PARTIAL SPLITTER VANE FOR REACTION HYDRAULIC TURBINE

Abstract: An elbow shaped draft tube (24) for a reaction hydraulic turbine has a splitter vane mounted within the draft tube that partially extends between 50 % and 80 % across the width of the draft tube to redirect flow about said elbow in the draft tube. The partial splitter vane (28) has opposing side edge surfaces spaced from the side walls of the draft tube to allow the peripheral flow to swirl around the splitter as it moves through the draft tube. The splitter vane does not result in any efficiency decrease for operating conditions below peak efficiency flow rates and still provides the full benefits at flow rates above the peak efficiency flow rate for a given head. The splitter vane results in much lower static and dynamic loads due to its smaller surface area and minimal blockage of the swirl component of the flow. A plurality of support posts (44) are embedded at one end in the draft tube and connected at the other end to position the splitter vane in non-contacting relation with the side walls of the draft tube.

Description: PARTIAL SPLITTER VANE FOR REACTION HYDRAULIC TURBINE Technical Field of the Invention The present invention relates to a reaction hydraulic turbine draft tube. In particular, the present invention relates to elbow type draft tubes having a splitter vane. Background of the Invention In a reaction hydraulic turbine, a draft tube is the portion of the flow passage between the exit of the turbine runner and the exit of the turbine. The purpose of the draft tube in a reaction hydraulic turbine is to recover a portion of the energy left in the flow at the runner exit. The draft tube outlet cross-sectional area is larger than that at the inlet. This results in typically lower outlet velocities than inlet velocities. It is desirable to minimize the kinetic energy left in the flow at the exit of the draft tube since most of this energy is lost when the flow exits the draft tube. Many draft tubes must turn the flow by 90 degrees or more, since the draft tube inlet flow is typically vertical and the outlet flow is typically horizontal. In small turbines the flow may be opposite. Such draft tubes are commonly known as elbow type draft tubes. One of the problems inherent in many previous draft tube designs is that the flow can separate from the profile of the draft tube as it is being redirected. This flow separation can result in a substantial loss in the efficiency of the turbine. Splitter vanes, sometimes called flow splitters, have been used in the past to improve the performance of poor draft tube designs. Poor performance is especially noticeable at operating points where the flow rate is greater than the flow rate at the peak efficiency point for a given head. The conventional splitter vane extends across the entire width of the draft tube and is anchored in the draft tube side walls. The splitter vane is located in the draft tube adjacent the elbow to force the water fluid passing through the draft tube to change direction. Such a splitter vane for an elbow shaped draft tube is disclosed in U.S. Patent 1 ,467,168 issued September 4, 1923 to Victor Kaplan. Alternatively, U.S. Patent 2,060,101 issued November 10, 1936 to Lewis Moody discloses mounting the flow splitter vane across the draft tube and anchoring the flow splitter to the side walls of the draft tube and a central pier extending longitudinally along the draft tube. While the use of flow splitter vanes improves performance, such flow splitter vanes do not facilitate the natural swirling flow of the water through the draft tube. The longitudinal extending piers further compound this problem. The flow at the exit of a turbine runner is by nature a typically swirling flow especially at flow rates below the flow rate corresponding to the peak efficiency for a given operating head. The use of a conventional splitter vane results in a decrease in draft tube efficiency for these part load conditions due to the resulting blockage of the swirl component of the flow. The conventional splitter vane is not feasible for large turbines since it results in a very large structure subject to very high static and dynamic loads due to the large surface area of the splitter vane extending across the entire width of the draft tube and impeding the natural swirl or vortex flow through the draft tube at flow rates below peak efficiency. There is a need for a draft tube having a flow splitter vane that does not result in any efficiency decrease for flow rates below peak efficiency flow rates and that still provides the full benefits at flow rates above the peak efficiency flow rate for a given head. SUMMARY OF THE INVENTION The present invention relates to a splitter vane mounted within an elbow shaped draft tube of a reaction hydraulic turbine that partially extends across the width of the draft tube to redirect flow about said elbow in the draft tube. The splitter vane has opposing side edge surfaces spaced from the side walls of the draft tube to permit swirl flow around the splitter vane within the draft tube. Such a splitter vane is referred to throughout the disclosure as a "partial splitter vane". The partial splitter vane of the present invention does not extend across the full width of the draft tube allowing the peripheral flow to swirl around the splitter as it moves through the draft tube. The partial splitter vane does not result in any efficiency decrease for these operating conditions below peak efficiency flow rates and still provides the full benefits at flow rates above the peak efficiency flow rate for a given head. The partial splitter vane is significantly smaller than a conventional splitter vane that extends across the entire width of the draft tube and this results in much lower static and dynamic loads due to its smaller surface area and minimal blockage of the swirl component of the flow by the partial splitter vane. This makes it feasible to use a partial splitter vane on large turbines as well as small turbines. In accordance with the present invention the splitter vane may extend across less than about 80% of the width of the draft tube. Preferably the width of the splitter vane extends between 50 and 80 percent of the width of the draft tube and has its opposing side edges spaced substantially the same distance from an adjacent one of the side walls of the draft tube. The opposing side edge surfaces of the splitter vane may diverge from one another in the direction of flow towards the outlet of the draft tube. Preferably, the draft tube includes a plurality of support posts embedded at one end in the draft tube and connected at the other end to position the splitter vane in non-contacting relation with the side walls of the draft tube. Preferably the support posts are mounted to a lower surface of the splitter vane. The support posts are surrounded by tubes shaped to minimize the effects of the posts on the flow within the draft tube. The draft tube in the preferably includes at least one pier adjacent the outlet extending into the draft tube. Preferably, the splitter vane further includes at least one pier receiving recess adapted to receive the pier and to support the splitter vane on the pier. In the preferred embodiment the splitter vane is offset across the width of, and to one side of, the draft tube. In accordance with one aspect of the present invention there is provided a draft tube for use in a turbine having a turbine runner. The draft tube comprises side walls having an inlet for positioning adjacent the turbine runner and an outlet defining a flow exit for the turbine. The side walls of the draft tube diverge in width between the inlet and the outlet. The draft tube has a curved elbow to position the outlet substantially perpendicular to the inlet. The draft tube has a splitter vane mounted within the draft tube extending about the elbow and partially extending across the width of the draft tube to redirect flow about said elbow in the draft tube. The splitter vane has opposing side edge surfaces spaced from the side walls to permit swirling flow around the splitter vane within the draft tube. BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the nature and objects of the present invention reference may be had, by way of example, to the following detailed description when taken in conjunction with the accompanying diagrammatic drawings wherein: Figure 1 is a side sectional view of a reaction hydraulic turbine including a draft tube and the partial flow splitter of the present invention; Figure 2 is a plan view of the partial flow splitter mounted within the draft tube; Figure 3 is an enlarged side sectional view illustrating the partial flow splitter mounted within the draft tube; Figure 4 is a plan view of the partial flow splitter; and, Figure 5 is a graph illustration the typical efficiency versus flow rate curve for a reaction hydraulic turbine at a given head. DETAILED DESCRIPTION OF EMBODIMENTS Referring to Figure 1 there is shown reaction hydraulic turbine 10. Turbine 10 includes a casing 12 throughwhich water enters the turbine 10. The water passes through stay vanes 14 and wicket gates 16 and past the turbine runner 18 mounted on a rotatable hub 20. The water passes from the turbine runner 18 to the inlet 22 of an elbow draft tube 24. Water flow is gradually directed to horizontal discharge outlet 26 of the draft tube 24. The draft tube 24 is usually constructed of a reinforced concrete and the upper part has a metal or cast plated covering. Located within the draft tube 24 adjacent the elbow of the draft tube, is a partial splitter vane 28. Referring to Figures 1 through 4, the partial splitter vane 28 is mounted within the draft tube 24, partially extending across the width of the draft tube 24, to redirect flow about the elbow in the draft tube 24. The splitter vane 28 has opposing side edge surfaces 30 that are spaced from the side walls 32 of the draft tube 24 by predetermined distances to permit swirling flow around the splitter vane 28 within the draft tube 24. The splitter vane 28 extends across less than about 80% of the width of the draft tube 24. In the preferred embodiment shown, the splitter vane 28 extends slightly more than 50% of the width of the draft tube 24. The splitter vane 28 has its opposed side edge surfaces 30 each spaced from the side walls 32 of the draft tube 24 so that the splitter vane 28 is offset across the width of the draft tube 24 as best seen in Figure 2. The side edge surfaces 30 are preferably rounded edges and preferably comprise piping. In Figures 2 and 4 the splitter vane 28 has diverging walls 30 that follow the divergence of the draft tube side walls 32. The splitter vane 28 is mounted on support posts 34 which have one end thereof 36 connected to and embedded in the lower concrete wall of the draft tube 24. The other end of the posts 36 pass through openings 38 in the splitter vane 28 to which the posts are welded at this end to the splitter vane 28. Further, the posts 34 are surrounded by tubes 46 which are shaped to minimize the resistance to flow within the draft tube 24. In the embodiment shown, the trailing edge 40 of the splitter vane 28 has two recessed apertures 42. The recessed apertures 42 are mounted to receive in mounting relationship therewith a corresponding concrete pier 44 extending from the draft tube 24. Referring to Figure 5, there is shown a graph of the efficiency of the turbine versus the flow rate for a given head. Curve 50 represents the partial splitter vane 28 of the present invention. Curve 60 represents a draft tube 24 without the use of a splitter vane. Curve 70 represents the use of a conventional splitter vane that would extend across the entire width of the draft tube 24. This graph illustrates that the partial splitter vane curve 50 has the advantages associated with the conventional splitter vanes at peak flow rates and has an improved efficiency over the use of a conventional splitter vane at flow rates below peak flow rates. This latter performance improvement is due to the partially splitter vane 24 being spaced from the side walls 32 of the draft tube 24 to allow the swirling flow within the draft tube to proceed through the draft tube 24 with reduced interference. It will be appreciated that alternative embodiments falling within the scope of the present invention may be apparent to those skilled in the art of refrigerator door construction and accordingly the present invention should not be limited to those embodiments herein described.

Claims: What is claimed is: 1. A reaction hydraulic turbine including a turbine runner and a draft tube, the draft tube having side walls defining an inlet adjacent the turbine runner and an outlet defining a flow exit for the turbine, the draft tube having an elbow to position the outlet substantially perpendicular to the inlet, the draft tube diverging in width between the inlet and the outlet, the improvement comprising a splitter vane mounted within the draft tube partially extending across the width of the draft tube to redirect flow about said elbow in the draft tube, and the splitter vane having opposing side edge surfaces spaced from the side walls to permit swirl flow around the splitter vane within the draft tube. 2. The reaction hydraulic turbine of claim 1 wherein splitter vane extends across less than about 80% of the width of the draft tube. 3. The reaction hydraulic turbine of claim 2 wherein the opposing side edge surfaces of the splitter vane diverge from one another in the direction of flow towards the outlet. 4. The reaction hydraulic turbine of claim 1 wherein the width of the splitter vane extends between 50 and 80 percent of the width of the draft tube and has its opposing side edges spaced substantially the same distance from an adjacent one of the side walls of the draft tube. 5. The reaction hydraulic turbine of claim 1 wherein the draft tube includes a plurality of support posts embedded at one end in the draft tube and connected at the other end to position the splitter vane in non-contacting relation with the side walls of the draft tube. 6. The reaction hydraulic turbine of claim 5 wherein the support posts are surrounded by tubes shaped to minimize the effects of the posts on the flow within the draft tube. 7. The reaction hydraulic turbine of claim 1 wherein the draft tube includes at least one pier adjacent the outlet extending into the draft tube, the draft tube further including a plurality of support posts embedded at one end in the draft tube and connected at the other end to position the splitter vane in the draft tube, the splitter vane further including at least one pier receiving recess adapted to receive the pier and to support the splitter vane on the pier. 8. The reaction hydraulic turbine of claim 7 wherein the support posts are surrounded by tubes shaped to minimize the effects of the posts on the flow within the draft tube. 9. The reaction hydraulic turbine of claim 5 wherein the support posts are mounted to a lower surface of the splitter vane. 10. The reaction hydraulic turbine of claim 8 wherein the support posts are mounted to a lower surface of the splitter vane. 11. The reaction hydraulic turbine of claim 1 wherein the splitter vane is mounted offset across the width of the draft tube. 12. A draft tube for use in a turbine having a turbine runner, the draft tube comprising: side walls having an inlet for positioning adjacent the turbine runner and an outlet defining a flow exit for the turbine, the side walls of the draft tube diverging in width between the inlet and the outlet; a curved elbow to position the outlet substantially perpendicular to the inlet; and, a splitter vane mounted within the draft tube extending about the elbow and partially extending across the width of the draft tube to redirect flow about said elbow in the draft tube, the splitter vane having opposing side edge surfaces spaced from the side walls to permit swirling flow around the splitter vane within the draft tube. 13. The draft tube of claim 12 wherein splitter vane extends across less than about 80% of the width of the draft tube. 14. The draft tube of claim 13 wherein the opposing side edge surfaces of the splitter vane diverge from one another in the direction of flow towards the outlet. 15. The draft tube of claim 12 wherein the width of the splitter vane extends between 50 and 80 percent of the width of the draft tube. 16. The draft tube of claim 12 wherein the draft tube includes a plurality of support posts embedded at one end in the draft tube and connected at the other end to position the splitter vane in non-contacting relation with the walls of the draft tube. 17. The draft tube of claim 16 wherein the support posts are surrounded by tubes shaped to minimize the effects of the posts on the flow within the draft tube. 18. The draft tube of claim 12 wherein the draft tube includes at least one pier adjacent the outlet extending into the draft tube, the draft tube further including a plurality of support posts embedded at one end in the draft tube and connected at the other end to position the splitter vane in the draft tube, the splitter vane further including at least one pier receiving recess adapted to receive the pier and to support the splitter vane on the pier. 19. The draft tube of claim 18 wherein the support posts are surrounded by tubes shaped to minimize the effects of the posts on the flow within the draft tube. 20. The draft tube of claim 16 wherein the support posts are mounted to a lower surface of the splitter vane. 21. The draft tube of claim 19 wherein the support posts are mounted to a lower surface of the splitter vane. 22. The draft tube of claim 12 wherein the splitter vane is offset across the width of the draft tube.

Inventors: ANGERER CHRISTIAN KARL, COULSON STUART THOMAS, NICHTAWITZ ALOIS, ANGERER, CHRISTIAN, KARL, COULSON, STUART, THOMAS, NICHTAWITZ, ALOIS
Applicants: ANGERER CHRISTIAN KARL, COULSON STUART THOMAS, GEN ELECTRIC CANADA, NICHTAWITZ ALOIS, VA TECH VOES MCE GMBH & CO, ANGERER, CHRISTIAN, KARL, COULSON, STUART, THOMAS, GENERAL ELECTRIC CANADA, INC., NICHTAWITZ, ALOIS, VA TECH VOES MCE GMBH & CO.
Application year: 2000
Main classification: F03B11
IPC codes: F03B3, F03B11, F03B13