JPS61160391A - Howling prevention propeller - Google Patents

Abstract

PURPOSE:To easily prevent local howling produced by being excited by Karman vortex generated at the trailing edge of a propeller blade by making cuts at the trailing edge of the propeller blade projecting from a boss, thereby changing frequency of local vibration of the propeller blade. CONSTITUTION:At a trailing edge of a propeller blade 1, a cut 7 and a cut 8 are formed so that a local part 9 is interposed in between. When the blade is made of a flat plate, frequency (fv) of the local vibration of the local part 9 is approximately halved by forming a distance (a) a length (b) of the cuts 7 and 8 with a same value. Even when the blade is not a plane but is of a wing profile where the distance (a) and the length (b) is not equal, the local vibration frequency (fv) of the local part 9 can be sufficiently lowered. The distance (a) and the length (b) are determined based on the calculation results of vibration modes of the blade 1. Thus, local vibration frequency (fv) is lowered to be different from the vibration frequency (fk) of the Karman vortex generated at the local part 9 so that the howling can be securely prevented from being produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a noise-preventing propeller suitable for use in a propulsion device of a ship or the like.

[Conventional technology]

BACKGROUND ART Conventionally, as a propeller used for ships, pumps, etc., a propeller 210' having a plurality of propeller blades 1 protruding from a boss portion 3, as shown in FIG. 2, has been used.

Note that in FIG. 2, only one of the plurality of propeller blades 1 is illustrated.

[Problem that the invention seeks to solve]

When the propeller 10' as described above rotates around the central axis of the boss portion 3 in the direction of the arrow shown in FIG.
As shown in the figure, a Karman vortex 6 is generated at the trailing edge of the propeller blade 1.

Note that FIG. 3 is a sectional view taken along arrow I-III along the rotational circumferential direction of the propeller blade 1 in FIG. 2.

The Karman vortices 6 generated at various locations on the trailing edge of the propeller blade 1 each have a constant vibration frequency rK, and this vibration frequency r can be approximately determined by the following equation.

r, = o, 20V/h --- (1) (1)
In the equation, ■ is the peripheral speed of rotation at the location where the Karman vortex 6 is generated, h is the thickness of the trailing edge 5 of the propeller blade 1, r is the radius of rotation at the above location, and the rotational speed of the propeller 10' is If n, V=2πrn
...It is obtained as (2).

When the frequency f of the Karman vortex 6 shown by equation (1) matches the frequency of local vibration of the propeller blade 1, the propeller blade 1 is partially excited by the vibration of the Karman vortex 6, A local vibration phenomenon occurs as shown in Fig. 2. In Fig. fjS2, a broken line 2' indicates an equal displacement line of local vibration of the propeller blade 1.

The above-mentioned local vibration phenomenon is called a so-called noise phenomenon, and this causes noise from the propeller 10', causing a problem in that the performance of the propeller 10' deteriorates.

In order to solve such problems, the thickness h of the trailing edge 5 of the propeller blade 1 where the noise phenomenon occurs is changed, and the vibration frequency f of the Karman vortex 6 generated in the above region is changed. A propeller that does not match the frequency f of the local vibration of the blade 1 has been proposed, but although the above-mentioned propeller can prevent the occurrence of the noise phenomenon,
Even if the blade wall 4 of the propeller blade 1 is slightly modified, it is inevitable that the performance of the propeller differs from the performance originally intended at the time of design.

Furthermore, after the propeller is manufactured, when the design is changed in order to prevent local noise generation in the propeller, a large amount of work is required to shape the propeller blade 1 by changing the thickness of the trailing edge 5. There is a problem in that it requires labor and expense.

Further, an additional member is provided near the trailing edge 5 of the propeller blade 1,
A propeller has also been proposed in which the periodicity of the Karman vortex 6 generated at the trailing edge 5 is disturbed to prevent localized noise generation caused by partial excitation of the propeller IX1 by the Karman vortex 6. The structure of propellers is complex, and manufacturing and maintenance thereof requires expense and labor.

In view of the above-mentioned circumstances, the present invention changes the frequency of the local vibration of the propeller blade to easily prevent the occurrence of local noise caused by excitation by the Karman vortex generated at the trailing edge of the propeller blade. The purpose of the present invention is to provide a noise-preventing propeller that makes it possible to

[Means for solving problems]

For this reason, the noise-preventing propeller of the present invention is provided with propeller blades that protrude from the boss, and the trailing edge of the propeller blade has an r&
It is characterized by being

[For production]

In the above-described noise-preventing propeller of the present invention, the notch formed in the trailing edge of the propeller blade changes the frequency of local vibration of the propeller blade, thereby preventing the occurrence of local noise. .

〔Example〕

Hereinafter, a noise-preventing propeller as an embodiment of the present invention will be explained with reference to the drawings. FIG. 1 is a front view of the propeller blade. It should be noted that in the drawings, the previously described reference numerals indicate substantially the same parts.

As shown in Figure 1, the propeller 1 rotates in the direction of the arrow.
0 is configured with a plurality of propeller blades 1 protruding from a boss portion 3 thereof.

Note that in FIG. 1, only one of the plurality of propeller blades 1 is illustrated.

On the other hand, at the trailing edge of the propeller blade 1, cuts 7 and 8 are formed so as to sandwich the local part 9 of the propeller blade 1.

Here, the above-mentioned local part 9 is a part where a local noise phenomenon occurs if the notches 7 and 8 are not formed.

By the way, when the above-mentioned propeller blade 1 is composed of a flat plate, if the distance a between the notches 7 and 8 and the length b of these notches 7 and 8 are made equal, the local area of the local part 9 will be The vibration frequency fv is reduced to about half.

Further, even if the propeller blade 1 is composed of a blade wall that is not a flat plate, and the above-mentioned interval a and length b are not equal, the frequency fv of the local vibration of the local part 9 can be sufficiently reduced as in the above case. I can do it.

Note that the dimensions of the opening distance a and the rising length b are determined based on the calculation results of the vibration mode of the propeller blade 1.

Further, in FIG. 1, a broken line 2 indicates an equal displacement line of local vibration of the propeller blade 1.

The noise-preventing propeller 10 of the present invention has the structure 1 &
9, where local noise phenomenon may occur.
, the frequency fv of the local vibration is lowered by the notches 7 and 8, and no longer matches the frequency f of the vibration of the Karman vortex (see reference numeral 6 in FIG. 3) generated in the local area 9.

Therefore, as is clear from comparing fractures #i2 and 2' showing equal displacement lines in FIGS. 1 and 2, the state of local vibration in the local part 9 changes, and the The vibration range is narrow (as a result, the noise phenomenon caused by the rotation of the propeller 10 is sufficiently prevented).

In addition, in the propeller 10 of the present invention, the generation of noise can be prevented without changing the variant shape of the propeller blade 1 (see reference numeral 4 in Figure 1'!3). Not only does the performance of the propeller blade 1 not be impaired, but there is also no need to provide additional members near the trailing edge of the propeller blade 1, and there is an advantage that manufacturing and maintenance costs and labor are not required.

Furthermore, even if the propeller 10 is an existing one, the design change to prevent local noise generation in the propeller 10 can be made by simply forming a new notch on the trailing edge of the propeller blade 1. It can be easily done with reasonable effort and expense.

In addition, in the propeller 10, the tips 7a of the notches 7 and 8 formed in the propeller blade 1.

It is desirable that a stop hole be formed in 8a to prevent cracks from occurring.

Further, the notch formed in the local part 9 of the propeller blade 1 is 1
It may be one piece or three or more pieces.

〔Effect of the invention〕

As detailed above, the noise-preventing propeller of the present invention has propeller blades protruding from the boss, and the trailing edge of the propeller blades has a notch to prevent local noise generation. This simple configuration sufficiently prevents localized noise generation, which can greatly contribute to noise prevention and improvement of propeller propulsion efficiency in ships and the like.

In addition, in the propeller of the present invention, the generation of noise can be easily prevented by simply forming a notch without impairing the propeller performance intended at the time of design, thereby reducing the cost and labor required for manufacturing and maintenance. It also has the advantage of being significantly reduced.

[Brief explanation of the drawing]

Fig. 1 is a front view of a propeller blade of a noise-preventing propeller as an embodiment of the present invention, Figs. 2 and 3 show a conventional propeller, and Fig. 2 is a front view of the propeller blade. ,
FIG. 3 is a sectional view taken along the line ■--■ in FIG. 2. 1. Propeller blade, 2. Broken line indicating equal displacement line, 3.
Boss part, 7...notch, 7a...notch tip, 8
...Incision, 8a...Incision tip, 9...Local area,
10...Propeller. Sub-Agent Patent Attorney Yoshihiko Iinuma Figure 1 2nd Theory □, r-
Figure 3

Claims (1)

[Claims] A noise-preventing propeller, comprising a propeller blade protruding from a boss, and a notch formed in the trailing edge of the propeller blade to prevent local noise generation.