Title of Invention

"BENT DRAFT TUBE OF HYDRAULIC MACHINERY"

Abstract

A bent draft tube of a hydraulic machinery, the bent draft tube connecting runner of the hydraulic machinery for converting a position energy of flowing water to a rotation energy and a downstream tailrace. The bent draft tube includes a bent portion connected to an exit of the runner, and an enlarging portion directed horizontally and connected to the bent portion, with a sectional area increasing toward a downstream side. A lowest point of an inner side of the bent portion of the bent draft tube among lowest points in a flow path of the bent draft tube is positioned on the enlarging portion side from a section including a closes point to a line of a rotary shaft of the hydraulic machinery. Fig. 1

Full Text

TITLE OF THE INVENTION BENT DRAFT TUBE OF HYDRAULIC MACHINERY CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2006-117659, filed on April 21, 2006; the entire contents of which are incorporated herein by reference. BACKGROUND OF THE INVENTION Field of the Invention [0002] The present invention relates to a bent draft tube of a hydraulic machinery. Description of the Background [0003] A bent draft tube of a hydraulic machinery has functions for leading flowing water from a runner exit to a tailrace and effectively utilizing a position energy of the flowing water at the runner exit, for simultaneously commutating the flow by enlarging slowly the flowing water path and reducing the flow speed, and thereby for efficiently converting a speed energy at the runner exit to a pressure energy. [0004] Fig. 9 is a conceptual diagram of a bent draft tube of a general Francis pump-turbine. As shown in Fig. 9, the flowing water from runner 11 passes through an upper draft 12 and a bent portion inlet section 13, and the flowing direction of the water is changed by a bent portion 14, and then the flowing water is decelerated by an enlarging portion 15, and thus the pressure is recovered. The enlarging portion 15 is formed to incline at a swing-up angle y to the side of a center line X of the hydraulic machinery from a lowest point 16 in the flow path of the draft tube in the horizontal direction so as to increase the sectional area toward the downstream side. Hereinafter, a section obtained by cutting a part of the draft tube along the surface perpendicular to a direction of an axial line (a center line S) of a tube path of the draft tube will be referred to as a "section" at the part. In Fig. 9, Y indicates a line of a rotary shaft of the hydraulic machinery and F indicates a depth of the draft tube. [0005] When the sectional area of the flow path of the enlarging portion 15 is wide, there is a case that a center pear for dividing the flow from the neighborhood of the enlarging portion 15 is installed, and the component in the rotational direction of the flow of flowing water from the runner is canceled effectively, and a flow commutation effect due to the prevention of a sudden increase in the sectional area is added, and thus the pressure may be recovered efficiently. [0006] There is a bent draft tube available such that the area of the section in the vertical direction within at least a predetermined range on the upstream side from the boundary of the bent portion among the upper parts of the draft tube increases as the distance from the runner exit gets longer, and a width in a longitudinal direction of the section in the vertical direction within the predetermined range is kept constant, and in the bent portion of the draft tube, a width in a horizontal direction of the section in the vertical direction is made wider than a width in the longitudinal direction thereof, and the loss in the bent portion is reduced, and the earth excavating amount is reduced (for example, refer to Patent Document 1). [0007] Here, assuming that a part of the draft tube is cut in a direction vertical to the axial line of the tube path of the draft tube, a section thus obtained is called "a section in the vertical direction" at the part of the draft tube. Further, assuming that a straight line is obtained which is a cross line of a plane including the section in the vertical direction of the draft tube and a plane including the axial line of the draft tube, a direction of the straight line is called as "a longitudinal direction" of the section in the vertical direction, and a direction perpendicular to the longitudinal direction is called as "a horizontal direction" of the section in the vertical direction. [0008] Generally, the draft tube is laid under the ground, so that it is necessary to excavate the ground according to the shape of the draft tube. In the bent draft tube of the hydraulic machinery with the enlarging portion 15 having a swing-up angle y on the side of the center line X of the hydraulic machinery, the earth excavating amount may be small. Further, the draft tube depth F is designed to be shallow, and thus the earth excavating amount may be reduced. Further there is a bent draft tube available such that the operation space and the excavating amount between a draft tube liner and a foundation concrete floor portion are reduced and in accordance with shortening of the construction work period, the construction cost is suppressed low (for example, refer to Patent Document 2). Patent Document 1: Japanese Patent Disclosure (Kokai) 2001-140741 Patent Document 2: Japanese Patent Disclosure (Kokai) 2002-168171 [0009] However, in the bent draft tube of the hydraulic machinery, aiming at a high performance, the draft tube is often designed to be deep, though at this time, the earth excavating amount is increased. When the bent draft tube is designed to be shallow, the pressure recovery by the bent draft tube cannot be realized efficiently, and the performance by the bent draft tube is reduced. [0010] Fig. 10 is a schematic diagram showing a flow mechanism in the bent draft tube. As shown in Fig. 10, when the bent draft tube is made shallow, a water flowing direction indicated by arrows 17 is changed suddenly in the neighborhood of the bent portion 14 exit, so that in the neighborhood of the top of the bent portion 14 exit and the top of the enlarging portion 15, a flow separation 18 is caused. Therefore, the speed energy cannot be collected efficiently at the runner exit, and as a result, a reduction in the performance of the bent draft tube is caused. This bad influence causes a remarkable reduction in the performance at a time of an overload operation at a high flow rate, compared with at a time of a partial load operation at a low flow rate. SUMMARY OF THE INVENTION [0011] The present invention is developed to solve the problem aforementioned, and is intended to provide a bent draft tube of a hydraulic machinery capable of suppressing a reduction in the performance at a time of an overload operation of a hydraulic machinery. [0012] According to an aspect of the present invention, there is provided a bent draft tube of a hydraulic machinery, the bent draft tube connecting runner of the hydraulic machinery for converting a position energy of flowing water to a rotation energy and a downstream tailrace. The bent draft tube includes a bent portion connected to an exit of the runner, and an enlarging portion directed horizontally and connected to the bent portion, with a sectional area increasing toward a downstream side. A lowest point of an inner side of the bent portion of the bent draft tube among lowest points in a flow path of the bent draft tube is positioned on the enlarging portion side from a section including a closest point to a line of a rotary shaft of the hydraulic machinery. [0013] According to the present invention, the lowest point of an inner side of the bent portion of the bent draft tube is defined as positioned on the enlarging portion side from the lowest point inside the flow path of the draft tube, and accordingly the draft tube is structured such that the curvature of an inner side of the bent portion further extends toward the enlarging portion. Therefore, the flow separation easily caused on the top of the draft tube can be suppressed, and the reduction in the performance at the time of the overload operation can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS [0014] A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: Fig. 1 is a conceptual diagram of a bent draft tube of a hydraulic machinery according to a first embodiment of the present invention; Fig. 2 is a characteristic diagram of the loss of the bent draft tube of the first embodiment of the present invention; Fig. 3 is a conceptual diagram of a bent draft tube of a hydraulic machinery according to a second embodiment of the present invention; Fig. 3A is a diagram showing the loss inside the bent draft tube of the second embodiment of the present invention; Fig. 4 is a characteristic diagram of the loss of the bent draft tube of the second embodiment of the present invention; Fig. 5 is a conceptual diagram of a bent draft tube of a hydraulic machinery according to a third embodiment of the present invention; Fig. 6 is a characteristic diagram of the loss of the bent draft tube of the third embodiment of the present invention; Fig. 7 is a conceptual diagram of a bent draft tube of a hydraulic machinery according to a fourth embodiment of the present invention; Fig. 8 is a characteristic diagram of the loss of the bent draft tube of the fourth embodiment of the present invention; Fig. 9 is a conceptual diagram of a bent draft tube of a Francis pump-turbine; and Fig. 10 is a schematic view of the flow mechanism in the draft tube. DETAILED DESCRIPTION OF THE INVENTION [0015] Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, the embodiments of this invention will be described below. [0016] (First embodiment) Fig. 1 is a conceptual diagram of a bent draft tube of a hydraulic machinery according to a first embodiment of the present invention. In Fig. 1, an illustration of a hydraulic machiner*y which is a water turbine or a pump-turbine is omitted. The upper draft 12 is constructed so that the sectional area thereof increases as the distance from the runner exit gets longer. Further, the enlarging portion 15 is constructed so that the lowest point 16 in the flow path of the draft tube is flat in the horizontal direction. Namely, among the lowest points 16 in the flow path of the draft tube, a closest point 16a to the line Y of the rotary shaft of the hydraulic machinery and subsequent points 16 (on the downstream side) are flat in the horizontal direction. [0017] On the other hand, the inner side of the bent portion 14 of the draft tube is expanded in the downstream side direction with predetermined swing-up angle toward the central line X of the hydraulic machinery. And it is constructed so that a lowest point 19 of the inner side of the bent portion 14 of the draft tube is located on the side of the enlarging portion 15 from the section including a lowest point 16a in the flow path of the draft tube which is closest to the line Y of the rotary shaft of the hydraulic machinery. [0018] Now, assuming that the distance from the line Y of the rotary shaft of the hydraulic machinery to the lowest point 16a inside the flow path of the draft tube as Le, and the distance from the line Y of the rotary shaft line Y of the hydraulic machinery to the lowest point 19 of the inner side of the bent portion of the draft tube as Lemin, the characteristic shown in Fig. 2 is obtained as a relationship between a loss of the bent draft tube and (Lemin-Le)/Le. [0019] As shown in Fig. 2, it is found that the loss of the bent draft tube of the hydraulic machinery is small within the range of (Lemin-Le)/Le from 0.10 to 0.85. Therefore, the position of the lowest point 19 of the inner side of the bent portion of the draft tube is decided so that 0.10 is held. [0020] According to the first embodiment, the lowest point 19 of the inner side of the bent portion of the draft tube is positioned on the side of the enlarging portion 15 from the lowest point 16a inside the flow path of the draft tube. Accordingly, the bent draft tube is constructed so that the curvature of the inner side of the bent portion 14 further extends toward the enlarging portion 15. Therefore, the flow separation easily caused on the top of the inside of the draft tube can be suppressed, and the reduction in the performance at the time of the overload operation can be suppressed. [0021] (Second embodiment) Fig. 3 is a conceptual diagram of a bent draft tube of a hydraulic machinery according to a second embodiment of the present invention. In Fig. 3, the illustration of the hydraulic machinery which is a water turbine or a pump-turbine is omitted. The second embodiment is characterized in that the bent draft tube has a straight line portion 20 defined by an extension line of the side of the upper draft 12 portion in the shape of the inner side of the bent portion 14 in the first embodiment shown in Fig. 1. [0022] In Fig. 3, the upper draft 12 is constructed so that the sectional area thereof increases as the distance from the runner exit gets longer. Further, the enlarging portion 15 is constructed so that the lowest point 16 in the flow path of the draft tube is flat in the horizontal direction. Further, the inner side of the bent portion of the draft tube is expanded in the downstream side direction with a predetermined swing-up angle toward the central line X of the hydraulic machinery. And it is constructed so that the lowest point 19 of the inner side of the bent portion of the draft tube is located on the side of the enlarging portion 15 from the section including the lowest point 16a in the flow path of the draft tube which is closest to the line Y of the rotary shaft of the hydraulic machinery. [0023] In such an inside shape of the bent portion 14, when taking a coordinate system in which the inlet section 13 of the bent portion 14 is taken as 0° and the section including the closest point 16a to the rotary shaft Y of the hydraulic machinery among the lowest points in the flow path of the draft tube forms an angle of 90°, the bent portion 14 is composed of with the shape having a straight line portion 20 defined as an extension line of the side of the upper draft 12 portion up to the section from 40° to 50° along the section of the bent portion 14 of the draft tube. The reason is that the water flowing through the bent portion 14 slowly expands the sectional area thereof in the flow direction, and thus the pressure is recovered, though the flow path is bent, and thus the flowing direction is changed and a loss is caused, so that the loss is intended to be reduced. [0024] Fig. 3A is a diagram showing the loss inside the bent draft tube of the second embodiment of the present invention. In Fig. 3A, the upper draft 12 is of so-called a truncated cone shape and is constructed so that the sectional area thereof increases as the distance from the runner exit gets longer. The section of the enlarging portion 15 is of rectangular shape, and the sectional area thereof increases toward a downstream side. The bent portion 14 is a portion onverting the shape from the truncated cone shape section of the upper draft 12 to rectangular shape section of the enlarging portion 15. In Fig. 3A, references R, Y and G shows that the loss inside the draft tube are large, intermediate and low, respectively. [0025] Fig. 4 is a characteristic diagram showing the loss of the bent draft tube of the hydraulic machinery when the section from the 0° position of the bent portion 14 to the lowest point 19 of the inner side of the bent portion 14 of the draft tube is formed in a straight line shape. As shown in Fig. 4, it is found that when within the range from the 40° position of the bent portion 14 to the 50° position thereof, the inside of the bent portion 14 is formed in a straight line shape, and thus the separation of the flow at this portion is suppressed and the loss can be reduced Further, in the draft tube with a shape having the straight line portion up to a position beyond the 50° position of the bent portion 14, the curvature of the inner side of the bent portion becomes excessively large, so that in the straight line portion and subsequent portion, the separation of the flow is caused easily. [0026] On the other hand, at each part of the draft tube from the inlet section 13 of the bent portion 14, assuming an angle formed between the straight line portion 20 of the inner side of the bent portion 14 and a perpendicular line to the central line X of the hydraulic machinery as a , an angle formed between a straight line connecting between the inlet section 13 of the bent portion 14 and the section at an angle of 5° with the inlet section 13 of the bent portion 14 with respect to a central line S (described below) of the draft tube and the perpendicular line to the central line X of the hydraulic machinery as /3 , the draft tube shape is decided as a. > /3 . Here, the central line S of the draft tube is obtained by connecting the center points of gravity of the sections obtained by cutting along the face perpendicular to the direction of the axial line (central line S) of the tube path of the bent draft tube. By doing this, the flowing direction not only on the inner peripheral side of the bent portion 14 but also on the outer peripheral side thereof is changed slowly. Therefore, the collision loss on the outer peripheral side of the bent portion 14 can be reduced, and the reduction in the performance at the time of the overload operation can be suppressed. [0027] According to the second embodiment, the portion of the inner side of the bent portion 14 within the predetermined range is formed in a straight line shape, and the separation is suppressed, and thereby the loss is reduced. So that the flow separation at the time of the overload operation can be suppressed, and the reduction in the performance at time of the overload operation of the bent draft tube of the hydraulic machinery can be suppressed. Further, the flowing direction not only on the inner peripheral side of the bent portion 14 but also on the outer peripheral side thereof is changed slowly. Thus the collision loss on the outer peripheral side of the bent portion 14 can be reduced, and the reduction in the hydraulic performance at the time of the overload operation can be suppressed. [0028] (Third embodiment) Fig. 5 is a conceptual diagram of a bent draft tube of a hydraulic machinery according to a third embodiment of the present invention. In Fig. 5, the illustration of the hydraulic machinery which is a water turbine or a pump-turbine is omitted. The third embodiment is characterized in that an inner side curvature p i of the bent portion 14, -an outer side curvature p o of the bent portion 14 and a flow path height He of the section of the bent portion 14 are kept in a predetermined relationship, the flowing direction of the water on the outer peripheral side of the bent portion 14 is slowly converted, and thereby the collision loss is reduced on the outer peripheral side of the bent portion 14 in the first embodiment or the second embodiment shown in Fig. 1. or Fig. 3. [0029] In Fig. 5, it is assumed that the inner side curvature of the bent portion 14 is p i, the outer side curvature of the bent portion 14 is p o, and the flow path height of the section of the bent portion 14 is He. Fig. 6 is a characteristic diagram showing the relationship between the loss of the bent draft tube of the hydraulic machinery and (I/(pi. + He) } / (I/p o) . As shown in Fig. 6, it is found that the loss of the bent draft tube of the hydraulic machinery is small within the range of {l/(pi + He)}/(l/po) from 1.5 to 2.4. Further, when the loss is beyond the range, if the value is smaller than the lower limit, the collision loss increases and if the value is larger than the upper limit, the pressure recovery rate is degraded, so that in either case, the loss is great. [0030] Therefore, so that 1.5 ^ {l/(pi + He)}/(l/po) ^ 2.4 is held, the shape of the bent portion 14 of the bent draft tube is decided. By doing this, the inner side shape of the bent portion is in a shape inclined toward the outer peripheral side in each section of the straight portion and subsequent portion. [0031] According to the third embodiment, the flowing direction on the outer peripheral side is converted slowly, so that the collision loss on the outer peripheral side of the bent portion can be reduced. Therefore, the reduction in the hydraulic performance at the time of the overload operation can be suppressed. [0032] (Fourth embodiment) Fig. 7 is a conceptual diagram of a bent draft tube of a hydraulic machinery according to a fourth embodiment of the present invention. In Fig. 7, the illustration of the hydraulic machinery which is a water turbine or a pump-turbine is omitted. The fourth embodiment is characterized in that, a flow path height Heo of the bent draft tube at the 90° position of the bent portion 14 is specified to be set within a predetermined range in any of the first to third embodiments. [0033] Assuming that the draft tube depth is F and the flow path height of the draft tube at the 90° position of the bent portion 14 (that is the closest point 16a to the rotary shaft Y of the hydraulic machinery among the lowest points in the flow path of the draft tube) is Heo, the height Heo of the flow path of the draft tube is decided so as to set Heo/F within a predetermined range. [0034] Fig. 8 is a characteristic diagram showing the relationship between the loss of the bent draft tube of the hydraulic machinery and Heo/F. As shown in Fig, 8, it is found that the loss of the bent draft tube of the hydraulic machinery is small within the range of Heo/F from 0.2 to 0.3. [0035] According to the fourth embodiment, the height Heo of the flow path of the draft tube at the position of the closest point 16a (the 90° position of the bent portion 14) to the rotary shaft Y of the hydraulic machinery among the lowest points in the flow path of the draft tube is specified within the predetermined range, so that the loss of the bent draft tube of the hydraulic machinery can be reduced. [0036] Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. We Claim: 1. A bent draft tube of a hydraulic machinery, said bent draft tube connecting runner of said hydraulic machinery for converting a position energy of flowing water to a rotation energy and a downstream tailrace, said bent draft tube comprising: a bent portion (14) connected to an exit of said runner; and an enlarging portion (15) directed horizontally and connected to said bent portion (14) , with a sectional area increasing toward a downstream side; and a lowest point (16) of an inner side of said bent portion (14) of said bent draft tube among lowest points (16) in a flow path of said bent draft tube being positioned on said enlarging portion (15) side from a section including a closest point (16a) to a line of a rotary shaft of said hydraulic machinery. 2. The bent draft tube a hydraulic machinery as claimed in claim 1, wherein: a shape of said draft tube is decided such that ratio of difference of Lemin and Le to Le is within 0.10 and 0.85, assuming that a distance from said line of said rotary shaft of said hydraulic machinery to a nearest point to said line of said rotary shaft among said lowest points (16a) inside said flow path of said draft tube is Le and a distance from said line of said rotary shaft of said hydraulic machinery to said lowest point (19) of said inner side of said bent portion (14) of said bent draft tube is Lemin. 3. The bent draft tube of said hydraulic machinery as claimed in claim 1, wherein: said bent portion (14) is provided with a shape of said inner side thereof having a straight line portion (20) defined as an extension line of a side of an upper draft portion (12) up to a section from 40° to 50° along a section of said bent portion (14) of said bent draft tube, taking a coordinate system in which an inlet section (13) of said bent portion (14) is taken as an angle of 0° and said section including said closest point (16a) to said rotary shaft of said hydraulic machinery among said lowest points in said flow path of said bent draft tube is taken as an angle of 90°. 4. The bent draft tube of said hydraulic machinery as claimed in claim 3, wherein: a shape of said bent draft tube is decided such that a is greater than ß at each said straight line portion (20) of said bent draft tube from said inlet section (13) of said bent portion (14), assuming an angle formed between said straight line portion of said inner side of said bent portion (14) and a perpendicular line to a central line of said hydraulic machinery as a, and an angle formed between a straight line connecting said inlet section (13) of said bent portion (14) and a section at angle of 5° with said inlet section (13) of said bent portion (14) with respect to a central line of said bent draft tube and said perpendicular line to said central line of said hydraulic machinery as ß; here, said central line of said bent draft tube is obtained by connecting center points of gravity of sections obtained by cutting along a face perpendicular to said direction of said axial line of a tube path of said bent draft tube. 5. The bent draft tube of said hydraulic machinery as claimed in any one of claims 1 to 4, wherein: a shape of said draft tube is decided such that ratio inverse of sum of pi, and He to inverse of po, is within 1.5 and 2.4 assuming that an inner side curvature of said bent portion (14) is pi, an outer side curvature of said bent portion (14) is po, and a flow path height of a section of said bent portion (14) is He. 6. The bent draft tube of said hydraulic machinery as claimed in any one of claim 1 to 4, wherein: a shape of said bent draft tube is decided such that ratio of Heo to F is within 0.2 and 0.3 assuming that a draft tube depth is F and a flow path height of said bent draft tube at a section including said closest point (16a) to said rotary shaft of said hydraulic machinery among said lowest points in said flow path of said draft tube is Heo.

Documents:

864-del-2007-Abstract-(22-07-2011).pdf

864-del-2007-abstract.pdf

864-del-2007-Claims-(22-07-2011).pdf

864-del-2007-claims.pdf

864-del-2007-Correspodence Others-(22-07-2011).pdf

864-del-2007-correspodence-others.pdf

864-del-2007-correspondence-others-1.pdf

864-del-2007-description (complete).pdf

864-del-2007-Drawings-(22-07-2011).pdf

864-del-2007-drawings.pdf

864-del-2007-form-1.pdf

864-del-2007-form-18.pdf

864-del-2007-form-2.pdf

864-del-2007-Form-3-(22-07-2011).pdf

864-del-2007-form-3.pdf

864-del-2007-form-5.pdf

864-del-2007-GPA-(22-07-2011).pdf