Performance of a bulb turbine suitable for low prototype head: model test and transient numerical simulation

In this paper, a bulb turbine, with unit specific speed of n(q)=223.1 min(-1), suitable for low prototype head was studied from aspect of its performance. Hydraulic model of the turbine was developed firstly, and then model turbine was designed and manufactured. Performance tests were carried out on high-accuracy hydraulic machinery model universal test rig located at IWHR, including energy, cavitation and pressure fluctuation tests, etc. In order to investigate internal flow field, three-dimensional transient turbulence numerical simulation was conducted on the tested turbine, adopting Reynolds-averaged Navier-Stocks control equations and RNG k-epsilon turbulence model. Test and simulation results show that: (1) hydraulic efficiency of model turbine eta(M) is up to 91.7%, at the optimum operating point of n(11o)=165.54 r/min versus Q(11o)=1.93 m(3)/s; (2) numerical results agree well with experimental resultsby comparing pressure fluctuation, which shows that pressure amplitude is very low at the optimum operating point; (3) hydraulic loss in Outflow domain accounts for more than 50% total hydraulic loss due to flow separation and secondary flow.