Cavitation in a Francis turbine runner comes in many different forms. Inflow cavitation is the most aggressive type, often causing significant erosion damage to the runner blades, and results from a mismatch in flow angles and blade angles at the runner inlet. It is often present when the machine is being operated at heads which are either well above, or well below, the design head. As mentioned earlier, the operational head ranges of turbines in China is typically much larger than those of comparable size units in North America. The runner designs for the Chinese market must be adapted to these demanding conditions.
Silt is also a concern for many project engineers in China.
Often, one bad flood season is enough to necessitate the shutdown of a machine for extensive repairs. Transportation limitations are another problem plaguing large projects in many countries, and China is no exception. The runner halves would then be reassembled and bolted together at site. The evolution of the technology can be clearly seen in their results. The design parameters which affect the flatness of performance curves for both wide head and flow variations have been identified and can now be easily controlled.