JPH01247296A - Turbulence resistance reducing device - Google Patents

Abstract

PURPOSE:To reduce the turbulence resistance of a fluid to a great extent with simple construction by furnishing a number of strings on the surface of a resistance member, which are extending in the fluid direction, and arranging these strings with a specific value of height and spacing. CONSTITUTION:A number of strings 12 extending in the fluid flowing direction are furnished on the surface of a resistance member (flat plate) 11, and when the height and spacing of these strings 12 are represented by h and S, respectively, and their corrected values by h*, S* according to h*=hu*/nu and S*=Su*/nu, where u* is expressed by (gamma/rho)<1/2>, gamma is friction factor of flat plate surface, rho is fluid density, and nu is dynamic factor of fluid viscosity, and then the h and S shall be raised so as to become h*<5 and S*<50. Thereby the resistance becomes smaller than the flat plate 11. Therein h*=5 corresponds to the thickness of the viscous bottom layer of a turbulence boundary layer, so that the resistance reduces when the outside dia. of the strings 12, i.e. h, is smaller than the thickness of this viscous bottom layer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a device for reducing fluid resistance, and more particularly to a device for reducing resistance due to turbulence in fluid flow.

(Prior art) In aircraft, ships, automobiles, and other fluid-related equipment,
Reducing fluid resistance is an important technical challenge.

When a fluid becomes turbulent, its resistance increases significantly. Therefore, there is a strong desire to reduce fluid resistance in turbulent flow.

As devices for reducing fluid resistance, various fluid dynamic means are known, such as streamlining the shape, for example.

One of them is known to utilize the Thoms effect.

The Thoms effect refers to the PPM of a liquid containing a polymer compound in a liquid.
This refers to a phenomenon in which fluid resistance is drastically reduced when mixed in an orderly manner.

Also developed by NASA is the Ribl
A fluid resistance reduction device using the above-mentioned method (et) is also attracting a great deal of attention.

The known glue bullet system, as shown in FIG. 4, is a method in which minute prets (ribs) 1 extending in the direction of fluid flow are provided on the surface of a resistor 2 of a fluid device or the like. The riblet 1 has various cross-sectional shapes as shown in FIG.

According to the resistor 2 provided with this riblet 1, a phenomenon in which fluid resistance is reduced is observed, similar to the Thoms effect.

(Problems to be Solved by the Invention) The above-mentioned known fluid resistance reducing device has the following drawbacks.

First, a resistance reducing device using a shape such as a streamline is not common because it imposes restrictions on the shape and structure of the resistor.

In addition, devices that utilize the Thoms effect require the mixing of polymer compounds into the liquid, which limits the fluids that can be used and is not applicable to the most demanding equipment such as aircraft, ships, and automobiles. The drawback was that it couldn't be done.

Furthermore, devices using riblets have not been put into practical use much at present.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a device that has a simple shape and can reliably and significantly reduce fluid resistance.

(Means for solving problems) The features of the present invention are as follows.

When a large number of filaments extending in the fluid flow direction are provided on the surface of the resistor, the height of the filaments is 11, and the interval between each filament is S, h*=hu*/ν S books=Su*/ ν u*=Pressure τ: Coefficient of friction on flat plate surface ρ: Density of fluid C: Coefficient of kinematic viscosity of fluid The height 11 and spacing S of the filaments were determined so that b*<5, S*<50. .

(Example) Before going into the explanation of the example, let me describe the circumstances that led to the present invention.6 Various theories have been proposed regarding the Thoms effect, but the inventors of the present invention have proposed the following regarding the Thoms effect. make a hypothesis,
I compared this with experimental results.

In other words, since a polymer compound is a chain compound, when a polymer is mixed into a liquid, the chain polymer compound becomes just like minute cilia and adheres to the surface of the resistor, which causes the fluid to flow. The idea was that the effect of reducing resistance would not be caused by acting on the

If this hypothesis is correct, the Thoms effect is considered to be the same as the state in which mixed cilia are implanted on the surface of a resistor. I tried measuring the resistance.

However, in this experimental result, the resistance of the fluid actually increased.

Therefore, the inventors of the present invention considered the reason for the increase in resistance as follows.

That is, referring to Fig. fj56, the fine cilia 4 implanted on the flat plate 3 are deformed by the fluid flow P, and a bent portion 4A is generated. It was thought that this curved portion 4A increased the resistance of the fluid.

In order to eliminate the defects that are thought to be caused by the fine cilia mentioned above, as shown in FIG. Experiments were conducted by changing the outer diameter and installation interval of the filament 5. As a result, it was confirmed that the fluid resistance was reduced depending on the outer diameter and spacing of the filamentous bodies 5. That is, it has been found that fluid resistance is reduced when the outer diameter of the filamentous body 5 is smaller than the viscous bottom layer of the turbulent boundary layer and the interval is equal to or less than a predetermined value.

On the other hand, it has not yet been completely elucidated why fluid resistance is reduced when a minute Libre 2F is installed on the surface of a fluid device. However, in the NASA study, no matter what shape the riblet is in, the height of the riblet must be greater than the thickness of the viscous bottom layer (i.e., protrude outward from the viscous bottom layer) in the turbulent boundary layer. It is said that the resistance reduction effect will not occur if this is the case. This is because, from the common knowledge of fluid mechanics, it was thought that it was impossible for protrusions or the like within the thickness of the viscous bottom layer to affect the flow of fluid.

However, it was confirmed that fluid resistance was reduced when the height of the filament was made lower than the thickness of the viscous bottom layer of the turbulent boundary layer, and the NASA glue bullet method found areas where drag was clearly reduced that had not been considered. It turns out that there is.

As mentioned above, the drag reduction effect of the Thoms effect bullet appears to be a completely different phenomenon, but according to research conducted by the present inventors, it has been found that they are very similar phenomena.

Experiments conducted by the inventors will be described below.

As shown in FIGS. 1 and 2, a filament 12 made of fishing line was attached to a flat plate 11, and this was placed in a wind tunnel to measure resistance.

The outer diameter of the filamentous body 12, that is, the height 11 is 0.12 hours.
, 3f of 0,090aon, 0.0641fin+!
Class II, the spacing S of filamentous bodies 12 is 2mu+, 1.5IO
+11.1.0+m, 0.75++oo, 0.5+o
Experiments were conducted with 5 types of +n.

To put the results of the above experiment qualitatively, the fluid resistance was reduced when the height 1] and the distance S were relatively small.

In Figure 3, the vertical axis is the correction value II* of the filament height, and the horizontal axis is the correction value S tree of the filament spacing. Resistance reduction rate (%) compared to the resistance value when no filament is installed
It represents.

here, h * = bu * / ν S car = Su*/ν , *477 Takumi τ: Friction coefficient of flat plate surface ρ: Density of fluid; ρ: Kinematic viscosity coefficient of fluid.

As you can see from the figure, 6 pieces 5, S*<SO It can be seen that the resistance is reduced compared to a flat plate.

In this, h = s corresponds to the thickness of the viscous bottom layer of the turbulent boundary layer, so when the outer diameter of the filament, that is, the height 11 is smaller than the thickness of the viscous bottom layer, the resistance was found to be reduced.

Comparing the results of the present invention with the NASA glue bullet method, the riblet method has b*>10, which is different from the results of the present invention.

It is not yet clear how this difference occurs, but in the riblet method, riblets are formed by simple machining on the surface of a flat plate, so adjacent riblets are loosely connected to each other. It is determined that this is because they are connected on a plane or on an inclined surface.

In the filamentous body according to the present invention, adjacent filamentous bodies are connected in a straight line. For this reason, we interpret that the behavior of the fluid inside the viscous bottom layer is different from that in the riblet method, leading to this result.

In the present invention described above, the filamentous body is composed of a fishing line, but the filamentous body of the present invention is not limited to one composed of a fishing line. For example, the present invention also includes those that form a structure equivalent to the filamentous body using paint, and furthermore, those that form a structure equivalent to the filamentous body of the present invention through surface treatment. be.

(Effects of the Invention) As described above, according to the present invention, the resistance acting on the resistor in turbulent flow can be greatly reduced with a simple configuration.

Furthermore, the resistance reduction effect due to the Thoms effect can be obtained by adding innovations to the fluid side, so it could not be obtained only with elements on the resistor side. However, according to the present invention, the resistance reduction effect equivalent to the Thoms effect can be achieved on the resistor side. It can be obtained with only these elements.

Therefore, it can be applied to aircraft, ships, automobiles, etc., and its applications are extremely wide.

[Brief explanation of the drawing]

FIG. 1 is a perspective view for explaining one embodiment of the present invention,
Figure jS2 is a sectional view taken along the line A-A in Figure 1, and Figure 3 shows the resistance resistance effect by comparing the resistance-reducing foil of the present invention with a flat plate, with the vertical axis showing h wood and the horizontal axis showing 8 pieces. Figure 4 is a cross-sectional view to explain the beam bullet method, Figure 5 (a) or 5) is a schematic cross-sectional view to explain the cross-sectional shape of the glue bullet in Figure 4, and Figure 6 is a cross-sectional view to explain the cross-sectional shape of the beam bullet method. FIG. 7 is a new view of the flat plate in which cilia were implanted and tested, and is a schematic cross-sectional view illustrating a flat plate with threads, which is an improved version of the flat plate shown in FIG. 6 and is the beginning of the present invention. 11: Flat plate 12: Filiform body Figure 1 '#1'' 4 Figure 5 (A) (B)
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Claims (1)

[Claims] When a large number of filamentous bodies extending in the fluid flow direction are provided on the surface of the resistor, the height of the filamentous bodies is h, and the interval between each filamentous body is S, h*=hu*/ν. S*=Su*/ν u*=√(τ/ρ), τ: Friction coefficient of flat plate surface ρ: Density of fluid ν: Kinematic viscosity coefficient of fluid so that h*<5, S*<50 A turbulent flow resistance reducing device characterized in that the height h and the interval S of filamentous bodies are determined.