A blade for a hydrokinetic turbine

Abstract

A blade for a hydrokinetic turbine has a body 1 ending in a mounting element 2, the body 1 having a leading edge 3 and a trailing edge 4. The trailing edge 4 comprises multiple sections 41-46 separated by turns, wherein at least two neighbouring turns have different chord lengths B1, B11, B2, B22, B3, B33 of their profile centre lines 31-36. The trailing edge thus has a zig-zag, saw-tooth, serrated or undulating profile. These blades may perform better when flow is varying or unstable. Different profiles are described for different flow conditions.

Description

TECHNICAL FIELD The present invention relates to a blade for a hydrokinetic turbine, in particular designed to operate on an axis of a turbine with a tubular housing. BACKGROUND Hydrokinetic turbines, hydroelectric power plants (power generators), propeller pumps operating in systems for the recovery of energy contained in water, oil or other liquid, comprise an electric generator having a rotational axis on which blades are mounted. Such turbines may be implemented as floating or stationary devices (anchored to a fixed object). The operation of the turbines in a horizontal or vertical installation is driven by a stream of water (e.g., a river) or by a liquid flowing via the turbine with a velocity depending on a difference of potential or kinetic energy in front of and behind the hydrokinetic turbine. A PCT application WO2015000964A1 discloses a hydroelectric turbine for use in a flowing body of water for generating electrical current. There is disclosed a housing, a turbine, an electricity generator connected to the turbine in a torque-transmitting manner, and an anchor device for anchoring the hydroelectric turbine to the bed of the body of water. There are known turbine blades which have a profile shaped such that a center line of the blade continuously shortens in a direction away from the blade mounting element, and the leading edge is straight or arcuate-linear. Furthermore, there are known blades which have a profile shaped such that the center line of the blade first lengthens and then shortens along a direction away from the blade mounting element. The change of shape occurs only at one point. The leading edge of the turbine blade is a straight line or an arc-linear line. A characteristic feature of the known blade shapes is that they have uniform trailing edges. In addition, the angle of the blades of high-speed water turbines is small and when the turbine starts to operate, its angle of attack is large, much larger than the optimal angle. In such a situation, flow separation occurs on the blades, the generated lifting force is small and thus the torque is small. SUMMARY There is a need to provide a new structure for a blade for a hydrokinetic turbine that would be more efficient than the structures known so far. The invention relates to a blade for a hydrokinetic turbine, the blade having a body terminated by a mounting element, wherein the body has a leading edge and a trailing edge, and wherein the trailing edge comprises multiple sections separated by turns, wherein at least two neighboring turns have different lengths of their profile center lines. The blade is designed particularly to operate in a radial orientation on an axis of a tubular housing of a hydrokinetic turbine. The blade according to the invention may be used in particular in hydrokinetic turbines having a horizontal or vertical axis of rotation (in particular, a turbine with a vertical axis can be used in vertical shafts or pipelines with very large diameters). The blade is attachable to the axis of rotation by means of the mounting element, which may have a form of a mounting mandrel or a mounting socket for receiving a rotor mandrel. In general, the trailing edge of the blade is non-linear and includes regular or irregular serrations, undulations, taperings, or steps. In the context of the present description, the term "a trailing edge section" is understood as a blade area along which the trailing edge has a shape described by a straight line or a curved line of a uniform shape. The term "a turn" is understood as a cross-section of the blade that crosses a point on the trailing edge at which the shape of the trailing edge changes. In particular, the turn is located at that point on the trailing edge, for which the tangent lines of the edge located aside said point differ significantly from one another (in particular, in terms of their inclination). Each turn can be characterized by a specific center line of the profile at the turning point. In general, the ratio of the absolute lengths B1-B3, B11-B33 of the boundary center lines of a given segment may be equal from 10 to 0.05. Such an irregular shape of the blade trailing edge improves the recovery of energy of the liquid stream, especially when the stream, such as a river, has different dynamic states. Moreover, the irregular shape facilitates operation of the blade under changing flow conditions that occur temporarily or over a long term in the river. Moreover, the irregular shape of the blade allows better adaptation of the blade to liquids of different viscosities and densities, which influence the hydraulic losses at the contact with the surface. By selecting specific dimensional values of the characteristics of the turbine blade (such as center lines lengths, distances between center lines etc.), it is possible to adapt the blade to operate with liquids flowing at a given speed (high or low), of a given density and viscosity. Thus, it is possible to adjust the shape of the trailing edge of the blade to operate with such liquids as water, mineral and synthetic oils, petroleum liquids and liquids containing relatively small-sized solids. The blade can be composed of separate modules connected to each other. The modules may be connected to each other by retaining locks which may occupy the entire side perimeter of the module or there may be local interruptions in the retaining locks. For example, a single module may have a convex lock on one side (configured to enter into the subsequent module) and a concave lock on the opposite side (configured to receive a convex lock of the preceding module). The module may have its core made of metal, and an outer shell made of plastic that forms the blade profile. Such simple design of a modular blade allows to manufacture it without a need for advanced manufacturing technologies and significant financial expenditures. If the blade is damaged locally, it can be repaired by simply recreating and replacing the damaged module. Every second section can be a tapering section having a boundary center line that is closer to the blade mounting element shorter than the boundary center line that is further away from the blade mounting element. The tapering sections allow to limit the separation of flow of water from the surface of the blade and thus increase the torque generated by the turbine blades, which should be greater than the resistance torque associated with friction of bearings and seals. Intermediate sections between the tapering sections may have lengths that increase towards the mounting element or may have lengths that decrease towards the mandrel or may have equal lengths. At least some of the intermediate sections between the tapering sections may have the trailing edge in a form of a straight line in a side projection, or in a form of a line concave towards the body in a side projection, or in a form of a line convex outside the body in a side projection. The blade may comprise three tapering sections, two intermediate sections located between the tapering sections and two end sections located outside the tapering sections. The tapering sections may have equal lengths or may have lengths that increase towards the mounting element. The invention also relates to a hydrokinetic turbine comprising a tubular body and an axis on which there are mounted radially the blades as described herein. BRIEF DESCRIPTION OF DRAWINGS The object of the present invention is shown by means of example embodiments in a drawing, wherein: Figs. 1-3 present a first embodiment of a blade in a side view; Fig. 4 presents a cross section of the blade across its turns; Fig. 5 presents blade modules in an exploded view; Fig. 6 presents a second embodiment of the turbine blade in a side view; Fig. 7 presents a third embodiment of the turbine blade in a side view; Fig. 8 presents a fourth embodiment of the turbine blade in a side view; Fig. 9 presents a fifth embodiment of the turbine blade in a side view; Fig. 10 presents an example of a hydrokinetic turbine having blades as disclosed herein. DETAILED DESCRIPTION A first embodiment of a turbine blade according to the present invention is presented in Figs. 1-5. The blade has a body 1 attachable to a rotational axis of the turbine by means of a mounting element in a form of a mandrel 2. The body 1 has a leading edge 3 and a trailing edge 4. The trailing edge 4 comprises a series of sections 41 -47 delimited by turns, as presented in Fig. 1. The sections 42, 44, 46 have a form of taperings, i.e. they get narrower towards the blade mandrel 2 - namely, boundary center lines 32, 34, 36 of these sections 42, 44, 46 that are closer to the blade mandrel 2 have lengths B11, B22, B33 shorter than lengths B1, B2, B3 of the boundary center lines 31, 33, 35 which are further away from the blade mandrel 2, as shown in Fig. 2. Apart from the tapering sections 42, 44, 46, the trailing edge has end sections 41, 47 and intermediate sections 43, 45. In the first embodiment as presented herein, the ratio of absolute lengths B1 :B11, B2:B22, B3:B33 of the boundary center lines 31-36 of the sections 42, 44, 46 is equal to about 1.2. The tapering sections 42, 44, 46 have a form which gets narrower in a direction towards the blade mandrel 2. In turn, the intermediate sections 43, 45 between the tapering sections 42, 44, 46 have a form which gets wider in a direction towards the blade mandrel 2. The length A1, A2, A3 of each of the tapering sections 42, 44, 46 is smaller than the length C1, C4 of each of the end sections 41, 47 and then the length C2, C3 of each of the intermediate sections 43, 45. The lengths A1-A3, C1-C3 are measured in a top view, along a line parallel to a mounting axis 0 of the mandrel 2. In turn, the lengths B1-B3, B11-B33 are measured as absolute lengths of particular center lines 11-16 as shown in Fig. 4. Fig. 4 presents cross sections of the blade across the turns in planes A-A - F-F perpendicular to the mounting axis O of the mandrel 2 and indicates their center lines 31-36. The blade is composed of modules 11-15 presented in Fig. 5. According to the first embodiment, the length C1 of the first end section 41 is smaller than the length C2 of the first intermediate section 43, which is in turn smaller than the length C3 of the second intermediate section 45. The first end section 41 and the intermediate sections 43, 45 have their trailing edge in a shape which is slightly concave towards the interior of the body 1. The tapering sections 42, 44, 46 have a substantially rectilinear shape of the edges. The trailing edge 4 is rounded at the position of the turns. Such a shape of the trailing edge 4 is particularly advantageous for rivers and other streams having a moderately stabilized flow, i.e., wherein the flow is more dynamic than a completely laminar flow. Fig. 6 presents a second embodiment of the turbine blade in a side view. Similarly as in the first embodiment, the trailing edge 4 comprises a series of sections 41-47, wherein the end section 41 and the intermediate sections 43, 45 have a trailing edge in a shape of a line that is convex (in a side projection) with respect to the body 1. Such a shape of the trailing edge 4 is particularly useful for improving adherence of the flow of liquid to the blade profile. This can be particularly advantageous in the case wherein the flow varies strongly and dynamically over short periods of time. The convex shape causes the blade profile to elongate locally, which allows better streamline. Fig. 7 presents a third embodiment of the turbine blade in a side view. Similarly as in the first embodiment, the trailing edge 4 comprises a series of sections 41-47, wherein the end section 41 and the intermediate sections 43, 45 have a trailing edge in a shape of a line that is concave (in a side projection) towards the body 1, with significantly higher curvatures as compared to the first embodiment. Such a shape of the trailing edge 4 is particularly advantageous when an incoming flow, e.g., of a river, flows very steadily and has a cross profile that is at least moderately established, and wherein the flow has no significant variations in dynamics. The concavity generates a local shortening of the blade profile, which reduces the contact distance between the water and the surface of the blade. This design is aimed at reducing the hydraulic losses arising from the flow streamline. Such a profile can therefore be used for a very stable flow in a river and for relatively small flow velocities of the liquid stream. Fig. 8 presents a fourth embodiment of the turbine blade in a side view. Similarly as in the first embodiment, the trailing edge 4 comprises a series of sections 41-47, wherein the shape of the sections is diverse: the end section 41 has a convex edge shape, and the first intermediate section 43 has a rectilinear edge shape, and the second intermediate section 45 has a concave edge shape. Such a shape of the trailing edge 4 is particularly advantageous for rivers and flows with a moderately stabilized flow, wherein it is possible that minor additional flow instabilities may occur over a short period of time. Such a shape is universal, as it is suitable for use in slow flowing rivers with possible side tributaries that cause local and momentary instabilities. Fig. 9 presents a fifth embodiment of the turbine blade in a side view. Similarly as in the first embodiment, the trailing edge 4 comprises a series of sections 41-47, wherein the section 42 between the end section 41 and the intermediate section 43 has edges with an inclination in an opposite direction with respect to the inclination of the edge of the tapering section 44, 46. Therefore, the section 42 may be called as a projection section. In other words, the section 42 has a longer boundary center line 32 which is closer to the blade mandrel 2 as compared to the boundary center line 31 which is located further away from the blade mandrel 2. Such a shape of the trailing edge 4 is also advantageous for rivers and flows with a moderately stabilized flow, wherein it is possible that minor additional flow instabilities can occur over a short period of time. In all embodiments presented herein, the inner end section 47 has a convex trailing edge. This is useful for the reason that in this are the blade is most stressed in terms of strength. Thus, such a profile of the edge provides a relatively high volume of blade material at this area. Alternatively, the end section 47 may be rectilinear or concave, depending on needs. Fig. 10 presents an embodiment of the turbine having tubular housing 9, inside of which the blades 1 are mounted at the rotation axis 8 in a radial direction perpendicularly to that axis. Although the invention is presented in the drawings and the description and in relation to its embodiments, these embodiments do not restrict or limit the presented invention. It is therefore evident that changes, which come within the meaning and range of equivalency of the essence of the invention, may be made. The presented embodiments are therefore to be considered in all aspects as illustrative and not restrictive. According to the abovementioned, the scope of the invention is not restricted to the presented embodiments but is indicated by the appended claims.

Claims

1. A blade for a hydrokinetic turbine, the blade having a body (1) terminated by a mounting element (2), wherein the body (1) has a leading edge (3) and a trailing edge (4), and wherein the trailing edge (4) comprises multiple sections (41-46) separated by turns, wherein at least two neighboring turns have different lengths (B1, B11, B2, B22, B3, B33) of their profile center lines (31-36).

2. The blade according to claim 1, wherein the blade is composed of separate modules (11-15) connected to each other.

3. The blade according to any of previous claims, wherein every second section is a tapering section (42, 44, 46) having a boundary center line (B11, B22, B33) that is closer to the blade mounting element (2) shorter than the boundary center line (B1, B2, B3) that is further away from the blade mounting element (2).

4. The blade according to claim 3 wherein intermediate sections (43, 45) between the tapering sections (42, 44, 46) have lengths that increase towards the mounting element (2).

5. The blade according to claim 3 wherein intermediate sections (43, 45) between the tapering sections (42, 44, 46) have lengths that decrease towards the mandrel (2).

6. The blade according to claim 3 wherein intermediate sections (43, 45) between the tapering sections (42, 44, 46) have equal lengths.

7. The blade according to any of claims from 3 to 6 wherein at least some of the intermediate sections (43, 45) between the tapering sections (42, 44, 46) have the trailing edge in a form of a straight line in a side projection.

8. The blade according to any of claims from 3 to 7 wherein at least some of the intermediate sections (43, 45) between the tapering sections (42, 44, 46) have the trailing edge, in a form of a line concave towards the body (1) in a side projection.

9. The blade according to any of claims from 3 to 8 wherein at least some of the intermediate sections (43, 45) between the tapering sections (42, 44, 46) have the trailing edge, in a form of a line convex outside the body (1) in a side projection.

10. The blade according to any of claims from 3 to 9 comprising three tapering sections (42, 44, 46), two intermediate sections (43, 45) located between the tapering sections (42, 44, 46) and two end sections (41, 47) located outside the tapering sections (42, 44, 46).

11. The blade according to any of claims from 3 to 9 wherein the tapering sections (42, 44, 46) have equal lengths (A1-A3).

12. The blade according to any of claims from 3 to 9 wherein the tapering sections (42, 44, 46) have lengths (A1-A3) that increase towards the mounting element (2).

13. A hydrokinetic turbine comprising a tubular body (9) and an axis on which there are mounted radially the blades (1) according to any of the previous claims.10

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