Variable pitch-type thruster

Abstract

A variable pitch-type thruster 2 according to one embodiment includes a propeller 4 including a boss 5 and a plurality of propeller blades 6. Each propeller blade 6 includes a blade tray 7 rotatably supported by the boss 5, and a first plate 81 and a second plate 82 joined to the blade tray 7. The first plate 81 and the second plate 82 are symmetrical to each other with respect to a pitch line that defines angles of the propeller blades 6 with respect to a rotation direction of the propeller 4, and form a tunnel-shaped loop opening along the pitch line. The distance from the pitch line to rear edges of the first plate 81 and the second plate 82 is greater than the distance from the pitch line to front edges of the first plate 81 and the second plate 82 in a circumferential cross section at a position 0.7 times the diameter of the propeller 4.

Description

Variable pitch thruster

[0001] The present disclosure relates to a variable pitch thruster mounted on a ship.

[0002] In a ship, a variable pitch thruster may be mounted in which the rotation direction of the propeller remains constant and the propulsion direction can be reversed by the pitch. For example, Patent Document 1 discloses a variable pitch side thruster including a propeller disposed in a horizontal hole penetrating the hull in the ship width direction.

[0003] The propeller includes a boss and a plurality of propeller blades. In order to generate equal propulsion forces in either propulsion direction, each propeller blade is flat. The angle of each propeller blade with respect to the rotation direction of the propeller is the pitch, and each propeller blade can be articulated in both directions from a state parallel to the rotation direction of the propeller.

[0004] Japanese Patent Application Laid-Open No. 11-180394

[0005] However, when the propeller blade is flat, the angle of incidence of the fluid at the leading edge is large when each propeller blade is articulated, so that flow separation is likely to occur.

[0006] Therefore, an object of the present disclosure is to make it difficult for flow separation to occur in a variable pitch thruster capable of reversing the propulsion direction by the pitch.

[0007] This disclosure provides a variable-pitch thruster in which the direction of thrust can be reversed by pitch, comprising a propeller including a boss and a plurality of propeller blades, each of the plurality of propeller blades including a blade disc supported by the boss so as to be rotatable about a spindle axis perpendicular to the axis of rotation of the propeller, and a first plate and a second plate joined to the blade disc, which are symmetrical with respect to a pitch line defining the angle of the propeller blade with respect to the direction of rotation of the propeller, which is the pitch, and forming a tunnel-shaped loop that opens along the pitch line, each of the first plate and the second plate having a leading edge located upstream of a flow opposite to the direction of rotation of the propeller and a trailing edge located downstream of the flow, wherein in a circumferential cross-section at a position 0.7 times the diameter of the propeller, the distance from the pitch line to the trailing edge is greater than the distance from the pitch line to the leading edge.

[0008] According to this disclosure, flow separation can be made less likely to occur in a variable-pitch thruster in which the direction of propulsion can be reversed by pitch.

[0009] This is a cross-sectional view of a part of a ship equipped with a variable-pitch thruster according to one embodiment as a side thruster. This is a perspective view of the thruster. This is a circumferential cross-sectional view of one propeller blade at a position 0.7 times the diameter of the propeller. Figures 4A to 4C schematically show the fluid flow to three propeller blades at different pitches. This is a diagram showing vortices generated on the outer and inner surfaces of the blade tips of the propeller blades. This is a side view of a first modified variable-pitch thruster. This is a side view of a second modified variable-pitch thruster. Figures 8A and 8B are circumferential cross-sectional views at a position 0.7 times the diameter of the propeller, showing another shape of the propeller blade.

[0010] Figure 1 shows a ship 1 equipped with a variable-pitch thruster 2 according to one embodiment as a side thruster. The hull 11 of the ship 1 is provided with a transverse hole 12 that penetrates the hull 11 in the width direction.

[0011] The variable-pitch thruster 2 includes a propeller 4 positioned within the horizontal hole 12, a gear case 32 that rotatably supports the propeller 4, and a strut 31 that penetrates the ceiling of the horizontal hole 12 and suspends the gear case 32. The variable-pitch thruster 2 allows the direction of thrust to be reversed by changing the pitch while the rotation direction of the propeller 4 remains constant.

[0012] A first rotating shaft extending vertically is arranged inside the strut 31, and a second rotating shaft extending axially through the horizontal hole 12 is arranged inside the gear case 32. One end of the second rotating shaft is connected to the first rotating shaft via a bevel gear, and the other end of the second rotating shaft is connected to the propeller 4.

[0013] The variable-pitch thruster 2 also includes a prime mover that rotates the first rotary shaft, which is located inside the hull 11 above the lateral opening 12. Furthermore, the variable-pitch thruster 2 includes a hydraulic system located inside the gear case 32 that changes the pitch of each propeller blade 6 of the propeller 4, which will be described later. The hydraulic system is known and therefore will not be described.

[0014] As shown in Figure 2, the propeller 4 includes a boss 5 located at the center of rotation and a plurality of propeller blades 6 located around the boss 5. Each propeller blade 6 has a pitch line 42, shown in Figure 3, which defines the angle of the propeller blade 6 with respect to the direction of rotation of the propeller 4, and is bidirectionally adjustable from a state parallel to the direction of rotation of the propeller 4. In Figure 3, the direction of rotation of the propeller 4 is indicated by an arrow.

[0015] Specifically, each propeller blade 6 includes a blade disc 7 supported by a boss 5 so as to be rotatable around a spindle axis 41 perpendicular to the rotation axis of the propeller 4, and a first plate 81 and a second plate 82 joined to the blade disc 7, extending from the blade disc 7 to the blade tip of the propeller blade 6.

[0016] In this embodiment, the first plate 81 is located near the gear case 32, and the second plate 82 is located far from the gear case 32. The first plate 81 and the second plate 82 are symmetrical with respect to the pitch line 42. The first plate 81 and the second plate 82 also form a tunnel-shaped loop that opens along the pitch line 42.

[0017] As shown in Figure 3, the first plate 81 includes a leading edge 81a located downstream of the propeller 4 in the direction of rotation, in other words, upstream of the flow opposite to the direction of rotation of the propeller 4, and a trailing edge 81b located upstream of the propeller 4 in the direction of rotation, in other words, downstream of the flow opposite to the direction of rotation of the propeller 4.

[0018] Similarly, the second plate 82 includes a leading edge 82a located downstream of the propeller 4 in the direction of rotation, in other words, upstream of the flow opposite to the direction of rotation of the propeller 4, and a trailing edge 82b located upstream of the propeller 4 in the direction of rotation, in other words, downstream of the flow opposite to the direction of rotation of the propeller 4.

[0019] In this embodiment, each propeller blade 6 is a backward-skewed blade. Therefore, as shown in Figure 2, the leading edge 81a and trailing edge 81b of the first plate 81 and the leading edge 82a and trailing edge 82b of the second plate 82 are curved such that, when viewed from the axial direction of the propeller 4, the central portion is concave in the opposite direction to the rotation direction of the propeller 4.

[0020] Each propeller blade 6 is a forward-skewed blade, and the leading edge 81a and trailing edge 81b of the first plate 81 and the leading edge 82a and trailing edge 82b of the second plate 82 may be curved such that, when viewed from the axial direction of the propeller 4, the central portion is convex in the direction of rotation of the propeller 4. Alternatively, each propeller blade 6 may be balanced-skewed such that the relative positions of the width centers of the first plate 81 and the second plate 82 with respect to the spindle axis 41 are reversed on the inside and outside in the radial direction of the propeller 4.

[0021] When the diameter of the propeller 4 is D, as shown in Figure 3, in the circumferential cross-section at position 0.7D, the distance from the pitch line 42 to the trailing edge 81b, 82b is greater than the distance from the pitch line 42 to the leading edge 81a, 82a. The circumferential cross-section is sometimes called a constant radius cross-section or an equiradial surface. In this embodiment, both ends of the first plate 81 and both ends of the second plate 82 are joined to each other in the radial direction of the propeller 4. Therefore, in the circumferential cross-section within the range excluding both ends of the first plate 81 and the second plate 82, the distance from the pitch line 42 to the trailing edge 81b, 82b is greater than the distance from the pitch line 42 to the leading edge 81a, 82a.

[0022] For example, in the circumferential cross-section at position 0.7D, the angle θ between the code line 81c connecting the front edge 81a and rear edge 81b of the first plate 81 and the pitch line 42 is 1 degree or more and 30 degrees or less, and the angle θ between the code line 82c connecting the front edge 82a and rear edge 82b of the second plate 82 and the pitch line 42 is 1 degree or more and 30 degrees or less. In each of the first plate 81 and the second plate 82, the angle θ may be 1 degree or more and 15 degrees or less.

[0023] Furthermore, the maximum width W of the propeller blade 6 in the direction perpendicular to the pitch line 42 is, for example, 2% to 50% of the diameter D of the propeller 4. The maximum width W of the propeller blade 6 may also be 3% to 20% of the diameter D of the propeller 4. For example, each propeller blade 6 is designed so that its maximum width W is within the range of 0.6D to 0.8D.

[0024] In this embodiment, the first plate 81 and the second plate 82 are both flat. That is, the camber line, which is the center line in the width direction of the first plate 81, coincides with the code line 81c, and the camber line, which is the center line in the width direction of the second plate 82, coincides with the code line 82c.

[0025] Furthermore, in this embodiment, the first plate 81 and the second plate 82 are curved in a convex shape so that they move away from each other as they move away from the blade dish 7, and then move closer together. In other words, each of the first plate 81 and the second plate 82 is curved such that the tangential inclination in the axial cross-section passing through the rotation axis of the propeller 4 changes in only one direction.

[0026] Furthermore, in this embodiment, the first plate 81 and the second plate 82 are smoothly connected at the wingtips of each propeller blade 6.

[0027] As described above, in the variable-pitch thruster 2 of this embodiment, the first plate 81 and the second plate 82 are spaced apart from each other from the leading edges 81a, 82a toward the trailing edges 81b, 82b. Therefore, as shown in Figures 4A to 4C, regardless of whether the first plate 81 or the second plate 82 is positioned upstream of the flow along the rotation axis of the propeller 4 when the propeller blade 6 is pitched, the inclination of the upstream plate with respect to the plane perpendicular to the rotation axis of the propeller 4 is small, and the inclination of the downstream plate with respect to the said plane is large. As a result, a questionable camber effect can be obtained while maintaining the symmetrical shape of the propeller blade 6, thereby making flow separation less likely to occur.

[0028] Furthermore, because the inclination of the upstream plate and the downstream plate are different with respect to the plane perpendicular to the rotation axis of the propeller 4, it is possible to prevent the incidence angle at the leading edge of the upstream plate from becoming excessively large for flow in the opposite direction to the rotation direction of the propeller 4, while keeping the incidence angle at the leading edge of the downstream plate for flow whose direction has been changed by the upstream plate to be about the same as that of the upstream plate. This allows the load to be distributed between the first plate 81 and the second plate 82.

[0029] Furthermore, in this embodiment, since the first plate 81 and the second plate 82 are smoothly connected at the wingtips of each propeller blade 6, the load distribution per unit area of ​​the outer surface of each propeller blade 6 can be gradually reduced toward the wingtips, and flow from the pressure surface to the negative pressure surface can be suppressed. For example, as shown in Figure 5, when the flow along the rotation axis of the propeller 4 is in the direction from the gear case 32 toward the propeller 4, the inner surface of the first plate 81 is the pressure surface and the outer surface is the negative pressure surface, while the outer surface of the second plate 82 is the pressure surface and the inner surface is the negative pressure surface.

[0030] Even if flow in occurs, the vortices generated on the outer surface of the tip of each propeller blade 6 and the vortices generated on the inner surface are in opposite directions, so the vortices cancel each other out, making it difficult for large tip vortices to form. In other words, the smooth connection between the first plate 81 and the second plate 82 suppresses the generation of tip vortices. For example, in Figure 5, on the outer surface of the tip of each propeller blade 6, a clockwise vortex is generated when viewed in the opposite direction to the rotation of the propeller 4, induced by the flow from the pressure surface to the negative pressure surface, that is, the flow from the outer surface of the second plate 82 to the outer surface of the first plate 81. On the other hand, on the inner surface of the tip of each propeller blade 6, a counterclockwise vortex is generated when viewed in the opposite direction to the rotation of the propeller 4, induced by the flow from the pressure surface to the negative pressure surface, that is, the flow from the inner surface of the first plate 81 to the inner surface of the second plate 82.

[0031] <Modifications> This disclosure is not limited to the embodiments described above, and various modifications are possible without departing from the gist of this disclosure.

[0032] For example, as in the first modified variable-pitch thruster 2A shown in Figure 6, the inner ends of the first plate 81 and the inner ends of the second plate 82 may be spaced apart from each other in the radial direction of the propeller 4. Also, as in the second modified variable-pitch thruster 2B shown in Figure 7, the first plate 81 and the second plate 82 may each have a wavy shape. However, if the first plate 81 and the second plate 82 are each curved in a convex shape as in the above embodiment, the first plate 81 and the second plate 82 can have a simple shape.

[0033] Furthermore, the first plate 81 and the second plate 82 may be connected at the wingtips of each propeller blade 6 in such a way that they form an obtuse angle.

[0034] Furthermore, the first plate 81 and the second plate 82 of each propeller blade 6 do not necessarily have to be flat. For example, as shown in Figure 8A, in the case of backward skew, where the first plate 81 and the second plate 82 are significantly shifted toward the opposite side of the rotation direction of the propeller 4 relative to the spindle shaft 41, the first plate 81 and the second plate 82 may be given a camber suitable for backward skew. Also, as shown in Figure 8B, in the case of forward skew, where the first plate 81 and the second plate 82 are significantly shifted toward the rotation direction of the propeller 4 relative to the spindle shaft 41, the first plate 81 and the second plate 82 may be given a camber suitable for forward skew.

[0035] <Summary> In a first aspect, the present disclosure provides a variable-pitch thruster in which the direction of thrust can be reversed by pitch, comprising a propeller including a boss and a plurality of propeller blades, each of the plurality of propeller blades including a blade disc supported by the boss so as to be rotatable about a spindle axis perpendicular to the axis of rotation of the propeller, and a first plate and a second plate joined to the blade disc, which are symmetrical with respect to a pitch line defining the angle of the propeller blade with respect to the direction of rotation of the propeller, which is the pitch, and forming a tunnel-shaped loop that opens along the pitch line, each of the first plate and the second plate having a leading edge located upstream of a flow opposite to the direction of rotation of the propeller and a trailing edge located downstream of the flow, wherein in a circumferential cross-section at a position 0.7 times the diameter of the propeller, the distance from the pitch line to the trailing edge is greater than the distance from the pitch line to the leading edge.

[0036] According to the above configuration, the first plate and the second plate are spaced apart from each other from the leading edge to the trailing edge. Therefore, regardless of whether the propeller blade is positioned upstream of the flow along the propeller's axis of rotation, the inclination of the upstream plate with respect to the plane perpendicular to the propeller's axis of rotation is small, while the inclination of the downstream plate with respect to the said plane is large. As a result, a subtle camber effect can be obtained while maintaining the symmetrical shape of the propeller blade, thereby making flow separation less likely to occur.

[0037] In a second embodiment, in the first embodiment, for example, in a circumferential cross-section at a position 0.7 times the diameter of the propeller, the angle between the code line connecting the leading edge and the trailing edge of the first plate and the second plate, and the pitch line, may be 1 degree or more and 30 degrees or less.

[0038] In a third embodiment, in the first or second embodiment, the first plate and the second plate may be convexly curved so that they move away from each other as they move away from the blade disc and then move closer together. This configuration allows the first plate and the second plate to have a simple shape.

[0039] In a fourth embodiment, in any of the first to third embodiments, for example, the maximum width of each propeller blade in a direction perpendicular to the pitch line may be 2% or more and 50% or less of the diameter of the propeller.

[0040] In a fifth embodiment, in any of the first to fourth embodiments, the first plate and the second plate may be smoothly connected at the wingtip of each propeller blade. This configuration makes it possible to suppress the generation of wingtip vortices.

[0041] 1. Ship 2. Variable-pitch thruster 4. Propeller 41. Spindle shaft 42. Pitch line 5. Boss 6. Propeller blade 7. Blade disc 81. First plate 81a. Leading edge 81b. Trailing edge 81c. Chord line 82. Second plate 82a. Leading edge 82b. Trailing edge 82c. Chord line

Claims

1. A variable-pitch thruster in which the direction of thrust can be reversed by pitch, comprising a propeller including a boss and a plurality of propeller blades, each of the plurality of propeller blades including a blade disc supported by the boss so as to be rotatable about a spindle axis perpendicular to the axis of rotation of the propeller, and a first plate and a second plate joined to the blade disc, which are symmetrical with respect to a pitch line defining the angle of the propeller blade with respect to the direction of rotation of the propeller which is the pitch, and which form a tunnel-shaped loop opening along the pitch line, each of the first plate and the second plate having a leading edge located upstream of the flow opposite to the direction of rotation of the propeller and a trailing edge located downstream of the flow, wherein in a circumferential cross-section at a position 0.7 times the diameter of the propeller, the distance from the pitch line to the trailing edge is greater than the distance from the pitch line to the leading edge.

2. In a circumferential cross-section at a position 0.7 times the diameter of the propeller, the angle between the code line connecting the leading edge and the trailing edge of the first plate and the second plate, respectively, and the pitch line is 1 degree or more and 30 degrees or less, according to claim 1.

3. The variable-pitch thruster according to claim 1 or 2, wherein the first plate and the second plate are convexly curved so that they move away from each other and then approach each other as they move away from the blade disc.

4. The variable-pitch thruster according to claim 1 or 2, wherein the maximum width of each propeller blade in a direction perpendicular to the pitch line is 2% or more and 50% or less of the diameter of the propeller.

5. The variable-pitch thruster according to claim 1 or 2, wherein the first plate and the second plate are smoothly connected at the wingtips of each propeller blade.

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