The comparative analysis of model and prototype test results of Bulb turbine

Transcription

1 IOP Conference Series: Earth and Environmental Science The comparative analysis of model and prototype test results of Bulb turbine To cite this article: M Benišek et al 2010 IOP Conf. Ser.: Earth Environ. Sci Related content - Bulb turbine operating at medium head: XIA JIANG case study F Loiseau, C Desrats, P Petit et al. - Experiences with the hydraulic design of the high specific speed Francis turbine J Obrovsky and J Zouhar - Investigation of free discharge through the hydro units of high head Francis turbine I Kuznetsov, A Zakharov, G Orekhov et al. View the article online for updates and enhancements. This content was downloaded from IP address on 12/09/2018 at 19:51

2 The comparative analysis of model and prototype test results of Bulb turbine 1. Introduction M Benišek 1, I Božić 1 and B Ignjatović 2 1 Faculty of Mechanical Engineering, Belgrade University Kraljice Marije 16, Belgrade, 11000, Serbia 2 Hydropower Plant Djerdap Pop Stojanova 2, Belgrade, 11000, Serbia mbenisek@mas.bg.ac.rs Abstract. This paper presents the problem of the hydropower plant oblique water inflow and its influence on the turbines operation. Oblique water inflow on the low head hydropower plant with bulb turbines influences turbine characteristics. The characteristics change occurs due to swirl incidence in the turbine inlet which spreads to the guide vanes inlet. Downstream, the flow conditions change is caused in the turbine runner in relation to the flow conditions without swirl inflow. Special attention is paid to the phenomenon of swirl flow incidence in the turbine conduit. With the aim of presenting and analyzing the oblique water inflow consequences on the hydropower plant operation, the existing turbine model tests results, performed in the laboratories, and the in situ prototype testing results have been used. The units on the Serbian side of HPP Djerdap 2 operate under the influence of oblique water inflow. This operation condition is revealed by qualitative observation during unit operation start. However, the oblique water inflow qualitative influence on the turbine characteristics is determined during the guarantee and complex test on unit A5 [1]. The hydraulic tests on the complete hydropower plant model are performed due to obtaining visual oblique water inflow sketch during different discharges and closed and opened overflow gates. а) b) Fig. 1 The visual flow obtained during hydraulic HPP model tests: a) all overflow gates are closed, b) all overflow gates are opened 3 The flow sketch during the closed overflow gates and HPP discharge Q E = 6400 m s and upstream water level GV = 39, 60 m is shown on Fig. 1a. The flow sketch during the opened overflow gates and HPP 3 discharge Q E = 3200 m s and upstream water level GV = 40,10 m is shown on Fig. 1a. c 2010 Ltd 1

3 The surface flows are designated by solid lines and the flows near the river bottom are designated by dash lines. When the overflow gates are closed, dead water occurs in front of the turbine gates and it causes flow turns with bigger angles in relation to the unit axis. This phenomenon is called oblique water inflow. When the overflow gates are opened flow conditions are better because there are not dead water and an oblique water inflow. It is clear that this case could not appear during normal HPP operation. Similar tests are performed due to finding solution for neutralizing oblique water inflow [3]. The oblique water inflow with angle δ (Fig. 2) causes contrariwise swirl flow incidence in the turbine conduit in relation to the runner rotation direction, and in that case it produces circumferential velocity component Δ c in the guide vanes inlet. u Fig. 2 Swirl flow in the turbine conduit as the HPP oblique water inflow consequence а) b) Fig. 3 The combinatory link of the runner and the guide vanes: a) velocity triangle for operation point without swirl (A) and with swirl (E), b) propeller characteristics for A and E The appearance of the circumferential velocity components Δ cu with the direction shown in Fig. 3a requests greater guide vanes opening α than model test guide vanes opening α. In cases of swirl flow (dash line) and without swirl flow (solid line) the propeller characteristics (the runner blades opening is constant β = const ) are shown in Fig. 3b. The diagrams α = f ( Q) are equal in both cases. The point A is equivalent to the turbine optimal efficiency in the operation without swirl, and the point E is equivalent to the turbine efficiency in the operation with swirl inflow. In Fig. 3a, there are relevant guide vanes openings for operating points A and E. If the turbine operates with ( β, α ) during the swirl flow condition and discharge Q A efficiency is η ha, and if the link is ( β, α ) and discharge is Q E, efficiency will be h E. In case of the axial water inflow to guide vanes, the turbine operates with the optimal efficiency ηh A and discharge Q A and if the link is ( β, α ) and discharge is Q E, efficiency will be η he. The flow determination for the runner η 2

4 representative cylindrical section m m (Fig. 3а and 3b) is performed due to obtaining the absolute velocity component Δ c in the runner inlet and its relation to the guide vanes opening during operation with and u without turbine inlet swirl. The greater values of the absolute velocity component Δ cu in the runner inlet for representative m m are determined by the flow calculations [4] and [5]. The relations Δ c = f ( Q H) and ( ) Δ c = f H Q are shown in Fig. 4a and 4b. u0, u0, а) b) Fig. 4 Increasing of the absolute velocity component Δ c for the bulb turbine in HPP Djerdap 2: а) Δ c = f ( Q H), b) Δ c = f ( H Q) u0, u u0, It will be possible to determine the corrected guide vanes opening α cor regarding the absolute velocity component Δ cu increased values [4]. In this paper special attention is given to the comparative analysis of the bulb turbine model and prototype tests results. The existing bulb turbine of HPP Djerdap 2 model tests were performed in: LMZ Laboratory in Saint Petersburg in 1980 with the model diameter D = 460mm, Laboratory of Hydraulic Machinery-EPFL Lausanne, in 2003 with the model diameter DM = 340mm. Tests are performed with the aim of comparing two turbine models: the Romanian revitalized one for HPP Portile de Fier and the Serbian existing one for HPP Djerdap 2. The models tests results are recalculated to the prototype diameter D = 7,5m. P The prototype of the bulb turbine with diameter DP = 7,5m was tested in HPP Djerdap 2 during the guarantee and complex unit A5 tests from 1986 till These measurements were done by INDEX method for three heads H = 10 m, 8, 45m and 4,8m. The unit A5 is situated in the middle of hydropower plant and it is under the influence of oblique water inflow. Measurements in the laboratories LMZ and LMH were performed with complete bulb turbine models including the conduits and draft tubes, which are geometrically similar to the prototype. These models are built into the test rigs with the regular coaxial inflow conditions, and there is an oblique water inflow during measurements in situ for unit A5. With the aim of presenting and analyzing the oblique water inflow consequences on the hydropower plant operation, the existing turbine model and prototype testing results are used and compared for the heads H = 10 m, 8, 45m and 4,8m. 2. The cam curves β = f ( α, H ) determination after the bulb turbine model and existing prototype tests The cam curves β = f ( α, H ) of HPP Djerdap 2 bulb turbines are determined for all tests and the M 3

5 following heads H = 10 m, 8, 45m and 4,8m : model tests in laboratories LMZ and LMH and unit A5 prototype test in situ. Model testing results are recalculated to the prototype with diameter D = 7, 5m. Also, the model testing results are used for determination runner β and guide vanes α opening angles relations, whereas the heads are recalculated from the relevant model hill chart. MF LMZ In table 1 there are values β, α and H for all combinatory links: β = f ( α, H ), β = f ( α, H ) LMH and β = f ( α, H ), with: o o o o o o o β = 10, 5,0,5,10,15,20 - runner blades opening, H = 10 m, 8, 45m and 4,8m - net heads, MF α - guide vanes opening determined in situ during an oblique water inflow, LMZ α - guide vanes opening determined model test in LMZ, LMH α - guide vanes opening determined model test in LMH. Table 1 The combinatory links determined in all three cases in: HPP Djerdap 2, LMZ and LMH β H MF α LMZ α LMH α LMZ Δα [ ] [m] [ ] [ ] [ ] [ ] [ ] ,5 29,0 30,0 4,5 3, ,0 36,8 37,1 4,2 3, ,5 42,4 44,0 5,1 3, ,0 47,6 50,9 5,4 2,1-10 8,45 38,0 32,2 34,2 5,8 3,8-5 8,45 46,2 39,6 40,0 6,6 6,2 0 8,45 52,8 45,2 46,3 7,6 6,5 5 8,45 59,3 50,9 53,2 8,4 6,1 10 8,45 65,0 58,4 62,1 6,6 2,9 15 8,45 72,0 65,7 75,0 6,3-3,0-10 4,8 42,8 41,5 41,8 1,3 1,0-5 4,8 53,5 49,6 51,7 3,9 1,8 0 4,8 61,2 56,4 57,9 4,8 3,3 5 4,8 68,0 62,9 65,8 5,1 2,2 10 4,8 75,0 70,5 74,6 4,5 0,4 P Δα LMH The deviations of guide vanes opening during the oblique water inflow α and α LMH LMZ MF LMZ LMH MF LMH ( Δ α = α α and Δ α = α α ) are given in table 1. LMZ MF α and laboratories model tests 3. Determination of efficiency η h = f ( QH, ) relations for the recalculated model tests results and the prototype test results The hydraulic efficiencies are determined for the relevant combinatory link operation β = f ( α, H ) during the prototype test, the model test in laboratory LMZ and the model test in laboratory LMH, where models MF LMZ efficiencies are recalculated on the prototype values. The efficiency values η h, η h and η LMH h for heads H = 10 m, 8, 45m and 4,8m are shown in figures 8, 9 and 10. The efficiency values differences of The prototype and recalculated model testing results LMZ MF LMZ LMH MF LMH Δ ηh = ηh ηh and Δ ηh = ηh ηh are minor and within the measuring error limits. Determination of the hydraulic characteristics by INDEX method is the main reason of such good values consistency. The method is relative because Winter-Kennedy discharge coefficient is determined by model testing results recalculation. Winter-Kennedy discharge coefficient of the prototype is determined by LMZ model testing results recalculation. (In the prototype hydraulic testing period there were only LMZ testing results.) 4

6 Because of the above mentioned the discharges, the efficiencies and the impeller mechanical powers have relative values. In case of HPP oblique water inflow condition, when there is no similarity between the model and the prototype, only combinatory link with maximum efficiency determination is reliable η h MF [-] H=10 m H=8,45 m H=4,8 m Q MF [m 3 /s] Fig. 8 Efficiency, discharge and head relations determined by INDEX method in situ on unit A η h LMZ [-] H=10 m H=8,45 m H=4,8 m Q LMZ [m 3 /s] Fig. 9 Efficiency, discharge and head relations determined by recalculation of LMZ model testing values η h LMH [-] H=10 m H=8,45 m H=4,8 m Q LMH [m 3 /s] Fig. 10 Efficiency, discharge and head relations determined by recalculation of LMH model testing values 5

7 The impeller mechanical power values are determined for relevant combinatory link operation β = f ( α, H ) during the prototype test, the model test in laboratory LMZ and the model test in laboratory LMH, where the models impeller mechanical powers are recalculated on the prototype values. The impeller mechanical power values differences of the prototype and recalculated model testing results LMZ MF LMZ LMH MF LMH Δ P = P P and Δ P = P P are minor and within the measuring error limits. m m m m m m 4. The bulb turbine characteristics for the combinatory link operation determined by the model and prototype tests In this chapter, the comparative characteristics of the measured turbine are shown in order to confirm the importance for the units combinatory links determination at HPP Djerdap 2 by INDEX method. The following propeller and cam curve figures 14, 15 and 16 performed by measuring [1] have been used for this analysis. The combinatory link operation points determined by recalculation of the model testing results (designated with A) and by the prototype INDEX testing results are added in the previous charts performed for oblique water inflow condition. A B A B These two operation regimes are compared and differences Δ Q = Q Q, Δ η = η η and A B Δ Pm = Pm Pm are given, which show how discharge, efficiency and power values decrease during the model test combinatory link operation ( A ), i.e. how discharge, efficiency and power values increase during the prototype with the oblique water inflow combinatory link operation ( B ). Fig. 14 The propeller and combinatory link characteristics for the head H = 10m Absolute deviations Δ ηh and Pm Δ during both regime operations are given in the following table 2. Regarding the results obtained by analysis and comparing the prototype and the model tests combinatory link operation regimes it is concluded how much efficiency and power are reduced in the case of the unadjusted combinatory link. 6

8 Fig. 15 The propeller and combinatory link characteristics for the head H = 8, 45m Fig. 16 The propeller and combinatory link characteristics for the head H = 4,8m 7

9 5. Conclusion Table 2 The absolute values of efficiency and internal power decreasing in case of the unadjusted combinatory link for oblique water inflow condition H Δη h ΔP m [m] [%] [MW] 10 1,80-3,00 1,23-1,89 8,45 3,30-5,40 1,06-4,13 4,8 0,40-3,40 0,10-0,99 With regard to the above mentioned results the conclusions are: Oblique water inflow to the units axes has influence on the bulb turbine (built in the Serbian part of HPP Djerdap 2) operation characteristics. Measuring by INDEX method was performed at unit A5 and regarding the results it has been concluded that there are influences on other units depending on inflow angle. Oblique water inflow changes the combinatory link characteristics β = f( α, H), so the guide vanes opening α must be increased for the same runner blade opening β and heads H in order to gain optimal efficiency. The results of the model and the prototype tests combinatory links determination for the heads H = 10 m, 8, 45m, 4,8m and the same runner blade opening β are given in table 1. Mutual deviations of the combinatory link are also given. The applied INDEX method is a relative method which is based on adopting the recalculated model efficiency values for Winter-Kennedy discharge coefficient determination. Regarding the above mentioned, this method gives, for the prototype test with an oblique water inflow, the same efficiency and power values as the recalculated values of the model test. However, the efficiency and power values were determined for the changed combinatory link characteristics with a greater guide vanes opening. The significant result, that shows the necessity of using INDEX test with the aim of the combinatory link determination when there are not normal water inflow conditions, indicates the efficiency and power decreasing for the combinatory link determined by the model testing, neglecting the fact that the combinatory link for an oblique water inflow has to be changed. There is a necessity for the new combinatory link determination of all units in HPP Djerdap 2, which are operating under oblique water inflow condition. Acknowledgments This work is supported by company Hydro Power Plants Djerdap and the Republic of Serbia Ministry of Science and Technological Development. Nomenclature D M D P H Q Q E c u P m Model runner diameter [m] Prototype runner diameter [m] Net head [m] Turbine prototype discharge [m 3 /s] Plant discharge [m 3 /s] Circumferential velocity component in the guide vanes inlet [m/s] Impeller mechanical power [MW] α β δ η h η h Guide vanes opening [ ] Runner blades opening [ ] Oblique water inflow with angle [ ] Hydraulic efficiency [-] Optimal hydraulic efficiency [-] References [1] Benišek M at all Guarantee and Complex Tests of Unit 5 Bulb Turbine at HPP Djerdap 2 (in Serbian) Faculty of Mechanical Engineering (Belgrade, Serbian) [2] HPP Djerdap Report about Model Hydraulic Conditions in Hydropower Plant Upstream and Downstream Institute for the development of water resource Jaroslav Černi (Belgrade, Serbian) 8

10 [3] HPP Djerdap Report about Hydraulic Model Water Inflow Tests on Units at HPP Djerdap 2 Institute for the development of water resource Jaroslav Černi (Belgrade, Serbian) [4] Vušković I and Benišek M 1981 Investigations of Flow in Bulb Turbine at HPP Djerdap 2 Institute Mihailo Pupin (Belgrade, Serbian) [5] Benišek M, Ignjatović B and Nedeljković M 1998 Oblique Inflow Influence on Bulb Turbine Characteristics J. EЛЕКТРОПРИВРЕДА UDK YU ISSN Belgrade 1 [6] HE Djerdap Report on Model Tests of Tube Turbine LMZ Laboratory (Leningrad, Russian) [7] LMH-EPFL 2003 Portile de Fier II Bulb turbines comparative model tests. Final Report No 472/473 [8] Benišek M, Ignjatović B and Vušković I 1982 Efficiency Scale-Up for Tube Turbines at the Operating Point of Best Efficiency and Outside the Point of Best Efficiency 11 th Symp. of IAHR (Amsterdam, Holand) 9