| description abstract | In previous works, the authors presented computational fluid dynamics (CFD) results, which showed that injectors with noticeably steeper nozzle and needle tip angles 110 deg & 70 deg and 150 deg & 90 deg, respectively, attain higher efficiency than the industry standard, which, according to available literature on the public domain, ranges from 80 deg to 90 deg for nozzle and 50–60 deg for needle tip angles. Moreover, experimental testing of the entire Pelton system showed that gains of about 1% in efficiency can be achieved; however there appears to be an upper limit beyond which steeper designs are no longer optimal. This study aims at providing further insight by presenting additional CFD analysis of the runner, which has been coupled with the jet profile from the aforementioned injectors. The results are compared by examining the impact the jet shape has on the runner torque profile during the bucket cycle and the influence this has on turbine efficiency. It can be concluded that the secondary velocities, which contribute to the development of more significant free-surface degradations as the nozzle and needle tip angles are increased, result in a nonoptimal jet runner interaction. | |
