WO2012050441A1 - Marine propeller with front and further blade - Google Patents

Marine propeller with front and further blade Download PDF

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Publication number
WO2012050441A1
WO2012050441A1 PCT/NL2011/050692 NL2011050692W WO2012050441A1 WO 2012050441 A1 WO2012050441 A1 WO 2012050441A1 NL 2011050692 W NL2011050692 W NL 2011050692W WO 2012050441 A1 WO2012050441 A1 WO 2012050441A1
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WO
WIPO (PCT)
Prior art keywords
blade
leading edge
front blade
marine propeller
aft
Prior art date
Application number
PCT/NL2011/050692
Other languages
French (fr)
Inventor
Jan Terlouw
Original Assignee
Jan Terlouw
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from NL2005491A external-priority patent/NL2005491C2/en
Application filed by Jan Terlouw filed Critical Jan Terlouw
Publication of WO2012050441A1 publication Critical patent/WO2012050441A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63H—MARINE PROPULSION OR STEERING
    • B63H1/00—Propulsive elements directly acting on water
    • B63H1/02—Propulsive elements directly acting on water of rotary type
    • B63H1/12—Propulsive elements directly acting on water of rotary type with rotation axis substantially in propulsive direction
    • B63H1/14—Propellers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63H—MARINE PROPULSION OR STEERING
    • B63H5/00—Arrangements on vessels of propulsion elements directly acting on water
    • B63H5/07—Arrangements on vessels of propulsion elements directly acting on water of propellers
    • B63H5/08—Arrangements on vessels of propulsion elements directly acting on water of propellers of more than one propeller
    • B63H5/10—Arrangements on vessels of propulsion elements directly acting on water of propellers of more than one propeller of coaxial type, e.g. of counter-rotative type
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63H—MARINE PROPULSION OR STEERING
    • B63H5/00—Arrangements on vessels of propulsion elements directly acting on water
    • B63H5/07—Arrangements on vessels of propulsion elements directly acting on water of propellers
    • B63H5/08—Arrangements on vessels of propulsion elements directly acting on water of propellers of more than one propeller
    • B63H5/10—Arrangements on vessels of propulsion elements directly acting on water of propellers of more than one propeller of coaxial type, e.g. of counter-rotative type
    • B63H2005/103—Arrangements on vessels of propulsion elements directly acting on water of propellers of more than one propeller of coaxial type, e.g. of counter-rotative type of co-rotative type, i.e. rotating in the same direction, e.g. twin propellers

Definitions

  • the invention relates to a marine propeller according to the precharacterizing portion of claim 1 .
  • a propeller is usually driven by a shaft and submerged under water. By rotating the propeller via the shaft in its main direction, a forward propulsion thrust is being generated. This thrust propels the vessel in a forward direction.
  • This ratio should be at least equal to a ratio between the axial distance between both propellers and the sum of blade distance plus the distance of the back blade with respect to the front blade in the rotational direction minus the width of the influence zone. If this ratio is respected, then according to this prior art document the mutual detrimental influence of both propellers will be small.
  • a disadvantage of the known marine propeller is that the propulsion efficiency is still relatively low.
  • angle of attack is within this disclosure defined as the angle between the rotational direction of the marine propeller and the direction of the camber line at the relevant leading edge.
  • the marine propeller will not only experience the effect of the rotational speed, but also of the water flowing in the direction of the propeller's axis towards the propeller. The combined effects of these will be referred to as flow angle of attack.
  • all (relative) dimensions and angles, as well as the sections in the exemplary embodiments, are given at 70% of the radius of the propeller, as is usual in the art.
  • a line intersects the leading edge of the front blade and the leading edge of the further blade is on a cylindrical plane which is coaxial with the hub, and has an angle with a plane perpendicular to the rotational axis of more than 0° and less than 45°. In particular, this angle is in the range of 5° to 30°. This results in a small gap between the front and further blades.
  • the camber of the front blade is larger than the camber of the aft blade.
  • Fig. 2 shows an aft view of the propeller of fig. 1 ;
  • Fig. 8 shows an isometric view of a third embodiment of a marine propeller according to the invention.
  • the hub 2 has a rotational axis 8.
  • the marine propeller 1 rotates around this rotational axis 8.
  • the main rotation direction R is clockwise.
  • the marine propeller 1 of this embodiment is a right hand propeller.
  • the marine propeller 1 produces a forward thrust i.e. a thrust parallel to the rotational axis and directed to the right in the side view of fig. 1.
  • the front blade 4 has a leading edge 10, a trailing edge 12.
  • the aft blade 6 has a leading edge 14 and a trailing edge 16.
  • the front blade has a pressure side 18 and a suction side 20.
  • the aft blade 6 has a pressure side 22 and a suction side 24.
  • the shape and angle of the blades 4, 6 cause an increase of the water pressure at the respective pressure sides 18, 22, and a decrease of the water pressure at the respective suction sides 20, 24.
  • Fig. 4 shows that the front blade 4 has a camber line 26, which is the line through the mid thickness of the front blade 4, and a cord line 27 which is the line that connects the leading edge 10 and the trailing edge 12.
  • the aft blade 6 has a camber line 28, which is the line through the mid thickness of the aft blade 6, and a cord line 29 which is the line that connects the leading edge 14 and the trailing edge 16.
  • the camber c f of front blade 4 is defined as the ratio between the maximum distance C f of the camber line 26 to the respective cord line 27, and the cord line length.
  • the camber c a is defined as the ratio between the maximum distance C a of the camber line 28 of the aft blade 6 to the respective cord line 29 and the cord line 29 length.
  • the leading edge 1 10 of the front blade 104 is positioned in front of the leading edge 1 14 of the aft blade 106 in the main rotation direction.
  • the leading edge 1 14 of the aft blade 106 is positioned an overlap distance D 0 in front of the trailing edge 1 12 of the front blade 104 in the main rotation direction.
  • the overlap distance D 0 is 25% of the aft blade cord length L A .
  • the overlap distance D 0 is more than 10%, in particular more than 20% of the aft blade cord length L A .
  • the overlap distance D 0 is less than 40%, in particular less than 30% of the further, or aft, blade cord length L A .
  • Such overlap distances result in an improved interaction between the water flow around the front and further blades.
  • the marine propeller 201 comprises a hub 202, a front blade 204 and a further, in this case aft, blade 206.
  • the marine propeller 201 of this exemplary embodiment comprises a multitude of front blades and a multitude of aft blades, in particular, two, three, four, five or six front blades and an equal number of aft blades.
  • the front blade 204 and the aft blade 206 are attached fixedly to the hub. This implies that their mutual distances are fixed as well. Reference is made to the first embodiment for the definitions that are used to describe this third embodiment.
  • the front blade 204 has a leading edge 210, and a trailing edge 212.
  • the leading edge 210 of the front blade 204 is positioned in front of the leading edge 214 of the aft blade 206 in the main rotation direction R.
  • the angle a B of a line through the leading edges of the front blade 204 and the further blade 206 is substantially 25°.
  • the aft blade cord length L A is less than 80%, in particular less than 70%, of the front blade cord length L f .
  • the aft blade cord length L A is more than 40%, in particular more than 50%, of the front blade cord length L f .
  • the overlap distance D 0 is more than 10%, in particular more than 20% of the aft blade cord length L A .
  • the overlap distance D 0 is less than 40%, in particular less than 30% of the further, or aft, blade cord length L A .
  • Such overlap distances result in an improved interaction between the water flow around the front and further blades.
  • the camber c f of the front blade is more than 5% x Lf, in particular more than 6% x Lf.
  • the camber c f of the front blade is less than 10%, in particular less than 8%.
  • Figs. 11 and 12 show the direction of the incoming water 230. This direction is a result of the velocity of the water flowing towards the propeller in axial direction, and the rotational speed of the propeller through the water. It is noted that for a given propeller, it is possible to determine a neutral flow direction wherein the propeller doesn't provide thrust.
  • the flow in use as shown in figs. 11 and 12, i.e. the flow wherein the propeller does provide thrust in the forward direction, is a few degrees less than this neutral flow direction.
  • the flow angle of attack a A relative to the further blade 206 is more than 1°, in particular more than 4°.
  • the flow angle of attack relative to the further blade is less than 7°, in particular less than 6°.
  • An angle etc is defined as the angle between the cord line 227 of the further blade 206 and the (extension of the) line connecting the leading edges 210 and 214 of the front 204 and further 206 blades.
  • a c of the third embodiment is 0°.
  • a c is preferably more than -6°.
  • Preferably ac is less than 13°.
  • a negative angle refers to a configuration wherein the extended part of the line connecting the leading edges 210 and 214 of the front 204 and further 206 blades, this is the part beyond the leading edge of the further blade 206, distal from the leading edge of the front blade 204, is at the suction side 224 of the further blade 206.
  • a negative angle refers to a relative small gap between the front blade 204 and the further blade 206.
  • a positive angle refers in this case to a configuration wherein the extended part of the line connecting the leading edges 210 and 214 of the front 204 and further 206 blades is at the pressure side 222 of the further blade 206.
  • a positive angle refers to a relative large gap between the front blade 204 and the further blade 206. It is noted that the propellers of the first and second embodiment fall within said range of ac too.
  • An angle aj is defined as the angle between the cord lines 227 and 229. aj is 3°. Preferably, the angle aj between the cord lines 227 and 228 is more than 1°, in particular more than 2°. Preferably, the angleaj between the cord lines 227 and 228 is less than 7°, in particular less than 4°.
  • the maximum value c of the camber of the front blade 204 occurs at more than 20% of the cord length L f , in particular more than 50% of the cord length L f measured from the leading edge 210.
  • the maximum value of the camber occurs at less than 70% of the cord length L f , in particular less than 65% of the cord length L f measured from the leading edge 210.
  • the gap between front and aft blade t is more than 1 %x Lf, and less than 15% of the cord length of the front blade Lf.
  • the aft blade is not placed directly on a hub, but is attached fixedly to the hub through the first blade, e.g. via props between the aft and the front blade.
  • the total mass and volume of the water displaced by the propeller per one shaft rotation resulting in a forward thrust is achieved with less input power on the propeller shaft in comparison with a conventional propeller with single blades.
  • the propeller blades are capable of performing with higher loads, or equal loads with a reduced blade area, compared to a propeller without a further blade.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • Ocean & Marine Engineering (AREA)
  • Structures Of Non-Positive Displacement Pumps (AREA)

Abstract

A marine propeller comprises a hub, a front blade (4) and a further blade (6). The hub defines a rotational axis for the propeller and is rotatable in a main rotation direction. The front blade and the further blade comprise a pressure side (18, 22), a suction side (20, 24), a leading edge (10, 14), and a trailing edge (12, 16). A total net pressure of the front blade has a stand-alone maximum value if the front blade is rotated at a design speed in the main rotation direction on a single marine propeller without the further blade. The further blade is positioned such relative to the front blade that a water flow around the further blade increases the total net pressure of the front blade with respect to the stand- alone maximum value.

Description

Title: Marine propeller with front and further blade
The invention relates to a marine propeller according to the precharacterizing portion of claim 1 . Such a propeller is usually driven by a shaft and submerged under water. By rotating the propeller via the shaft in its main direction, a forward propulsion thrust is being generated. This thrust propels the vessel in a forward direction.
DE-1 .094.622 discloses a marine propeller with a hub, three front blades, and three back blades. Each front blade is positioned in front of a suction side of a respective back blade, and the leading edge of the front blade is in front of the leading edge of the back plate in the main rotation direction. It is recognized as a problem in this prior art document that double propellers have adverse flow characteristics, as the mutual influence of both propellers have not been taken account for. According to DE-1 .094.622 this is solved by taking account of the ratio between the forward speed and the rotational speed of the propeller. This ratio should be at least equal to a ratio between the axial distance between both propellers and the sum of blade distance plus the distance of the back blade with respect to the front blade in the rotational direction minus the width of the influence zone. If this ratio is respected, then according to this prior art document the mutual detrimental influence of both propellers will be small.
A disadvantage of the known marine propeller is that the propulsion efficiency is still relatively low.
It is an object of the current invention to overcome at least one problem of the prior art, or at least to provide an alternative. In particular, it is an object of the current invention to provide a marine propeller with a front blade and a further blade, which propeller has a better efficiency than the one which is known from DE-1 .094.622.
The current invention achieves its object by means of a marine propeller according to claim 1 .
A marine propeller comprises a hub, a front blade and a further blade. The hub defines a rotational axis for the marine propeller. The marine propeller is rotatable in a main rotation direction. The front blade and the further blade are attached to the hub, and each comprise a pressure side, a suction side, a leading edge, and a trailing edge. A total net pressure of the front blade is generatable by pressures on the respective suction and pressure sides. The total net pressure of the front blade has a stand-alone maximum value if the front blade is rotated at a design speed in the main rotation direction on a single marine propeller without the further blade. The front blade is positioned in front of the suction side of the further blade in the direction of the rotational axis. The leading edge of the front blade is positioned in front of the leading edge of the further blade in the main rotation direction. The leading edge of the further blade is positioned in front of the trailing edge of the front blade in the main rotation direction. The further blade is positioned such relative to the front blade that a water flow around the further blade increases the total net pressure of the front blade with respect to the stand-alone maximum value if the propeller is rotated at the design speed in the main rotation direction.
The increase of the total net pressure results in a higher efficiency of the front blades of the marine propeller, than the same front blades would have on a single marine propeller, while the front blades of the marine propeller of DE-1.094.622 have a lower efficiency than the same front blades would have on a single marine propeller.
In particular, an angle of attack on the leading edge of the front blade is less than 0°. This increases the water flow at the suction side of the front blade.
It is noted that the term angle of attack is within this disclosure defined as the angle between the rotational direction of the marine propeller and the direction of the camber line at the relevant leading edge. In use, the marine propeller will not only experience the effect of the rotational speed, but also of the water flowing in the direction of the propeller's axis towards the propeller. The combined effects of these will be referred to as flow angle of attack. It is further noted that all (relative) dimensions and angles, as well as the sections in the exemplary embodiments, are given at 70% of the radius of the propeller, as is usual in the art.
In an embodiment, a line intersects the leading edge of the front blade and the leading edge of the further blade, is on a cylindrical plane which is coaxial with the hub, and has an angle with a plane perpendicular to the rotational axis of more than 0° and less than 45°. In particular, this angle is in the range of 5° to 30°. This results in a small gap between the front and further blades.
In a variant, a minimum distance between the pressure side of the front blade and the suction side of the further blade is less than one third of a cord line of the front blade. This results in a small gap between the front and further blades as well. Such a small gap influences the water flow between the front and the further blade, which leads to a higher efficiency and/or bearing capacity of the blades.
In an embodiment, the camber of the front blade is larger than the camber of the aft blade.
The invention further relates to a vessel provided with a shaft, wherein a marine propeller according to the invention is attached to an end of the shaft, and the suction sides of the front and further blades are facing a direction wherein the vessel is designed to be thrust. In particular, one end of the shaft protrudes outside of the vessel, the marine propeller is attached to the protruding end, and the front and further blades are facing a forward direction. Alternatively, a vessel may be propelled by any kind of azimuth thruster(s) with the marine propeller according the invention mounted on the shaft, where any given trust angle relative to the centreline of the vessel will be possible.
The invention will be explained in more detail with reference to preferred embodiments which are shown in the attached drawings, in which:
Fig. 1 shows a side view of a marine propeller according to the invention;
Fig. 2 shows an aft view of the propeller of fig. 1 ;
Fig. 3 shows a section along line Ill-Ill of fig. 2;
Fig. 4 shows an enlarged view of fig. 3;
Fig. 5 shows the view of fig. 4 with flow lines;
Fig. 6 shows the front blade of the embodiment of figs. 1-5 with a comparison of pressure distribution lines;
Fig. 7 shows in cross section a profile of a second embodiment according to the invention;
Fig. 8 shows an isometric view of a third embodiment of a marine propeller according to the invention;
Fig. 9 shows a side view of the propeller of fig. 8;
Fig. 10 shows an aft view of the propeller of fig. 8;
Fig. 1 1 shows a section along line XI-XI of fig. 10; and
Fig. 12 shows the section of fig. 1 1 , relative to direction of incoming flow.
Figs. 1 -3 show a marine propeller which is denoted in its entirety with reference numeral 1 , according to a first embodiment of the invention. The marine propeller 1 comprises a hub 2, a front blade 4 and a further, in this case aft, blade 6. In this exemplary embodiment there is only one front blade 4 and one aft blade 6. However, in practice there will be a multitude of front blades and a multitude of aft blades, in particular, two, three, four, five or six front blades and an equal number of aft blades. The front blade 4 and the aft blade 6 are attached fixedly to the hub. This implies that their mutual distances are fixed as well.
The hub 2 has a rotational axis 8. The marine propeller 1 rotates around this rotational axis 8. In the aft view of fig. 2, the main rotation direction R is clockwise. Put differently, the marine propeller 1 of this embodiment is a right hand propeller. When rotated in the main rotation direction, the marine propeller 1 produces a forward thrust i.e. a thrust parallel to the rotational axis and directed to the right in the side view of fig. 1. The front blade 4 has a leading edge 10, a trailing edge 12. Likewise the aft blade 6 has a leading edge 14 and a trailing edge 16. The front blade has a pressure side 18 and a suction side 20. Likewise, the aft blade 6 has a pressure side 22 and a suction side 24. When rotated in the main rotation direction, the shape and angle of the blades 4, 6 cause an increase of the water pressure at the respective pressure sides 18, 22, and a decrease of the water pressure at the respective suction sides 20, 24.
The front blade 4 is positioned in front of the suction side 24 of the aft blade 6 in the direction of the rotational axis 8. The term "in front of" is related to the direction of the thrust, if the propeller 1 is rotated in the main rotation direction. The leading edge 10 of the front blade 4 is positioned in front of the leading edge 14 of the aft blade 6 in the main rotation direction. The leading edge 14 of the aft blade 6 is positioned in front of the trailing edge 12 of the front blade 4 in the main rotation direction.
Fig. 4 shows that the front blade 4 has a camber line 26, which is the line through the mid thickness of the front blade 4, and a cord line 27 which is the line that connects the leading edge 10 and the trailing edge 12. The aft blade 6 has a camber line 28, which is the line through the mid thickness of the aft blade 6, and a cord line 29 which is the line that connects the leading edge 14 and the trailing edge 16. The camber cf of front blade 4 is defined as the ratio between the maximum distance Cf of the camber line 26 to the respective cord line 27, and the cord line length. The camber ca is defined as the ratio between the maximum distance Ca of the camber line 28 of the aft blade 6 to the respective cord line 29 and the cord line 29 length.
The front blade 4 has a front blade cord length Lf. The front blade 4 further has an entry angle, or angle of attack, cif. ccf is the angle between the rotational direction R and the direction of the camber line 26 at the leading edge 10. The leading edge 14 of the aft blade 6 is a distance d in the rotational direction R backwards of the leading edge 10 of the front blade 4. The leading edges 10, 14 have a mutual distance a in the direction of the rotational axis 8. The ratio between a and d determines a mutual blade angle ab; ab = tan (a/d). The trailing edge 12 of the front blade 4 has a minimum distance t to the suction side 24 of the aft blade 6.
According to the invention, the aft blade 6 is positioned such relative to the front blade 4 that a water flow around the aft blade 6 increases the total net pressure over the front blade 4, when the propeller rotates in the main rotation direction R. The resulting water flow is shown in fig. 5, while a net pressure line distribution 32 over the front blade 4 is shown in fig. 6. By net pressure is meant the total pressure effect on the front blade 4 of the decreased pressure at the suction side 20 and the pressure side 18. Figure 6 also shows the net pressure distribution 32 of the same blade 4 in case there is no further or aft blade. The difference between the pressure lines 30 and 32 results in an extra thrust that is achieved according to the invention.
In particular, the camber line 26 of the front blade 4 has at the leading edge an angle of attack af of less than 0°. This negative angle is possible thanks to the presence of the aft blade 6 which produces an upwards flow which causes the stagnation point to be shifted around towards the pressure side 20 of the front blade 4. Therefore, the leading edge 10 of the front blade 4 is pointing backwards with respect to the forward direction of the vessel and its propeller 1. Due to this orientation, more water is forced over the front blade 4. This results in higher velocities at the suction side 20 of the front blade 4, which in turn decreases the pressure at this suction side 20.
The ratio between t and cord length Lf is less than 1 :3, preferably less than 1 :4. ab is preferably less than 45°. The relation between t and Lf and/or the value of ab results in a relative small gap between the front blade 4 and aft blade 6.
The trailing edge 12 of the front blade 4 is in a high speed region 34 (fig.5) of the flow around the forward side of the aft blade 6. The trailing edge velocity on the front blade 4 is therefore higher than if the front blade is used alone. Because of this higher trailing edge velocity, the velocities along the entire suction side 20 of the front blade 4 are greatly increased causing a further reduction of pressure suction side 20 of the front blade 4 resulting in higher lift (Fig.6).
The camber cf of the front blade 4 is larger than the camber ca of the aft blade 6.
The aft blade 6 operates efficiently at a higher angle of attack, than it could do when there were no front blade. The maximum allowable angle of attack is dictated by the point where cavitation at the leading edge and separation on the trailing edge starts to appear. By introducing the front blade, the aft blade will be able to work at higher angles of attack, thus capable to perform with higher loads, or equal loads with a reduced blade area.
The second embodiment of fig. 7 shows in cross section a profile of a marine propeller 101 . The position of this section is comparable to that of the first embodiment, as shown in fig. 3. The marine propeller 101 comprises a hub (not shown), a front blade 104 and a further, in this case aft, blade 106. The marine propeller 101 of this exemplary embodiment comprises a multitude of front blades and a multitude of aft blades, in particular, two, three, four, five or six front blades and an equal number of aft blades. The front blade 104 and the aft blade 106 are attached fixedly to the hub. This implies that their mutual distances are fixed as well. Reference is made to the first embodiment for the definitions that are used to describe this second embodiment.
The front blade 104 has a leading edge 1 10, and a trailing edge 1 12. Likewise the aft blade 106 has a leading edge 1 14 and a trailing edge 1 16. The front blade 104 has a pressure side 1 18 and a suction side 120. Likewise, the aft blade 106 has a pressure side 122 and a suction side 124. The front blade 104 is positioned in front of the suction side 124 of the aft blade 106 in the direction of the rotational axis. The front blade 104 has a front blade cord length Lf. The aft blade 106 has a aft blade cord length LA. The aft blade cord length LA is 66% of the front blade cord length Lf.
The leading edge 1 10 of the front blade 104 is positioned in front of the leading edge 1 14 of the aft blade 106 in the main rotation direction. The leading edge 1 14 of the aft blade 106 is positioned an overlap distance D0 in front of the trailing edge 1 12 of the front blade 104 in the main rotation direction. The overlap distance D0 is 25% of the aft blade cord length LA.
The front blade 104 has a camber line 126, and a camber <¾ of 0.067. This maximum value of the camber occurs at 20% of the cord length Lf, measured from the leading edge 1 10. The profile shape of the aft blade 106 is based upon NACA 66-306, a=0.8.
Several variants of the above configuration are possible within the scope of the invention.
Preferably, the aft blade cord length LA is less than the front blade cord length Lf. More preferably, the aft blade cord length LA is less than 90%, in particular less than 75%, of the front blade cord length Lf. Preferably, the aft blade cord length LA is more than 25%, in particular more than 50%, of the front blade cord length Lf.
Preferably, the overlap distance D0 is more than 10%, in particular more than 20% of the aft blade cord length LA. Preferably, the overlap distance D0 is less than 40%, in particular less than 30% of the further, or aft, blade cord length LA. Such overlap distances result in an improved interaction between the water flow around the front and further blades.
Preferably, the camber Cf of the front blade is more than 0.054, in particular more than 0.06. Preferably, the camber Cf of the front blade is less than 0.08, in particular less than 0.074. Preferably, the maximum camber Cf of the front blade occurs within a range of 15% to 25% of the cord length Lf, measured from the leading edge, in particular within a range of 18% to 22% of the cord length Lf, measured from the leading edge. Such camber values result in an increased efficiency of the combination of the front and further blades A third embodiment of a profile of a marine propeller 201 is comparable to that of the first embodiment. Figs. 8-12 show that the marine propeller 201 comprises a hub 202, a front blade 204 and a further, in this case aft, blade 206. The marine propeller 201 of this exemplary embodiment comprises a multitude of front blades and a multitude of aft blades, in particular, two, three, four, five or six front blades and an equal number of aft blades. The front blade 204 and the aft blade 206 are attached fixedly to the hub. This implies that their mutual distances are fixed as well. Reference is made to the first embodiment for the definitions that are used to describe this third embodiment. The front blade 204 has a leading edge 210, and a trailing edge 212. Likewise the aft blade 206 has a leading edge 214 and a trailing edge 216. The front blade 204 has a pressure side 218 and a suction side 220. Likewise, the aft blade 206 has a pressure side 222 and a suction side 224. The front blade 204 is positioned in front of the suction side 224 of the aft blade 206 in the direction A of a rotational axis 208. The front blade 204 has a front blade cord length Lf. The aft blade 206 has an aft blade cord length LA. The aft blade cord length LA is 66% of the front blade cord length Lf.
The leading edge 210 of the front blade 204 is positioned in front of the leading edge 214 of the aft blade 206 in the main rotation direction R. The angle aB of a line through the leading edges of the front blade 204 and the further blade 206 is substantially 25°.
The leading edge 214 of the aft blade 206 is positioned an overlap distance D0 in front of the trailing edge 212 of the front blade 204 in the main rotation direction R. The overlap distance D0 is 25% of the aft blade cord length LA.
The front blade 204 has a camber line 226, a cord line 227, and a camber <¾ of 8% x Lf. This maximum value of the camber occurs at c (fig. 12), which is at 60% of the cord length Lf, measured from the leading edge 210. The profile shape of the aft blade 206 is preferably based upon NACA 66-306, but thickness may be increased subject on class requirements for blade strength. The further blade 206 has a camber line 228, and a cord line 229.
Preferably, the aft blade cord length LA is less than the front blade cord length Lf.
More preferably, the aft blade cord length LA is less than 80%, in particular less than 70%, of the front blade cord length Lf. Preferably, the aft blade cord length LA is more than 40%, in particular more than 50%, of the front blade cord length Lf.
Preferably, the overlap distance D0 is more than 10%, in particular more than 20% of the aft blade cord length LA. Preferably, the overlap distance D0 is less than 40%, in particular less than 30% of the further, or aft, blade cord length LA. Such overlap distances result in an improved interaction between the water flow around the front and further blades.
Preferably, the camber cf of the front blade is more than 5% x Lf, in particular more than 6% x Lf. Preferably, the camber cf of the front blade is less than 10%, in particular less than 8%. Such camber values result in an increased efficiency of the combination of the front and further blades
Figs. 11 and 12 show the direction of the incoming water 230. This direction is a result of the velocity of the water flowing towards the propeller in axial direction, and the rotational speed of the propeller through the water. It is noted that for a given propeller, it is possible to determine a neutral flow direction wherein the propeller doesn't provide thrust. The flow in use as shown in figs. 11 and 12, i.e. the flow wherein the propeller does provide thrust in the forward direction, is a few degrees less than this neutral flow direction. Preferably, the flow angle of attack aA relative to the further blade 206 is more than 1°, in particular more than 4°. Preferably the flow angle of attack relative to the further blade is less than 7°, in particular less than 6°.
An angle etc is defined as the angle between the cord line 227 of the further blade 206 and the (extension of the) line connecting the leading edges 210 and 214 of the front 204 and further 206 blades. ac of the third embodiment is 0°. In general, ac is preferably more than -6°. Preferably ac is less than 13°. In this case, a negative angle refers to a configuration wherein the extended part of the line connecting the leading edges 210 and 214 of the front 204 and further 206 blades, this is the part beyond the leading edge of the further blade 206, distal from the leading edge of the front blade 204, is at the suction side 224 of the further blade 206. In other words: a negative angle refers to a relative small gap between the front blade 204 and the further blade 206. Reversely, a positive angle refers in this case to a configuration wherein the extended part of the line connecting the leading edges 210 and 214 of the front 204 and further 206 blades is at the pressure side 222 of the further blade 206. In other words: a positive angle refers to a relative large gap between the front blade 204 and the further blade 206. It is noted that the propellers of the first and second embodiment fall within said range of ac too.
An angle aj is defined as the angle between the cord lines 227 and 229. aj is 3°. Preferably, the angle aj between the cord lines 227 and 228 is more than 1°, in particular more than 2°. Preferably, the angleaj between the cord lines 227 and 228 is less than 7°, in particular less than 4°.
Preferably, the maximum value c of the camber of the front blade 204 occurs at more than 20% of the cord length Lf, in particular more than 50% of the cord length Lf measured from the leading edge 210. Preferably, the maximum value of the camber occurs at less than 70% of the cord length Lf, in particular less than 65% of the cord length Lf measured from the leading edge 210.
Several variants of the above embodiments are possible within the scope of the invention. Preferably, the blades are fixed with respect to each other in the axial and circumferential direction. In an embodiment, at least one of the blades could rotate with respect to the hub, as is known with controllable pitch propellers. Such a rotation may be coupled for the front and further blade, or individual. There may be two or more further blades for each front blade.
Preferably, the gap between front and aft blade t is more than 1 %x Lf, and less than 15% of the cord length of the front blade Lf.
In a variant the aft blade is not placed directly on a hub, but is attached fixedly to the hub through the first blade, e.g. via props between the aft and the front blade. As a result of the invention, the total mass and volume of the water displaced by the propeller per one shaft rotation resulting in a forward thrust, is achieved with less input power on the propeller shaft in comparison with a conventional propeller with single blades. Moreover, the propeller blades are capable of performing with higher loads, or equal loads with a reduced blade area, compared to a propeller without a further blade.

Claims

Claims
1 . Marine propeller comprising a hub (2), a front blade (4) and a further blade (6), wherein
the hub (2) defines a rotational axis (8) for the marine propeller (1 ),
the marine propeller is rotatable in a main rotation direction (R),
the front blade (4) and the further blade (6) are attached to the hub (2), and each comprise a pressure side (18, 22), a suction side (20, 24), a leading edge (10, 14), and a trailing edge (12, 16),
a total net pressure of the front blade (4) is generatable by pressures on the respective suction and pressure sides,
the total net pressure of the front blade (4) has a stand-alone maximum value (32) if the front blade (4) is rotated at a design speed in the main rotation direction (R) on a single marine propeller without the further blade (6),
the front blade (4) is positioned in front of the suction side (24) of the further blade (6) in the direction of the rotational axis (8), the leading edge of the front blade (4) is positioned in front of the leading edge of the further blade (6) in the main rotation direction (R), and the leading edge of the further blade (6) is positioned in front of the trailing edge of the front blade (4) in the main rotation direction (R); characterised in that,
the further blade (6) is positioned such relative to the front blade (4) that a water flow around the further blade (6) increases the total net pressure (30) of the front blade (4) with respect to the stand-alone maximum value (32) if the propeller is rotated at the design speed in the main rotation direction (R).
2. Marine propeller according to claim 1 , wherein an angle of attack (otf) on the leading edge of the front blade (4) is less than 0°.
3. Marine propeller according to claim 1 , or 2, wherein a line intersects the leading edge (10) of the front blade (4) and the leading edge (14) of the further blade (6), is on a cylindrical plane which is coaxial with the hub (2), and has an angle (ο¾) with a plane perpendicular to the rotational axis of more than 0° and less than 45°.
4. Marine propeller according to any of the preceding claims, wherein a minimum distance (t) between the pressure side (18) of the front blade (4) and the suction side (24) of the further blade (6) is less than one third of a cord line (LF) of the front blade (4).
5. Marine propeller according to any of the preceding claims, wherein the camber (cf) of the front blade (4) is larger than the camber (ca) of the aft blade (6).
6. Marine propeller according to any of the preceding claims, wherein a line intersects the leading edge (10) of the front blade (4) and the leading edge (14) of the further blade
(6), and has a flow angle of attack relative to a local direction of an incoming water flow of more than 0° and less than 20°.
7. Marine propeller according to any of the preceding claims, wherein a line intersects the leading edge (10) of the front blade (4) and the leading edge (14) of the further blade
(6), is on a cylindrical plane which is coaxial with the hub (2), and has an angle (ac) with a cord line (29) of the further blade (6) within a range of 6° towards the suction side (24) of the further blade (6) and 13° towards the pressure (22) side of the further blade (6).
8. Vessel provided with a shaft, wherein a marine propeller (1 ) according to any of the preceding claims is attached to an end of the shaft, and the suction sides (20, 24) of the front and further blades are facing a direction wherein the vessel is designed to be thrust.
PCT/NL2011/050692 2010-10-11 2011-10-11 Marine propeller with front and further blade WO2012050441A1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
NL2005491 2010-10-11
NL2005491A NL2005491C2 (en) 2010-10-11 2010-10-11 Marine propeller with front and further blade.
NL2005968 2011-01-07
NL2005968 2011-01-07

Publications (1)

Publication Number Publication Date
WO2012050441A1 true WO2012050441A1 (en) 2012-04-19

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PCT/NL2011/050692 WO2012050441A1 (en) 2010-10-11 2011-10-11 Marine propeller with front and further blade

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104340348A (en) * 2013-07-31 2015-02-11 应用热流分析中心股份有限公司 Combined propeller blade structure
CN114245786A (en) * 2019-09-23 2022-03-25 沃尔沃遍达公司 Propeller for ship

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB382297A (en) * 1931-07-21 1932-10-21 Franz Melcher Improvements in and relating to counter-running double or multiple propellers in media of all kinds
DE1094622B (en) 1957-10-12 1960-12-08 Volkswerft Stralsund Veb Double propeller, preferably for ships
GB2204643A (en) * 1986-09-03 1988-11-16 Dennis George Bourne Marine propeller

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB382297A (en) * 1931-07-21 1932-10-21 Franz Melcher Improvements in and relating to counter-running double or multiple propellers in media of all kinds
DE1094622B (en) 1957-10-12 1960-12-08 Volkswerft Stralsund Veb Double propeller, preferably for ships
GB2204643A (en) * 1986-09-03 1988-11-16 Dennis George Bourne Marine propeller

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104340348A (en) * 2013-07-31 2015-02-11 应用热流分析中心股份有限公司 Combined propeller blade structure
CN114245786A (en) * 2019-09-23 2022-03-25 沃尔沃遍达公司 Propeller for ship
CN114245786B (en) * 2019-09-23 2023-08-04 沃尔沃遍达公司 Propeller for ship

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