Claims:1.A partial accelerating duct positioned around a marine screw propeller, wherein the partial duct is integrally formed duct symmetrical about a vertical plane perpendicular to the axis of the propeller,
CHARACTERIZED IN THAT
the duct having an inner radius in the vertical direction (Rv) wherein the inner radius being smaller than the radius (Rh) in the horizontal plane on the propeller axis facilitating maximum flow accelerations in the upper parts of the marine screw propeller and maximum wake fraction values and

predetermined spaces/gaps being provided between blade tip and duct inner surface where the blade tip is entering or leaving the duct avoiding the formation of strong vortices.

2. Partial duct as claimed in claim 1, wherein the distance of the duct from the propeller blade tip varies along the circumference.

3. Partial duct as claimed in claim 1, wherein on rotation of the propeller blades, the propeller has a minimum distance from the inner surface of the partial duct in the vertical position and distance substantially increases in the horizontal blade positions.

4. Partial duct as claimed in claim 1, wherein the duct suppresses the tip vortex shed from the propeller blade tips.

5. Partial duct as claimed in claim 1, wherein the tip clearance varies between 0.5% to 2%.

6. Partial duct as claimed in claim 1, wherein the horizontal radius (Rh) varies between 1.4 to 1.6 times the vertical radius (Rv).

7. Partial duct as claimed in claim 1, wherein the inlet radius (Ri) can be greater than the outlet radius (Ro) varying in the range of 10% to 20%.
, Description:FIELD OF INVENTION
The present invention in general relates to a partial accelerating duct around a marine propeller and, more particularly, to a duct in which the distance of the duct from the propeller blade tip varies along the circumference.

BACKGROUND ART
The hydrodynamic efficiency is the key to ship propulsion which depends on the thrust and torque characteristics for marine screw propellers. Ducted propellers or Kort nozzles provide greater thrust at higher propeller loadings. Ducts of different geometries are also used as pre-swirl devices ahead of the propeller. These ducts are energy saving devices which modify the flow field and increase the propulsion efficiency by reducing certain losses.
The partial duct proposed here should provide increased thrust at higher loading conditions and help in reduction of ship motions when operating in waves. Proper optimization is required to arrive at an optimal configuration regarding the partial duct geometry depending on the vessel design and propeller loading conditions. In general, the partial duct can effectively act like a hybrid device being an integral part of the propeller and also act as an energy saving device.
The concept of ducted propellers have been previously known, which comprises of a marine propeller working within an annular duct or shroud. The most popular form of duct used is an accelerating duct which accelerates the flow through the propeller. Ducted propellers have applications in a range of marine vessels, particularly those operating at low speed and/or high propeller loadings. This is due to the increased thrust, a part of which is supplied by the duct,
and resulting in an overall improvement of propulsion efficiency. Considerable research has been dedicated towards the hydrodynamic design and performance of ducted propellers. The present invention proposes a partial duct around a marine propeller which should provide thrust and hence improve propulsion efficiency in a range of propeller loadings and also influence the motion characteristics of the vessel in waves.

Reference is made to “A case study for the effect of a flow improvement device (a partial wake equalizing duct) on ship powering characteristics” by Emin Korkut, Ocean Engineering Volume 33, Issue 2, February 2006, Pages 205-218, which discloses the duct designs wherein they are placed in front of the propeller, and help in improvement of propulsion efficiency by modifying the flow into the propeller. Two different hull forms were generated from the original hull form of the vessel to optimise the stern flow of the vessel. A possible energy saving concept, such as partial wake equalizing duct was investigated in this manner. Resistance, self-propulsion and flow visualization measurements were performed with the hull models to explore the effect of partial wake equalizing ducts on the powering characteristics of the hull form. Analysis of the results indicates that the partial wake equalizing duct concept with an appropriate stern design affects not only the flow characteristics at the aft-end, but also the propulsion characteristics. In comparison to this, the present invention discloses a partial accelerating duct positioned around the propeller such that the inner radius of the duct in the vertical direction (Rv) is smaller than the radius (Rh) in the horizontal plane at the propeller axis. The duct design enables acceleration of the flow in the outer radii of the upper half of the propeller where the wake fractions are higher due to the presence of the hull. This causes a more uniform circumferential velocity distribution over the outer radii of the propeller blades. Again, depending on the vessel forward velocity and the propeller rotational speed, the duct generates a thrust which gives a higher propulsion efficiency for vessel operations at greater propeller loadings.
Reference is made to “A numerical study for effectiveness of a wake equalizing duct” by FahriCelik, Ocean Engineering 34 (2007) 2138–2145, disclosing A numerical study is carried out for calculating effect of the wake equalizing duct (WED) on the propulsion performance of a chemical tanker. Analysis is performed using a CFD tool based on the solution of Reynolds averaged Navier–Stokes (RANS) equation. It was concluded that propeller characteristics and resistance of the ship are slightly affected by the presence of the WED, but an additional thrust is also produced by the WED positioned forward of the propeller. It is also found that the maximum gain obtained by using an appropriate WED design is about 10%. In comparison to this, the present invention discloses a partial duct positioned around the propeller which generates thrust and also accelerates the flow into the outer radii of the propeller. The effect is stronger at higher loadings and hence applicable for vessels like tugs, trawlers, and inland vessels for which propeller loadings are higher.

Reference is further made to “Mewis Duct – New Developments, Solutions and Conclusions” by Friedrich Mewis, Thomas Guiard, Second International Symposium on Marine Propulsors, smp’11, Hamburg, Germany, June 2011, which introduced the Mewis Duct (MD) as a novel type of Energy Saving Device (ESD) consisting of a duct with stator fins located in the vessel stern ahead of the propeller. Model tests performed for several projects in different tanks worldwide show that the MD not only reduces the required power by up to 8 % with a mean saving averaged over 35 tests of 6.5 %, but also significantly reduces the vibration excitation by reducing pressure pulses by up to 80 %. The cavitation behaviour of the propeller is positively affected, and the MD tends to improve the course stability of unstable vessels. In comparison to this, the present invention discloses a partial duct positioned around the propeller which generates thrust and also accelerates the flow into the outer radii of the propeller. The propulsion performance of a vessel fitted with the proposed partial duct is found to improve (reductions of power requirement of up to 5 % is observed) at higher propeller loadings.
Yet another reference is made to “Influence of ducted propeller on seakeeping in waves” by Anirban Bhattacharyya and Sverre Steen, Ocean Engineering Volume 91, 15 November 2014, Pages 243-251, disclosing the performance of a 120 m single screw cargo vessel fitted alternately with a conventional ducted and an open propeller are compared with respect to heave and pitch motions, added resistance, and propulsion efficiency in a series of regular head wave conditions. The forces generated by the duct were found to have very little effect on the ship motions in waves. It was concluded that the relative size of a duct should be much larger, for example which is the case for tugs, to have significant effect on the vessel performance in waves. The present invention discloses a partial duct positioned around the propeller which produces thrust providing higher total thrust at high propeller loadings compared to an open propeller. The applicability will be mainly for tugs, trawlers, and inland vessels. However, compared to a conventional ducted propeller of annular section, the present invention produces higher vertical forces which would influence the motion characteristics of the vessel.
Reference is made to “JP2016190591A”, disclosing a propeller front device as illustrated in figure 2 is fixed on a stern of a hull of a ship, and arranged on a position on the furthermore front side of a propeller. The propeller front device has a fin extending to a separating direction from the stern, a support part 62 supporting the fin and the stern in the relatively rotatable state and working as a revolving shaft of relative rotation between the fin and the stern, and a fixing part 64 for fixing the fin to the stern. In comparison to this, the present invention discloses a partial duct, wherein the inner radius of the duct in the vertical direction (Rv) is smaller than the radius (Rh) in the horizontal plane on the propeller axis causing flow accelerations in the upper parts of the marine screw propeller.
Reference is made to “JP2015221652A”, disclosing astern duct as illustrated in figure 1 to be attached to the front of a propeller attached to the stern of a hull is characterized in that a duct body 11 is generally formed into an arc shape of an angular range of 180 degrees to 270 degrees. While the hull is viewed to the front from the back, the duct body 11 is attached to the stern by support means so that the duct center line Yd of the duct body 11 may have an inclination angle in the rotation direction of the propeller with respect to the propeller center line of the vertical direction of the propeller while the hull is being viewed from the back to the front. In comparison to this, the present invention discloses a partial duct, covering the upper half of the propeller in the angular range of 270 degrees to 90 degrees as illustrated in figure 3. The gap between the propeller blade tip and the duct inner surface is minimum in the vertical position (0 degree) and gradually increases to a maximum value at the propeller axis.
Reference is made to “US442615A”, disclosing a casing, made cylindrical or conical in external form and internally tapering in curved lines from the forward end toward the center, forming a throat where it is of smallest internal diameter, and enlarging in straight or curved lines aft of the propeller. Through the casing are oblique openings 3, (preferably tapering in form) inclined so as to diverge toward the rear of the casing, which openings 3 permit water to enter from the exterior of the casing and discharge water rearwardly. In comparison to this, the present invention discloses a partial duct, wherein the inner radius of the duct in the vertical direction (Rv) is smaller than the radius (Rh) in the horizontal plane on the propeller axis causing flow accelerations in the upper parts of the marine screw propeller.
Reference is made to “US2566525A”, disclosing an inwardly protruding member which during the astern propulsion uniformly detaches the water jet from the inner nozzle surface after the water jet has passed the screw. The water, therefore, escapes from the nozzle as a closed flow and at a greater velocity depending upon the inclination of the screw blades and the speed of rotation. Not only is the non-uniform or one-sided adherence of the water jet to the nozzle wall eliminated but also the astern or backward thrust of the same is considerably increased and the undesirable arbitrary swinging of the stern to one or the other side of the ship is eliminated. Moreover, the backward thrust is increased and the objectionable trend of the ship of swinging its stern to one side is further reduced. In comparison to this, the present invention discloses a partial duct around the propeller which modifies the inflow into the propeller and provides thrust at higher propeller loadings, leading to improved propulsion efficiency.
Reference is made to “US3508517A”, disclosing a nozzle of the Kort type for propelling a ship, the nozzle having inclined ducts to eliminate or reduce any zone of stagnant water that forms aft of the propeller, and the ducts form supplemental inlets into the nozzle on the reverse motion. In comparison to this, the present invention discloses a partial duct, wherein the inner radius of the duct in the vertical direction (Rv) is smaller than the radius (Rh) in the horizontal plane on the propeller axis causing flow accelerations in the upper parts of the marine screw propeller.
Reference is made to “US3738307A”, disclosing a propeller nozzle in which the geometry of the nozzle profile varies. With such a propeller nozzle, the hull stream in the propeller zone can be changed to a field of a more rotationally symmetrical nature. In comparison to this, the present invention discloses a partial duct, wherein the inner radius of the duct in the vertical direction (Rv) is smaller than the radius (Rh) in the horizontal plane on the propeller axis causing flow accelerations in the upper parts of the marine screw propeller, especially at the outer radii close to the inner surface of the duct.
Reference is made to “US8246401B2”, disclosing a Kort nozzle configured rotatable around the rudder axis of a ship, for which the occurrence of recirculations or swirls is avoided or reduced with an angular position with respect to a longitudinal axis of the ship. To obtain a globally uniform flow pattern as far as possible, at least one opening is provided in each of two central areas of a nozzle ring enveloping a ship's propeller. In comparison to this, the present invention discloses a partial duct, wherein the inner radius of the duct in the vertical direction (Rv) is smaller than the radius (Rh) in the horizontal plane on the propeller axis causing flow accelerations in the upper parts of the marine screw propeller.
Accordingly, there is a need for a partial duct to be integrated with the marine propeller such that the propeller operates in a partly open and partly ducted condition for each full rotation. The duct provides acceleration to the incoming flow, increasing the velocity in the upper half of the propeller, mainly at the outer radii of the propeller disk providing a more uniform circumferential inflow. The duct also generates thrust which improves the propulsion efficiency of the vessel at high propeller loadings.
SUMMARY OF THE INVENTION
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.
An object of the present invention is to provide a partial duct positioned around a marine screw propeller, wherein the inner radius of the duct in the vertical direction (Rv) is smaller than the radius (Rh) in the horizontal plane on the propeller axis causing flow accelerations in the upper parts of the marine screw propeller.

An object of the present invention is to provide a partial duct with gaps at points of propeller blade tip entering or leaving the duct.

An object of the present invention is to provide a partial duct wherein the distance of the duct from the propeller blade tip varies along the circumference.

An object of the present invention is to provide a partial duct wherein the marine propeller has a minimum distance from the inner surface of the partial duct in the vertical position and distance substantially increases in the horizontal blade positions.

An object of the present invention is to provide a partial duct wherein the duct suppresses the tip vortex shed from the propeller blade tips.

An object of the present invention is to provide a partial duct, wherein the minimum tip clearance in the vertical position is varying between 0.5% to 2% of the propeller diameter.

An object of the present invention is to provide a partial duct wherein the wherein the horizontal radius (Rh) varies between 1.4 to 1.6 times the vertical radius (Rv).

Yet another object of the present invention is to provide a partial duct wherein the inlet radius (Ri) can be greater than the outlet radius (Ro) by10% to 20%.
In accordance with an aspect of the present disclosure, it is to provide a partial accelerating duct positioned around a marine screw propeller. The partial duct is integrally formed duct symmetrical about a vertical plane perpendicular to the axis of the propeller. The partial duct, wherein the inner radius of the duct in the vertical direction (RV) is smaller than the radius (Rh) in the horizontal plane on the propeller axis causes flow accelerations in the upper parts of the marine screw propeller where the nominal wake fraction values are higher. The distance of the duct from the propeller blade tip varies along the circumference being minimum in the vertical blade position, and maximum in the horizontal plane of the propeller axis, the formation of strong vortices due to the propeller blade tip entering or leaving the duct
Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The above and other aspects, features and advantages of the embodiments of the present disclosure will be more apparent in the following description taken in conjunction with the accompanying drawings, in which:
Figure 1 illustrates a perspective view of a stern duct, as prior art.
Figure 2 illustrates a schematic side view showing the stern of a ship equipped with a marine reaction fin apparatus of an embodiment of a propeller forward device, as prior art.
Figure 3illustrates a front view of partial duct around a propeller.
Figure 4 illustrates sectional view along A-A’ generation.
Figure 5 illustrates circulation around duct section and thrust.
Figure 6 illustrates the isometric view of the partial duct.
Figure 7 illustrates the proposed partial duct on the ship.
Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.
DETAILED DESCRIPTION
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding, but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purpose only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents.
It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a component surface" includes reference to one or more of such surfaces.
All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which various embodiments belong. Further, the meaning of terms or words used in the specification and the claims should not be limited to the literal or commonly employed sense, but should be construed in accordance with the spirit of the disclosure to most properly describe the present disclosure.
The terminology used herein is for the purpose of describing particular various embodiments only and is not intended to be limiting of various embodiments. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising" used herein specify the presence of stated features, integers, steps, operations, members, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, members, components, and/or groups thereof. Also, Expressions such as "at least one of," when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.
The present disclosure will now be described more fully with reference to the accompanying drawings, in which various embodiments of the present disclosure are shown. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the various embodiments set forth herein, rather, these various embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the present disclosure. Furthermore, a detailed description of other parts will not be provided not to make the present disclosure unclear. Like reference numerals in the drawings refer to like elements throughout.
The subject invention lies in providing a partial accelerating duct around a marine propeller more particularly to a duct in which the distance of the duct from the propeller blade tip varies along the circumference.
According to one embodiment of the present invention, a partial accelerating duct is positioned around a marine screw propeller wherein the partial duct is integrally formed and is symmetrical about a vertical plane perpendicular to the axis of the propeller. The partial duct, wherein the inner radius of the duct in the vertical direction (Rv) is smaller than the radius (Rh) in the horizontal plane on the propeller axis causing maximum flow accelerations in the upper parts of the marine screw propeller where maximum wake fraction values are observed. The distance of the duct from the propeller blade tip gradually varies along the circumference hence providing a larger gap between the blade tip and the duct inner surface where the blade tip enters or leaves the duct in order to avoid the formation of strong vortices.
Design of the partial duct
As illustrated in figures 3 and 4, a partial duct around the marine screw propeller for which the distance of the duct from the propeller blade tip varies along the circumference. The duct is symmetrical about a vertical plane perpendicular to the axis of the propeller. As the propeller blade rotates, it has a minimum distance from the inner surface of the duct in the vertical position, and this distance gradually increases in the horizontal blade positions. The presence of the duct suppresses the tip vortex shed from the propeller blade tips as in a standard ducted propeller. For this partial duct, a gradual transition is designed for the propeller blades operating from the 'ducted condition' to the 'open condition' by giving an elliptical geometry to the duct.
Hence, the inner radius of the duct in the vertical direction (Rv) is smaller than the radius (Rh) in the horizontal plane on the propeller axis. This causes maximum flow accelerations in the outer radii of the upper parts of the propeller disc where wake fraction values are maximum, and this effect reduces as the distance of the duct from the blade tip increases. A larger gap is provided at the points where the blade tip enters or leaves the duct to avoid the formation of strong vortices. As illustrated in figure 5 the circulation around the duct generates lift, a component of which is visualized as duct thrust, similar to a ducted propeller.
The design components of the partial duct are illustrated in figure 6. The main duct is semi-elliptical in shape with ends marked by 'a' and 'c' the centre of the duct span is marked by 'b' where it is attached to the ship hull through a cylindrical fixing arrangement ‘d’. The cross section of the duct is uniform throughout. The two ends of the duct 'a' and 'b' are smoothened to reduce the strength of tip vortices and the drag of the duct. The standard dimensions of the partial duct will be governed by the diameter of the propeller of the ship around which it is fitted. The standard partial duct should have a vertical radius (RV) measured at the centre plane (at the part marked b) marginally higher than the propeller diameter with a tip clearance of 0.5% to 2% of the propeller diameter. The horizontal radius (Rh) can vary from 1.4 to 1.6 times RV. As the duct is accelerating in nature the radius at the inlet (RI) should be larger by about 10%-20% of the radius at the outlet (Ro).

As illustrated in figure 7, the location of the duct with respect to a ship and the stern region of a ship fitted with a partial duct around the propeller and a rudder. 'h' is the ship hull, 'p' is the propeller, 'r' is the rudder, and 'D' is the partial duct attached to the ship hull using the fixing arrangement 'd'. The duct is positioned such that the propeller lies in the central plane of the partial duct.

Example

The applicability of the propeller of the present invention was evaluated. The efficiency of the duct at high propeller loadings was evaluated using model test self-propulsion experiments using a ship model fitted alternately with and without the partial duct around the propeller. The improvement in propeller thrust/torque ratio '?(T/Q)' under three heavily loaded conditions are presented in Table 1. Propeller loading is defined using the non-dimensional parameter 'Js' given by the ratio of the ship forward speed and the propeller rotational speed. Table 1 illustrates the propulsion performance comparison at high propeller loadings.

Table 1
Js ?(T/Q)
0.30 5%
0.20 4%
0.19 4%

The influence of the partial duct on the velocity distribution is numerically investigated by studying the circumferential distribution of nominal wake in the propeller plane. The differences in wake fraction due to the presence of the partial duct are presented in Table 2 for different radial locations expressed as fractions of the propeller radius. The maximum decrease in nominal wake fraction (?w max.), as well as the average decrease (?w avg.) over the upper half of the propeller disk at five radial locations are shown. The results indicate that the partial duct provides acceleration to the inflow into the propeller, the effect being higher at the outer radii leading to lower wake fraction values at the corresponding locations. Table 2 illustrates the decrease in nominal wake fraction due to partial duct.
Table 2
r/R ?w max. ?w avg.
0.6 8% 5%
0.7 12% 8%
0.8 15% 11%
0.9 23% 16%
1.0 35% 23%

Based on the above-mentioned results, some of the non-limiting advantages of the present invention are:

• The flow acceleration due to the duct will be only in the upper sections of the propeller plane, where the velocity deficits are greater due to higher wake fraction. Hence the duct can be optimized with respect to the hull configurations to obtain more uniform flow into the propeller plane.

• The vertical component of lift generated by the partial duct is not nullified due to its partial profile. Hence this can help in reduction of the vessel motions, typically heave and pitch, in waves. Under calm water conditions this can also be utilized for trim balancing based on the operation condition.

• Considering the operation of inland vessels, the duct can provide flow acceleration without the risk of debris getting into the gap between the duct and propeller, as for a standard ducted propeller design.

Although a partial accelerating duct around a marine propeller has been described in language specific to structural features, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific methods or devices described herein. Rather, the specific features are disclosed as examples of implementations of a Partial Accelerating Duct around a Marine Propeller.