Air flow evaluation method and evaluation system

Abstract

To enable an air drift due to a film thickness change of an oil film to be appropriately observed, even for an object of a three-dimensional structure.SOLUTION: The present invention includes the steps of: preparing an automobile vehicle; applying a coating of oil film to an observation surface of the vehicle; generating an air flow on the observation surface; and evaluating an air drift on the observation surface from a change of a film thickness of the oil film in a state of an air flow having occurred to the observation surface. The step for applying a coating of the oil film involves forming an oil film as a specific oil film which, when the observation surface includes an inclined or a vertical plane, is applied to the inclined or the vertical plane, oil viscosity and film thickness of which are set so that a drift speed of the specific oil film before an air flow is generated after application to the inclined or the vertical plane is 1.5 mm / minute or less.SELECTED DRAWING: Figure 13

Description

[Technical Field]

[0001] The technology disclosed herein belongs to the technical field of air flow evaluation methods and evaluation systems. [Background technology]

[0002] In the design of moving objects such as vehicles, there is a demand for designs that reduce aerodynamic resistance while enhancing the design of the moving object. Aerodynamic resistance is largely due to the air flow over the surface of the moving object. Therefore, if we can observe the air flow over the surface of the moving object, it will be possible to design a moving object that achieves both design and aerodynamic resistance reduction.

[0003] For example, Patent Document 1 discloses a wind tunnel testing method in which an actual vehicle is placed on a vehicle stand located inside a wind tunnel and the influence of wind passing through the wind tunnel on the actual vehicle is measured. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3716158 [Non-patent literature]

[0005] [Non-Patent Document 1] Tianshu Liu et al, AIAA JOURNAL, Vol.46, No.2, February 2008, p.476-p.485. Summary of the Invention [Problem to be solved by the invention]

[0006] Although the test method described in Patent Document 1 can measure the effect of aerodynamic resistance on a moving body (here, a vehicle), it is difficult to identify the parts that cause aerodynamic resistance and the air flow in those parts. In order to balance the design of a moving body with the reduction of aerodynamic resistance, a method for visualizing the air flow on the surface of a moving body is required.

[0007] The fluorescent oil film method, as described in Non-Patent Document 1, is known as a method for visualizing air flow on the surface of a moving object. In this method, a fluorescent oil film, which is an oil film containing a fluorescent dye, is applied to the surface of the object to be observed, and changes in the thickness of the fluorescent oil film due to fluid friction stress are captured as changes in the luminescence intensity of the fluorescent oil film. This makes it possible to observe the air flow occurring on the surface of the object to be observed as a distribution of friction stress vectors.

[0008] However, because moving objects such as vehicles have a three-dimensional structure, the surfaces to be observed are not limited to horizontal planes, but also include inclined planes that are inclined relative to the horizontal direction and vertical planes that are perpendicular to the horizontal direction. If an oil film is simply formed on these surfaces, the oil that forms the film will move due to its own weight. If this oil movement causes the oil film to become thinner in parts, or if changes in the oil film due to oil movement and changes in the oil film due to air flow occur simultaneously, it becomes difficult to properly evaluate the air flow.

[0009] For objects with high speeds (over 300 km / h) and high airflow velocities near the surface, such as aircraft, it is possible to observe oil flow by increasing the oil viscosity to suppress its movement. However, for objects with relatively slow speeds (20 km / h to 180 km / h), such as vehicles and drones, if the oil viscosity is too high, the fluid friction stress generated on the surface makes it difficult for the oil to flow, making it difficult to properly evaluate airflow. In particular, because the fluid friction stress is relatively small at the area where the air separates, it is difficult to evaluate airflow with highly viscous oil.

[0010] The technology disclosed here has been developed in consideration of these points, and its purpose is to enable appropriate observation of air flow due to changes in oil film thickness, even for objects with a three-dimensional structure. [Means for solving the problem]

[0011] In order to solve the above problems, the inventors of the present application conducted extensive research and found that by appropriately adjusting the thickness of the oil film and the viscosity of the oil that makes up the oil film, it is possible to appropriately reduce the effect of the oil film moving due to its own weight when the oil film is formed on an inclined or vertical surface.

[0012] That is, the technology disclosed herein is directed to an evaluation method for evaluating airflow around an object by observing an oil film applied to an observation surface located on the surface of the object, and includes an object preparation step of preparing an object with a three-dimensional structure having an inclined or vertical surface on its surface as the object, an oil film application step of applying an oil film to the observation surface of the object, a flow step of generating an airflow on the observation surface of the object, and an evaluation step of evaluating the airflow on the observation surface from changes in the film thickness of the oil film during the flow step.When the observation surface includes the inclined or vertical surface, the oil film application step is a step of forming an oil film with an oil viscosity and film thickness set so that the movement speed of the specific oil film on the inclined or vertical surface after application to the inclined or vertical surface and before generating the airflow is 1.5 mm / min or less.

[0013] This reduces the effect of oil movement due to its own weight on oil movement due to fluid friction stress. As a result, air flow can be evaluated by observing changes in oil film thickness even on inclined and vertical surfaces. Therefore, even for objects with a three-dimensional structure, it is possible to properly observe air flow due to changes in oil film thickness.

[0014] According to research by the inventors of the present application, the specific oil film is preferably an oil film having a viscosity of 10 centistokes (cs) to 100cs and a film thickness of 30 μm or less.

[0015] In particular, according to the research of the present inventors, it is preferable that the specific oil film is an oil film in which the viscosity of the oil is 10cs or more and less than 30cs and the film thickness is 10μm or less, or an oil film in which the viscosity of the oil is 30cs or more and less than 50cs and the film thickness is 20μm or less.

[0016] In this way, by optimizing the thickness and viscosity of the specific oil film, it is possible to suppress the movement of the oil due to its own weight while allowing the oil to move by fluid friction even at a relatively low movement speed, which allows more appropriate observation of air flow due to changes in the oil film thickness.

[0017] According to research by the inventors of the present application, it is preferable that the specific oil film is formed so that the thickness of the specific oil film becomes thinner as the viscosity of the oil decreases.

[0018] In other words, the lower the viscosity of the oil, the easier it is for the oil to move under its own weight. Therefore, the lower the viscosity of the oil, the thinner the film thickness is made, reducing the mass of the oil. This makes it possible to minimize the movement of oil under its own weight, and more appropriately observe the air flow due to changes in the oil film thickness.

[0019] In the air flow evaluation method, the oil film application process may be configured to be a process of applying the oil also to a portion of the object located immediately upstream of the observation surface when the inclined surface included in the observation surface is an inclined surface that slopes downward from the upstream side toward the downstream side of the air flow generated in the flow process, or when the vertical surface included in the observation surface is a vertical surface that extends perpendicular to the flow direction of the air flow.

[0020] In other words, if it takes a long time for the air flow velocity to reach the desired velocity during the flow process, the oil film may move before the desired velocity is reached, and the oil film may become excessively thin when the desired velocity is reached. In contrast, if oil is applied to the portion immediately upstream of the observation surface, the oil in that portion will move and be supplied to the observation surface, preventing the oil film from becoming excessively thin. This allows for more appropriate observation of the air flow due to changes in the oil film thickness.

[0021] In the air flow evaluation method, the specific oil film may be a fluorescent oil film formed from a fluorescent oil that is a mixture of oil and a fluorescent dye, the evaluation process may be a process of observing a change in film thickness from the luminescence intensity when light is irradiated onto the specific oil film, and the object preparation process may include a process of attaching a white film to the glass surface when the observation location of the object includes a glass surface.

[0022] That is, when the glass surface is bare, the light irradiated onto the specific oil film is transmitted through the glass surface, weakening the luminous intensity of the specific oil film. By attaching a white film to the glass surface, the light is reflected by the film, making it possible to maximize the luminous intensity of the specific oil film. This allows for more appropriate observation of air flow due to changes in oil film thickness, particularly when using an actual vehicle.

[0023] In the air flow evaluation method, the object may be an automobile vehicle, the observation surface may include a rear portion of the vehicle including the rear window of the vehicle as the inclined surface, and the flow process may be a process of causing air to flow from the front side of the vehicle toward the rear side of the vehicle.

[0024] That is, the rear surface of a vehicle, including the rear window, has a wide inclined surface, and when air flows from the front side of the vehicle to the rear side of the vehicle, it becomes an area where the air separates, resulting in relatively small fluid friction. On the other hand, vortices are generated by the separation of air at the rear surface of the vehicle, and these vortices attract the vehicle and generate aerodynamic resistance, making it an area of ​​high importance for evaluation. As described above, if the specific oil film is properly configured, it becomes possible to properly evaluate the air flow even at such a rear surface of the vehicle. In particular, it becomes possible to properly observe the air flow using an actual vehicle.

[0025] In the method for evaluating air flow in which the object is a vehicle, the observation surface may further include a front portion of the vehicle including the front window of the vehicle as the inclined surface, and the specific oil film formed on the front portion of the vehicle may be an oil film with a higher oil viscosity and a thicker film thickness than the specific oil film formed on the rear portion of the vehicle.

[0026] That is, the air flow velocity is higher at the front of the vehicle than at the rear of the vehicle. When the air flow velocity is high, the fluid friction stress is relatively large, so even with highly viscous oil, the oil film moves sufficiently due to the fluid friction stress. Furthermore, when the fluid friction stress is high, the amount of oil film that moves increases, so it is preferable to make the film thickness as thick as possible to prevent oil film breakdown. In this way, by selecting appropriate specific oil film conditions depending on the observation location, it becomes possible to more appropriately observe air flow using an actual vehicle.

[0027] In the method for evaluating air flow, it is preferable that the viscosity and film thickness of the oil constituting the specific oil film are set to such a value that when a panel material other than the object is placed horizontally and an oil film is applied, and then the panel material is turned vertical, the movement speed of the oil film is 1.5 mm / min or less.

[0028] With this configuration, the movement speed of the oil film formed on the vertical surface can be experimentally investigated, and the viscosity of the oil constituting the specific oil film and the film thickness of the specific oil film can be appropriately set, which allows for more appropriate observation of the air flow due to changes in the oil film thickness.

[0029] The technology disclosed herein also relates to an air flow evaluation system. Specifically, the system evaluates air flow around an object by observing an oil film applied to an observation surface located on the surface of the object, and includes: an automobile vehicle as the object; a flow generating device that generates an air flow on the surface of the vehicle; an imaging device that captures an image of the oil film applied to the observation surface while the air flow is generated by the flow generating device; and an evaluation device that evaluates the air flow on the observation surface by determining the thickness of the oil film from the image captured by the imaging device, wherein the observation surface to which the oil film is applied is a rear surface of the vehicle including a rear window, the flow generating device is disposed at the front of the vehicle and generates air flow from the front to the rear of the vehicle, and the specific oil film applied to the rear surface of the vehicle has an oil viscosity and film thickness that are set so that the specific oil film moves at a speed of 1.5 mm / min or less after being applied to the rear surface of the vehicle and before the air flow is generated.

[0030] This configuration also suppresses oil movement due to its own weight and allows oil to move due to fluid friction even at relatively low movement speeds. This allows airflow to be properly observed from changes in the thickness of the specific oil film at the rear of a vehicle, which has an inclined surface and low fluid friction. As a result, airflow on the surface of an actual vehicle, which is a three-dimensional object, can be properly observed. [Effects of the Invention]

[0031] As described above, the technology disclosed herein makes it possible to appropriately observe air flow due to changes in oil film thickness even for objects with three-dimensional structures. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1 is a schematic diagram illustrating an evaluation system according to an exemplary embodiment. [Figure 2] FIG. 2 is an enlarged perspective view showing the rear window and its vicinity. [Figure 3] FIG. 3 is a schematic diagram for explaining the principle of the fluorescent oil film method. [Figure 4] FIG. 4 is a schematic diagram showing an experimental system for setting specific oil film conditions. [Figure 5] FIG. 5 is a flowchart showing an experiment for setting the conditions for a specific oil film. [Figure 6] FIG. 6 is a cross-sectional view showing a calibrator for calibrating the film thickness relative to the emission intensity. [Figure 7] FIG. 7 is a graph showing the relationship between the emission intensity and the film thickness. [Figure 8] FIG. 8 is a graph showing the results of measuring the luminescence intensity when the oil viscosity is 10 cs. [Figure 9] FIG. 9 is a graph showing the amount of oil movement when the oil viscosity is 10 cs. [Figure 10] FIG. 10 is a graph showing the amount of oil movement when the oil viscosity is 30 cs. [Figure 11] FIG. 11 is a graph showing the amount of oil movement when the oil viscosity is 50 cs. [Figure 12] FIG. 12 is a graph showing the amount of oil movement when the oil viscosity is 100 cs. [Figure 13] FIG. 13 is a table showing the viscosity and film thickness of a specific oil film. [Figure 14] FIG. 14 is a flowchart for evaluating air flow. [Figure 15] FIG. 15 is an image showing the distribution of friction stress vectors around the rear window. DETAILED DESCRIPTION OF THE INVENTION

[0033] Hereinafter, exemplary embodiments will be described in detail with reference to the drawings. In the following description, the terms "upper," "lower," "front," "rear," "right," and "left" refer to the upper, lower, front, rear, right, and left directions as seen from the vehicle.

[0034] <Evaluation system configuration> Fig. 1 shows a schematic diagram of an air flow evaluation system 1 (hereinafter referred to as system 1) according to this embodiment. This system evaluates air flow on the surface of a vehicle 10 using the fluorescent oil film method. Here, we will explain the case where the observation surface is the area around the rear window 10a (see Fig. 2) on the back of the vehicle 10 (hereinafter referred to as the vehicle rear surface), and evaluate the air flow on this observation surface.

[0035] The system 1 comprises a vehicle 10 as an object to be observed, a flow generating device 2 that generates an air flow on the surface of the vehicle 10, a lighting device 3 that irradiates light onto the back of the vehicle 10, an imaging device 4 that photographs the back of the vehicle 10, and a calculator 5 that evaluates the air flow from the image acquired by the imaging device 4.

[0036] Vehicle 10 is an automobile. The rear surface of vehicle 10, which is the observation surface, forms an inclined surface that slopes downward toward the rear. In particular, in this embodiment, as shown in FIG. 1, in order to generate an airflow from the front to the rear of vehicle 10, the rear surface of vehicle 10 forms an inclined surface that slopes downward from the upstream side to the downstream side of the airflow. Note that in this specification, an inclined surface refers to a surface whose acute angle with respect to the horizontal plane is 20 degrees or more.

[0037] As shown in FIG. 2, the rear surface of the vehicle is covered with a white film 11 (hereinafter referred to as white film 11). More specifically, the white film 11 is attached so as to cover the glass surface of the rear window 10a from the front side. Furthermore, at the rear of the vehicle 10, the gap between the back door 1b of the trunk portion and the body is covered with the white film 11 so as to close the gap. During observation, an oil film is applied on top of the white film 11. In the following explanation, this oil film applied to the rear surface of the vehicle is referred to as a specific oil film.

[0038] The specific oil film is made of a fluorescent oil, which is a mixture of silicone oil and a fluorescent dye at a predetermined ratio. The fluorescent dye is a dye that emits light when exposed to at least ultraviolet (UV) light.

[0039] The flow generating device 2 is disposed in front of the vehicle 10 and causes air to flow from the front to the rear of the vehicle 10. The flow generating device 2 is a device that blows wind at a speed equivalent to the wind generated by running the vehicle, and is configured to be able to blow wind at a speed of, for example, 20 km / hour to 180 km / hour. The flow generating device 2 is configured, for example, by an electric fan.

[0040] The lighting device 3 is a lighting device capable of emitting ultraviolet light. The lighting device 3 is configured, for example, with an LED light. In FIG. 1, the lighting device 3 emits light from above, but in reality, like the imaging device 4, it is disposed at the rear of the vehicle 10 and arranged to emit light from the rear of the vehicle 10 onto the rear surface of the vehicle. A plurality of lighting devices 3 may be disposed. For example, one lighting device 3 may be disposed on each of the left and right sides of the rear of the vehicle 10 so that light is emitted onto the observation surface from the left and right. Furthermore, when there are a plurality of observation surfaces, a plurality of lighting devices 3 are disposed according to the number of observation locations.

[0041] The imaging device 4 is configured by, for example, a CCD (Charge Coupled Device) camera. The imaging device 4 captures a video of the specific oil film applied to the rear of the vehicle 10, specifically, the rear surface of the vehicle, in a state where an air flow is generated by the flow generating device 2. When there are multiple observation points, multiple imaging devices 4 are provided according to the number of observation points.

[0042] The calculator 5 is a device based on a well-known microcomputer. The calculator 5 includes a calculation unit 51, a storage unit 52, and a control unit 53. The calculator 5 may also include, for example, a display unit such as a display, an input unit such as a keyboard, and the like, although these are not shown. The storage unit 52 stores various data and information such as calculation processing programs. The calculation unit 51 is a central processing unit (CPU) that performs various calculation processes based on the information stored in the storage unit 52 and information input via the input unit. The storage unit 52 stores images acquired by the imaging device 4 and programs for operating the control unit 53. The control unit 53 outputs control signals to controlled objects and performs various controls based on the data stored in the storage unit 52 and the calculation results of the calculation unit 51.

[0043] In the above-mentioned fluorescent oil film method, the calculation unit 51 of the computer 5 calculates the thickness of the oil film from each image constituting the video captured by the imaging device 4, and evaluates the air flow on the surface of the vehicle 10. This method of evaluating the air flow from changes in film thickness will be described with reference to FIG. 3.

[0044] Figure 3 shows a fluorescent oil film OF formed on a horizontally spreading sample S, with an airflow generated along the surface. The oil film OF is partially swept away by the airflow, causing it to ripple. This results in variations in the oil film's thickness. The thicker the oil film OF formed from fluorescent oil, the higher its luminescence intensity, and the thinner the film, the lower its luminescence intensity. Therefore, by illuminating the oil film OF with light from the illumination device 3 and capturing the resulting luminescence with the imaging device 4, changes in film thickness can be observed as changes in luminescence intensity. The film thickness can then be calculated from the luminescence intensity, allowing for quantitative determination of changes in film thickness. Furthermore, the film thickness distribution can be used to determine locations where airflow separations and vortexes occur.

[0045] Furthermore, the vector of the oil film movement can be obtained by analyzing the change over time in the film thickness distribution (the change over time in the light emission distribution) from the video captured by the imaging device 4. Since the movement of the oil film is caused by air flow, the air flow can be evaluated by obtaining the vector of this oil film movement.

[0046] In this way, by determining the thickness of the oil film from the luminescence intensity, the air flow on the surface of sample S can be evaluated. Here, in vehicle 10, if the portion of the vehicle that extends approximately horizontally (for example, the hood or roof) is like sample S shown in FIG. 3, the oil film will not generally move unless an external force is applied. However, as mentioned above, the rear surface of vehicle 10 is an inclined surface. For this reason, there is a risk that the oil in the specific oil film applied to this portion will move due to its own weight. If the oil moves due to its own weight, the specific oil film will become partially thin, or if changes in film thickness due to oil movement and changes in film thickness due to air flow occur simultaneously, it will become difficult to properly observe the air flow.

[0047] Therefore, the inventors of the present application conducted extensive research and established the conditions for the specific oil film, particularly the viscosity of the oil that constitutes the specific oil film and the film thickness of the specific oil film, so that air flow can be observed even when the observation surface is an inclined surface. The conditions for the specific oil film will be explained in detail below with reference to Figures 4 to 13.

[0048] <Setting specific film thickness conditions> FIG. 4 shows a schematic diagram of an experimental system 100 for setting the conditions of a specific oil film, and FIG. 5 shows a flowchart for setting the conditions of a specific oil film.

[0049] (Step S11) To set the conditions for a specific oil film, first, in step S11, the measuring instruments of the experimental system 100 are arranged.

[0050] As shown in FIG. 4, the experimental system 100 includes a panel 101 arranged perpendicular to a wall 110, and an LED lighting device 102 and a camera 103 arranged on a floor 111.

[0051] The panel 101 is made of an aluminum plate. A white film 11 is attached to the entire surface of the panel 101. This white film 11 is made of the same material as the white film 11 attached to the rear of the vehicle in the above-mentioned evaluation system 1. During the experiment, an oil film is applied to the surface of the film. After the placement of the measuring instruments is complete, the panel 101 is removed to allow the oil film to be applied.

[0052] The LED lighting device 102 is placed behind the camera 103. It is placed above the camera 103 so that it irradiates the panel 101 with light from above the camera 103. The LED lighting device 102 irradiates the entire surface of the panel 101 with light.

[0053] The camera 103 is disposed so that its optical axis is perpendicular to the panel 101. The camera 103 is composed of a CCD camera.

[0054] (Step S12) Next, in step S12, the film thickness is calibrated relative to the emission intensity. As shown in FIG. 6, film thickness calibration is performed using a calibrator 120 having a recess 121 whose bottom surface is inclined at a constant gradient. Grease 122 is applied to the surface of the calibrator 120 except for the recess 121. After the recess 121 is filled with fluorescent oil, the recess 121 is covered from above by a glass plate 123. This glass plate 123 is intended to prevent leakage of the fluorescent oil when the calibrator 120 is placed on an inclined or vertical surface. Although not shown, the glass plate 123 has an area larger than the recess 121 when viewed from above so that it can cover the entire recess 121.

[0055] Film thickness calibration is performed by filling the recess 121 with fluorescent oil, placing the glass plate 123 on top, and then irradiating the fluorescent oil in the recess 121 with light and measuring the luminescence intensity. Figure 7 shows the results of film thickness calibration. This figure shows the results of film thickness calibration performed on fluorescent oil with a viscosity of 50 cs. The dashed-dotted curve C in Figure 7 represents the actual measurement results, and the solid line in Figure 7 represents the calibration line L obtained as a result of the calibration. In Figure 7, the horizontal axis represents the film thickness of the fluorescent oil filled in the recess 121, and the position where the film thickness is 0 μm is the boundary between the surface of the calibrator 120 and the shallow end of the recess 121. The luminescence intensity is observed even at the 0 μm film thickness on curve C because, as shown in Figure 6, an oil film with a thickness equal to the thickness of the grease 122 is actually formed.

[0056] The calibration line L is obtained by calculating an approximate line from the portion of the actual measurement results where the film thickness is less than 50 μm, and then horizontally moving the approximate line so that it passes through the origin while maintaining the slope.

[0057] The film thickness calibration as described above is performed for the fluorescent oil of each viscosity to be measured, and the calibration line L is calculated for the fluorescent oil of each viscosity.

[0058] (Step S13) Next, in step S13, fluorescent oil is applied to panel 101. The application work is performed by placing panel 101 in a horizontal position and spraying the fluorescent oil from above. More specifically, the application work is performed by placing a sprayer at a position about 50 cm above the horizontally placed panel 101 and spraying the fluorescent oil onto panel 101 in several steps.

[0059] (Step S14) Next, in step S14, in order to confirm the thickness of the oil film applied to the panel 101, light is irradiated onto the panel 101 and the luminescence intensity of the oil film at that time is detected.

[0060] (Step S15) In step S15, it is determined whether the oil film formed on panel 101 has the desired thickness. This determination is made by applying the emission intensity detected in step S14 to the calibration line L calculated in step S12 to calculate the film thickness. If the answer is YES, which means the oil film has the desired thickness, the process proceeds to step S16, but if the answer is NO, which means the oil film does not have the desired thickness, the process returns to step S13 and fluorescent oil is applied again.

[0061] (Steps S16 to S18) In step S16, video shooting is started. Specifically, the LED lighting device 102 and the camera 103 are turned on.

[0062] Next, in step S17, the panel 101 is placed on the wall in a position perpendicular to the horizontal direction, resulting in the panel 101 being in the state shown in FIG.

[0063] Then, in step S18, panel 101 is photographed for a predetermined time (for example, 5 minutes), and then the photographing is terminated.

[0064] (Step S19) Next, in step S19, the moving speed of the fluorescent oil due to its own weight is calculated based on the images acquired in steps S16 to S18, and the viscosity and film thickness at which the moving speed is 1.5 mm / min or less are extracted.

[0065] Figure 8 shows the results of detecting the luminescence intensity when the viscosity of the fluorescent oil is 10 cs and the film thickness is 30 μm. This luminescence intensity curve is a curve that shows the luminescence intensity at each position in the y direction (the up-down direction when the panel 101 is held vertically) at an arbitrary point in the x direction (the horizontal direction when the panel 101 is held vertically) of the panel 101. The horizontal axis represents the position in the y direction of the panel 101, with the top end being 0 mm and the bottom end being 200 mm. The positions where the luminescence intensity peaks indicate that the film thickness in that area is thick.

[0066] As shown in Figure 8, when the oil film conditions are a viscosity of 10 cs and a film thickness of 30 μm, the peak near 0 mm immediately after the start of measurement gradually shifts in the y direction. This indicates that the fluorescent oil is moving downward due to its own weight. By calculating the amount of movement of this peak, it is possible to calculate the movement speed of the oil film (strictly speaking, the movement speed of the fluorescent oil that makes up the oil film).

[0067] Figure 9 shows the amount of movement of fluorescent oil when the viscosity of the fluorescent oil is 10cs. Figure 10 shows the amount of movement of fluorescent oil when the viscosity of the fluorescent oil is 30cs. Figure 11 shows the amount of movement of fluorescent oil when the viscosity of the fluorescent oil is 50cs. Figure 12 shows the amount of movement of fluorescent oil when the viscosity of the fluorescent oil is 100cs. In Figures 9 to 12, the dashed straight line indicates the amount of movement when the movement speed is 1.5mm / min. In other words, the condition where the slope is less than the slope of the dashed line is an appropriate condition for a specific oil film.

[0068] As shown in Figure 9, when the viscosity is 10cs, the slope is greater than the dashed line when the film thickness is 30μm and 20μm, but is smaller than the dashed line when the film thickness is 10μm. This shows that when the viscosity of the fluorescent oil is 10cs, the effect of the fluorescent oil's own weight can be ignored if the film thickness is 10μm or less.

[0069] As shown in Figure 10, when the viscosity is 30cs, the slope is greater than the dashed line when the film thickness is 30μm, but when the film thickness is 20μm or less, the slope is smaller than the dashed line. This shows that when the viscosity of the fluorescent oil is 30cs, the effect of the fluorescent oil's own weight can be ignored if the film thickness is 20μm or less.

[0070] As shown in Figure 11, when the viscosity is 50cs, the slope is slightly larger than the dashed line when the film thickness is 30μm, but when the film thickness is 20μm or less, the slope is smaller than the dashed line. This shows that when the viscosity of the fluorescent oil is 50cs, the effect of the fluorescent oil's own weight can be ignored if the film thickness is 20μm or less. Furthermore, when the viscosity is 50cs, when the film thickness is 10μm or less, the oil hardly moves, and it was difficult to calculate the amount of movement from the emission intensity, so the amount of movement is 0mm.

[0071] As shown in Figure 12, when the viscosity is 100cs, the slope is slightly larger than the dashed line when the film thickness is 40μm, but when the film thickness is 30μm or less, the slope is smaller than the dashed line. This shows that when the viscosity of the fluorescent oil is 100cs, the effect of the fluorescent oil's own weight can be ignored if the film thickness is 30μm or less. Furthermore, when the viscosity is 100cs, when the film thickness is 30μm or less, the oil hardly moves, and it was difficult to calculate the movement amount from the emission intensity, so the movement amount is 0mm.

[0072] FIG. 13 is a table showing whether or not the conditions for a specific oil film are suitable. In the table of FIG. 13, × indicates an unsuitable condition for a specific oil film, and ○ indicates a suitable condition for a specific oil film. The conditions indicated by ○ are those under which the oil film movement speed calculated from the peak position of the luminescence intensity curve is 1.5 mm / min or less. These conditions are those under which the oil film movement speed is 1.5 mm / min or less when the panel 101 is positioned vertically. Therefore, they correspond to viscosity and film thickness such that when an oil film is applied to a vertical surface, the movement speed of the oil film constituting the oil film is 1.5 mm / min or less. Since the movement speed of the oil film formed on a vertical surface under these conditions is 1.5 mm / min or less, when an oil film is formed on an inclined surface with a fluorescent oil viscosity and film thickness that meets these conditions, the movement speed of the oil film will naturally be 1.5 mm / min or less. Therefore, the conditions indicated by ○ correspond to the oil viscosity and film thickness conditions under which the oil film travels at a speed of 1.5 mm / min or less after being applied to an inclined or vertical surface.

[0073] As shown in Figure 13, in the inventors' experiments, measurements were also taken when the viscosity of the fluorescent oil was 5cs, but in this case the volatility of the fluorescent oil was so high that the fluorescent oil evaporated during the measurement, making it impossible to perform the measurement. If the volatility of the fluorescent oil is too high, it becomes difficult to observe changes in film thickness, so all viscosities of 5cs are deemed unsuitable.

[0074] As shown in Figure 13, it can be seen that the appropriate conditions for the specific oil film are a fluorescent oil viscosity of 10cs to 100cs and a film thickness of 30μm or less. More specifically, it can be seen that the appropriate conditions for the specific oil film are a fluorescent oil viscosity of 10cs or more but less than 30cs and a film thickness of 10μm or less, or a viscosity of 30cs or more but less than 50cs and a film thickness of 20μm or less. Thus, the lower the viscosity of the fluorescent oil, the thinner the film thickness. This is because the lower the viscosity, the easier the oil flows, and if the film thickness is thick, the oil film will move under its own weight.

[0075] <Air flow evaluation> Next, a description will be given of a process for evaluating airflow using the system 1. Here, a case will be described in which the rear of the vehicle is used as the observation surface.

[0076] FIG. 14 is a flowchart of the process for assessing airflow by system 1.

[0077] First, in step S201, the process sets up measuring instruments, including a flow generating device 2, a lighting device 3, and an imaging device 4, around the vehicle 10.

[0078] Next, in step S202, the process attaches the white film 11 to the rear surface of the vehicle 10. As shown in FIG. 2, the white film 11 is attached to the front surface of the rear surface of the vehicle so as to cover the entire rear window 10a, which is a glass surface.

[0079] Next, in step S203, the process performs film thickness calibration, which is the same as the method in step S12 in the flowchart of the experiment described above (see FIG. 5).

[0080] Next, in step S204, the process applies fluorescent oil from above the white film 11. At this time, the fluorescent oil is applied from the upstream side of the airflow that will be generated later. In this embodiment, in order to generate an airflow from the front to the rear, the fluorescent oil is applied from the upper side of the rear of the vehicle. The fluorescent oil is applied to the rear of the vehicle by spraying. In this way, a specific oil film is applied to the rear of the vehicle. Also, in this step S204, the same fluorescent oil is applied to the roof portion located immediately upstream of the airflow with respect to the rear of the vehicle. The fluorescent oil applied here is fluorescent oil whose viscosity meets the conditions for a specific oil film.

[0081] Next, in step S205, the process activates the lighting device 3 and the imaging device 4 to check the luminous intensity of the specific oil film applied in step S204.

[0082] Next, in step S206, the process uses the calculator 5 to calculate the film thickness from the emission intensity confirmed in step S205, and determines whether the film thickness satisfies the film thickness condition for the specific oil film. As mentioned above, the film thickness condition varies depending on the viscosity of the fluorescent oil. If the result is YES, that is, the film thickness condition set based on the viscosity of the fluorescent oil is met, the process proceeds to step S207. If the result is NO, that the film thickness condition is not met, the process returns to step S204 and re-applies the fluorescent oil.

[0083] In step S207, the process activates the flow generating device 2 to send air toward the vehicle 10. The air speed at this time corresponds to the speed of the wind generated while the vehicle is running, and is set depending on the content of the evaluation.

[0084] Next, in step S208, the process starts to capture a video of the specific oil film applied to the rear of the vehicle. Here, the imaging device 4 captures a video.

[0085] Next, in step S209, the process calculates the luminescence intensity from the image acquired in step S208, and calculates the distribution of the film thickness of the specific oil film from the luminescence intensity.

[0086] Then, in step S210, the process evaluates the air flow at the rear of the vehicle from the film thickness distribution calculated in step S209 and the change in the distribution over time. After step S210, the evaluation ends.

[0087] FIG. 15 shows an example of friction stress vectors analyzed from a photographed image of the specific oil film. The evaluation conditions under which the analysis results of FIG. 15 were obtained were a viscosity of the fluorescent oil constituting the specific oil film of 10 cs and a film thickness of the specific oil film of 20 μm. The speed of the airflow generated by the flow generating device 2 was 72 km / h. In this evaluation, the rear window 10a was rounded so that its center was located further rearward than the left and right ends.

[0088] In Figure 15, air flow is represented by multiple lines, and air flows in the direction of each line. As shown in Figure 15, it can be seen that turbulence occurs in the air flow near the center of the rear window 10a in the left-right direction. This is due to air separation and the generation of vortices. In particular, because the rear window 10a of the vehicle used in this evaluation has a rounded shape, it is predicted that air separation will be more likely to occur in the center in the left-right direction. As can be seen from Figure 15, the results obtained in this evaluation are consistent with this prediction. Therefore, it can be said that by appropriately setting the conditions for the specific oil film, it was possible to sufficiently observe air flow, and in particular visualize air flow, even for an object with a three-dimensional structure having an inclined surface such as the rear window 10a.

[0089] Here, we have described the case of evaluating airflow at the rear of a vehicle, but the front of the vehicle, including the windshield, may also be used as the observation surface. When a portion located upstream of the airflow, such as the front of the vehicle, is used as the observation surface, a fluorescent oil with high viscosity is used to form a thick oil film, compared to when a portion located downstream of the airflow is used as the observation surface. The air flow velocity at the front of the vehicle is higher than at the rear of the vehicle. This is because a high air flow velocity increases fluid friction stress, and even a fluorescent oil with high viscosity can sufficiently move the oil film due to fluid friction stress. Furthermore, when fluid friction stress is high, a thin oil film may move and cause the oil film to break. For this reason, it is preferable to use a fluorescent oil with high viscosity to make the film thickness as thick as possible.

[0090] Furthermore, when the observation surface is the hood or roof, it is preferable to use fluorescent oil with a higher viscosity than when the rear of the vehicle is used as the observation surface. This is because the air speed is fast and fluid friction stress is relatively large in parts that extend almost horizontally, such as the hood or roof, so using fluorescent oil with a high viscosity and making the film thickness as thick as possible allows for more accurate evaluation of the air flow.

[0091] Therefore, in this embodiment, the airflow evaluation method includes an object preparation step (step S201) of preparing a vehicle 10 having an inclined surface on its surface; an oil film application step (step S204) of applying an oil film to the observation surface of the vehicle 10; a flow step (step S207) of generating an airflow on the observation surface of the vehicle 10; and an evaluation step (steps S209 and S210) of evaluating the airflow on the observation surface based on changes in the oil film thickness during the flow step. The oil film application step is a step in which, when the observation surface includes an inclined surface, a specific oil film is applied to the inclined surface, with an oil viscosity and film thickness set so that the specific oil film moves at a speed of 1.5 mm / min or less after application to the inclined surface and before generating an airflow. This reduces the impact of oil movement due to gravity on oil movement due to fluid friction stress. As a result, airflow can be evaluated by observing changes in oil film thickness even on inclined surfaces that are inclined in both the vertical and horizontal directions, such as the rear window 10a. Therefore, even for objects with a three-dimensional structure, it becomes possible to properly observe air flow due to changes in oil film thickness.

[0092] In particular, in this embodiment, the viscosity and film thickness of the oil constituting the specific oil film are set to a value such that the oil film travels at a speed of 1.5 mm / min or less when the panel 101 is placed horizontally and then turned vertical. This allows the travel speed of the oil film formed on a vertical surface to be experimentally investigated and the viscosity of the oil constituting the specific oil film and the film thickness of the specific oil film to be appropriately set. Since the oil travel speed on a vertical surface is 1.5 mm / min or less, the oil travel speed on an inclined surface will naturally be 1.5 mm / min or less. This allows the conditions of the specific oil film (oil viscosity and film thickness) to be more appropriately set. This allows for more appropriate observation of air flow due to changes in the oil film thickness.

[0093] In this embodiment, the specific oil film is an oil film with an oil viscosity of 10 cs to 100 cs and a film thickness of 30 μm or less. More specifically, the specific oil film is an oil film with an oil viscosity of 10 cs or more but less than 30 cs and a film thickness of 10 μm or less, or an oil viscosity of 30 cs or more but less than 50 cs and a film thickness of 20 μm or less. In this way, by optimizing the film thickness and oil viscosity of the specific oil film, it is possible to suppress oil movement due to its own weight while allowing the oil to move due to fluid friction even at a relatively low movement speed. This allows for more appropriate observation of air flow due to changes in the oil film thickness.

[0094] In this embodiment, the specific oil film is formed so that the lower the viscosity of the oil, the thinner the film thickness. In this way, the lower the viscosity of the oil, the thinner the film thickness is, and by reducing the mass of the oil, it is possible to minimize the movement of the oil due to its own weight. This allows for more appropriate observation of air flow due to changes in the oil film thickness.

[0095] Furthermore, in this embodiment, when an inclined surface included in the observation surface is an inclined surface that slopes downward from the upstream side to the downstream side of the airflow, such as the rear surface of the vehicle, oil is also applied to a portion of the vehicle 10 located immediately upstream of the observation surface, such as the roof portion. This allows oil to be supplied from the immediately upstream portion even if it takes time for the airflow velocity to reach the desired velocity and the specific oil film on the observation surface moves before the desired velocity is reached. As a result, the film thickness of the specific oil film can be prevented from becoming excessively thin, allowing for more appropriate observation of airflow due to changes in the oil film thickness.

[0096] Furthermore, in this embodiment, the specific oil film is a fluorescent oil film formed from a fluorescent oil, which is a mixture of oil and a fluorescent dye, and the evaluation process is a process of observing changes in film thickness from the luminescence intensity when the specific oil film is irradiated with light, and the object preparation process includes a process (step S202) of attaching a white film 11 to the rear window 10a, which is a glass surface. By attaching the white film 11 to the rear window 10a, light is reflected by the white film 11, making it possible to maximize the luminescence intensity of the specific oil film. This allows for more appropriate observation of air flow due to changes in oil film thickness, particularly air flow observation using an actual vehicle.

[0097] In this embodiment, the oil film conditions are changed depending on the position of the observation surface. In particular, when the front part of the vehicle, including the windshield, is used as the observation surface, the oil film is made to have a higher fluorescent oil viscosity and a thicker film thickness than the rear part of the vehicle. Also, when a part that extends approximately horizontally, such as the hood or roof, is used as the observation surface, the oil film is made to have a higher fluorescent oil viscosity and a thicker film thickness than the rear part of the vehicle. In this way, by setting the conditions of the oil film formed at each observation location to conditions suitable for observation depending on the strength of the air flow, it is possible to more appropriately observe the air flow due to changes in the oil film thickness.

[0098] This embodiment also includes a film thickness calibration process (step S203) for determining the luminescence intensity of the oil film relative to the oil film thickness. The film thickness calibration process involves filling fluorescent oil into a recess 121 of a calibrator 120 having a bottom surface sloping at a constant gradient, and measuring the luminescence intensity of the filled fluorescent oil to perform calibration. This allows the film thickness of a specific oil film to be calculated as accurately as possible from the luminescence intensity. This allows for quantitative evaluation of air flow, and more appropriately observes air flow due to changes in oil film thickness.

[0099] (Other embodiments) The technology disclosed herein is not limited to the above-described embodiments, and can be substituted within the scope of the claims.

[0100] For example, in the above-described embodiment, the evaluation method was a fluorescent oil film method using fluorescent oil. However, the evaluation of air flow is not limited to this, and an oil film method using oil that does not contain fluorescent dye may also be used. Even with this method, the movement of the oil film due to the air flow can be identified by acquiring an image, so that the air flow can be evaluated.

[0101] Furthermore, in the above-described embodiment, the evaluation was performed using an actual vehicle 10, but this is not limiting, and a model that mimics the shape of the vehicle 10 may be used. In this case, if the model is made of a white material, the step of attaching the white film 11 can be omitted.

[0102] In the above-described embodiment, the vehicle rear surface serving as the observation surface is an inclined surface that slopes downward from the upstream side to the downstream side of the airflow. However, the observation surface may be a vertical surface that extends perpendicular to the airflow direction, such as the rear surface of a so-called box-type vehicle. Even in this case, it is preferable to apply oil not only to the vertical surface but also to the roof portion located immediately upstream of the vertical surface in the airflow direction.

[0103] In the above-described embodiment, the air flow is evaluated at the rear of the vehicle 10. However, the air flow at the side doors and pillars of the vehicle 10 can also be appropriately evaluated by setting the oil film conditions to those set in this embodiment.

[0104] The above-described embodiments are merely examples and should not be construed as limiting the scope of the present disclosure. The scope of the present disclosure is defined by the claims, and all modifications and variations that fall within the scope of the claims equivalents are within the scope of the present disclosure. [Industrial Applicability]

[0105] The technology disclosed herein is useful as a method for evaluating air flow around an object by observing an oil film applied to the surface of the object. [Explanation of symbols]

[0106] 1. Rating System 2. Flow generator 4. Imaging device 5. Computer (evaluation device) 10 vehicles 10a Rear window 120 Calibrator 121 recess

Claims

1. An evaluation method for evaluating air flow around an object by observing an oil film applied to an observation surface located on the surface of the object, comprising: an object preparation step of preparing a three-dimensional object having an inclined surface or a vertical surface on the surface as the object; an oil film application step of applying an oil film to the observation surface of the object; a flow process for generating an air flow on the observation surface of the object; an evaluation step of evaluating the air flow on the observation surface from a change in the thickness of the oil film during the flow step, When the observation surface includes the inclined surface or the vertical surface, the oil film application step is a step of applying a specific oil film, which is an oil film to be applied to the inclined surface or the vertical surface serving as the observation surface, with the viscosity of oil and the film thickness set so that the movement speed of the specific oil film after application to the inclined surface or the vertical surface serving as the observation surface and before generating the air flow is 1.5 mm / min or less; The specific oil film is an oil film having a viscosity of 10 centistokes (cs) to 100 cs and a film thickness of 30 μm or less, The method for evaluating air flow, characterized in that the oil film application process is also a process of applying the oil to a portion of the object located immediately upstream of the observation surface when the inclined surface included in the observation surface is an inclined surface that slopes downward from the upstream side to the downstream side of the air flow generated in the flow process, or when the vertical surface included in the observation surface is a vertical surface that extends perpendicular to the flow direction of the air flow.

2. The method for evaluating air flow according to claim 1, The method for evaluating air flow is characterized in that the specific oil film is an oil film having a viscosity of the oil of 10 cs or more and less than 30 cs and a film thickness of 10 μm or less, or an oil film having a viscosity of the oil of 30 cs or more and less than 50 cs and a film thickness of 20 μm or less.

3. The method for evaluating air flow according to claim 1 or 2, The method for evaluating air flow is characterized in that the thickness of the specific oil film is set according to the viscosity of the oil.

4. The method for evaluating air flow according to any one of claims 1 to 3, The specific oil film is a fluorescent oil film formed of a fluorescent oil, which is a mixture of oil and a fluorescent dye, The evaluation step is a step of observing a change in film thickness from an emission intensity when the specific oil film is irradiated with light, A method for evaluating air flow, characterized in that the object preparation step includes a step of attaching a white film to the glass surface when the observation location of the object includes a glass surface.

5. The method for evaluating air flow according to any one of claims 1 to 4, the object is an automobile vehicle, the observation surface includes a rear surface of the vehicle including a rear window of the vehicle as the inclined surface, the flowing step is a step of flowing air from the front side of the vehicle to the rear side of the vehicle. A method for evaluating air flow.

6. The method for evaluating air flow according to claim 5, the observation surface further includes a vehicle front portion including a front window of the vehicle as the inclined surface, A method for evaluating air flow, characterized in that the specific oil film formed on the front portion of the vehicle is an oil film with a higher oil viscosity and a thicker film thickness than the specific oil film formed on the rear portion of the vehicle.

7. An evaluation method for evaluating air flow around an object by observing an oil film applied to an observation surface located on the surface of the object, comprising: an object preparation step of preparing a three-dimensional object having an inclined surface or a vertical surface on the surface as the object; an oil film application step of applying an oil film to the observation surface of the object; a flow process for generating an air flow on the observation surface of the object; an evaluation step of evaluating the air flow on the observation surface from a change in the thickness of the oil film during the flow step, When the observation surface includes the inclined surface or the vertical surface, the oil film application step is a step of applying a specific oil film, which is an oil film to be applied to the inclined surface or the vertical surface serving as the observation surface, with the viscosity of oil and the film thickness set so that the movement speed of the specific oil film after application to the inclined surface or the vertical surface serving as the observation surface and before generating the air flow is 1.5 mm / min or less; The method for evaluating air flow is characterized in that the viscosity and film thickness of the oil constituting the specific oil film are set to such a value that when a panel material other than the object is placed horizontally and an oil film is applied, and then the panel material is turned vertical, the movement speed of the oil film is 1.5 mm / min or less.

8. An evaluation system for evaluating air flow around an object by observing an oil film applied to an observation surface located on the surface of the object, comprising: An automobile vehicle as the object; a flow generating device that generates an air flow on the surface of the vehicle; an imaging device for capturing an image of the oil film applied to the observation surface while the air flow is generated by the flow generating device; an evaluation device that calculates the thickness of the oil film from the image acquired by the imaging device and evaluates the air flow on the observation surface, the observation surface to which the oil film is applied is a rear surface of the vehicle including a rear window of the vehicle, the flow generating device is disposed at the front side of the vehicle and generates a flow of air from the front side of the vehicle toward the rear side of the vehicle; The oil film applied to the rear surface of the vehicle is an oil film whose viscosity and film thickness are set so that when a panel material other than the object is placed horizontally and the panel material is then turned vertical, the oil film moves at a speed of 1.5 mm / min or less.

Images