a. Review, briefly, the phenomenon of cavitation in hydraulic turbines and indicate the places where it is likely to occur. Describe the possible effects it can have upon turbine operation and the turbine's structural integrity. What strategies can be adopted to alleviate the onset of cavitation?
b. A Francis turbine is to be designed to produce 27 MW at a shaft speed of 94 rpm under an effective head of 27.8 m. Assuming that the optimum hydraulic efficiency is 92% and the runner tip speedjet speed ratio is 0.69, determine
a. the power specific speed;
b. the volume flow rate;
c. the impeller diameter and blade tip speed.
c. A 1/10 scale model is to be constructed to verify the performance targets of the prototype turbine and to determine its cavitation limits. The head of water available for the model tests is 5.0 m. When tested under dynamically similar conditions as the prototype, the NPSH HS of the model is 1.35 m. Determine for the model
a. the speed and the volume flow rate;
b. the power output, corrected using Moody's equation to allow for scale effects (assume a value for n = 0.2);
c. the suction specific speed ΩSS.
d. The prototype turbine operates in water at 30°C when the barometric pressure is 95 kPa. Determine the necessary depth of submergence of that part of the turbine most likely to be prone to cavitation.