Axial turbine with adjustable pitch blades

Abstract

Axial turbine with a stationary runner ring (8) and a runner, and wherein the runner comprises a hub (1) and at least three blades (2) which are rotating about axes, and wherein the blade rotational axes are perpendicular to the rotational axis of the turbine, and wherein each blade comprises a leading edge (3) and an outer edge (4), and wherein the outer edges each comprise a leading end (5) and a trailing end (6), and wherein the stationary runner ring comprises a spherical region, and wherein the leading edges are swept forward, and wherein the blades are designed to be hanging, so that an axial shift of the outer edges is such that the leading ends of the outer edges are arranged within the spherical region of the runner ring in a swiveling position of the blades which corresponds to a maximum permitted degree of opening.

Description

[0001]27997 / HZTAxial turbine with adjustable pitch bladesThe invention relates to an axial turbine with a runner comprised of adjustable pitchblades. Such turbines are also known as Kaplan turbines and are typically used in run-of-river power plants. The axial turbine according to the invention is characterized byturbine components designed to reduce damage to fish passing through the associatedhydropower plant when compared to fish passing through hydropower plants with conventional axial turbines. Axial turbines designed to reduce the mortality of passing fish are known from the stateof the art. For example, EP 3973176 B1 discloses such an axial turbine which has aprotective device designed to force fish towards the axis of rotation of the turbine. This allows a safe design of the blades to be concentrated on a partial area of the blade which is closest to the turbine axis of rotation. The protective unit is preferably at leastpartially integrally connected to the blade. In a preferred embodiment, the protectiveunit has at least one contour element, wherein the contour element preferably at leastpartially forms the leading edge of the blade. According to claim 3 of EP 3973176 B1, the leading edge of the blade is at least substantially sickle-shaped. For a discussion of the disadvantages of the axial turbine disclosed in EP 3973176B1, reference is made to the embodiment shown in Figure 2 of the correspondingdescription, which concerns an axial turbine with adjustable pitch blades. In the bladeposition shown, the leading edges are inclined upwards. Due to the crescent shape, the blade has a distinctive tip. A wedge-shaped gap is arranged between the tip and the stationary outer turbine ring. A direct collision between a fish and the tip couldseriously injure the fish. Fish can also become trapped in such a large gap.The task of the invention is to provide an axial turbine with adjustable pitch blades inwhich the disadvantages described are avoided and fish survival is improved.27997 / HZTAccording to the invention, the task is solved by an embodiment according to the independent claim. Further advantageous embodiments of the present invention can be found in the sub-claims. The invention is explained below with reference to figures. The figures show in detail:Fig. 1: Axial turbine according to the invention in axial viewFig. 2: Axial turbine according to the invention in axial viewFig. 3: Axial turbine according to the invention in a view perpendicular to the axisFig. 4: Axial turbine according to the invention in a view perpendicular to the axisFig.5: Axial turbine according to the invention in axial view Figure 1 shows a section of an axial turbine according to the invention in a view in thedirection of the turbine axis of rotation. In Figure 1, this axis of rotation is indicated bythe small cross and is referred to below as the ‘turbine axis’ or just the ‘axis’. Thedirection of rotation of the turbine is indicated by the arc-shaped arrow. The axial turbine comprises a runner, which in turn comprises a hub, which is labeled 1. The runner alsocomprises at least three adjustable pitch blades, which are connected to the hub 1. Forthe sake of clarity, only one blade is shown in Figure 1 and is designated 2. The pitchof the blades 2 is adjustable about blade rotational axes that are perpendicular to theturbine axis (see Figures 3 and 4) and intersect at a point on the turbine axis. Each blade 2 comprises a leading edge, which is designated 3, and an outer edge, which is designated 4. The outer edge 4 extends in a circumferential direction between two points, which are labeled 5 and 6 in Figure 1. In the following, point 5, which is inthe leading direction of rotation, is referred to as the ‘front end of the outer edge’ andpoint 6, which is in the trailing direction of rotation, is referred to as the ‘rear end of theouter edge’. The leading edge 3 of the blade extends between the leading end of theouter edge and a point which is labeled 7 in figure 1 and is referred to below as the‘hub-near end of the leading edge’. The turbine runner is arranged in a stationary ring,which is labeled 8.27997 / HZTIn the illustration in figure 1, the blades are pivoted so that the leading and trailing ends (5 and 6) of the outer edge are in a plane that is perpendicular to the turbine axis (seeFigure 3). Since axial turbines are usually designed with a vertical turbine axis, thisposition of the blades is also called the ‘horizontal position’. Axial turbines according to the invention are characterized, among other things, by the fact that the leading edges 3 of the blades in the horizontal position shown in Figure 1 have a shape that can be called ‘swept forward’. A detailed description of this ‘sweptforward’ designation is provided in connection with Figure 2.Figure 2 shows the same view as Figure 1, with various connecting lines drawn between certain points of the blade and the turbine axis, which serve to characterize the leading edges of the blades according to the invention. The connecting line of the axis with the trailing end 6 of the outer edge serves as a reference line for each blade and is labeled cl6. This connecting line cl6 serves as the zero line of the angle measurement. Positive angles are measured in the direction of rotation. Anotherconnecting line joins the leading end 5 of the outer edge with the axis and is labeledcl5. The angle between the connecting line cl5 and the connecting line cl6 is referred to as φ5. To measure an angle, the corresponding connecting lines are projected into aplane that is perpendicular to the axis. Another connecting line connects the hub end 7of the leading edge with the axis and is labeled cl7. The angle between the connectingline cl7 and the connecting line cl6 is referred to as φ7. Figure 2 also shows a dashed arc around the axis. The dashed arc marks the points that have a radial distance of75% of the radial distance from the hub radius to the outer runner radius, indicated R.There exists at least one point x on the leading edge within this circular arc for whichthe below noted relationship (I) is valid. A connecting line between the turbine axis andthis point is labeled clx. The angle between the connecting line clxand the connecting line cl6 is referred to as φx. A leading edge according to the invention is shaped such that the following relationships apply to the angles defined above: φ5 > φ7 > φx (I)27997 / HZTThe preceding section serves as a definition for the shape of the leading edge according to the invention, which is hereinafter referred to by the term ‘swept forward’.This term is also used in the claims to keep them short and easy to understand.The design of the leading edge of the blades according to the invention is not intended to force fish towards the axis of rotation of the turbine, as claimed in EP 3973176 B1, but is intended to reduce the potential damage that a fish may suffer if it collides with a blade in the region of the leading edge. The inventors have recognized that the potential damage in such a collision is proportional to the relative speed between a fish and a blade. This relative speed is greater if the collision with a blade occurs at a point furtherfrom the turbine axis than if the collision occurs closer to the hub, as the absolute speedof a blade increases linearly with the distance from the axis. Therefore, the outer regionof the blade leading edge is the critical region in terms of fish mortality in the event of acollision. The inventors have recognized that the force of the collision can be reducedby defining a leading edge that creates an angle β2 with the radial direction. The collisionis then not frontal, but in an oblique direction, which leads to a reduction in the relative speed of the collision. This reduction is particularly large if the relationship for the angle β2 shown in connection with Figure 5 is fulfilled. Blade leading edge thickness, as well as the relative velocity between a fish and a passing blade, can have a large impact of fish survival. As an additional measure toincrease the survival probability in the event of a collision with the blade leading edge,it is provided according to the invention that the blade features a sufficiently blunt or rounded shape along the entire leading edge. It is therefore provided according to theinvention that the edge radius of the leading edge is at least 1.0% of the runner diameterover its entire length. Figure 3 shows an axial turbine according to the invention in a view perpendicular tothe turbine axis, which is indicated by the vertical dashed line. The viewing direction ofthe image runs along the rotational axis of a blade. This blade rotational axis is indicatedby the central cross. Only the outer edge of the associated blade is shown. The blade is in the horizontal position, as the dashed line connecting the leading end of the outer27997 / HZTedge to the trailing end of the outer edge is perpendicular to the turbine axis. Figure 3also shows the spherical contour of the stationary runner ring. The center of the spherelies at the intersection of the rotational axes of the blades. The blade rotational axesintersect on the axis of the axial turbine. To allow water to reach the stationary runner ring and flow away from it, the spherical region of the stationary runner ring cannot be closed on the inflow and outflow sides; instead, tubular channel sections are connected at these points, which ensure the inflow and outflow of the driving water. The upper transition point and the lower transition point from the spherical to the tubular shapecan be located at different distances from the intersection of the blade rotational axes.The outer edges of the blades are shaped in such a way that they adapt to the sphericalrunner ring as closely as possible. This keeps the width of the gaps between the outer edges of the blades and the stationary runner ring as small as possible. In conventional axial turbines, this mainly serves to minimize secondary flows around the turbine, whichwould lead to a loss of efficiency and cavitation. As large gaps on the periphery of theblades also pose a danger to fish, minimizing gaps also serves to improve fish survival during turbine operation. However, if the blades are swung far away from the horizontalposition, i.e., when the blades are opened, one or both ends of the outer edges mayextend beyond the spherical region. It is detrimental in terms of fish mortality if this isthe case for the leading end of the outer edge, as a wedge-shaped gap then formswithin this region of the turbine. Gaps at the trailing end of the outer edges also produceregions that can result in mechanical damage to passing fish, in addition to generatingpotentially harmful secondary flows but generally have a much lower impact onmortality than gaps at the leading edge. The inventors have recognized that the problem described is exacerbated in the case of an axial turbine in which the leading edges of the blades have the shape accordingto the invention, i.e., which are swept forward, as the leading end of the outer edge thenprojects particularly far and can therefore protrude particularly early from the spherical region of the stationary runner ring when the blades are opened. According to the invention, this negative effect is counteracted by the blades being designed to be‘hanging’, as shown in Figure 3. The term ‘hanging blade’ refers to a blade whose27997 / HZTrotational axis is perpendicular to the turbine axis, but in which, in the horizontalposition, the distance from the plane, in which the ends of the outer edge lie, to theintersection of the blade rotational axes is not zero. Instead, the invention assumes avalue h, which is greater than zero, so that the entire outer edge in the direction of flowof the driving water is shifted by h relative to the plane which is perpendicular to theturbine axis, and which runs through the intersection of the blade rotational axes. Inaccordance with the invention, the distance h is selected to be large enough so that the leading end of the outer edges does not leave the spherical region of the stationaryrunner ring at the largest permissible degree of opening of the blades.The distance h is referred to below as the ‘axial shift of the outer edges in the flowdirection of the driving water’. As explained above, this axial shift refers to the horizontalposition of the blades. Figure 4 shows an axial turbine according to the invention in a state in which the blades are fully open. The leading end of the outer edge is located completely in the spherical region of the stationary runner ring. It is clear that if the axial shift h of the outer edges in the flow direction of the driving water were to be reduced, this would result in the outer edge shifting diagonally upwards to the right, as a result of which the leading end of the outer edge would increasingly protrude beyond the spherical region of thestationary runner ring in the pitch position shown.Figure 5 shows further advantageous aspects of the present invention. For this purpose, two angles are defined, one of which is labeled β1and the other β2. Both angles refer to a projection in a plane perpendicular to the axis.The angle β1 refers to the end 7 of the leading edge near the hub and to a point on theleading edge that is at a radial distance from the hub corresponding to 25% of the radial distance from the hub radius to the outer runner radius, indicated R. This distance is indicated by the dotted arc labeled 25%R. A first leg of β1is formed by the connecting line between the aforementioned point and between the hub-near end 7 of the leadingedge. The second leg of β1 extends radially from the end 7 of the leading edge near27997 / HZTthe hub, which represents the apex of β1. The angle β1defined in this way is referred to below as the ‘hub sided angle of the leading edge’. The angle β2refers to the front end 5 of the outer edge and to a point on the leading edge which has a radial distance from the hub corresponding to 75% of the radial distance from the hub radius to the outer runner radius, indicated R. This distance is indicated by the dotted arc labeled 75%R. A first leg of β2is formed by the connecting line between the aforementioned point and between the leading end 5 of the outer edge. The second leg of β2 extends radially from the axis to the leading end 5 of the outer edge, which represents the apex of β2. The angle β2defined in this way is referred to below as the ‘tip angle of the leading edge’. It is advantageous if the hub sided angle β1of the leading edge is greater than or equal to 15°. It is particularly advantageous if β1is ≥ 20°. The hub sided angle β1of the leadingedge indicates how much the leading edge curves back from the hub against thedirection of rotation. By ensuring that the leading edge is sufficiently curved back, largetorques acting in the closing direction of the blades are avoided during operation of the axial turbine. This makes the mechanical design of the axial turbine much easier in this respect and saves costs.It is advantageous if the tip angle β2 of the leading edge is greater than or equal to 30°.It is particularly advantageous if β2 is ≥ 45°. The inventors have designed an axial turbine according to the invention, in which β2 is ≥ 30°, and calculated the survival rate of eels that collide with the leading edge in the outer region of the leading edge according to the rules known from the prior art. The results were compared with the corresponding values of a comparable conventional axial turbine (where β2 isapproximately 0°). The survival rate of 0.61 m length eels colliding in the outer regionof the leading edge increased from 61.5% for a conventional axial turbine to 98.2% for an axial turbine according to the invention.27997 / HZTList of reference symbols 1hub2 blade3 leading edge4 outer edge5 leading end of the outer edge6 trailing end of the outer edge7 hub end of the leading edge8 runner ring

Claims

27997 / HZTPatent claims1. An axial turbine comprising a stationary runner ring (8) and a runnerrotatable about an axis and disposed in the stationary runner ring (8), and wherein the runner comprises a hub (1) and at least three blades (2) that are adjustable in pitch about blade rotational axes and wherein these blade rotational axes are perpendicular to the turbine axis and intersect ata point on the axis, and wherein each blade (2) comprises a leading edge (3) and an outer edge (4), and wherein the outer edges (4) each comprise a leading end (5) and a trailing end (6), and wherein the stationary runner ring (8) comprises a spherical region, and wherein the leading edges (3) are swept forward, and wherein the blades (2) are designed to be hanging, so that in a horizontal position of the blades (2) an axial shift of the outer edges (4) in a flow direction of a driving water is such that theleading ends (5) of the outer edges (4) are arranged within the spherical region of the stationary runner ring (8) in a pitch position of the blades (2),which corresponds to a maximum permitted degree of opening.

2. The axial turbine according to claim 1, wherein each blade (2) has a tipangle β2 of the leading edge (3) which is greater than or equal to 30°.

3. The axial turbine according to claim 1, wherein each blade (2) has a tipangle β2of the leading edge (3) which is greater than or equal to 45°.

4. Axial turbine according to any one of claims 1 to 3, wherein each blade (2)has a hub sided angle β1 of the leading edge (3) which is greater than or equal to 15°.

5. Axial turbine according to any one of claims 1 to 3, wherein each blade (2)has a hub sided angle β1 of the leading edge (3) which is greater than or equal to 20°.27997 / HZT6. The axial turbine according to any one of the preceding claims, whereinan edge radius of the leading edges (3) over an entire length of the leading edges (3) is at least 1.0% of the diameter of the runner.

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