Frictional resistance reduction device, moving body, and frictional resistance reduction method

Abstract

To reduce friction resistance generated between a movable body and a fluid.SOLUTION: A friction resistance reduction device 20 comprises a face sheet 30 for being brought into contact with a fluid F, and a vibration source 40 that applies vibrations to the face sheet 30. A vibration frequency is in the range of 10-250 kHz, and the maximum amplitude of the vibration is in the range of 10-20 μm.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a frictional resistance reduction device, a moving body, and a frictional resistance reduction method. [Background technology]

[0002] Conventionally, moving bodies such as automobiles, airplanes, and ships have been used. When these moving bodies move through a fluid such as air or water, they encounter resistance from the fluid. When a moving body encounters resistance from a fluid, there are problems such as a decrease in the moving body's speed and an increase in the moving body's energy consumption. To solve these problems, research is being conducted to reduce the resistance that moving bodies encounter from a fluid. The resistance that moving bodies encounter from a fluid mainly includes pressure resistance (shape resistance) and friction resistance. Of these, research on pressure resistance has progressed relatively well, and various technologies have been proposed to reduce pressure resistance.

[0003] Research into reducing frictional resistance is also underway. Conventional techniques for reducing frictional resistance include providing irregularities such as riblets or grooves on the surface that comes into contact with the fluid, making the surface that comes into contact with the fluid superhydrophobic (ultra-water-repellent), and forming an air layer on the surface that comes into contact with the fluid. However, these techniques have not yet achieved a sufficient effect of reducing frictional resistance.

[0004] Another known technique for reducing frictional resistance is to apply vibrations to a surface in contact with a fluid. Patent Documents 1 and 2 disclose techniques for reducing frictional resistance with a fluid by applying ultrasonic vibrations to a surface in contact with the fluid. Non-Patent Document 1 also discloses a technique for reducing frictional resistance with a fluid by applying transverse waves perpendicular to the direction of fluid flow to a surface in contact with the fluid. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 110096 / 1983 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-185409 [Non-patent literature]

[0006] [Non-Patent Document 1] Yiqing Du et al., "Suppressing Wall Turbulence by Means of a Transverse Traveling Wave," Science 288 (5469), May 19, 2000, pp. 1230-1234 Summary of the Invention [Problem to be solved by the invention]

[0007] However, there is a problem in that a sufficient effect of reducing frictional resistance is not obtained even with the techniques disclosed in Patent Documents 1 and 2 and Non-Patent Document 1. For example, the technique disclosed in Non-Patent Document 1 only achieves a maximum frictional resistance reduction effect of about 20 to 30% in an idealized model.

[0008] Dolphins are known to be able to swim at high speeds in the ocean. The present inventor focused on this point and conducted research into the mechanism by which dolphins are able to swim at high speeds in the ocean. Dolphins are known to be able to perceive the terrain and the location of prey fish by emitting ultrasonic waves and listening to the reflected sounds. As a result of this research, the present inventor discovered that the ultrasonic waves emitted by dolphins are involved in the mechanism by which dolphins are able to swim at high speeds in the ocean. Specifically, the present inventor discovered that the ultrasonic waves emitted by dolphins vibrate their skin, thereby significantly reducing the frictional resistance between the skin and seawater. Based on a hypothesis, the present inventor conducted a large-scale fluid simulation using a simplified flat plate model and was the first to discover that so-called small-amplitude, wave-like ultrasonic vibrations can significantly reduce frictional resistance. Furthermore, the present inventor clarified the characteristics of ultrasonic vibrations on the wall of a moving object that can significantly reduce frictional resistance.

[0009] The present invention has been made in consideration of the above points, and has as its object to reduce the frictional resistance that occurs between the surface of a moving body and a fluid. [Means for solving the problem]

[0010] The frictional resistance reduction device according to the present invention comprises: The device comprises a surface plate that comes into contact with a fluid, and a vibration source that applies wave-like vibrations to the surface plate, The frequency of the vibration is 10 kHz or more and 250 kHz or less, The maximum amplitude of the vibration is not less than 10 μm and not more than 20 μm.

[0011] In the device for reducing frictional resistance according to the present invention, the wavelength of the wave-like vibration may be not less than 100 μm and not more than 150 μm.

[0012] The moving body according to the present invention is The friction resistance reduction device is provided.

[0013] The method for reducing frictional resistance according to the present invention comprises: a step of applying wave-like vibrations from a vibration source to a surface plate that comes into contact with the fluid; The frequency of the vibration is 10 kHz or more and 250 kHz or less, The maximum amplitude of the vibration is not less than 10 μm and not more than 20 μm. [Effects of the Invention]

[0014] According to the present invention, it is possible to reduce the frictional resistance occurring between the wall surface of the moving body and the fluid. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram schematically showing a moving body equipped with a frictional resistance reduction device according to the present invention. [Figure 2] FIG. 2 is a diagram showing a frictional resistance reduction device. [Figure 3]FIG. 3 is a diagram for explaining vibration of the vibration source of the frictional resistance reduction device. [Figure 4] FIG. 4 is a diagram showing an example of the results of the turbulence simulation. [Figure 5] FIG. 5 is a diagram showing an example of the results of the turbulence simulation. [Figure 6] FIG. 6 is a diagram showing an example of the results of the turbulence simulation. [Figure 7] FIG. 7 is a graph showing an example of the friction resistance coefficient calculated by the turbulence simulation. [Figure 8] FIG. 8 is a graph showing another example of the frictional resistance coefficient calculated by the turbulence simulation. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of the present invention will be described below with reference to the drawings. In the drawings attached to this specification, the scale and aspect ratios of the actual objects have been appropriately changed and exaggerated for the sake of ease of illustration and understanding.

[0017] Furthermore, terms used in this specification that specify shapes, geometric conditions, and their degrees, such as "parallel," "orthogonal," and "identical," as well as values ​​of lengths and angles, are not to be construed as being bound by strict meanings, but rather as including a range within which similar functions can be expected.

[0018] FIG. 1 is a schematic diagram of a mobile body 10 equipped with a frictional resistance reduction device 20 according to the present invention, and FIG. 2 is a diagram illustrating the frictional resistance reduction device 20. The mobile body 10 of this embodiment travels through a fluid F. While FIG. 1 illustrates an example in which the mobile body 10 is an automobile, the mobile body 10 is not limited to automobiles. The mobile body 10 includes land mobile bodies, water mobile bodies, underwater mobile bodies, and air mobile bodies. Land mobile bodies include, for example, automobiles such as passenger cars, buses, and trucks, and trains such as trains, bullet trains, and linear motor cars. Water mobile bodies include, for example, ships such as passenger ships, cargo ships, fishing boats, research vessels, yachts, and canoes. Underwater mobile bodies include, for example, submarines. Air mobile bodies include, for example, airplanes, helicopters, and drones. The mobile body 10 may be a manned mobile body or an unmanned mobile body.

[0019] Examples of the fluid include gases such as air, and liquids such as fresh water and seawater. When the mobile body 10 is a land mobile body or an air mobile body, the fluid may be gases such as air. When the mobile body 10 is an underwater mobile body, the fluid may be liquids such as fresh water and seawater. When the mobile body 10 is an aquatic mobile body, the fluid may be liquids such as fresh water and seawater and / or gases such as air.

[0020] The frictional resistance reduction device 20 according to the present invention can be applied not only to the moving body 10 but also to any location where frictional resistance may occur between the moving body and a fluid. The frictional resistance reduction device 20 can also be applied to, for example, oil and natural gas pipelines, buildings, factories, power plants, bridges, houses, and other structures, as well as wind power generation devices, wave power generation devices, and the like.

[0021] The frictional resistance reduction device 20 of this embodiment includes a surface plate (wall surface of a moving body) 30 that comes into contact with the fluid F, and a vibration source 40 that applies vibrations (ultrasonic vibrations) to the surface plate 30. The surface plate 30 includes a pair of main surfaces 32, 34. The pair of main surfaces 32, 34 includes a first surface 32 that comes into contact with the fluid F and a second surface 34 that faces the first surface 32.

[0022] In the example shown in FIG. 1 , the frictional resistance reduction device 20 is provided on the roof of the mobile body 10. In this case, the first surface 32 of the surface plate 30 forms the surface of the roof of the mobile body 10. However, this is not limiting, and the surface plate 30 may be installed so that the first surface 32 forms the surface of another part of the body of the mobile body 10. Furthermore, the surface plate 30 may be installed so that the first surface 32 forms the surface of a window such as a front window, side window, or rear window of the mobile body 10. Note that the "surface" of the roof, body, window, etc. refers to the surface that comes into contact with a fluid (air) F outside the mobile body 10.

[0023] In the example shown in FIG. 1 , when the moving body 10 moves toward the left of the paper in the fluid F, the fluid F flows toward the right of the paper relative to the moving body 10 (see the arrows in FIGS. 1 and 2 ). In the example shown in FIGS. 1 and 2 , the first surface 32 of the faceplate 30 is disposed so as to extend in a direction parallel to the flow direction of the fluid F (the direction of the arrow), but this is not limited thereto. The first surface 32 may extend in a direction inclined at an angle relative to the flow direction of the fluid F. The angle between the extension direction of the first surface 32 and the flow direction of the fluid F may be greater than or equal to 0 degrees and less than 90 degrees. Preferably, the angle between the extension direction of the first surface 32 and the flow direction of the fluid F may be greater than or equal to 0 degrees and less than 45 degrees. More preferably, the angle between the extension direction of the first surface 32 and the flow direction of the fluid F may be greater than or equal to 0 degrees and less than 30 degrees.

[0024] In this embodiment, the vibration source 40 applies ultrasonic vibrations having a specific frequency and maximum amplitude to the surface plate 30, thereby significantly reducing the frictional resistance generated between the fluid F and the surface plate 30 (first surface 32). Such a frictional resistance reduction device 20 will be described in detail below.

[0025] The surface plate 30 can be made of a material such as metal, glass, ceramics, or resin. From the viewpoint of properly transmitting vibrations from the vibration source 40 to the entire surface of the surface plate 30, it is preferable that the material of the surface plate 30 has a certain degree of rigidity. The surface plate 30 may be a flat plate formed entirely in a flat shape, or a curved plate formed entirely in a curved shape. In particular, the first surface 32 of the surface plate 30 may be either a flat surface or a curved surface.

[0026] The vibration source 40 has a function of applying vibrations having a predetermined frequency and maximum amplitude to the surface plate 30. In particular, the vibration source 40 may have a function of applying wave-like ultrasonic vibrations to the surface plate 30 along the extension direction of the surface plate 30. When the frictional resistance reduction device 20 is incorporated into the moving body 10, the vibration source 40 may have a function of applying wave-like ultrasonic vibrations to the surface plate 30 along the movement direction of the moving body 10. When the frictional resistance reduction device 20 has multiple vibration sources 40, the vibrations generated by the vibration sources 40 have a phase difference from each other, so it is important to induce waves (traveling waves, backward waves, standing waves) along the wall of the moving body (surface plate 30).

[0027] The vibration source 40 has a vibrator that generates vibrations. Examples of vibrators that can be used include electrostrictive and magnetostrictive vibrators, such as a bolted Langevin (BL) vibrator, a ferrite vibrator, and a PZT (lead zirconate titanate) vibrator. The vibrator of this embodiment is configured to generate ultrasonic vibrations. In particular, the vibrator is configured to generate ultrasonic vibrations having a specific frequency and maximum amplitude, as described below. In the example shown in FIG. 2 , the vibration source 40 is arranged so as to contact a portion of the second surface 34 of the faceplate 30. The vibration source 40 may also be arranged so as to contact the entire second surface 34 of the faceplate 30. The vibration source 40 applies vibrations to the faceplate 30 via the second surface 34. This causes the first surface 32 of the faceplate 30 to vibrate at a predetermined frequency and maximum amplitude. However, the present invention is not limited to this. The vibration source 40 may also be arranged so as to contact a portion of the first surface 32 of the faceplate 30. The vibration source 40 may also be arranged so as to contact an edge surface of the faceplate 30. The end face is a face that connects the first face 32 and the second face 34 of the surface plate 30 to each other.

[0028] In this embodiment, the frictional resistance reduction device 20 further includes a control unit 42, an input unit 44, and a display unit 46. The control unit 42 controls the vibration source 40 and the display unit 46. In particular, the control unit 42 controls the vibration source 40 so that it vibrates at a predetermined frequency and maximum amplitude. The control unit 42 also transmits information about the vibration source 40 to the display unit 46. The input unit 44 receives instructions from a user. The input unit 44 transmits a signal corresponding to the content input by the user to the control unit 42. The control unit 42 receives the signal from the input unit 44 and controls the vibration source 40 based on this signal. The content of the instructions input to the input unit 44 is not particularly limited, and may be, for example, turning on / off the vibration of the vibration source 40, various vibration-related settings, etc. The display unit 46 displays information about the vibration source 40 based on the signal received from the control unit 42. The information displayed on the display unit 46 is not particularly limited, and may be, for example, the on / off state of the vibration of the vibration source 40, vibration-related settings, etc.

[0029] The control unit 42 is configured by, for example, a CPU (Central Processing Unit). The control unit 42 may include one CPU or multiple CPUs. The control unit 42 may include a volatile or non-volatile storage device for storing information related to the vibration of the vibration source 40. The input unit 44 may include, for example, a button, a keyboard, a mouse, a touch panel, etc. The display unit 46 may include, for example, a liquid crystal display, an organic electroluminescence display, or a cathode ray tube (CRT) display. The input unit 44 and the display unit 46 may be integrated. For example, a liquid crystal display may be used as the display unit 46, and a touch panel overlaid on the liquid crystal display may be used as the input unit 44.

[0030] Next, the vibration generated by vibration source 40 will be described in detail. FIG. 3 is a diagram for explaining the vibration of vibration source 40. The vibration imparted to surface plate 30 from vibration source 40 is, for example, a sine wave as shown in FIG. 3. In this embodiment, the frequency of the vibration imparted to surface plate 30 from vibration source 40 is 10 kHz or more and 250 kHz or less. Furthermore, the maximum amplitude A of the vibration imparted to surface plate 30 from vibration source 40 is 10 μm or more and 20 μm or less.

[0031] The present inventors conducted extensive research into the mechanism by which dolphins are able to swim at high speeds in the ocean and discovered that ultrasonic waves emitted by dolphins travel through their skin, vibrating it and significantly reducing the frictional resistance that occurs between their skin and seawater. Further research into the ultrasonic waves emitted by dolphins revealed that ultrasonic vibrations with a frequency of 10 kHz to 250 kHz and a maximum amplitude A of 10 μm to 20 μm exhibit a particularly significant effect in reducing frictional resistance. In the frictional resistance reduction device 20 of this embodiment, ultrasonic vibrations with this specific frequency and maximum amplitude A are applied from the vibration source 40 to the surface plate 30, thereby significantly reducing the frictional resistance that occurs between the fluid F and the surface plate 30.

[0032] It has traditionally been believed that applying ultrasonic vibrations with a relatively large maximum amplitude A to a surface in contact with a fluid would produce a greater frictional resistance reduction effect. For example, in the prior art disclosed in the aforementioned Patent Document 2, ultrasonic vibrations with a large maximum amplitude A exceeding 20 μm were applied to a surface in contact with a fluid. However, as a result of further research into the characteristics of ultrasonic waves emitted by dolphins, the present inventors discovered that ultrasonic vibrations with a small maximum amplitude A of 10 μm to 20 μm produce a much greater frictional resistance reduction effect than ultrasonic vibrations with a large maximum amplitude A exceeding 20 μm, as previously believed. Thus, it was previously unknown that applying ultrasonic vibrations with a small maximum amplitude A of 10 μm to 20 μm can produce a much greater frictional resistance reduction effect. As will be described later using turbulence simulation results, the present inventors have demonstrated that this embodiment can reduce frictional resistance 100%, i.e., to zero, and may even be able to make frictional resistance negative under certain conditions. The fact that the frictional resistance is negative means that a driving force can be obtained from the fluid F by the vibration applied to the surface plate 30, which is a major technological advancement that overturns conventional wisdom.

[0033] The mechanism by which a significant frictional resistance reduction effect is achieved when the frequency of the vibration applied to the surface plate 30 from the vibration source 40 is 10 kHz or more and 250 kHz or less, and the maximum amplitude A is 10 μm or more and 20 μm or less, is presumed to be as follows: When the fluid F moves relative to the surface plate 30 (first surface 32), the flow direction of the fluid F may reverse in the vicinity of the first surface 32. This reversal of the flow direction may occur particularly when the first surface 32 has minute irregularities.

[0034] The same phenomenon occurs in the above-mentioned technology of providing irregularities such as riblets and grooves on a surface in contact with a fluid. In conventional technology, this phenomenon generates vortices in the fluid flow, resulting in the existence of an area where the fluid flow direction is reversed near the surface in contact with the fluid. As a result, the conventional technology also exhibits a frictional resistance reduction effect, but the effect is insufficient.

[0035] In the frictional resistance reduction device 20 of this embodiment, by vibrating the surface plate 30 at a frequency of 10 kHz to 250 kHz and a maximum amplitude A of 10 μm to 20 μm, the fluid F near the first surface 32 also vibrates with the same velocity component as the velocity component of the surface plate 30. As a result, the reversed velocity component of the fluid F near the first surface 32 interacts with the velocity component of the fluid F generated by the vibration of the surface plate 30, and the reversed velocity component of the fluid F, i.e., the velocity component along the traveling direction of the moving body 10, increases. This produces a significant effect of reducing wall friction resistance.

[0036] The wavelength λ of the vibrations applied from the vibration source 40 to the surface plate 30 is preferably 100 μm or more and 150 μm or less. When the vibrations applied from the vibration source 40 to the surface plate 30 have such a wavelength λ, an even greater effect of reducing frictional resistance can be achieved.

[0037] The relative velocity of the vibrations imparted from the vibration source 40 to the surface plate 30 may be 5 m / sec or more and 15 m / sec or less. Here, the relative velocity of the vibrations refers to the propagation speed of the vibrations, also called the phase velocity. When the vibrations imparted from the vibration source 40 to the surface plate 30 have such a relative velocity, an even greater frictional resistance reduction effect can be achieved.

[0038] The vibrations applied from the vibration source 40 to the surface plate 30 are wave-like ultrasonic vibrations. The wave-like ultrasonic vibrations may be any of progressive waves, backward waves, and standing waves. When the vibrations are progressive waves, the vibrations proceed in the same direction as the direction of travel of the fluid F. For example, in the example shown in Figures 1 and 2, when the vibrations are progressive waves, the vibrations proceed to the right of the page, the same as the direction of travel of the fluid F. When the vibrations are backward waves, the vibrations proceed in the opposite direction to the direction of travel of the fluid F. For example, in the example shown in Figures 1 and 2, when the vibrations are backward waves, the vibrations proceed to the left of the page, the opposite to the direction of travel of the fluid F. When the vibrations are standing waves, the vibrations do not proceed in either direction but continue to vibrate in place. Preferably, the vibrations applied from the vibration source 40 to the surface plate 30 are progressive waves or standing waves. More preferably, the vibrations applied from the vibration source 40 to the surface plate 30 are progressive waves. This allows for an even greater frictional resistance reduction effect.

[0039] Next, the method for reducing frictional resistance according to this embodiment will be described.

[0040] First, the user inputs an instruction to the input unit 44 (first input step). In the first input step, an instruction to start (turn ON) vibration of the vibration source 40 is input. This input can be performed by pressing a vibration start button, pressing a key on a keyboard corresponding to start vibration, clicking an area corresponding to start vibration using a mouse, touching an area corresponding to start vibration using a touch panel, or the like. The first input step may be performed while the surface plate 30 is in contact with the fluid F. Alternatively, the first input step may be performed while the surface plate 30 is not in contact with the fluid F, and then the surface plate 30 comes into contact with the fluid F. Alternatively, the first input step may be performed while the moving object 10 is stationary or while the moving object 10 is moving. In addition to the above, various settings related to vibration may also be performed in the first input step. The input unit 44 transmits a signal corresponding to the content input by the user to the control unit 42.

[0041] When the control unit 42 receives a signal from the input unit 44 instructing the vibration source 40 to start vibrating, the control unit 42 controls the vibration source 40 to vibrate. In particular, the control unit 42 vibrates the vibrator of the vibration source 40. As a result, the vibration source 40 applies vibration to the surface plate 30 that comes into contact with the fluid (vibration applying step). The frequency of this vibration is 10 kHz or more and 250 kHz or less, and the maximum amplitude A is 10 μm or more and 20 μm or less.

[0042] The control unit 42 transmits information such as the ON / OFF state of vibration of the vibration source 40 and settings related to vibration to the display unit 46. The display unit 46 displays information related to the vibration source 40 based on the signal received from the control unit 42 (display step).

[0043] When stopping the vibration of the vibration source 40, the user inputs an instruction to the input unit 44 (second input step). In the second input step, an instruction to stop (turn off) the vibration of the vibration source 40 is input. This input is performed in the same manner as the first input step, using a button, keyboard, mouse, touch panel, or the like. The second input step may be performed while the surface plate 30 is in contact with the fluid F. Alternatively, the second input step may be performed after the surface plate 30 is no longer in contact with the fluid F. Alternatively, the first input step may be performed while the moving object 10 is moving, or after the moving object 10 has stopped. The input unit 44 transmits a signal corresponding to the content input by the user to the control unit 42.

[0044] When the control unit 42 receives a signal from the input unit 44 instructing the vibration source 40 to stop vibrating, the control unit 42 controls the vibration source 40 to stop vibrating the vibration source 40 .

[0045] The frictional resistance reduction device 20 of this embodiment comprises a surface plate 30 that comes into contact with the fluid F and a vibration source 40 that imparts vibrations to the surface plate 30, the vibration frequency being 10 kHz or more and 250 kHz or less, and the maximum amplitude of the vibration being 10 μm or more and 20 μm or less.

[0046] The method for reducing frictional resistance in this embodiment includes a step of applying vibration from a vibration source 40 to a surface plate 30 that comes into contact with a fluid F, the vibration frequency being 10 kHz or more and 250 kHz or less, and the maximum amplitude of the vibration being 10 μm or more and 20 μm or less.

[0047] According to the frictional resistance reduction device 20 and the frictional resistance reduction method, by applying ultrasonic vibrations having a frequency of 10 kHz to 250 kHz and a maximum amplitude A of 10 μm to 20 μm to the surface plate 30, it is possible to achieve a much greater frictional resistance reduction effect than conventional techniques. In particular, as shown in the simulation results described below, according to the frictional resistance reduction device 20, the moving body 10, and the frictional resistance reduction method of this embodiment, it is possible to make the frictional resistance zero. Furthermore, depending on the conditions, it is also possible to make the frictional resistance negative.

[0048] The moving body 10 of this embodiment is equipped with the above-described frictional resistance reduction device 20.

[0049] Such a moving body 10 can achieve a much greater reduction in frictional resistance than conventional technology, thereby effectively suppressing a decrease in the speed of the moving body 10. It can also effectively reduce the energy consumption of the moving body 10. Therefore, it becomes possible to stably achieve both high-speed movement performance and environmental friendliness in the moving body 10.

[0050] In the frictional resistance reduction device 20 of this embodiment, the wavelength of the vibration is not less than 100 μm and not more than 150 μm.

[0051] Such a frictional resistance reduction device 20 can exert an even greater effect in reducing frictional resistance.

[0052] An example of a computer simulation carried out by the present inventor will be described below, but the present invention is not limited to the results of the following simulation.

[0053] A turbulent flow simulation using a computational fluid dynamics method was performed to calculate the frictional resistance that occurs between the fluid F and the surface plate 30 when wave vibrations are applied to the surface plate 30. For the fluid simulation, ANSYS Fluent 16.0 was used, and the turbulent flow simulation was performed using a two-dimensional flat plate model.

[0054] Figures 4 to 6 show an example of the results of a turbulent flow simulation. Figure 4 shows the entire model used in the turbulent flow simulation. Figure 5 shows an enlarged view of a portion near the surface of the top plate in Figure 4. Figure 6 shows a further enlarged view of a portion near the surface of the top plate in Figure 5. The white (uncolored) areas in Figures 4 to 6 represent the top plate. The colored areas represent the fluid. The horizontal dimension of the top plate in Figure 4 is the "length" of the top plate. In this simulation, the top plate has fine irregularities on its surface. The height from the lowest concave part to the highest convex part in this irregularity is 40 μm, and the arrangement pitch of the convex parts (the pitch between two adjacent convex parts) is 0.15 mm. The horizontal axis X and vertical axis Y in Figure 6 represent positions relative to the origin in the horizontal and vertical directions, respectively, and are expressed in meters (m).

[0055] In this model, the surface plate was fixed, and when a fluid flowed across the surface plate from left to right on the paper, the flow velocity at each position and the value of the frictional resistance occurring on the surface plate were calculated by simulation.

[0056] The turbulent flow simulation conditions are as follows: For each condition, turbulent flow simulation was performed for multiple values ​​within the range of values. <Surface plate> Length: 100mm~1000mm <Fluid> Flow velocity: 5m / sec~12.5m / sec Reynolds number Re: 1.26 x 10 6 (Re = length (L) × flow velocity (U) / dynamic viscosity (ν)) <Vibration> Frequency: 10kHz~250kHz Maximum amplitude A: 10μm~20μm Wavelength λ: 100μm~150μm Relative velocity: 5m / sec~15m / sec Kinematic viscosity coefficient (ν): 1.0×10 -6 m 2 ·s -1

[0057] Among these, the results of the turbulent flow simulation carried out under the following conditions are shown in FIGS. <Surface plate> Length (L): 1000mm <Fluid> Flow velocity (U): 12.5m / sec Reynolds number Re: 1.26 x 10 6 <Vibration> Frequency: 100kHz Maximum amplitude A: 20μm Wavelength λ: 150μm Relative velocity: 15m / sec Kinematic viscosity coefficient (ν): 1.0×10 -6 m 2 ·s -1

[0058] In Figures 4 to 6, the distribution of fluid speed (flow velocity) is shown by the shade of color. The shade of color indicates the relative magnitude of the flow velocity. Darker areas (closer to black) indicate a relatively slower flow velocity, and lighter areas (closer to white) indicate a relatively faster flow velocity.

[0059] As clearly shown in Figures 5 and 6, there is a dark area, or area of ​​low flow velocity, between two adjacent convexities on the surface of the top plate, around which a clockwise vortex is generated. The fluid on the opposite side of this vortex from the top plate flows in a direction roughly aligned with the overall fluid flow (arrow 51). In contrast, the fluid on the closer side of this vortex has reversed its flow direction, flowing in a direction roughly opposite to the overall fluid flow (arrow 52). This reversed fluid flow near the surface of the top plate exerts a force on the top plate toward the left of the page. This significantly reduces the frictional resistance between the fluid and the top plate.

[0060] Figures 7 and 8 are graphs showing the friction coefficients calculated by simulation. Figure 7 shows the friction coefficient when the frequency of the vibration applied to the surface plate is 100 kHz. Figure 8 shows the friction coefficient when the frequency of the vibration applied to the surface plate is 200 kHz. In Figures 7 and 8, the horizontal axis (t / T) represents the dimensionless time, and the vertical axis (C f ) indicates the friction resistance coefficient.

[0061] Friction resistance coefficient (C f ) is calculated using the following formula: C f =D f / (ρ×U×L / 2) where D f is the friction resistance, ρ is the density of the fluid, U is the velocity of the fluid (flow velocity), and L is the length of the surface plate. Note that the friction resistance coefficient (C f ) is a dimensionless number. When the surface plate is subjected to frictional resistance in the same direction as the fluid flow, that is, when the surface plate is subjected to a force in the right direction in Figures 4 to 6, the frictional resistance coefficient (C f ) takes a positive value. On the other hand, when the surface plate is subjected to frictional resistance in the direction opposite to the fluid flow, that is, when the surface plate is subjected to a force directed to the left in Figures 4 to 6, the frictional resistance coefficient (C f ) takes a negative value.

[0062] In Figures 7 and 8, G1 is a graph of a turbulent flow simulation using a coarse computational grid, G2 is a graph of a turbulent flow simulation using a fine computational grid, and G3 is a graph of a turbulent flow simulation using a very fine computational grid.

[0063] In the graphs shown in Figs. 7 and 8, the coefficient of friction (C f ) is a negative value. This indicates that in the model shown in Figures 4 to 6, when the fluid flows to the right, the surface receives a force to the left. In other words, the flow of the fluid generates a negative frictional resistance between the fluid and the surface. Therefore, according to the simulation results, it can be seen that the vibration applied to the surface generates a propulsive force from the fluid. [Explanation of symbols]

[0064] 10 Mobile 20 Friction resistance reduction device 30 Surface plate 32 Page 1 34 2nd page 40 Vibration source 42 Control Unit 44 Input section 46 Display section

Claims

1. A frictional resistance reduction device comprising: a surface plate that comes into contact with a fluid; and a vibration source that applies vibration to the surface plate, The frequency of the vibration is 10 kHz or more and 250 kHz or less, The frictional resistance reduction device, wherein the maximum amplitude of the vibration is 10 μm or more and 20 μm or less.

2. The device for reducing frictional resistance according to claim 1 , wherein the wavelength of the vibration is not less than 100 μm and not more than 150 μm.

3. A moving body comprising the frictional resistance reduction device according to claim 1 or 2.

4. providing vibrations from a vibration source to a surface plate that contacts the fluid; The frequency of the vibration is 10 kHz or more and 250 kHz or less, The method for reducing frictional resistance, wherein the maximum amplitude of the vibration is 10 μm or more and 20 μm or less.

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