Physic of secondary flow phenomenon in distributor and bifurcation pipe of Pelton turbine

In Pelton turbine, two-phase homogeneous model is the fundamental base to investigate the flow inside the turbine. Meanwhile, flow pattern in section of the distributor and bifurcation pipe produces the secondary flow which influences the shape of the jet downstream 6 nozzles. This paper numerically investigated the dynamic process using CFX commercial code under different operating conditions. Volume of Fluid(VOF) model was used to capture the air/water interface. This work focuses on the jet bifurcation problem which can seriously influence the Pelton turbine performance and furthermore it is not yet investigated in hydraulic research. Results indicate that the shape of the distributor induces the secondary flow and Dean vortex structure which are symmetric with the central horizontal plane of the pipe and nozzles. On the other hand, this sequence of vortex develops and transits along the flow and finally affects the shape of jet. Effect of secondary flow in the distributor stretches the jet flow in vertical direction and compress it in horizontal direction. Meanwhile, bifurcating phenomenon is observed outside the nozzle which is also obtained in classical experimentations. This study reveals that the secondary flow is important to be taken into consideration to optimize the performance of Pelton turbine. (C) 2018 Published by Elsevier Ltd.