The present invention relates to a turbine blade comprising a bottom surface and a top surface and a leading surface and a trailing surface, wherein a pressure surface and a suction surface are connected along the leading surface and the trailing surface, wherein the pressure surface and the suction surface are extended over profiles constructed of component curves, wherein a profile forming the suction surface comprises starting from the leading surface: at least one segment which has a curve inflection point and which is formed by two convex curves comprising a first convex curve having a first mean curvature radius and a first curvature length and a second convex curve having a second mean curvature radius and a second curvature length, and by one concave curve having a third mean curvature radius and a third curvature length, successively located one after the other starting from the side of the leading surface; and a terminal segment which is located behind the endmost segment having a curve inflection point and formed by a concave curve having a terminal mean curvature radius and a terminal curvature length.

Such a turbine blade may be used in any arbitrary turbine, and in particular it may be employed in water turbines and wind turbines. The present invention relates also to a turbine comprising such a turbine blade.

Background of the invention

From the prior art turbine blades are known comprising a body with a top surface and a bottom surface, which are fixed on a hub of a turbine shaft about a rotation axis thereof. The blades are oriented with a leading surface facing the direction of a propelling medium stream which together with a trailing surface defines a pressure surface and a suction surface forming the blade. Generally, a distance between the pressure surface and the suction surface is variable along a blade and diminishes in the direction toward the trailing surface. In basic arrangements, the thickness of a blade is the greatest in the area corresponding approximately to 1/3 of the distance between the leading surface and the trailing surface as it provides its high efficiency and reliability of a blade operation, assuming predefined dependencies between the direction of a water or air inflow and the direction of a blade orientation. Constant efforts to achieve better and better performances and efficiencies of wind and water turbine operation result in developing new turbine constructions, in particular new blade profiles.

Publication PL186359 discloses a water axial flow turbine blade comprising a leading edge and a trailing edge and an arched internal edge and an arched external edge. A convex suction surface of this blade is made of a plate of a constant thickness and has a shape of a segment of (approximately elliptical) cylinder surface.

Publication EP2022979A1 discloses a wind turbine blade having an elongated body with an aerodynamic profile having a leading edge, a trailing edge and suction and pressure sides between the leading edge and the trailing edge which has, on at least one part of the wind turbine blade, a trailing edge region, the transversal section of which increases in the direction of the trailing edge. Said trailing edge region preferably has a divergent form with a curved concave surface on its lower part.

Publication US2011097210A discloses a turbine blade profile comprising modified suction and pressure surfaces. Radially corresponding surface characteristics of the pressure and suction surfaces at a spanwise local portion of the blade are formed to cooperatively define at least one of a camber line and a thickness distribution plot of the blade as having a radius of curvature with at least two sign changes. The number of sign changes decreases along a radial dimension of the blade measured from the spanwise local portion.

It has been the object of the present invention to provide a turbine blade of an improved construction providing high efficiency of an operation and ensuring operation safety maintenance for the whole speed range - based on the assumption of a relative low turbine rotational speed. The turbine blade according to the present invention should be suitable for both water turbines as well as for wind turbines.

Summary of the invention

According to the present invention there is provided a turbine blade of the kind mentioned in the outset which is characterised in that for each segment having a curve inflection point:

- the ratio of the third mean curvature radius to the first mean curvature radius ranges from 0.55 to 0.95, - the ratio of the second mean curvature radius to the third mean curvature radius ranges from 0.35 to 0.75,

- the ratio of the third curvature length to the first curvature length ranges from 0.55 to 0.95,

- the ratio of the second curvature length to the first curvature length ranges from 0.35 to 0.75;

and for the terminal segment:

- the terminal mean curvature radius is smaller than the first mean curvature radius of the preceding adjacent segment having a curve inflection point,

- a chord of the terminal segment is slanted relative to a chord of the preceding adjacent segment having a curve inflection point at an obtuse angle;

- the ratio of the length of the chord of the terminal segment to the length of the chord of the preceding adjacent segment having a curve inflection point ranges from 0.55 to 0.95.

Each of the above defined component curves forming the blade profile constituting the suction surface and characterized by its characteristic mean curvature radius may be any arbitrary smooth curve such as for example a curve constituting as a whole a circle segment or a higher degree curve formed by a number of individual normal arcs or a spline curve.

A chord of a given segment of a profile of a turbine blade according to the present invention is a line segment connecting endpoints of the segment with each other, in other words it is a line segment connecting its beginning with its end point).

The turbine blade according to the present invention preferably comprises a number of the segments having curve inflection points, wherein for each pair of such segments:

- the ratio of the length of the chord of a given segment to the length of the chord of the preceding adjacent segment located in front of the given segment toward the leading surface, ranges from 0.55 to 0.95;

and/or

- the ratio of an angle of a slant of the chord of a given segment relative to the chord of the adjacent segment located in front of this given segment toward the trailing surface, to the angle of a slant of the chord of this given segment relative to the chord of the adjacent segment located in front of this given segment toward the leading surface, ranges from 0.55 to 0.95.

Adjacent chords of adjacent segments on the suction surface are preferably slanted relative to each other at obtuse angles that preferably range from 100° to 170°. The top length of the chord of the whole blade profile in the position of the top surface is greater than or equal to the bottom length of the chord of the whole blade profile in the position of the bottom surface.

The chord of the whole blade profile according to the present invention is a line segment connecting the external edge of the leading surface with the external edge of the trailing surface, i.e. a line segment connecting the starting point of the first segment with the endpoint of the terminal segment.

The chord of the whole blade profile in the position of the bottom surface is preferably slanted relative to the chord of the whole blade profile in the position of the top surface at an angle ranging from 0° to 45°, and more preferably ranging from 10° to 20°.

The position of the external edge of the leading surface in the top surface is preferably linearly dislocated along the blade rotation axis outward in the direction from the external edge of the leading surface in the bottom surface to a given distance, wherein the ratio of this given dislocation distance to the blade profile top chord length ranges from 0.05 to 0.75.

The profile forming the pressure surface of the blade according to the present invention may be any arbitrary curve featuring an aerodynamic or hydrodynamic profile depending on medium for which the blade is designed.

According to the present invention there is also provided a turbine comprising a hub which is rotatable about a rotation axis, and a number of turbine blades such as the one defined above, which are mounted circumferentially on the hub, wherein an acute angle of a slant of the chord of the whole blade profile in the position of the bottom surface relative to the rotation axis of the hub ranges from -25° to +55°. The turbine blade according to the present invention generates a considerable acceleration of a fluid stream or air stream flowing over the first two curves of the first and second mean curvature radiuses of the successive profile segments, and thus contributes to a considerable pressure decrease along these curves. Such a pressure reduction along these curves in the successive profile segments allows for achieving a high efficiency of harnessing energy of a fluid stream or a gas stream. This effect results directly in high values of a power coefficient with additionally preferable reduction of a turbine rotational speed.

Furthermore, it has been unexpectedly discovered that in a case of a use of the turbine blade according to the present invention in a water turbine arrangement, additional effects of a water aeration and a water purification are achieved and an erosional downcutting (constituting a considerable problem in similar solutions known from the prior art) induced by such a turbine is significantly reduced. Importantly, a low rotational speed of the turbine according to the present influences also positively on an improved safety of fishes and other aquatic organisms.

Brief description of drawings

The invention shall be described and explained below in connection with the attached drawings in which:

Fig. 1 is a perspective view of the first embodiment of the turbine blade according to the present invention provided with two segments having curve inflection points, wherein the first embodiment is seen from the side of a suction surface,

Fig. 2 is a view depicting geometry of a profile of the turbine blade of Fig. 1 ;

Fig. 3 depicts relative positions of the bottom surface and the top surface of the blade of Fig. 1 relative to each other;

Fig. 4 is a view of the turbine blade of Fig. 1 as seen in the direction perpendicular relative to the blade rotation direction (wherein the blade rotation direction is indicated with a horizontal arched arrow with the head pointing left) wherein the view depicts the shape of the leading edge and the trailing edge of the blade;

Fig. 5 is a view depicting geometry of a profile of the second embodiment of a turbine blade according to the present invention; and

Fig. 6 is a view depicting geometry of a profile of a general embodiment of a turbine blade according to the present invention. As depicted in Fig. 1 , the first embodiment of a turbine blade according to the present invention comprises a top surface 1 , a bottom surface 2, a leading surface 3 and a trailing surface 4. A pressure surface 5 and a suction surface 6 are connected along external edges of the leading surface 3 and external edges of the trailing surface 4, wherein the pressure and suction surfaces 5, 6 are extended over the profiles which are composed of a number of curves.

The pressure surface 5 is formed by a curve having an aerodynamic or hydrodynamic profile extended between points determined - in a cross-section of the blade profile - by an external edge the leading surface 3 and an external edge of the trailing surface 4.

The profile of the suction surface 6 contains at least one segment SEG having a curve inflection point C. In this embodiment, the suction surface 6 comprises two segments SEG1 , SEG2 with curve inflection points C1 , C2, respectively. Each of the segments SEG1 , SEG2, starting from the side of the leading surface 3, comprises two convex curves comprising a first convex curve KA1 , KA2 extending respectively between points A1 (on the external edge of the leading surface 3), A2 and B1 , B2; a second convex curve KB1, KB2 extending respectively between points B1 , B2 and C1 , C2; and one terminal concave curve KC1 , KC2 extending between the curve inflection point C1 , C2 and the endpoint of the respective segment SEG1 , SEG2; wherein the curves are successively located one after the other along the profile starting from the side of the leading surface 3.

The first two convex curves KA1 , KA2 are characterized by means of the first mean curvature radiuses RA1 , RA2 and the first curvature lengths LA1 , LA2 thereof. The second convex curvatures KB1 , KB2 are characterized by means of the second mean curvature radiuses RB1. RB2 and the second curvature lengths LB1. LB2 thereof. The third concave curves KC1 , KC2 are characterized by means of the third mean curvature radiuses RC1 , RC2 and the third curvature lengths LC1. LC2 thereof.

The above identified dimensions are selected for each one of the segments SEG1 , SEG2 having the curve inflection point C1 , C2, in such a manner that the following conditions are fulfilled: - the ratio RC1 :RA1 , RC2:RA2 of the third mean curvature radius RC1 , RC2 to the first mean curvature radius RA1 , RA2, ranges from 0.55 to 0.95,

- the ratio RB1 :RC1 , RB2:RC2 of the second mean curvature radius RB1 , RB2 to the third mean curvature radius RC1 , RC2, ranges from 0.35 to 0.75,

- the ratio LC1 :LA1 , LC2:LA2 of the third curvature length LC1 , LC2 to the first curvature length LA1 , LA2, ranges from 0.55 to 0.95,

- the ratio LB1 :LA1 , LB2:LA2 the second curvature length LB1 , LB2 to the first curvature length LA1 , LA2, ranges from 0.35 to 0.75.

In front of the second segment SEG2 having the curve inflection point C2 toward the trailing surface 4, a terminal segment SEGt is formed in the profile of the suction surface 6 between the endpoint of the segment SEG2 and the terminal point 4t on the external edge of the trailing surface 4, and comprises a convex curve Kt characterized by a terminal mean curvature radius Rt and a terminal curvature length Lt.

The terminal mean curvature radius Rt is selected in such a manner that this radius Rt is smaller that the first mean curvature radius RA2 of the preceding adjacent segment SEG2 having the curve inflection point C2.

For each of the segments SEG1 , SGE2, SEGt, appropriate chords CH1 , CH2, CHt are defined constituting line segments connecting their beginnings with their endpoints, wherein the starting point of the first segment SEG1 and the endpoint of the terminal segment SEGt constitute also the points determined in a cross-section of the blade profile respectively by external edge of the leading surface 3 and external edge of the trailing surface 4.

The chords CH1 , CH2, CHt adjacent relative to each other of the adjacent segments SEG1 , SEG2, SEGt on the suction surface 6 are slanted relative to each other at obtuse angles a(1 ;2, 2;t) which preferably range from 100° to 170°. In particular, the chord CHt of the terminal segment SEGt is slanted relative to the chord CH2 of the preceding adjacent segment SEG2 having the curve inflection point C2 at an obtuse angle a(2;t). The angle a(1 ;2) may for example amount 155° and the angle a(2;t) may for example amount 160°. The length LCHt of the chord CHt of the terminal segment SEGt is selected in such a manner that the ratio LCHt:LCH2 of this length LCHt to the length LCH2 of the chord CH2 of the preceding adjacent segment SEG2 having the curve inflection point C2, ranges from 0.55 to 0.95.

Fig. 3 presents a relative positioning of the pressure surface 5 and the suction surface 6 in the position of the bottom surface 2 and the top surface 1 of the blade, respectively. In Fig. 3, a hub 7 of a turbine is symbolically visualized with dashed lines, wherein on this hub 7 the turbine blade according to the present invention may be mounted. The rotation axis O of the hub 7 is parallel relative to the stream of propelling medium (such as a water stream or an air stream; represented by vertical arrows), and it constitutes also the rotation axis of the turbine blade. The rotation direction of the hub 7 with the blade is symbolically depicted with a horizontal arrow with the head pointing right. The turbine blade is appropriately oriented relative to the rotation axis O and the direction of the propelling medium stream. The orientation of the turbine blade may be determined by a slant of the chord CHdown of the whole blade profile in the position of the bottom surface 2 relative to the rotation axis O of the hub 7, wherein the slant is defined by an acute angle g ranging from -25° to +55°.

As presented in this embodiment, the profiles in the position of the bottom 2 and top 1 surface, respectively, are rotated relative to each other, and the lengths of the chords CHdown and CHup of the whole blade profile in the position of the bottom 2 and top 1 surface, respectively, are different, wherein CHup > CHdown. The chords CHup and CHdown of the whole blade profile are line segments connecting the external edge of the leading surface 3 with the external edge of the trailing surface 4.

Such a twisting of the blade profile in the position of the bottom surface 2 relative to the blade profile in the position of the top surface 1 of the blade results from the shaping of the leading surface 3 and the trailing surface 4 as non-ruled surfaces (as visible in Fig. 4), and is determined as an angle b of a slant of the chord CHdown in the position of the bottom surface 2 relative to the chord CHup in the position of the top surface 1. The angle b ranges from 0° to 45°, and preferably ranges from 10° to 20°; and the angle b may for example amount 15°. The position of the point 3up of the external edge of the leading surface 3 for the top surface 1 is linearly dislocated along the rotation axis O of the hub 7, and thus also along the rotation axis of the blade, outward in the direction from the point 3down of the external edge of the leading surface 3 for the bottom surface 2 to a certain distance M, which - as presented in Fig. 3 - is determined in parallel relative to the direction of the propelling medium stream (such as for example a water stream or an air stream; represented by vertical arrows) along the rotation axis O. The distance M may according to the present invention range preferably from 0.05 CHup to 0.75 CHup. This linear dislocation distance M may for example amount 0.2 CHup.

Fig. 5 presents another embodiment of the profile of the turbine blade according to the present invention. The suction surface profile of this blade comprises only one segment SEG1 having the curve inflection point C1 and one terminal segment SEGt.

The radiuses and curve lengths and chords lengths of the component curves KA1 , KB1 , KC1 and Kt of this profile fulfill the following conditions that are indispensable according to the present invention:

RC1 :RA1 = 0.55 - 0.95,

RB1 :RC1 = 0.35 - 0.75,

LC1 :LA1 = 0.55 - 0.95,

LBT.LA1 = 0.35 - 0.75,

Re < RA1 ,

LCHt:LCH1 = 0.55 - 0.95.

The chords CH1 , CHt of the adjacent segments SEG1 , SEGt on the suction surface 6 are slanted relative to each other at an obtuse angle a(1 ;t) which preferably ranges from 100° to 170°.

Generally, the suction surface 6 of the turbine profile according to the present invention comprises n segments SEG1-SEGn having curve inflection points C1-Cn and one completely convex terminal segment SEGt. In such a general embodiment of the profile according to the present invention as shown in Fig. 6:

- for any arbitrary index„x”, the radiuses and lengths of the component curves KAx, KBx, KCx of the segments SEGx having curve inflection points C fulfill the following conditions that are indispensable according to the present invention:

RCx:RAx = 0.55 - 0.95,

RBx:RCx = 0.35 - 0.75,

LCxiLAx = 0.55 - 0.95,

LBx:LAx = 0.35 - 0.75,

- the parameters of the curve Kt of the terminal segment SEGt fulfill the following conditions that are indispensable according to the present invention:

Rt < RAn,

LCHtLCHn = 0.55 - 0.95,

90°<(a(n;t))<180°, i.e. the angle (a(n;t)) is an obtuse angle.

Furthermore, according to the present invention it is preferable if in such a general embodiment of the profile of the blade according to the present invention as shown in Fig. 6, for any arbitrary index„x” for any pair of segments (SEGx-1-SEGx) having curve inflection points Cx-1 , Cx, both or at least one of the following conditions are/is fulfilled:

LCHx:LCHx-1 = 0.55 - 0.95; and/or

a(h;h+1):a(h-1 ;n) = 0.55 - 0.95.

Additionally, in the embodiment shown in Fig. 6, the chords CFM-CHn, CHt of the adjacent segments SEG1-SEGn, SEGt on the suction surface 6 are preferably slanted relative to each other at obtuse angles a(1...n;2...t) which preferably range from 100° to 170°.

The figures are not necessarily to scale, and some features may be exaggerated or minimized, in order to provide better the invention illustration. These and other factors however should not be considered as limiting the spirit of the invention, the intended scope of protection of which is defined in the appended claims. Therefore the presented embodiments should not be regarded as limiting the scope of protection defined in the patent claims.