JP2004161208A - Marine propeller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a marine propeller capable of establishing a further enhanced effect for preventing root erosion. <P>SOLUTION: The section shape of the root of each vane of this marine propeller 1 has a thickness profile such that the maximum thickness position Tmax lies nearer the tail than the center C of the vane chord length L and satisfies the condition 0.1L≤▵L≤0.4L, where ▵L is the retreating dimension from the center C of the vane chord length L to the maximum thickness position Tmax. The radius of curvature r of the vane rear end face is set between 30% and 50% of the maximum vane thickness T, not including 30%, preferably 35% or more of the maximum vane thickness T. The propeller 1 can suppress generation of cavitation effectively, and enhance the effect for preventing the root erosion. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a marine propeller used as a propulsion device for a marine vessel. In particular, the present invention relates to a marine propeller capable of further improving the effect of preventing root erosion.
[0002]
Problems to be solved by the prior art and the invention
In many cases, erosion (erosion, erosion) due to cavitation occurs on a marine propeller, which is a propulsion unit of a marine vessel. Among erosion of a marine propeller, erosion mainly occurring at a root (root) of a boss of a propeller is referred to as root erosion. It is said that this route erosion is likely to occur on a propeller operating in a diagonal flow (a propeller whose propeller shaft is inclined with respect to the traveling direction of the ship). The reason is that when the propeller operates in a diagonal flow, the flow flowing into the blade fluctuates during one revolution, and cloud-like cavitation occurs at the root of the blade where the fluctuation width (change in the angle of attack of the flow) is the largest. It is thought to occur. A more detailed description of the cavitation of marine propellers is given in, for example, "New Version Cavitation Basics and Recent Advances", edited by Yoji Kato, "8.4 Marine Propulsor" published by Maki Shoten.
[0003]
If the route erosion is severe, the wings may break during sailing. In such a case, a distress accident or the like may occur, which is a major problem that impairs the safety of the operation of the ship. In addition, route erosion is often found in high-speed boat propellers used for high-speed boats such as two-axis ferries and security boats, and is becoming an important problem in recent years in conjunction with the speeding-up of ships. For this reason, various proposals have conventionally been made to avoid the adverse effects of route erosion.
[0004]
For example, the following (1) and (2) are known as countermeasures for route erosion.
(1) Method of forming cavitation preventing holes on the wing surface:
However, this method has problems in that it is difficult to specify the position where the hole is formed, or it is technically difficult to form a hole, and the strength of the blade is reduced due to the formation of the hole.
[0005]
(2) Marine propeller disclosed in JP-A-8-91291:
This marine propeller will be described with reference to FIGS. 8 and 9.
FIG. 8 is a perspective view of a marine propeller disclosed in Japanese Patent Application Laid-Open No. 8-91291.
FIG. 9 is a sectional view of a blade root portion of the marine propeller disclosed in the publication.
[0006]
As shown in FIG. 8, the marine propeller 100 includes a cylindrical boss 101 and a plurality of wings 102 (five in FIG. 8) extending radially from the outer periphery of the boss 101. The length from the root 102a of the blade 102 to the blade tip 102b (R-boss radius) is referred to as the blade length. In the above-mentioned publication, a portion that is equal to or less than half of the blade length (a portion inside from the reference symbol Rr in FIG. 8) is called a blade root portion, and the cross-sectional shape of the blade root portion is set as follows. That is, as shown in FIG. 9, the cross-sectional shape of the blade root portion is such that the wall thickness gradually decreases from the maximum thickness position (maximum thickness T) to the rear end of the blade, and the rear end also has a thickness t. And roundness (round surface) between the wing side surfaces. Further, it is said that it is preferable to set the thickness t of the rear end to 30% to 60% of the maximum thickness T, and to coat the wing surface with a nylon resin.
[0007]
According to the above publication, the use of such a marine propeller 100 reduces the cavitation range by about 30% as compared with a conventional marine propeller, and reduces the progress of surface roughness on the rear side of the wing. The result is stated. However, recently, there has been a demand for a marine propeller that is more excellent in the effect of preventing route erosion.
[0008]
SUMMARY OF THE INVENTION The present invention has been made to meet such a demand, and has as its object to provide a marine propeller capable of further improving the effect of preventing route erosion.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, a marine propeller of the present invention is a marine propeller having wings extending in a radial direction from an outer periphery of a boss having a rotation center axis.In a wing thickness profile of a wing root of the wing, The maximum blade thickness position is on the rear end side of the center of the chord length, and the radius of curvature of the blade rear end surface is more than 30% and not more than 50% of the maximum blade thickness.
[0010]
Here, the “wing thickness profile of the blade root” will be described. FIG. 10 is a diagram for explaining the blade thickness profile of the blade root, and is a cross-sectional view perpendicular to the rotation axis of the propeller. In this figure, (part of) the outer peripheral line B of the boss and the surface line W of one wing are shown. Between the blade surface line W and the boss outer peripheral line B, there is a radius RL at the blade root. In the figure, the size of the boss and the radius are exaggerated. Dotted lines indicate straight lines (two straight lines) obtained by extending the blade surface from the blade-side starting point SP of the radius RL to the boss outer peripheral line B. Then, intersections p1 and p2 between the two straight lines and the boss outer peripheral line B are set, and a portion between these two points p1 and p2 is defined as P. The blade thickness profile of the blade root means a shape in which this portion P is developed.
[0011]
According to the present invention, since the maximum blade thickness position of the blade is located on the trailing end side of the center of the chord length, a low pressure region is easily generated near the trailing edge of the blade. The root cavitation generated in this low pressure region is in a so-called supercavitation state (the rear end of the cavitation is behind the rear end of the wing). Therefore, the cavitation collapse occurs after the trailing edge of the wing, and erosion hardly occurs.
[0012]
Further, by making the radius of curvature of the trailing edge of the blade more than 30% and less than or equal to 50% of the maximum blade thickness, the hydrodynamic point at the trailing edge of the blade varies more greatly. Therefore, a pressure fluctuation occurs in which the angle of attack is reduced more effectively in proportion to the magnitude of the angle flowing into the blade. That is, pressure fluctuations occurring on the surface where cavitation occurs can be further reduced. Thereby, the occurrence of root cavitation can be suppressed, and the collapse pressure of cavitation can be reduced, so that erosion hardly occurs.
[0013]
In the marine propeller of the present invention, it is preferable that a retreat dimension ΔL from the center of the chord length L to the maximum blade thickness position satisfies 0.1L ≦ ΔL ≦ 0.4L.
Further, it is preferable that a radius of curvature of the trailing edge of the blade is close to 50% of the maximum blade thickness.
In these cases, the occurrence of erosion can be further suppressed.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, description will be made with reference to the drawings.
FIG. 1 is a front view of a marine propeller according to an embodiment of the present invention.
FIG. 2 is a sectional view showing a blade thickness profile at a blade root of the marine propeller.
FIG. 3 is a sectional view showing a blade thickness profile of a marine propeller according to another embodiment of the present invention (an embodiment different from FIG. 1).
[0015]
As shown in FIG. 1, a marine propeller 1 according to the present embodiment includes a cylindrical boss 2 and a plurality of wings 3 (four in FIG. 1) extending radially from the outer periphery of the boss 2. I have. The point that the boat propeller is composed of the boss and the wing is the same as the conventional one. The length from the root 3a of the wing 3 to the wing tip 3b (R-boss radius) is called the wing length. In the present invention, it is preferable to have a blade thickness profile described below at a position within 20% of the blade length from the root 3a of the blade (a portion inside from the symbol Rr in FIG. 1).
[0016]
In the present embodiment, the cross-sectional shape of the blade root of blade 3 is set as follows. That is, in the blade thickness profile of the blade root in FIG. 2, the maximum blade thickness position Tmax is located on the rear end side (right side in FIG. 2) of the center C of the chord length L, and the center C of the chord length L From the maximum blade thickness position Tmax is set so as to satisfy 0.1 L ≦ ΔL ≦ 0.4 L. The radius of curvature r of the blade rear end face is set to be more than 30% of the maximum blade thickness T and 50% or less (more preferably, close to 50% of the maximum blade thickness T). That is, the thickness of the blade rear end is formed in the range of 60% to 100% of the maximum blade thickness T. When the propulsion performance of the blade 3 is particularly important (when some cavitation is allowed), the radius of curvature r of the blade rear end surface can be reduced to 30% of the maximum blade thickness T.
[0017]
The cross-sectional shape of the blade root of the blade 3 can also be set as shown in the blade thickness profile of FIG. That is, the wing 3 ′ has a maximum wing thickness position Tmax set as close as possible to the wing rear end, and a semicircular wing rear end surface having a diameter of the maximum wing thickness T at the position Tmax. ing. That is, the wing 3 ′ in FIG. 3 has a large roundness at the rear end of the wing, and becomes thinner toward the front end of the wing.
[0018]
Next, comparison of the route erosion prevention performance between the marine propeller according to the present invention and the conventional marine propeller will be described.
FIG. 4 is a diagram conceptually showing a cavitation collapse state assumed in the marine propeller according to the present invention.
FIG. 5 is a view conceptually showing a cavitation collapse state assumed in a marine propeller disclosed in Japanese Patent Application Laid-Open No. 8-91291.
FIG. 6 is a diagram conceptually showing a cavitation collapse state assumed in a typical conventional marine propeller.
FIG. 7 is a graph showing a pressure distribution of a wing surface assumed in each marine propeller having the wing thickness profile of FIGS. 4 to 6.
[0019]
The propeller blade shown in FIG. 4 is the marine propeller according to the embodiment of the present invention described in the blade thickness profile of FIG.
The propeller blade shown in FIG. 5 is a marine propeller disclosed in Japanese Patent Application Laid-Open No. 8-91291 described above with reference to FIG.
The propeller blade shown in FIG. 6 is a conventional typical marine propeller 10 (hereinafter, referred to as a normal propeller).
The maximum thickness position Tmax of the marine propeller and the normal type propeller 10 disclosed in Japanese Patent Application Laid-Open No. Hei 8-91291 is slightly before (0% L to 20% L) the center in the chord direction. The cross section of the normal type propeller 10 has a gradually reduced thickness from the maximum thickness position Tmax to the trailing edge, and has a sharp shape with almost no thickness at the trailing edge of the blade.
[0020]
With reference to FIG. 7, a comparison of the pressure distribution on the wing surface of each marine propeller will be described.
In the graph of FIG. 7, -Cp on the vertical axis represents the water pressure on the blade surface, and C on the horizontal axis represents the position in the chord length direction. Note that the reason why the pressure is displayed as -Cp is that when the inflow speed is high, the pressure becomes negative, and this is displayed as upward.
In the graph, the line of Cp = −σ indicates a boundary line above which the cavitation is likely to occur, and a line below which the cavitation starts to collapse.
[0021]
In the graph of FIG. 7, a curve α indicated by a solid line represents the pressure distribution of the propeller according to the present invention of FIG. 4, and a curve β indicated by a dashed line represents the pressure distribution of the propeller disclosed in Japanese Unexamined Patent Publication No. Hei 8-91291 of FIG. A curve γ indicated by a dotted line represents the pressure distribution of the normal type propeller in FIG. In the conventional propeller, since the trailing edge of the blade is sharp and has little wall thickness, the pressure distribution curve γ shows a low pressure at the leading edge of the blade and a high pressure at the trailing edge. On the other hand, the propeller of the present invention has a low pressure near the blade trailing edge because the trailing edge of the blade is thick. Further, with respect to the propeller disclosed in Japanese Patent Application Laid-Open No. Hei 8-91291, the pressure distribution curve β has a substantially intermediate value between α and γ.
[0022]
The following can be understood from this pressure distribution. That is, in the propeller and the normal type propeller disclosed in Japanese Patent Application Laid-Open No. HEI 8-91291, since the cavity easily collapses on the wing surface as shown in FIGS. 5 and 6, root erosion easily occurs particularly at the trailing edge of the wing. . On the other hand, in the propeller according to the present invention, a low-pressure region is generated behind the trailing edge of the blade, and root cavitation generated in the low-pressure region is in a so-called supercavitation state. It occurs substantially behind the trailing edge of the wing. Thus, the propeller of the present invention is less likely to cause erosion than the propellers of FIGS.
[0023]
As described above, in the propeller of the present embodiment, a low-pressure region is likely to be generated in the vicinity of the trailing edge of the wing, and the generated root cavitation becomes so-called supercavitation, and the collapse of the cavitation occurs substantially behind the trailing edge of the wing. . As a result, the collapse of cavitation occurring on the wing surface can be significantly reduced, so that the occurrence of root erosion can be suppressed.
[0024]
【The invention's effect】
As is clear from the above description, according to the present invention, the occurrence of cavitation can be suppressed more effectively, and the effect of preventing route erosion can be improved.
[Brief description of the drawings]
FIG. 1 is a front view of a marine propeller according to an embodiment of the present invention.
FIG. 2 is a sectional view showing a blade thickness profile at a blade root of the marine propeller.
FIG. 3 is a sectional view showing a wing thickness profile of a marine propeller according to another embodiment of the present invention.
FIG. 4 is a diagram conceptually showing a cavitation collapse state assumed in the marine propeller according to the present invention.
FIG. 5 is a view conceptually showing a cavitation collapse state assumed in a marine propeller disclosed in Japanese Patent Application Laid-Open No. 8-91291.
FIG. 6 is a diagram conceptually showing a cavitation collapse state assumed in a typical conventional marine propeller.
FIG. 7 is a graph showing a pressure distribution of a wing surface assumed in each marine propeller having the wing thickness profile of FIGS. 4 to 6;
FIG. 8 is a perspective view of a marine propeller disclosed in Japanese Unexamined Patent Publication No. 8-91291.
FIG. 9 is a sectional view of a blade root portion of the marine propeller disclosed in the publication.
FIG. 10 is a view for explaining a blade thickness profile of a blade root, and is a cross-sectional view perpendicular to a rotation axis of a propeller.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Marine propeller 2 Boss 3 3 'Wing 3a Wing root 3b Wing tip

Claims (4)

A marine propeller including wings extending radially from an outer periphery of a boss having a rotation center axis,
In the blade thickness profile of the blade root of the blade, the maximum blade thickness position is located on the rear end side from the center of the chord length, and the radius of curvature of the blade rear end surface exceeds 30% of the maximum blade thickness and is 50% or less. A marine propeller characterized by the following. 2. The marine propeller according to claim 1, wherein the cavitation collapse occurring around the wing occurs substantially behind the trailing edge of the wing. 3. The marine propeller according to claim 1, wherein a retreat dimension ΔL from a center of the chord length L to the maximum blade thickness position satisfies 0.1 L ≦ ΔL ≦ 0.4 L. 4. 4. The marine propeller according to claim 1, wherein a radius of curvature of the wing rear end face is close to 50% of the maximum wing thickness.

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