GB2527527A

GB2527527A - Water jet propeller

Info

Publication number: GB2527527A
Application number: GB1411185.0A
Authority: GB
Inventors: David Alexander Duncan
Original assignee: TEIGNBRIDGE PROPELLERS INTERNAT Ltd
Current assignee: TEIGNBRIDGE PROPELLERS INTERNAT Ltd
Priority date: 2014-06-24
Filing date: 2014-06-24
Publication date: 2015-12-30
Anticipated expiration: 2034-06-24
Also published as: GB2527527B; GB201411185D0

Abstract

A propeller has a hub (1, Fig 1) and a number of blades (3, Fig 1) attached to the hub. The blades each include a body having a radially inner root (4, Fig 1) connected to the hub, a radially outer tip (5, Fig 1), and an intermediate section (6, Fig 1) extending along at least 90% of the length of the blade between the root and the tip. At every radial position along the intermediate section, across substantially the full width of the blade, the pitch of a pressure side 13 of the blade is greater than the pitch of the opposite suction side 12 of the blade to increase the velocity of water flow at the outlet end of the propeller relative to the velocity of water flow at the inlet end of the propeller. The suction side of the blade may be convex and the pressure side of the blade may be concave.

Description

WATER JET PROPELLER

TECHNICAL FIELD OF THE INVENTION

This invention relates to propellers, particularly (but not exclusively) marine propellers.

BACKGROUND

A propeller works by taking in water at one end and expelling it at the opposite end. The blades of a propeller are set at an angle of attack to the direction of water flow. As the blades rotate they pull water in on a suction side of the blades and expel it at a pressure side of the blades. The volume and speed of water exiting from the propeller is substantially the same as the volume and speed of water entering the propeller, and a conventional propeller is restricted by the volume of water it can pull in at higher speeds. If the angle of attack becomes too high for the water flow, or if the speed of the water flow becomes too much for the angle of attack, the water stream will separate from the blades and cavitation will occur. Cavitation reduces thrust and can cause erosion which will seriously damage a propeller.

The present invention seeks to provide a new and inventive form of propeller which enables higher thrust to be achieved at greater propeller speeds with reduced risk of cavitation.

SUMMARY OF THE INVENTION

The present invention proposes a propeller having a hub and a plurality of blades attached to the hub, said blades each comprising a body having a radially inner root connected to the hub, a radially outer tip, and an intermediate section extending between the root and the tip, said intermediate section including a suction side and a pressure side on opposite sides of said blade extending between an inlet end of the propeller and an outlet end of the propeller, wherein said intermediate section extends along at least 9O% of the length of the blade between the root and the tip, and at each radial position along said intermediate section the pitch of the pressure side of said blade is greater than the pitch of the opposite suction side of the blade to increase the velocity of water flow at the outlet end of the propeller relative to the velocity of water flow at the inlet end of the propeller.

The propeller thus creates an outlet water jet of increased velocity which augments the thrust of the propeller.

The invention also provides a propeller wherein, at every radial position along an intermediate section of each blade, the pitch of the pressure side of the blade is greater than the pitch of the opposite suction side of the blade across substantially the full width of the respective side between the inlet end and the outlet end of the propeller.

The invention also provides a propeller wherein the suction side of each blade is convex and the pressure side of the blade is concave.

The invention also provides a propeller wherein, at each radial position along an intermediate section of each blade, the pressure side of the blade has a chord length greater than the suction side of the blade to provide a trailing surface extending between the pressure side and the suction side.

The invention also provides a propeller having hub which may be provided with ports adjacent to the trailing edge of each blade to introduce gases at the outlet end of the propeller.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description and the accompanying drawings referred to therein are included by way of non-limiting example in order to illustrate how the invention may be put into practice. In the drawings: Figure 1 is an end view of a water jet propeller in accordance with the invention, viewed from the outlet end of the propeller; Figure 2 is an axial section through the water jet propeller; and Figure 3 is a section through a blade of the water jet propeller on the line Ill-Ill (Figure 1).

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to Fig.s 1 and 2, the water jet propeller has a hub 1 secured to a propeller shaft 2 and a plurality of radially-extending propeller blades 3 attached to the hub. In this example there are five blades but the number of blades which a propeller has may vary. The blades 3 are substantially identical, each comprising a body having a radially inner root 4 connected to the hub in known manner, a radially outer tip 5, and an intermediate section 6 extending between the root 4 and the tip 5. To achieve an effective water jet effect the intermediate section preferably extends along at least 90% of the length of the blade between the root 4 and the tip 5, but as in this example, in most cases the intermediate section will extend along substantially the full length of the blade from root to tip. The blades are inclined with respect to the axis of the hub 1 so that each blade has a leading edge 7 at a water inlet end 8 of the propeller and a trailing edge 9 at a water outlet end 10 where the hub is provided with a nose cone 11.

At every radial position along the intermediate section 6 the blade has the following features which in the present embodiment are exemplified at a single position shown in the cross section of Fig. 3. The blade has a suction side 12 and a pressure side 13 on opposite sides of the blade, both of which extend between the inlet end 8 and outlet end 10. Across the full width of the blade between the inlet end 8 and outlet end 10 the pitch of the pressure side 13 is greater than the pitch of the opposite suction side 12 relative to the direction of travel A, which is opposite to the direction of water flow. It will also be noted that suction side of the blade 12 is convex and the pressure side 13 is concave. In addition, the pressure side of the blade has a chord length which is greater than the suction side of the blade to provide a trailing surface 14 extending between the pressure side 13 and the suction side 12.

The relatively shallow pitch at the suction side of the blade keeps the risk of cavitation to a minimum, but the increased pitch and concave configuration of the pressure side of the blade increases the velocity of water flow at the outlet end 10 relative to the velocity of water flowing in at the inlet end 8. The relatively large width of pitch face at the pressure side 13 further enhances the efficiency of the propeller.

Although the volume of water entering and exiting from the propeller remains the same the flow velocity is higher in the water stream exiting from the propeller. It is important to note that the water jet created by the propeller is not reduced in diameter, which would reduce the efficiency of the propeller, because the water stream contains a void created by the wedge-shaped propeller blades. This void takes the form of a spiraling helical column of water vapour created by the low pressures induced at the inclined trailing surface 14 whilst at the same time reducing the danger of cavitation at both the pressure and suction faces which would lead to a reduction in propeller thrust and erosion of the blade surface.

Returning to Fig. 2, the spiraling column of water vapour may be augmented with air or exhaust gases to increase the outlet velocity and further increase the efficiency of the water jet propeller. These gases may be passed along one or more passages 15 in the propeller shaft 2 and/or hub 1 and radial ports 16 in the propeller hub to enter the low pressure region at the root end of each trailing surface 14.

The water jet propeller has several advantages: * Higher speeds can be reached with reduced risk of cavitation.

* The propeller produces higher thrust.

* The size of the propeller can be reduced.

* Vessel appendage drag is reduced as a smaller propeller and mountings are required.

* Increased displacement of the vessel is avoided as the volume of water pulled in under the vessel is not any greater.

Whilst the above description places emphasis on the areas which are believed to be new and addresses specific problems which have been identified, it is intended that the features disclosed herein may be used in any combination which is capable of providing a new and useful advance in the art.

Claims

CLAIMS1. A propeller having a hub and a plurality of blades attached to the hub, said blades each comprising a body having a radially inner root connected to the hub, a radially outer tip, and an intermediate section extending between the root and the tip, said intermediate section including a suction side and a pressure side on opposite sides of said blade extending between an inlet end of the propeller and an outlet end of the propeller, wherein said intermediate section extends along at least 9Q% of the length of the blade between the root and the tip, and at each radial position along said intermediate section the pitch of the pressure side of said blade is greater than the pitch of the opposite suction side of the blade to increase the velocity of water flow at the outlet end of the propeller relative to the velocity of water flow at the inlet end of the propeller.
2. A propeller according to Claim 1 wherein, at every radial position along said intermediate section, the pitch of the pressure side of the blade is greater than the pitch of the opposite suction side of the blade across substantially the full width of the respective side between the inlet end and the outlet end of the propeller.
3. A propeller according to Claim 1 or 2 wherein the suction side of the blade is convex and the pressure side of the blade is concave.
4. A propeller according to any preceding claim wherein, at each radial position along said intermediate section, the pressure side of the blade has a chord length greater than the suction side of the blade to provide a trailing surface extending between the pressure side and the suction side.
5. A propeller according to any preceding claim in which the hub is provided with ports adjacent to the trailing edge of each blade to introduce gases at the outlet end of the propeller.
6. A propeller substantially as described with reference to the drawings.