Performance Analysis Of Bulb Turbine Consider With Tip Clearance

Along with modern computer technology's fast development, computational fluid dynamics (CFD)has obtained considerable achievement in the study of hydraulic mechanics and became more and more common used in the flow field numerical simulation of hydraulic mechanics. This dissertation adopts CFD software CFX5 to conduct three-dimensional numerical simulation of bulb turbine's flow field, estimated the turbine's efficiency, and analyzed the different tip clearance flows under different operating points and different tip clearances.The first procedure is to construct the bulb turbine model by CAD soft ware, to obtain the three-dimensional model of guide vane and runner. Then adopted Reynolds time-average N-S equation, k- turbulence model and unstructured mesh , and the governing equations are discredited with Finite Volume Method based on Finite Element Method, and the pressure correction method is proposed in numerical calculation. It selects six teams of unit rotate speed and eleven teams of discharge guide vane angle, viz. 66 operating conditions in all, and then simulated the flow field of bulb turbine under these operating conditions, also estimated the efficiency. Based on the results of this calculation the turbine's equal discharge curve and equal efficiency curve were plotted. By comparing the results of numerical simulation and experimental results the origin of error has been in-depth studied, thus validated the reliability of this calculation method.Three different conditions are selected, including the small angle 0 of blade, the design condition angle 20 and the big angle 30. numerical calculated three conditions tip clearance flow of bulb turbine include the tip clearance is 0mm, 0.25mm,0.5mm,1.0mm. the turbine efficiency tip clearance leakage and depressing of calculation head are calculated every conditions based on the numerical calculation.Thoroughly analyzed the distribution character of tip clearance leakage flow, under different operating conditions, on the surface of blade and in the clearance. The effects of tip clearance leakage flow are not very considerable at the condition of =20, but will be intensified at other operating conditions. When the blade angle =0, the leakage flow started at the leading edge of the runner blade ranged from blade pressure side to suction side; when blade angle =30, the clearance flow started at the tip of leading edge and ranged first from pressure side to suction side and then changed direction from suction side to pressure side at the middle of the tip clearance. Therefore, the tip clearance leakage flows are not uniform; the flows changed with change of operating conditions and clearance positions.