Ship stern near-hull flow field adjusting method

Abstract

The invention relates to a ship stern near-hull flow field adjusting method, which comprises the following steps of: 1, calculating a flow field near a hull according to a ship type and a working condition, and selecting a position where a spoiler is arranged; according to numerical calculation and a model test, a streamline near a stern and a hull is obtained, and a spoiler is arranged at the downward flowing position of the streamline in front of a stern shaft; 2, evaluating the drag reduction effect corresponding to each attack angle by adopting numerical calculation; comparing the total resistance value R0 before the spoiler is additionally mounted with the total resistance Ri of the ship after the spoiler is additionally mounted to determine which attack angle is finally adopted; 3, evaluating the ship resistance reducing effect of the spoiler, and judging whether the scheme of the spoiler continues to be modified or not according to the effect; the anti-drag effect of the device is verified by means of numerical calculation or model test and the like. The spoiler is arranged on the ship body in front of the tail shaft, and water flow is adjusted from obliquely downward flow to horizontally backward flow, so that the resistance of the ship is reduced, and the propelling efficiency of the propeller is improved.

Description

Technical Field

[0001] The invention relates to the technical field of ship drag reduction, in particular to a method for regulating a flow field near a hull at a stern of a ship. Background Art

[0002] The world's major shipbuilding countries are stepping up research on ship drag reduction technology to meet the goals of the shipping industry such as green and low-carbon. For displacement ships represented by the three major mainstream ship types, there is a downward flow velocity component near the hull in front of the tail shaft. This flow causes the water flow here to cause more energy loss than the horizontal backward flow. By arranging spoilers, the local water flow in the corresponding area is forced to change its flow direction and flow horizontally backward, thereby reducing the resistance of the ship. Compared with reducing the resistance of the ship by changing the line shape, the use of this device to adjust the flow field is not restricted by the layout of the cabins in the ship, and there is no need to adjust the overall line shape of the ship. Since the modulated water flow has a greater speed in the horizontal backward direction than the original oblique downward flow field, its propeller has a higher relative rotation efficiency, so the spoiler also has a certain improvement function on the propeller propulsion efficiency. The process of designing spoilers according to the flow direction of the water near the hull can be incorporated into the numerical calculation and model test of the ship line optimization, and no additional supporting test facilities are required. Although other new drag reduction methods have certain practical value in engineering applications, they have high implementation costs, strong systematization, and strong complexity. A large amount of computing resources are required to implement the design, and model experiments are also relatively complex.

[0003] Therefore, we propose a method for regulating the flow field near the hull at the stern of a ship. Summary of the invention

[0004] In view of the shortcomings in the above-mentioned existing production technology, the applicant provides a method for adjusting the flow field near the hull at the stern of a ship. By arranging a spoiler on the hull in front of the stern shaft, the water flow is adjusted from flowing obliquely downward to flowing horizontally backward, thereby reducing the ship's resistance and improving the propeller propulsion efficiency.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A method for adjusting the flow field near the hull at the stern of a ship comprises the following steps:

[0007] Step 1: Calculate the flow field near the hull according to the ship type and working conditions, and select the location of the spoiler;

[0008] The streamlines near the stern hull are obtained based on numerical calculations and model tests, and spoilers are arranged where the streamlines start to flow downward in front of the stern shaft.

[0009] Step 2: Design the angle of attack of the spoiler to the incoming flow;

[0010] Numerical calculations are used to evaluate the drag reduction effect corresponding to each angle of attack;

[0011]

[0012] Among them, R i is the total resistance value after installing the spoiler; i = 1, 2...n; F·n x Resistance on the wet surface area of ​​the ship; Compare the total resistance value R0 before the installation of spoilers and the total resistance R after the installation of spoilers i Decide which angle of attack to use;

[0013] Step 3: Evaluate the effect of spoilers in reducing ship resistance and decide whether to continue modifying the spoiler plan based on the effect;

[0014] The drag reduction effect of the device is verified by numerical calculation or model test.

[0015] It is further characterized by:

[0016] In the third step, the resistance reduction d is required to be greater than 2%:

[0017] d=R1 / R0>2%.

[0018] According to the local water flow velocity in three orthogonal directions, the differential expression of the streamline direction is:

[0019]

[0020] In the first step, the spoiler is arranged at a position after the streamline changes from oblique upward flow from the bilge to oblique downward flow.

[0021] The beneficial effects of the present invention are as follows:

[0022] The present invention has a compact and reasonable structure and is easy to operate. By arranging a spoiler on the hull in front of the stern shaft, the water flow is adjusted from flowing obliquely downward to flowing horizontally backward, thereby reducing the resistance of the ship and improving the propeller propulsion efficiency. Flow field information such as the direction of the water flow near the hull is obtained by means of numerical calculations, model tests and the like. An inclined spoiler is arranged at a suitable position to force the water flow flowing obliquely downward and backward at a specific position to flow horizontally backward. The detour plate is arranged according to the angle of attack of the water flow near the outer shell of the ship. It is necessary to ensure that the spoiler can adjust the direction of the water flow upward without causing flow separation on the back of the spoiler due to an excessively large angle of attack. The velocity component of the water flow behind the spoiler in the vertical direction as a whole will also be reduced. The device makes the flow near the wall of the downstream hull regular.

[0023] At the same time, the present invention also has the following advantages:

[0024] (1) The structure is simple and the mechanism of the flow field is clear. The spoiler is installed on the outside of the hull and is relatively independent of the ship design. It can further improve the performance of the ship without interfering with the shape of the hull. After the device is arranged, the drag reduction effect is significant, which effectively supports the design of ships with higher energy efficiency requirements. By arranging a spoiler on the hull in front of the stern shaft, the water flow is adjusted from oblique downward flow to horizontal backward flow, thereby reducing the ship's resistance and improving the propeller propulsion efficiency.

[0025] (2) Starting from the flow mechanism near the wall behind the ship, a method of reducing the ship's resistance by adding spoilers to change the local flow field. The flow field information near the wall in front of the ship's tail shaft is obtained by means of numerical calculation, model experiment or actual ship measurement. Spoilers are arranged according to the actual situation of the flow field, forcing the water flow of the spoilers and its downstream to change the flow direction to achieve the purpose of reducing the ship's resistance. The present invention also improves the propulsion performance of the propeller to a certain extent by modulating the direction of the water flow, which can effectively improve the speed of the ship. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of streamlines near the hull in front of the propeller shaft of the present invention.

[0027] Figure 2 It is a schematic diagram of the streamlines near the hull after the spoiler is installed in front of the propeller shaft of the present invention.

[0028] Figure 3 It is a schematic diagram of the angle of attack of the spoiler of the present invention and the local incoming flow.

[0029] Figure 4 This is a schematic diagram of the stern flow field before the spoiler is installed according to the present invention.

[0030] Figure 5 This is a schematic diagram of the flow field at the stern of a ship after a spoiler is installed according to the present invention. DETAILED DESCRIPTION

[0031] The specific implementation of the present invention is described below in conjunction with the accompanying drawings.

[0032] like Figure 1-Figure 5 As shown, a method for adjusting the flow field near the hull at the stern of a ship comprises the following steps:

[0033] Through numerical calculations, model tests and other means, the flow field information such as the direction of the water flow near the hull is obtained. Spoilers with inclined angles are arranged at appropriate positions to force the water flow flowing obliquely downward and backward at a specific position to flow horizontally backward. Flow detours are arranged according to the angle of attack of the water flow near the hull of the ship. It is necessary to ensure that the spoiler can adjust the direction of the water flow upward without causing flow separation on the back of the spoiler due to excessive angle of attack. The overall velocity component of the water flow behind the spoiler in the vertical direction will also decrease. This device makes the flow near the wall of the downstream hull regular. According to the differential expression of the streamline direction of the velocity components Vx, Vy, and Vz of the local water flow velocity in three orthogonal directions:

[0034]

[0035] Calculate the flow field near the hull and select the location of the spoiler according to the ship type and working conditions;

[0036] The streamlines near the stern hull are obtained by numerical calculations, model tests and other means, and spoilers are arranged where the streamlines start to flow downward in front of the stern shaft. This position should be the position after the streamlines change from flowing obliquely upward from the bilge to flowing obliquely downward. This arrangement can change the direction of the water flow in the flow field behind the stern to the greatest extent, thereby reducing the ship's resistance.

[0037] exist Figure 2 The spoiler is arranged at the position shown, and the spoiler acts like a hydrofoil. In order to allow the water flow on both sides of the spoiler to flow out along the trailing edge of the spoiler, the attack angle of the spoiler cannot be too large to avoid flow separation on the back of the spoiler. Flow separation will increase resistance and reduce the ability to change the streamline near the hull.

[0038] After installing the spoiler, the overall impact of the hull on the surrounding water flow becomes smaller, thereby reducing the ship's resistance.

[0039] Figure 4 , Figure 5 The flow field at the stern before and after the installation of the spoiler is given respectively. The DPC cloud diagram represents the dynamic pressure coefficient, and the lines represent the friction lines, which are similar to the streamlines around the hull. In front of the stern shaft outlet, on both sides of the hull, near the hull, there is generally a streamline flowing from the bottom of the ship to along the hull, and backward and upward. This streamline begins to turn to flow backward and downward when it flows to a position close to the height of the tail shaft. The spoiler is arranged at the position where this streamline begins to turn and flow downward, so that the energy of this downward flow is weakened. The flow behind the spoiler is more of a horizontal backward flow rather than a downward and rearward flow. In this way, from an energy perspective, the flow interference of the hull on the surrounding water flow is reduced, thereby achieving the effect of drag reduction.

[0040] Design the angle of attack of the spoiler to the incoming flow.

[0041] The purpose of setting up spoilers is to change the direction of the water flow that originally started to flow downward, so the spoiler must have a certain angle of attack on the horizontal and local flow. Numerical calculations are used to evaluate the drag reduction effect corresponding to each angle of attack, and the total resistance value R0 without the baffles installed is compared with the total resistance R0 of the ship after the baffles are installed. i , i = 1, 2...n. This determines the final angle of attack. The total resistance value R i is the resistance on the wet surface area of ​​the ship F·n x Points:

[0042]

[0043] Evaluate the effectiveness of the device in reducing ship resistance and, based on the effectiveness, determine whether to continue modifying the spoiler solution in terms of position and angle of attack.

[0044] The drag reduction effect of the device is verified by numerical calculation or model test. If the ship resistance can be reduced at the position selected in the previous step and the effect of reducing resistance meets the given requirements, the design is considered to be completed. If the amount of resistance reduction d is required to be greater than 2%:

[0045] d=R1 / R0>2%.

[0046] In the prior art, the appendages arranged at the rear of the ship are often intended to induce vortices, and to avoid premature separation of the boundary layer by generating vortices early, thereby reducing the pressure difference resistance on the hull. There are also appendages arranged at the rear of the ship to generate vortices for the purpose of improving the wake of the ship, thereby improving the propeller propulsion efficiency and achieving the effect of reducing the power received by the ship. This device reduces the resistance of the ship by changing the flow direction of the water flow near the wall of the stern, and can also achieve the effect of reducing the power received by the ship. The device of the present invention only requires the ability to change the direction of the water flow, and does not require the generation of vortices, so a flatter shape can be used, which can avoid the occurrence of natural cavitation. The mechanism of acting on the flow field is simple, and compared with similar previous equipment, it has better practicality in engineering.

[0047] The present invention arranges a spoiler on the hull in front of the stern shaft to adjust the water flow from flowing obliquely downward to flowing horizontally backward, thereby reducing the resistance of the ship and improving the propeller propulsion efficiency. Flow field information such as the direction of the water flow near the hull is obtained by means of numerical calculation, model testing and the like. An inclined spoiler is arranged at a suitable position to force the water flow flowing obliquely downward and backward at a specific position to flow horizontally backward. The detour plate is arranged according to the angle of attack of the water flow near the outer shell of the ship. It is necessary to ensure that the spoiler can adjust the direction of the water flow upward without causing flow separation on the back of the spoiler due to an excessively large angle of attack. The velocity component of the water flow behind the spoiler in the vertical direction as a whole will also be reduced. The device makes the flow near the wall of the downstream hull regular.

[0048] The present invention starts from the flow mechanism near the wall behind the ship, and changes the local flow field by adding spoilers to reduce the resistance of the ship. The flow field information near the wall in front of the ship's tail shaft is obtained by means of numerical calculation, model experiment or actual ship measurement. The spoilers are arranged according to the actual situation of the flow field, and the water flow of the spoilers and their downstream is forced to change the flow direction to achieve the purpose of reducing the resistance of the ship. The present invention also improves the propulsion performance of the propeller to a certain extent by modulating the direction of the water flow, which can effectively improve the speed of the ship.

[0049] The solution proposed by the present invention has a simple structure and a clear mechanism of action on the flow field. The spoiler is installed on the outside of the hull and is relatively independent of the ship design, which can further improve the performance of the ship without interfering with the shape of the hull. After the device is arranged, the drag reduction effect is significant, which effectively supports the design of ships with higher energy efficiency requirements. By arranging a spoiler on the hull in front of the stern shaft, the water flow is adjusted from oblique downward flow to horizontal backward flow, thereby reducing the resistance of the ship and improving the propeller propulsion efficiency.

[0050] The above description is an explanation of the present invention, not a limitation of the present invention. The scope of the present invention is defined in the claims. Any form of modification may be made within the scope of protection of the present invention.

Claims

1. A method for regulating the flow field near the hull at the stern of a ship, characterized in that: The steps include: Step 1: Calculate the flow field near the hull according to the ship type and working conditions, and select the location of the spoiler; The streamlines near the stern hull are obtained based on numerical calculations and model tests, and spoilers are arranged where the streamlines start to flow downward in front of the stern shaft. Step 2: Design the attack angle of the spoiler to the incoming flow; Numerical calculations are used to evaluate the drag reduction effect corresponding to each angle of attack; Among them, R i is the total resistance value after installing the spoiler; i = 1, 2...n; F·n x Resistance on the wet surface area of ​​the ship; Compare the total resistance value R0 before the installation of spoilers and the total resistance R after the installation of spoilers i Decide which angle of attack to use; Step 3: Evaluate the effect of spoilers in reducing ship resistance and decide whether to continue modifying the spoiler plan based on the effect; The drag reduction effect of the device is verified by numerical calculation or model test.

2. A method for adjusting the flow field near the hull at the stern of a ship according to claim 1, characterized in that: In the third step, the resistance reduction d is required to be greater than 2%: d=R1 / R0>2%.

3. A method for adjusting the flow field near the hull at the stern of a ship according to claim 2, characterized in that: According to the local water flow velocity in three orthogonal directions, the differential expression of the streamline direction is:

4. A method for adjusting the flow field near the hull at the stern of a ship according to claim 1, characterized in that: In the first step, the spoiler is arranged at a position after the streamline changes from oblique upward flow from the bilge to oblique downward flow.

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