship of the same level with the CFD simulation data includes:

[0065] The flow data corresponding to the actual ship include water velocity data, pressure data and cavitation data; at the same time, based on CFD simulation to simulate the flow between the propeller and the rudder, it is set according to the geometry of the actual ship, operating conditions and fluid characteristics;

[0066] Compare and analyze the flow data of the actual ship with the CFD simulation data to determine the optimal gap size between the propeller and the rudder;

[0067] If there is a significant difference between the simulation data and the actual ship data, the CFD model is adjusted, and multiple iterations of adjustment and verification are carried out until the CFD simulation results match the actual ship data;

[0068] According to CFD numerical analysis, cavitation occurs between the dummy rudder and the rudder blade. The cavitation erodes the rudder blade top plate and the dummy rudder bottom plate, causing damage to the rudder body and the dummy rudder.

[0069] As a preferred technical solution of the present invention, the CFD model is adjusted, and the adjustment direction includes improving grid division, adjusting boundary conditions and modifying fluid model parameters.

[0070] As a preferred technical solution of the present invention, the adjustment logic of the gap size between the propeller and the rudder includes:

[0071] Raise the gap between the dummy rudder and the rudder blade, raise the top plate of the leading edge of the rudder blade by 410mm, so that the gap between the rudder blade and the dummy rudder is about 400mm higher than the propeller, which can avoid the influence of the propeller wake. The raised part is made into a stepped structure at 840mm from the center of the rudder stock, and the gap between the raised top plate and the bottom plate of the dummy rudder is reduced to 40mm to prevent the propeller's rotating wake from entering the gap;

[0072] A spoiler with a width of about 150 mm is added to the upper edge of the slot rudder blade. The spoiler is flush with the rudder blade top plate, and its line shape is the rudder blade top plate line shape offset 150 mm outward, which can further block the propeller's rotating wake from entering the gap.

[0073] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A rudder design method for avoiding cavitation erosion, characterized in that: The following steps are involved: Step S1: analyzing and evaluating the assembly method of the dummy rudder and the rudder blade based on the CFD simulation data, and determining that the top of the rudder blade is designed to be stepped; Step S2: Compare and analyze the flow data corresponding to the actual ship with the same steps with the CFD simulation data to determine the size of the gap between the propeller and the rudder.

2. A rudder design method for avoiding cavitation erosion according to claim 1, characterized in that: The rotating wake of the propeller enters the gap between the dummy rudder and the rudder blade and produces cavitation erosion. CFD is used to numerically analyze the cavitation between the dummy rudder and the rudder blade to predict the occurrence of cavitation erosion.

3. A rudder design method for avoiding cavitation erosion according to claim 2, characterized in that: The analysis of CFD simulation data based on computational fluid dynamics includes the following steps: A three-dimensional motion model is established based on the assembly method of the dummy rudder and the rudder blade; the three-dimensional motion model is divided into N grid units, and the flow velocity of the rotating wake of the propeller entering the gap between the dummy rudder and the rudder blade is obtained based on the grid units; Based on prior knowledge, the boundary conditions of the dummy rudder and rudder blade assembly and the initial state of the rotating wake are obtained; Analyze the simulation results based on the dynamic equations of computational fluid dynamics to evaluate the flow data corresponding to the assembly method of the dummy rudder and the rudder blade; Based on the size of the flow data, the assembly method of the dummy rudder and the rudder blade that meets the design requirements is obtained, and based on the assembly method of the dummy rudder and the rudder blade, it is determined that the top of the rudder blade is designed to be stepped.

4. A rudder design method for avoiding cavitation erosion according to claim 3, characterized in that: The step of comparing and analyzing the flow data corresponding to the actual ship of the same level with the CFD simulation data includes: The flow data corresponding to the actual ship include water velocity data, pressure data and cavitation data; at the same time, based on CFD simulation to simulate the flow between the propeller and the rudder, it is set according to the geometry of the actual ship, operating conditions and fluid characteristics; Compare and analyze the flow data of the actual ship with the CFD simulation data to determine the optimal gap size between the propeller and the rudder; If there is a significant difference between the simulation data and the actual ship data, the CFD model is adjusted, and multiple iterations of adjustment and verification are carried out until the CFD simulation results match the actual ship data; According to CFD numerical analysis, cavitation occurs between the dummy rudder and the rudder blade. The cavitation erodes the rudder blade top plate and the dummy rudder bottom plate, causing damage to the rudder body and the dummy rudder.

5. A rudder design method for avoiding cavitation erosion according to claim 4, characterized in that: Adjust the CFD model by improving meshing, adjusting boundary conditions, and modifying fluid model parameters.

6. A rudder design method for avoiding cavitation erosion according to claim 5, characterized in that: The logic for adjusting the gap size between the propeller and the rudder includes: Raise the gap between the dummy rudder and the rudder blade, raise the top plate of the leading edge of the rudder blade by 410mm, so that the gap between the rudder blade and the dummy rudder is about 400mm higher than the propeller, which can avoid the influence of the propeller wake. The raised part is made into a stepped structure at 840mm from the center of the rudder stock, and the gap between the raised top plate and the bottom plate of the dummy rudder is reduced to 40mm to prevent the propeller's rotating wake from entering the gap; A spoiler with a width of about 150 mm is added to the upper edge of the slot rudder blade. The spoiler is flush with the rudder blade top plate, and its line shape is the rudder blade top plate line shape offset 150 mm outward, which can further block the propeller's rotating wake from entering the gap.

7. A rudder design device for avoiding cavitation erosion, based on the implementation of a rudder design method for avoiding cavitation erosion according to any one of claims 1 to 6, characterized in that: It includes a simulation design module and a comparison analysis module, and each module is connected by wire or wirelessly; The simulation design module analyzes and evaluates the assembly method of the dummy rudder and the rudder blade based on CFD simulation data, and determines that the top of the rudder blade should be designed to be stepped; The comparison and analysis module compares and analyzes the flow data corresponding to the actual ship with the same steps with the CFD simulation data to determine the size of the gap between the propeller and the rudder.

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