PROPELLER FOR A WATER VEHICLE

Abstract

A propeller for a water vehicle is provided, comprising a hub and at least two blades, said blades extending outwards from the hub in the radial direction, and the propeller having a uniform blade distribution. The problem addressed by the invention is to provide a propeller for a water vehicle which allows unwanted generation of noise to be efficiently reduced or avoided. According to the invention, the angular distance between the blade tips of two consecutive blades of the propeller varies in relation to the angular distance between the blade tips of two other consecutive blades.

Claims

1. A propeller for a watercraft, comprising: a hub; and at least two blades that extend from the hub in an outward radial direction, wherein the propeller has a uniform blade separation, wherein the centers of mass of the at least two blades in relation to the hub have the same radial spacing to the hub, and/or the at least two blades have the same weight, and wherein the angular spacing between the blade tips of two successive blades of the propeller varies in relation to the angular spacing between the blade tips of two other successive blades.

2. The propeller as claimed in claim 1, wherein at least two blades of the propeller have a different course of blade skew.

3. The propeller as claimed in claim 1, wherein a course of a generatrix of a first blade deviates from a course of a generatrix of at least one further blade.

4. The propeller as claimed in claim 1, wherein at least two blades have different extents in a radial direction.

5. The propeller as claimed in claim 1, wherein a pitch course of the first blade deviates from a pitch course of the at least one further blade.

6. The propeller as claimed in claim 6, wherein, in the case of an even number of blades and at least four blades, in each case two diametrically oppositely situated blades are of identical form.

7. The propeller as claimed in claim 1, wherein centers of mass of the at least two blades lie in a same axial plane in relation to the hub.

8. The propeller as claimed in claim 7, wherein the course of a blade rake is adapted to the course of blade skew.

9. The propeller as claimed in claim 1, wherein a length of the generatrix in a radial direction of at least one blade deviates from a length of the generatrix of at least one further blade.

10. The propeller as claimed in claim 1, wherein a spacing of the blade tips of two successive blades is selected such that, at a design point, pressure pulses generated by the blade tips counteract the excitation of the hull by pressure pulses of upstream blade tips.

11. A propeller for a watercraft, comprising: a hub; and at least two blades that extend from the hub in an outward radial direction, wherein the propeller has a uniform blade separation, and wherein the angular spacing between the blade tips of two successive blades of the propeller varies in relation to the angular spacing between the blade tips of two other successive blades.

12. The propeller according to claim 11, wherein centers of mass of the at least two blades in relation to the hub have the same radial spacing to the hub and/or the at least two blades have the same weight.

13. The propeller as claimed in claim 11, wherein at least two of the blades of the propeller have a different course of blade skew.

14. The propeller as claimed in claim 11, wherein a course of a generatrix of a first blade of the at least two blades deviates from a course of a generatrix of at least one further blade of the at least two blades.

15. The propeller as claimed in claim 11, wherein a pitch course of a first blade deviates from a pitch course of the at least one further blade.

16. A watercraft, comprising: propeller including a hub and at least two blades that extend from the hub in an outward radial direction, wherein the propeller has a uniform blade separation, and wherein the angular spacing between the blade tips of two successive blades of the propeller varies in relation to the angular spacing between the blade tips of two other successive blades.

17. The watercraft according to claim 16, wherein centers of mass of the at least two blades in relation to the hub have the same radial spacing to the hub and/or the at least two blades have the same weight.

18. The watercraft as claimed in claim 16, wherein at least two of the blades of the propeller have a different course of blade skew.

19. The watercraft as claimed in claim 16, wherein a course of a generatrix of a first blade of the at least two blades deviates from a course of a generatrix of at least one further blade of the at least two blades.

20. The watercraft as claimed in claim 16, wherein a pitch course of a first blade deviates from a pitch course of the at least one further blade.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Practical embodiments of the system described herein are described below in conjunction with the appended drawings, in which:

[0035] FIG. 1 shows a first embodiment of a propeller according to an embodiment of the system described herein with three blades in a plan view onto the propeller plane;

[0036] FIG. 2 shows the first embodiment from FIG. 1 with plotted generatrices and radial straight lines through the roots, according to an embodiment of the system described herein;

[0037] FIG. 3 shows the first embodiment from FIGS. 1 and 2 with indicated skew angles, according to an embodiment of the system described herein;

[0038] FIG. 4 shows a second embodiment of a propeller according to an embodiment of the system described herein with four blades in a plan view onto the propeller plane;

[0039] FIG. 5 shows a third embodiment of a propeller according to the an embodiment of the system described herein with four blades in a plan view onto the propeller plane;

[0040] FIG. 6 shows a fourth embodiment of a propeller according to the an embodiment of system described herein with six blades in a plan view onto the propeller plane;

[0041] FIG. 7 shows a schematic illustration of generated pressure pulses, according to an embodiment of the system described herein;

[0042] FIG. 8 shows a diagram of the course of the profile thicknesses and of the chord lengths of the radii sections of an exemplary blade profile, according to an embodiment of the system described herein;

[0043] FIG. 9 shows a diagram of the distribution of profile thicknesses and chord lengths in a plan view onto the propeller plane, according to an embodiment of the system described herein;

[0044] FIG. 10 shows a scaled radii section of a blade profile, according to an embodiment of the system described herein;

[0045] FIG. 11 shows volume elements generated from the profile thicknesses, according to an embodiment of the system described herein;

[0046] FIG. 12 shows a course of the profile thicknesses and chord lengths with a shift of the profiles in the outer portion of the blade, according to an embodiment of the system described herein;

[0047] FIG. 13 shows a course of the profile thicknesses and chord lengths with a shift of the profiles over the entire blade extent, according to an embodiment of the system described herein; and

[0048] FIG. 14 shows a comparison of the generatrix with skew with the course of the generatrix of the initial design, according to an embodiment of the system described herein.

DESCRIPTION OF VARIOUS EMBODIMENTS

[0049] FIG. 1 illustrates a propeller 10 for a watercraft in a first embodiment of the system described herein. In the present case, the propeller 10 is illustrated in a plan view onto the propeller plane in the direction of the axis of rotation of the propeller 10. The axis of rotation of the propeller 10 consequently extends into the plane of the drawing.

[0050] The propeller 10 has a hub 12, which is illustrated only schematically. In the present case, three blades 14a, 14b, 14c extend in a radial direction from the hub 12.

[0051] The blades 14a, 14b, 14c have a respective blade tip 16a, 16b, 16c, wherein the blade tip 16a, 16b, 16c is defined as location which generates the most intense negative-pressure area and at which the tip vortex of the blade 14a, 14b, 14c arises. In the embodiment shown, the blade tips 16a, 16b, 16c are in each case the center of gravity of the radially outermost profile section. As mentioned above, a profile section is in each case a section through the blades 14a, 14b, 14c which lies on a cylindrical surface.

[0052] The angular spacing between the respective blade tips 16a, 16b, 16c of the blades 14a, 14b, 14c may vary. In the embodiment shown here, the angular spacing between the first blade tip 16a of the first blade 14a and the second blade tip 16b of the second blade 14b amounts to 114.27. The angular spacing between the second blade tip 16b and the third blade tip 16c likewise amounts to 114.21, and the angular spacing between the third blade tip 16c and the first blade tip 16a amounts to 131.52.

[0053] FIG. 2 shows the propeller 10 from FIG. 1 once again, wherein in each case one generatrix 18a, 18b, 18c is additionally shown here. The generatrix 18a, 18b, 18c connects in each case the centers of gravity of the individual profile sections of the corresponding blade 14a, 14b, 14c.

[0054] The region in which the blades 14a, 14b, 14c are attached to the hub 12 is the root region. The center of gravity of the radially innermost profile section is also referred to as root point 20a, 20b, 20c. In FIG. 2, aside from the generatrices 18a, 18b, 18c, a radial straight line 22a, 22b, 22c through the root 20a, 20b, 20c is also shown (dashed line), which runs in each case orthogonally with respect to and through the axis of rotation of the propeller 10 and through the root 20a, 20b, 20c of the respective blade 14a, 14b, 14c. The angular spacing of the radial straight lines 22a, 22b, 22c through the root 20a, 20b, 20c denotes the blade separation. The blade separation may be uniform, that is to say the angular spacing of the radial straight lines 22a, 22b, 22c through the root 20a, 20b, 20c may be equal between all successive blades 14a, 14b, 14c. For example, in the case of three blades 14a, 14b, 14c, the angular spacing between two successive radial straight lines 22a, 22b, 22c through the root 20a, 20b, 20c is in each case 120.

[0055] The radial straight line 22a, 22b, 22c through the root 20a, 20b, 20c and the generatrix 18a, 18b, 18c intersect at the root 20a, 20b, 20c. The blades 14a, 14b, 14c shown here are blades 14a, 14b, 14c with a so-called balanced skew, that is to say the generatrix 18a, 18b, 18c extends in the direction of rotation relative to the radial straight line 22a, 22b, 22c through the root 20a, 20b, 20c in an inner radial portion, and extends counter to the direction of rotation relative to the radial straight line 22a, 22b, 22c through the root 20a, 20b, 20c in a radially outer portion. In an embodiment, the intersection point of the generatrix 18a, 18b, 18c of each blade 14a, 14b, 14c with the radial straight line 22a, 22b, 22c through the root 20a, 20b, 20c has a radial spacing to the propeller axis which corresponds to approximately 0.7 times the propeller radius.

[0056] The varying angular spacing between the blade tips 16a, 16b, 16c may be, in the first embodiment, caused by a different course of the generatrices 18a, 18b, 18c and a different skew angle.

[0057] The skew angle is illustrated in FIG. 3. Although different definitions are also used in the literature, in the context of this application the skew denotes the angle between a tangent 24a, 24b, 24c, running radially with respect to the propeller axis, to the outermost or foremost point of the generatrix 18a, 18b, 18c in the direction of rotation, and a radial tangent 26a, 26b, 26c to the trailing edge of the respective blade 14a, 14b, 14c. In an embodiment, all three skew angles are different, for example, where the skew angle of the first blade 14a amounts to 39.48, the skew angle of the second blade 14b amounts to 35.90, and the skew angle of the third blade 14c amounts to 32.31.

[0058] It is pointed out that a varying angular spacing of the blade tips 16a, 16b, 16c can also be achieved if, in the case of an equal skew angle, in each case only the course of the generatrices 18a, 18b, 18c of the three blades varies.

[0059] FIG. 4 illustrates a second embodiment of a propeller 100. Four blades 114a, 114b, 114c, 114d are arranged on the hub 112 of this second embodiment. The mutually diametrically oppositely situated blades 114a, 114b, 114c, 114d in each case may be of identical form, and one pair of diametrically oppositely situated blades 114a, 114c may differ from the other blade pair 114b, 114d. That is to say, the first blade 114a and the third blade 114c may have, with respect to the radial straight line through the root (not illustrated in FIG. 4), an identical course of the generatrices (not illustrated in FIG. 4) and likewise an identical skew angle. The same may apply to the second blade 114b and the fourth blade 114d, wherein their course of the generatrices and skew angles may deviate from those of the first blade 114a and of the third blade 114c.

[0060] The angular spacing between the first blade tip 116a and the second blade tip 116b and the angular spacing between the third blade tip 116c and the fourth blade tip 116d each may amount to 100.50. The angular spacing between the second blade tip 116b and the third blade tip 116c and the angular spacing between the fourth blade tip 116d and the first blade tip 116a each may amount to 79.50.

[0061] FIG. 5 shows a third embodiment of a propeller 200, on the hub 210 of which there are likewise arranged four blades 214a, 214b, 214c, 214d. The four blades 214a, 214b, 214c, 214d may have in each case a different course of the generatrix in relation to the radial straight line through the root and a different skew angle.

[0062] In this third embodiment, each of the angular spacings between the individual blade tips 216a, 216b, 216c, 216d may be different. The angular spacing between the first blade tip 216a and the second blade tip 216b may amount to 100.93. The angular spacing between the second blade tip 216b and the third blade tip 216c may amount to 79.46. The angular spacing between the third blade tip 216c and the fourth blade tip 216d may amount to 85.37, and the angular spacing between the fourth blade tip 216d and the first blade tip 216a may amount to 94.25.

[0063] The fourth embodiment of a propeller 300 as shown in FIG. 6 has six blades 314a, 314b, 314c, 314d, 314e, 314f, which each extend in a radial direction proceeding from the hub 312. In each case two mutually diametrically oppositely situated blades may be of identical form. The angular spacing between the first blade tip 316a and the second blade tip 316b, and also between the fourth blade tip 316d and the fifth blade tip 316e, may amount to 62.86. The angular spacing between the second blade tip 316b and the third blade tip 316c, and also the fifth blade tip 316e and the sixth blade tip 316f, may amount to 70.50. The angular spacing between the third blade tip 316c and the fourth blade tip 316d, and also between the sixth blade tip 316f and the first blade tip 316a, may amount to 46.64.

[0064] FIG. 7 schematically shows a pressure course for two different propellers, according to an embodiment. The dashed line shows a pressure course 28 of a propeller known from the prior art with four identical blades. The successive blade tips have in each case the same angular spacing, and, in the case of a constant rotation speed, the maxima of the pressure pulses follow one another with the same frequency and amplitude. These pressure pulses cause highly uniform excitation of the hull. If the frequency of the pressure pulses caused by such a propeller with identical blades lies close to a natural frequency of the hull of the watercraft, then the hull is caused to perform a resonant vibration, and a considerable noise burden and dynamic loading of the hull can occur.

[0065] The solid line illustrates a pressure course 30 for an example of a propeller according to the system described herein with four blades. This could, for example, be a propeller according to the third embodiment, wherein the four blades have in each case different angular spacings.

[0066] As can be clearly seen, the maxima of the pressure pulses in the curve 30 occur aperiodically, and repeat only after one full revolution of the propeller. Furthermore, a different course of the generatrices and of the skew angles gives rise to a different magnitude of the pressure prevailing at the blade tip, and thus a different amplitude of the calculated signal. Thus, a uniform and in particular resonant excitation of a hull is avoided, and noise generation is counteracted in an effective manner.

[0067] The above description has discussed primarily the blade geometry of the propeller in the plan view onto the propeller plane in an axial direction. In this view, the angular spacing between the blade tips of successive blades of a propeller can be seen, which is of importance for the reduction of harmonic excitations of the hull. Design freedom exists with regard to the specification of other geometrical features of the propeller blades. For example, chapter 3 of the book Marine Propellers and Propulsion, 3rd edition, by the author: John Carlton, ISBN: 9780080971230, describes the laws for the specification of the propeller and blade geometry. Below, on the basis of an example, geometry specifications will be discussed which define a functional and balanced propeller.

[0068] In order to realize a propeller with different angular spacings between the blade tips, the following process can be followed for each blade:

[0069] 1. Establishing the Cylindrical Balance

[0070] In a first step, an arbitrary number of radii sections of the blade may be selected, at which the profiles are defined. A radial profile thickness distribution and a profile length distribution may be selected. An exemplary course of the profile thickness and of the chord length versus the radius is illustrated in FIG. 8. These distributions yield, in a plan view without skew, the propeller blade illustrated in FIG. 9. The generatrix of the blade runs straight upward in FIG. 9, and connects the chord center of the blade profiles in the respective radii sections. The chord center coincides with the respective profile center of gravity in the selected profiles. In the case of the distribution of the blade profiles without skew as shown in FIG. 9, the generatrix corresponds to the radial straight line through the root. The dotted line represents the leading edge (L.E.) and the dashed line represents the trailing edge (T.E.).

[0071] To shift the position of the blade tips, the following approach is expedient.

[0072] In general, use may be made of similar thickness distributions of the blade profiles across all radii sections. The thickness distribution may have a fixed shape factor which indicates what fraction of the product of chord length and maximum profile thickness is covered by the area of the radii section. The area of a profile consequently may be approximated very closely by the product of

profile thickness*chord length*shape factor.

An example of a course of a scaled profile is schematically illustrated in FIG. 10. Volume elements may be generated from the profile areas in a manner dependent on the radial spacing. The different sizes of these volume elements over the radius of the propeller can be seen in FIG. 11.

[0073] These volume elements also correspond to the radial distribution of the percentage fractions in the overall weight of the blade which determine the position of the center of gravity of the blade both in a radial direction and in a circumferential direction. In order to obtain a balanced propeller, all blades should have the same weight, and their centers of gravity should be distributed uniformly over the entire circumference of the propeller.

[0074] If the blade tips are shifted counter to the direction of rotation, then the overall center of gravity of the propeller also shifts in the same direction, correspondingly to the percentage fraction of the shifted volume elements. In a first step, the shift of the blade tips for the blades may be selected. The course of the profile thicknesses and chord length with a shift of the profiles in the outer portion of the blade counter to the direction of rotation thereof, that is to say toward the trailing edge (T.E.), is illustrated in FIG. 12.

[0075] In the second step, the radially inner radii sections should be shifted in the opposite direction in order to shift the center of gravity again such that it runs through the root (profile center of the profile adjoining the hub). If the initial position of the blade tip from FIG. 9 is to be shifted to the position in FIG. 12, the course of the generatrix in the region from 0.2 to 0.7 of the propeller radius should be shifted in the direction of rotation, that is to say toward the leading edge (L.E.), until the center of gravity lies at 0 again, that is to say passes through the root.

[0076] This course of the generatrix is illustrated in FIG. 13. In the case of large contour gradients, it must be observed that the number of supporting points must be selected to be correspondingly high.

[0077] 2. Establishing the Axial Balance

[0078] For this purpose, according to Carlton (l.c., chapter 3.4, pages 33-35), the blade rake attributable to the blade skew (skew induced rake) is calculated and is plotted negatively as a rake. FIG. 14 shows a comparison of the generatrix with skew course with the course of the generatrix of the initial design of the blade profile.

[0079] The features of the system described herein disclosed in the present description, in the drawings and in the claims may be both individually and combinatively essential to the realization of the invention in its various embodiments. The invention is not restricted to the described embodiments. It may be varied within the scope of the claims and taking into consideration the knowledge of a person of relevant skill in the art. Other embodiments of the system described herein will be apparent to those skilled in the art from a consideration of the specification and/or an attempt to put into practice the system described herein disclosed herein. It is intended that the specification and examples be considered as illustrative only, with the true scope and spirit of the invention being indicated by the following claims.