JPS61188296A - Propeller for ship - Google Patents

Abstract

PURPOSE:To disturb a separated flow and suppress the generation of a ringing sound by providing protrusions within the area on the tip side of a propeller blade where response coefficient to the primary or secondary oscillation mode exceeds by 5% of the maximum value and at the flow separation point in the frailing edge of the blade. CONSTITUTION:Two or more protrusions 2 with the height exceeding five times the thickness excluding a boundary layer are provided along the frailing edge of the blade within the area on the tip side of a propeller blade 1 where response coefficient to the primary or secondary oscillation mode of the propeller blade main body 1 exceeds by 5% of the maximum value and at the flow separation point in the frailing edge of the blade, or in the vicinity thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of a marine propeller, and particularly to a structure of a propeller that can appropriately suppress generation of noise without substantially impairing propeller performance.

[Prior art and its problems] In a ship, when a propeller blade is rotating, fluid flows along the propeller blade and leaves the blade's trailing edge, but at this time, a regular vortex (separated vortex) is generated at the blade's trailing edge. . This vortex flow is called a Karman vortex street, and when the frequency of this Karman vortex street matches the frequency of the blade surface of the propeller blade itself, a resonance phenomenon occurs and powerful vibrations occur. When this vibration is within the audible range, a so-called ringing sound is generated.

This kind of noise is undesirable because it gives a feeling of discomfort to crew members and passengers, and can also cause vibrations in the hull.Therefore, as a conventional countermeasure, the trailing edge of the propeller blade has been machined into a predetermined shape. Proposals have also been made to provide holes or grooves in the trailing edge of the blade. However, the effects of these proposals are not sufficiently clear, and there is a risk that modifying the shape of the propeller body in this way may reduce the performance and strength of the propeller. No consideration was given to this, and there were major problems in putting it into practical use.

[Means for solving the problem] The present invention was made in view of such conventional problems,
It is an object of the present invention to provide a marine propeller that can appropriately suppress the generation of noise without causing deterioration in strength or propeller performance.

For this reason, the present invention provides a fluid separation point at the blade tip side region where the response factor for the primary or secondary vibration mode of the propeller blade body is 5% or more of its maximum value, and at the fluid separation point at the blade trailing edge. A plurality of protrusions having a height of five times or more than the boundary layer exclusion thickness are provided at intervals along the trailing edge of the propeller blade at nearby positions. It disturbs the separation flow that causes noise without impairing the performance of the propeller itself, effectively suppressing the noise.

Hereinafter, details of the present invention will be explained based on FIGS. 1 and 2.

The present invention is characterized in that a plurality of protrusions are provided in a limited specific region and position of a propeller blade body.

As mentioned above, the noise is caused by the regular vortices generated by the separation flow at the trailing edge of the blade.
The present invention uses protrusions to generate a three-dimensional flow in the separated flow, thereby actively imparting disturbance to the separated flow. As shown in FIG. 1, the present invention is limited to the blade tip side region where the response coefficient of the body (1) to the primary or secondary vibration mode is 5% or more of its maximum value.

A major reason why conventional noise prevention measures have the above-mentioned problems is that the mechanism of noise generation has not been sufficiently elucidated. In view of these points, the present inventors have elucidated the mechanism of noise generation in detail, and have specifically studied measures to prevent the noise. First, the inventors
We studied the vibration modes of propeller blades and found that most of the noise that requires countermeasures is caused by the primary or secondary vibration modes, and furthermore, we investigated the ease of vibration of propeller blades in these vibration modes, and the vibration response of propeller blades. )It was investigated.

Figures 3(a) to 3(c) show some examples of vibration modes of propeller blades, where (a) is the primary vibration mode;
(b) is a secondary vibration mode, and (c) is a tertiary vibration mode. The primary vibration mode is when the blade vibrates like a fan from near the root, the secondary vibration mode is when the blade vibrates in a bending manner at the center of the blade, and the tertiary vibration mode is when only the tip of the blade vibrates partially. , the higher the rotational speed, the higher the vibration mode. Furthermore, when the rotational speed is in a higher range, the vibration mode becomes 4th order, 5th order, etc. After examining the relationship between the normal rotation speed range (rotation speed range during steady operation) of marine propellers and propeller vibration, we found that most of the vibrations in this propeller rotation speed range are in the primary and secondary vibration modes. Therefore, it has been found that countermeasures against noise caused by these vibration modes are both necessary and sufficient. The ease of vibration in this vibration mode is
Basically the lower end area of the propeller blade. That is, Fig. 4 shows the propeller radial direction position (r/R) for a certain propeller blade for such primary and secondary vibration modes.
(distance from the propeller axis when the distance R from the propeller axis to the blade tip is 1)
The response coefficient tends to be in the lower wing end region. There is an extremely strong correlation between this response coefficient and the generation of noise, and the noise occurs in the range where the response coefficient is high, specifically in the propeller blade tip side where the response coefficient is 5% or more of its maximum value. In other words, it has been found that countermeasures to prevent noise generation are particularly effective in this propeller blade tip side region. On the other hand, in other areas (lower end side area of the blade), noise countermeasures are hardly necessary and are actually harmful to propeller performance.

In other words, basically adding protrusions to the propeller blade itself will impair the basic performance of the propeller such as thrust, and from this perspective, the formation of protrusions as a noise countermeasure should be kept to the minimum necessary. It is necessary to keep it at that. In this sense, the area where the protrusion (2) is provided is the blade tip area where noise can be prevented, specifically at least the primary or secondary blade tip area.
It is limited to the blade tip side region where the response coefficient for the next vibration mode is 5% or more of its maximum value. More specifically, compare the blade tip region where the response coefficient to the primary vibration mode is 5% or more of its maximum value and the blade tip region where the response coefficient to the secondary vibration mode is 5% or more of its maximum value. , it is preferable to select the area whose lower limit is lower, and use this as the reference. If the protrusion installation range is limited in this way, the loss of propeller performance can be suppressed to a range that hardly causes any problems in practical use. For example, the fourth
In the example of the propeller blade shown in the figure, the response coefficient in the secondary vibration mode is equal to or greater than (response coefficient maximum value × 0.05) in the region of 0, 71 r / R or more, and the response coefficient in the primary vibration mode is (Response coefficient maximum value xo, 05) or more is in the region of 0,75 r/R or more,
Therefore, at least less than 0°71 r/R −
A protrusion (2) is provided in the L end side region. In addition,
The leading edge of the propeller blade does not have a large effect on noise, and it is difficult to process protrusions in this area.
In addition, this results in an unnecessary increase in the rotational torque of the blade, so it is generally preferable not to provide the protrusion in a range exceeding 0.95 r/R.

Further, the installation position of the protrusion (2) is limited to the fluid separation point at the trailing edge of the blade or its vicinity in the blade tip side region as described above. The noise is caused by the separation flow at the trailing edge of the fluid flowing along the propeller blade.
The protrusion of the present invention is intended to disturb this separated flow, and for this reason, it is necessary to install the protrusion at or near the fluid separation point where the separated flow occurs. In particular, it is preferable to install it slightly closer to the leading edge of the propeller blade than the separation point of the propeller blade body.

On the other hand, the configuration of the protrusion itself is also specified as follows. That is, as mentioned above, the purpose of attaching the protrusion to the trailing edge side of the present invention is to disturb the regular generation of separation vortices by actively applying disturbance to the boundary layer, which is the source of trailing edge separation vortices. However, the purpose is to make it difficult for resonance with the propeller blade natural frequency to occur. Therefore, from this point of view, the relationship between the boundary layer and the height h of the protrusion (2) is an important point that requires consideration.

An important parameter that influences the characteristics of the boundary layer is the boundary layer exclusion thickness. The protrusion height h can be specified in relation to the boundary layer exclusion thickness, and specifically,
It has been found that the height required is at least five times the boundary layer exclusion thickness at the mounting position. The boundary layer thickness itself is difficult to measure compared to the boundary layer exclusion thickness, but in general, in the case of turbulent flow, the boundary layer thickness is said to be about eight times the exclusion thickness.
Therefore, it can be said that the protrusion height h, whose lower limit is 5 times the boundary layer exclusion thickness, corresponds to approximately 60% or more of the boundary layer thickness, and the protrusion height h is equivalent to the boundary layer thickness. It can be inferred that an effective disturbance effect cannot be obtained unless the range is covered.

The shape of this protrusion is not particularly limited, but generally a pin shape (circular shape) is used. This protrusion causes a three-dimensional flow in the separated flow generated from the trailing edge of the blade, and therefore is preferably columnar (prismatic or cylindrical) with vertical side surfaces.

The above-mentioned protrusions are located in the above-mentioned areas and positions.
They are arranged at multiple locations along the trailing edge of the propeller blade. Although the number of protrusions is not particularly limited, it is preferable to have a large number of protrusions from the viewpoint of disturbing the generation of separated flow by the turbulence generated by each protrusion.

[Example] Actual ship propeller (7) 1/20 (diameter 245 mm
) experiments were conducted using the model. This propeller blade is
Calculate the response coefficients of the primary and secondary vibration modes and set them to 0.
, 75 r/R ~ 0 , 95 r/R (7) with the fifth
Six wooden pin protrusions were attached as shown in the figure. and,
The noise generated by this propeller and a propeller without a pin was investigated. Also, the height of the installed pin is 2.1
mm, which is 10 to 15 times the boundary layer exclusion thickness at the pin removal position described below.

r/R boundary layer exclusion thickness 0.6 0.20 0.7 0.19 0.8 0.16 0.9 0.17 0.95 0.14 Figure 6 shows the rotation speed of each propeller and the generated This shows the relationship between sound pressure and O.For propellers without pins,
While the noise based on the primary vibration mode is loud around 15 rotations/sec, and the noise based on the secondary vibration mode is loud at 23 rotations/sec or higher, the present invention with a pin attached The propellers of 2000 and 2000 properly suppress noise generation in these rotational speed ranges.

[Effects of the Invention] According to the present invention described above, generation of noise can be effectively suppressed without impairing propeller performance or strength.

[Brief explanation of the drawing]

1 and 2 schematically show one propeller blade of the propeller of the present invention, with FIG. 1 being a front view and FIG. 2 being a sectional view taken along line II--II in FIG. 1. Figures 3(a) to 3(c) show examples of vibration modes of propeller blades. FIG. 4 shows the response coefficient of a certain propeller blade at a position in the propeller radial direction. Fifth
The figure is an explanatory view showing the mounting position of the protrusion in the embodiment of the present invention. FIG. 6 shows the noise generation situation of the propeller shown in the example in comparison with a propeller without countermeasures. In the figure, (1) indicates the propeller blade body, and (2) indicates the protrusion.

Claims (1)

[Claims] In the blade tip side region where the response coefficient for the primary or secondary vibration mode of the propeller blade body is 5% or more of its maximum value, and at or near the fluid separation point at the blade trailing edge, there is a boundary layer exclusion thickness of 5%. A marine propeller comprising a plurality of protrusions that are twice as high or more in height and are provided at intervals along the trailing edge of the propeller blade.