James Bicheno Francis

James Bicheno Francis

James Francis was a British-American engineer and founding member of the American Society of Civil Engineers (ASCE). His turbine was developed through systematic experiments aimed at improving earlier water turbine designs, particularly the inward-flow turbine developed by Samuel B. Howd. Adjustable guide vanes (or wicket gates) made it possible to regulate the flow through the turbine and maintain a nearly constant rotational speed as operating conditions changed. The guide vanes were controlled by a centralised mechanism that allowed all vanes to be adjusted simultaneously. Francis used systematic experiments and mathematical methods to optimise turbine design. His work established important principles that contributed to the development of modern hydraulic turbine design. After numerous improvements, the Francis turbine came into widespread use around the world.

Francis Turbine

The Francis turbine is a reaction turbine, which means that the pressure of the water decreases as it flows through the runner and transfers energy to it. It has a radial-axial flow design, with adjustable guide vanes and fixed runner blades.

The flow rate through the turbine can be controlled by adjusting the opening of the guide vanes. After passing through the guide vanes, the water is directed towards the fixed blades of the runner. Here it transfers pressure and kinetic energy to the runner and then leaves it approximately parallel to the turbine axis before flowing through the draft tube.

Francis turbines can achieve efficiencies exceeding 90% and are used over a wide range of medium to high heads, typically from several tens to several hundreds of metres. Their output ranges from a few kW to hundreds of MW. The runners of Francis turbines installed in the biggest hydroelectric power plants in the world can have a diameter of more than 10 metres. The Francis turbine is one of the most widely used types of water turbine, and reversible Francis pump-turbines are commonly used in pumped-storage power plants. Modern Francis turbines are individually optimised to suit the hydraulic conditions of each installation.

4 pictures

4 pictures

Some of the world’s largest Francis turbines are installed at the Three Gorges hydroelectric power plant in China. Their runners are 10.9 m in diameter, and each generating unit has a rated capacity of 700 MW.

Francis Turbine On-line interactive 3D model