Propulsion device for imparting thrust to a fluid

Abstract

A propulsion device for imparting thrust to a fluid, comprising a central hub (10, 110, 210) having a front end portion (11) and a rear end portion (12) and rotating about a rotational axis (A) extending longitudinally between the front end portion (11) and the rear end portion (12), and at least two propulsion structures (20, 120, 220) protruding radially from the hub (10, 110, 210) and evenly distributed on the circumference of the hub (10, 110, 210). Each propulsion structure (20, 120, 220) comprises a front propulsion element (30) extending from a front inner end portion (31) to a front outer end portion (32). A rear propulsion element (40) extends from a rear inner end portion (41) to a rear outer end portion (42). An outer guide element (60) extends from the front outer end portion (32) to the rear outer end portion (42). An inner guide element (70) extends from the front inner end portion (31) to the rear inner end portion (41) at an inner guide element distance (IG). An elongated front distance member (35) and an elongated rear distance member (45) extend radially from the hub (10) to the inner guide element (60). At least one intermediate propulsion element (50) is disposed between the front propulsion element (30) and the rear propulsion element (40) and extends radially from the inner guide element (70) to the outer guide element (60). The outer circumferences of the inner guide element (70), the front distance member (35), the rear distance member (45) and the hub (10) define an open space allowing free passage of the fluid.

Description

[Technical Field]

[0001] The present disclosure relates generally to the field of propulsion devices for generating thrust in fluids. The propulsion devices disclosed herein can be used in a variety of applications, such as propulsion of aerial vessels, including ships and drones, and for generating forced fluid flows, such as fans, blowers, and liquid pumps. [Background technology]

[0002] A conventional screw propeller typically comprises a rotating hub and two or more blades fixed to the hub and projecting radially therefrom, the blades arranged at a pitch that traces a helical spiral resembling a helical screw line.

[0003] Such conventional screw propellers typically have relatively high rotational resistance, resulting in high motor loads and low energy efficiency. Furthermore, conventional screw propellers are subject to cavitation, which can damage the blades, cause undesirable vibrations, and generate noise. Furthermore, such conventional screw propellers typically exhibit significant slip, further reducing energy efficiency.

[0004] Patent Document 1 discloses a screw propeller including a hub and a plurality of radially supporting main blades fixed to the hub. Each main blade is connected to a first auxiliary blade located forward of the main blade and a second auxiliary blade located rearward of the main blade. The tips of the main and auxiliary blades extend radially beyond the connection points of the main and auxiliary blades. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] UK Patent Application Publication No. 188206 Summary of the Invention [Problem to be solved by the invention]

[0006] It is an object of the present invention to provide an improved propulsion device for generating thrust in a fluid.

[0007] Another object is to provide a propulsion device that exhibits high efficiency.

[0008] A further object is to provide a propulsion device that generates axial flow with relatively little separation.

[0009] Yet another object is to provide a propulsion device that exhibits relatively low resistance to fluids.

[0010] Yet another object is to provide a propulsion device that prevents cavitation.

[0011] A further object is to provide a propulsion device that has relatively low slippage. [Means for solving the problem]

[0012] In general, all terms used in the claims should be interpreted according to their ordinary meaning in the art unless expressly defined otherwise herein. All references to "a / an / the element, apparatus, component, means, step, etc." should be openly interpreted as referring to at least one instance of the element, apparatus, component, means, step, etc., unless expressly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless expressly stated.

[0013] According to a first aspect, the present disclosure provides a propulsion device as set forth in claim 1. The propulsion device is arranged to exert a thrust on a fluid. The propulsion device includes a central hub having forward and aft ends and rotating about a rotation axis extending longitudinally between the forward and aft ends, and at least two propulsion structures projecting radially from the hub and evenly distributed around the circumference of the hub. Each propulsion structure includes a forward propulsion element extending radially from a forward inner end to a forward outer end and a rear propulsion element extending radially from an aft inner end to an aft outer end. The outer guide element extends from the forward outer end to the aft outer end at a radial outer guide element distance from the rotation axis, and the inner guide element extends from the forward inner end to the aft inner end at a radial inner guide element distance from the rotation axis. An elongated forward distance member and an elongated rear distance member extend radially from the hub to the inner guide elements. At least one intermediate propulsion element is disposed between the front and rear propulsion elements and extends radially from the inner guide element to the outer guide element. Longitudinal projections of the front, middle, and rear propulsion elements at least partially overlap. The inner guide element, the front distance member, the rear distance member, and the outer periphery of the hub define an open space that allows the free passage of fluid.

[0014] By providing a propulsion device with intermediate propulsion elements extending from an inner guide element positioned radially away from the hub, the propulsion device provides an additional thrust-generating surface at the periphery of the propulsion device. The thrust-generating region located at the periphery of the propulsion device provides higher axial and tangential thrust and lower resistance than the central blade region of a conventional screw propeller. Therefore, the intermediate propulsion elements improve the efficiency of the propulsion device by increasing thrust while maintaining low resistance. The inner and outer guide elements extending longitudinally between all the propulsion elements in a single propulsion structure reduce radial flow and promote axial flow generation. This increases the axial component of the flow generated by the propulsion device while maintaining low lateral flow separation. This also contributes to improving the efficiency of the propulsion device. The outer and inner guide elements also increase the rigidity of the propulsion device, allowing the propulsion elements to be relatively thin and reducing vibration. The outer guide elements further reduce cavitation at the periphery of the propulsion elements, thereby reducing wear on the propulsion elements and reducing noise and other vibrations.

[0015] The propulsion device has been demonstrated to have high efficiency, low resistance in both the axial and circumferential directions, highly concentrated axial flow, low lateral separation, low cavitation, and low levels of noise and other vibrations.

[0016] In one embodiment of the propulsion device, the longitudinal projections of the front, middle and rear propulsion elements completely overlap, which further reduces axial resistance.

[0017] The axial projections of the chord lines of the forward, aft, and intermediate thrust elements may have essentially constant lengths. Thus, the axial projections of the thrust elements exhibit a rectangular or diamond shape. This allows for a large active thrust element area while maintaining a short chord line. This increases thrust while minimizing cavitation.

[0018] The maximum chord line of each of the forward, aft, and intermediate propulsion elements may be a short chord line, as defined by NACA standard nomenclature. Thus, the propulsion elements have a relatively short circumferential extension in their working area radially outward of the inner guide element, thereby reducing cavitation.

[0019] The inner guide element distance (IG) can be at least 40% of the outer guide distance (OG), meaning that the intermediate propulsion element is located a sufficient distance from the axis of rotation to provide a large thrust against resistance.

[0020] The outer guide elements may project rearward from the rear outer end, the projecting portions of the outer guide elements providing so-called winglets that effectively reduce cavitation.

[0021] The outer and inner guide elements may present an outwardly convex, substantially constant longitudinal cross section, which reduces circumferential resistance.

[0022] The outer and inner guide elements may present an inwardly concave substantially constant longitudinal cross section, which further reduces the circumferential resistance.

[0023] The radius of curvature of the convex or concave shape may be substantially equal to the radial distance from the axis of rotation to the outer and inner guide elements, respectively, which also reduces circumferential resistance.

[0024] The distance between the leading edge and trailing edge of each of the leading, trailing, and intermediate thrust elements may be essentially constant, which also allows for a large working thrust element area while keeping the chord line relatively short.

[0025] The front distance member and the rear distance member may be longitudinally aligned.

[0026] The front distance member and the rear distance member may be positioned to extend radially from the front inner end and the rear inner end, respectively, toward the hub.

[0027] Each propulsion structure may comprise a plurality of intermediate propulsion elements, preferably two or three, which further enhances the advantage of locating the active propulsion element area around the periphery of the propulsion device.

[0028] The propulsion device may include two propulsion structures spaced circumferentially apart by 180 degrees, three propulsion structures spaced circumferentially apart by 120 degrees, four propulsion structures spaced circumferentially apart by 90 degrees, five propulsion structures spaced circumferentially apart by 72 degrees, or six propulsion structures spaced circumferentially apart by 60 degrees.

[0029] Further objects and advantages of the propulsion devices according to the first, second and third aspects will become apparent from the following description of exemplary embodiments and the appended claims.

[0030] Aspects and embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a perspective view of a propulsion device according to a first embodiment.

[0032] [Figure 2a-c] 2a to 2c are side, front and rear plan views of the propulsion device shown in FIG.

[0033] [Figure 3] FIG. 3 is a perspective view of a propulsion device according to a second embodiment.

[0034] [Figure 4] FIG. 4 is a perspective view of a propulsion device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0035] Detailed Description Aspects of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which specific embodiments of the invention are shown.

[0036] These aspects may, however, be embodied in many different forms and should not be construed as limiting; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of all aspects of the invention to those skilled in the art. Like reference numerals refer to like elements throughout the specification.

[0037] The propulsion devices shown in all of Figures 1-4 are intended for marine propulsion. Other embodiments within the scope of the present disclosure that are not shown may be used in other applications, such as propulsion of airships, including drones, or for generating forced fluid flows, such as fans, blowers, and pumps.

[0038] The marine propulsion device according to the embodiment shown in Figures 1-2c includes a central hub 10 that rotates about a central rotational axis A. In the illustrated example, the hub 10 is positioned to channel exhaust gases from an outboard or inboard engine (not shown) through the interior of the hub. The hub has a conical end taper from a forward end 11 to an aft end 12. The hub 10 includes a central bore 13 extending longitudinally from the forward end 11 to the aft end 12. A cylindrical, internally splined sleeve member 14 extends centrally through the bore 13. The sleeve member 14 is secured to the inner wall of the bore 13 by four radial struts 15 such that an annular passage is formed within the bore 13 around the sleeve member 14 for exhaust gas discharge.

[0039] The propulsion device further comprises two propulsion structures 20 spaced 180° apart and fixed to the circumferential surface of the hub 10. Both propulsion arrangements are identical and for simplicity only one will be described below.

[0040] Each of the propulsion structures 20 includes a front propulsion element 30, a rear propulsion element 40, and an intermediate propulsion element 50. The front propulsion element 30 includes a front inner end 31 and a front outer end 32. Correspondingly, the rear propulsion element 40 includes a rear inner end 41 and a rear outer end 42.

[0041] The outer guide elements 60 extend parallel to the rotation axis A from the forward outer end 32 to the aft outer end 42. The outer guide elements 60 are disposed at a radial outer guide element distance OG from the rotation axis A. The outer guide elements 60 project axially a short distance rearward of the rear propulsion element 40, forming rearwardly projecting winglets 61.

[0042] The inner guide element 70 extends parallel to the rotation axis A from the front inner end 31 to the rear inner end 41. The inner guide element 70 is fixed to the outer periphery of the hub by an elongated front distance member 35 and an elongated rear distance member 45. The distance members 35, 45 each extend radially from the hub to the inner guide element 70. In the illustrated example, the front distance member 35 forms a radially inward extension of the front thrust element 30, and the rear distance member forms a radially inward extension of the rear thrust element 40. However, in other embodiments (not shown), the distance members may be located at other longitudinal positions of the inner guide element, as long as they maintain the inner guide element 70 radially spaced apart from the hub 10.

[0043] The inner guide element 70 is disposed at a radial inner guide element distance IG from the rotation axis A. The inner guide element distance IG is shorter than the outer guide element distance OG but greater than the maximum outer diameter of the hub 10. That is, the inner guide element 70 is disposed radially between the outer periphery of the hub and the outer guide element 60. In the illustrated example, the inner guide element distance IG is approximately 60% of the outer guide element distance OG. The inner guide element distance IG is preferably 40% to 75% of the outer guide element distance OG.

[0044] The radially outer surface of the outer guide element 60 is convex with a radius of curvature essentially equal to the outer guide element distance OG. The radially inner surface of the outer guide element 60 is concave with a radius of curvature essentially equal to the outer guide element distance OG.

[0045] Similarly, the inner guide element 70 has an outer convex surface and an inner concave surface, both of which exhibit a radius of curvature essentially equal to the inner guide element distance IG, thereby reducing circumferential resistance of the propulsion device.

[0046] The intermediate propulsion element 50 is longitudinally centrally disposed between the front propulsion element 30 and the rear propulsion element 40 and extends radially from the inner guide element 70 to the outer guide element 60. The intermediate propulsion element 50 has an intermediate inner end 51 fixed to the inner guide element 70 and an intermediate outer end 52 fixed to the outer guide element 60.

[0047] From the above, it can be seen that the front distance member 35, the rear distance member 45, the outer periphery of the hub 10, and the inner guide element 70 define an open space through which the fluid (in this case water) can flow freely and which does not provide axial or circumferential resistance as the propulsion device rotates.

[0048] The front thrust element 30, the rear thrust element 40, and the middle thrust element 50 have essentially the same shape. In each thrust element 30, 40, 50, the leading edge is arranged essentially parallel to the trailing edge. Furthermore, the axial projection of the thrust element is essentially rhomboidal. Additionally, the circumferential widths of the thrust elements 30, 40, 50, the inner guide element 70, and the outer guide element 60 are essentially equal.

[0049] The circumferential width of the propulsion elements 30, 40, 50 can also be expressed by the length of the chord line (or chord) running through each propulsion element from the leading edge to the trailing edge, and the axial projection of this chord line. With the propulsion device according to the present disclosure, it is possible to obtain a satisfactory thrust while keeping the chord line and its axial projection short, compared to conventional screw propellers. This is a major advantage, since a short or small chord line reduces the risk of cavitation. It is shown that the chord line of the propulsion elements 30, 40, 50 is preferably a so-called short chord line or small chord line, in accordance with NACA standard terminology.

[0050] FIG. 3 shows a second embodiment of a propulsion device comprising a hub 110 and three propulsion structures 120 spaced 120° apart around the circumference of the hub 110 .

[0051] FIG. 4 shows a third embodiment of a propulsion device comprising a hub 210 and four propulsion structures 220 spaced 90° apart around the circumference of the hub 210 .

[0052] In the embodiment shown in Figures 3 and 4, the hubs 110, 210 and respective propulsion structures 120, 220 are essentially identical to the hub 10 and propulsion structure 20 shown in Figures 1 to 2c and a description thereof will not be repeated here.

[0053] In embodiments not shown, each propulsion structure may include two or more intermediate propulsion elements disposed between the leading and trailing propulsion elements. In such cases, the intermediate propulsion elements extend radially between an inner guide element spaced a distance from the hub and an outer guide element, the outer guide element extending between the outer ends of the leading and trailing propulsion elements. In such embodiments, each propulsion structure includes a total number of working propulsion elements disposed between the inner and outer guide elements equal to the sum of the intermediate propulsion elements plus two.

[0054] In further embodiments not shown, each propulsion structure may comprise two or more elongated distance members connecting the inner guide element to the hub.

[0055] In all of the propulsion structures shown and described above, it is preferred that all of the propulsion elements of the propulsion structure are longitudinally aligned and completely overlap longitudinally.

[0056] Aspects of the present disclosure have been described above primarily with reference to certain embodiments and examples thereof. However, as will be readily apparent to those skilled in the art, other embodiments besides those disclosed above are equally possible within the scope of the present invention, as defined by the appended claims. [Aspect 1] A propulsion device for imparting thrust to a fluid, comprising: a central hub (10, 110, 210) having a forward end (11) and an aft end (12) and rotating about an axis of rotation (A) extending longitudinally between said forward end (11) and said aft end (12); and at least two propulsion structures (20, 120, 220) projecting radially from said hub (10, 110, 210) and evenly distributed around the circumference of said hub (10, 110, 210), each propulsion structure (20, 120, 220) comprising: a forward propulsion element (30) extending radially from a forward inner end (31) to a forward outer end (32); a rear propulsion element (40) extending radially from a rear inner end (41) to a rear outer end (42); an outer guide element (60) extending from said front outer end (32) to said rear outer end (42) at a radial outer guide element distance (OG) from the axis of rotation (A); an inner guide element (70) extending from said front inner end (31) to said rear inner end (41) at a radial inner guide element distance (IG) from the rotation axis (A); - an elongated front distance member (35) and an elongated rear distance member (45), the front distance member (35) and the rear distance member (45) extending radially from the hub (10) to the inner guide element (60); - at least one intermediate propulsion element (50) arranged between the front propulsion element (30) and the rear propulsion element (40) and extending radially from the inner guide element (70) to the outer guide element (60); - the longitudinal projections of the front propulsion element (30), the middle propulsion element (50) and the rear propulsion element (40) at least partially overlap, - the inner guide element (70), the front distance member (35), the rear distance member (45) and the outer periphery of the hub (10) define an open space allowing the free passage of fluid; Propulsion device. [Aspect 2] 2. The propulsion device of claim 1, wherein a longitudinal projection of the front propulsion element (30), a longitudinal projection of the middle propulsion element (50), and a longitudinal projection of the rear propulsion element (40) completely overlap. [Aspect 3] A propulsion device according to aspect 1 or 2, wherein the length of the axial projection of the chord line of the front propulsion element (30), the length of the axial projection of the chord line of the rear propulsion element (40), and the length of the axial projection of the chord line of the middle propulsion element (50) are substantially constant. [Aspect 4] 4. The propulsion device according to any one of aspects 1 to 3, wherein the maximum chord lines of each of the front propulsion element (30), the rear propulsion element (40), and the middle propulsion element (50) are short chord lines defined by extending over a maximum of 60% of an angular range. [Aspect 5] 5. The propulsion device according to any one of aspects 1 to 4, wherein the inner guide distance (IG) is at least 40% of the outer guide distance (OG), preferably 40% to 75%. [Aspect 6] Aspects 6. The propulsion device according to any one of aspects 1 to 5, wherein the outer guide element (60) projects rearward from the rear outer end (42). [Aspect 7] A propulsion device according to any one of aspects 1 to 6, wherein the outer guide element (60) and / or the inner guide element (70) have an essentially constant longitudinal cross section that is outwardly convex. [Aspect 8] Aspect 8. The propulsion device according to any one of aspects 1 to 7, wherein the outer guide element (60) and / or the inner guide element (70) have an essentially constant longitudinal cross section that is inwardly concave. [Aspect 9] 9. The propulsion device according to claim 7 or 8, wherein the radius of curvature of the convex or concave shape is essentially equal to the radial distance (OG, IG) from the rotation axis (A) to the outer guide element (60) and / or the inner guide element (70), respectively. [Aspect 10] 10. The propulsion device according to any one of aspects 1 to 9, wherein the distance between the leading edge and the trailing edge of each of the leading propulsion element (30), the trailing propulsion element (40), and the intermediate propulsion element (50) is essentially constant along the radial extension of the propulsion elements (30, 40, 50). [Aspect 11] Aspects 11. The propulsion device of any one of aspects 1 to 10, wherein the front distance member (35) and the rear distance member (45) are aligned in the longitudinal direction. [Aspect 12] 12. The propulsion device according to any one of aspects 1 to 11, wherein the front distance member (35) and the rear distance member (45) are disposed as radial extensions from the front inner end (31) and the rear inner end (41) toward the hub (10), respectively. [Aspect 13] Aspect 13. The propulsion device of any one of aspects 1-12, wherein each propulsion structure comprises a plurality of, preferably two or three, intermediate propulsion elements. [Aspect 14] 14. The propulsion device of any one of aspects 1-13, comprising two propulsion structures (20) circumferentially spaced 180° apart, three propulsion structures (120) circumferentially spaced 120° apart, four propulsion structures (220) circumferentially spaced 90° apart, five propulsion structures circumferentially spaced 72° apart, or six propulsion structures circumferentially spaced 60° apart.

Claims

1. A propulsion device for imparting thrust to a fluid, comprising: a central hub (10, 110, 210) having a forward end (11) and an aft end (12) and rotating about an axis of rotation (A) extending longitudinally between said forward end (11) and said aft end (12); and at least two propulsion structures (20, 120, 220) projecting radially from said central hub (10, 110, 210) and evenly distributed around the circumference of said central hub (10, 110, 210), each propulsion structure (20, 120, 220) comprising: a forward propulsion element (30) extending radially from a forward inner end (31) to a forward outer end (32); a rear propulsion element (40) extending radially from a rear inner end (41) to a rear outer end (42); an outer guide element (60) extending parallel to the rotation axis (A) from the front outer end (32) to the rear outer end (42) at a radial outer guide element distance (OG) from the rotation axis (A); an inner guide element (70) extending parallel to the rotation axis (A) from the front inner end (31) to the rear inner end (41) at a radial inner guide element distance (IG) from the rotation axis (A); an elongated front distance member (35) and an elongated rear distance member (45), the distance members (35, 45) extending radially from the central hub (10) to the inner guide element (70); at least one intermediate propulsion element (50) disposed between the front propulsion element (30) and the rear propulsion element (40) and extending radially from the inner guide element (70) to the outer guide element (60); an axial projection of the front propulsion element (30), an axial projection of the middle propulsion element (50), and an axial projection of the rear propulsion element (40) at least partially overlap; the inner guide element (70), the front distance member (35), the rear distance member (45) and the outer periphery of the central hub (10) define an open space that allows the free passage of fluid; the length of the axial projection of the chord line of the front propulsion element (30), the length of the axial projection of the chord line of the rear propulsion element (40), and the length of the axial projection of the chord line of the middle propulsion element (50) are essentially equal to one another; Propulsion device.

2. 2. The propulsion device according to claim 1, wherein an axial projection of the front propulsion element (30), an axial projection of the middle propulsion element (50), and an axial projection of the rear propulsion element (40) completely overlap.

3. 2. A propulsion device according to claim 1, wherein the radially inner guide element distance (IG) is at least 40%, preferably 40% to 75% of the radially outer guide element distance (OG).

4. 2. The propulsion device of claim 1, wherein the outer guide element (60) projects rearwardly from the rear outer end (42).

5. 2. The propulsion device according to claim 1, wherein the outer guide element (60) and / or the inner guide element (70) have an essentially constant, outwardly convex, cross-section perpendicular to the axial direction.

6. 2. The propulsion device according to claim 1, wherein the outer guide element (60) and / or the inner guide element (70) have an essentially constant, inwardly concave, transverse cross section.

7. 7. A propulsion device according to claim 5 or 6, wherein the radius of curvature of the convex or concave shape is essentially equal to the radial distance (OG, IG) from the axis of rotation (A) to the outer guide element (60) and / or the inner guide element (70), respectively.

8. 2. The propulsion device according to claim 1, wherein the distance between the leading edge and the trailing edge of each of the leading, aft and intermediate propulsion elements is essentially constant along the radial extension of the propulsion elements.

9. The propulsion device of claim 1 , wherein the front distance member (35) and the rear distance member (45) are axially aligned.

10. 2. The propulsion device according to claim 1, wherein the forward distance member (35) and the aft distance member (45) are arranged as radial extensions from the forward inner end (31) and the aft inner end (41), respectively, towards the central hub (10).

11. 2. The propulsion device of claim 1, wherein each propulsion structure comprises a plurality of, preferably two or three, intermediate propulsion elements.

12. 2. The propulsion device of claim 1, comprising two propulsion structures (20) circumferentially spaced 180° apart, three propulsion structures (120) circumferentially spaced 120° apart, four propulsion structures (220) circumferentially spaced 90° apart, five propulsion structures circumferentially spaced 72° apart, or six propulsion structures circumferentially spaced 60° apart.

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