3. Model tests

Calculations of three-dimensional viscous fluid flows in turbomachinery have made great strides in recent years. Nevertheless, the study of two-phase flows remains a major problem for numerical engineers. Cavitation, i.e. the formation of bubbles or vapour pockets in the flow, is a specific feature of hydraulic turbines once the pressure within the liquid reaches the vapour pressure p _va . It is therefore not possible to calculate a complete efficiency hill that is sufficiently precise to verify the turbomachine's operating guarantees. The scale model is still the only means of verifying the power, efficiency and cavitation performance of the prototype machine. The International Electrotechnical Commission (IEC) has drawn up standards for scale-model testing, in which most manufacturers, independent laboratories and national companies are represented....