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Numerical Study of Flow Stability of1000MW Hydro Turbine under Small Opening Condition

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Tutor: WangHongJie
School: Harbin Institute of Technology
Course: Fluid Machinery and Engineering
Keywords: Francis turbine,flow stability,CFD,small opening
CLC: TK730
Type: Master's thesis
Year:  2012
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Abstract:
Due to the need of rapid developing economy, and the requirement of CO2releasereduction of China, hydro electircity has obtained an improving position in thestate¡¯s energy development policy. A notalbe number of large hydro plants is underconstruction nowadays on upper reaches of the Yangtze River, however, theincreasing unit capacity will weaken the stiffness of the unit, and lead to a stabitityand virbration problem. During the overspeed test of the Three Gorges unit, anabnormal vibration has appeared under very small opening condition. Thus, toavoid the same problem happen on the newly bulit1000MW hydro units, a detailtheoretic and numerical analysis should be taken to find out causes and solution ofthe abnormal vibration.To achieve this goal, a numerical simulation of the turbine¡¯s internal flow fieldhas been taken. The flow structure and pressure fluctuation in the whole flowpassage has been obtained through both steady and unsteady CFD simulation. Theimpact of different overlap length has been considered.In the first place, ateady state simulation of turbine¡¯s internal flow field undersmall opening condtion has been taken to study the differences between smallopening and normal work conditions. A series of working conditions around7%guide vane opening has been studied, and then a detail small opening characteristicchart of the turbine has been obtained. The range of turbine mode, braking mode,and reverse pump mode has been ascertained.Unsteady CFD calculation of turbine mode, braking mode and reverse pumpmode has been conducted. Pressure fluctuation and radial force variation on therunner have been studied through FFT analysis. The spectrum has been obtainedand the cause of each main frequency has been analyzed. Comparing pressurefluctuation under different working mode, this paper pointed out the possibleworking condition that may lead to oscillation.The infect of overlap length of guide vanes has been studied in this paper.Applying the same simulation configuration, the change of velocity and pressurefield has been obtained. Main characteristics of hydro turbine and pressurefluctuation and force variation have been further analyzed. The possible way todissipate the abnormal vibration by select a appropriate overlap length has beendiscussed.
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