Hi all! I am learning things about turbomachinery, starting with the Pelton Wheel. The analysis of seems to be straighforward, but I still have some questions. I refer to this website: http://www.du.edu/~jcalvert/tech/fluids/turbine.htm There is a blade velocity u. I would like to know if this is the initial starting speed of the wheel? That means even if there is no jet on the wheel, the Pelton wheel is rotating by its own (either by motor etc), is this true? I don't see why we need to do so...It's apparent from the efficiency relation that when u=0, efficiency=0 too. But, physically, it is hard for me to imagine what's happening. When the wheel is not rotating initally and when there is a jet of water impacting on the wheel, isn't there should also be an energy transfer from the jet to the wheel and the wheel will then rotate? How come the efficiency being zero? Second, actually I don't really know the objective of having the Pelton wheel turbine. Do we want to accelerate rotation of the wheel? or we just want the wheel to rotate at certain constant speed? If the latter is true, that means when there is jet impacting on the wheel, it will still be rotating at u? So the power output is just used to overcome the frictional things? It seems strange... If the former is true, that means the wheel will keep on accelerating? But the maximum speed is restricted by the velocity of the jet, v? It seems strange also. I am really stucked here. Please kindly help.