The structure characteristics of the Francis turbine
Author: source: date: 2017-05-09 11:55:24
The effect of the water guide system of the Francis turbine:
1. To start or stop the machine;
2. To guide the flow into the wheel in a favorable direction;
3. Adjust the flow into the wheel, so that the output of the turbine to adapt to changes in external load requirements.
The structure feature of the Francis turbine:
The flow of water from the radial direction into the runner, and axially away from the wheel, so sometimes it called "radial axial flow turbine." This turbine has two types: they are vertical shaft and horizontal shaft, the vertical axis types is commonly used in the micro-hydropower station.
Francis turbine is suitable for medium and low head and medium and small flow of hydropower stations. This turbine is mainly composed of vortex chamber, runner, water guide, draft pipe and so on. Then, we will separately describe their effect and structure.
The runner is the heart of the turbine, the energy of the water is converted into mechanical energy by it, usually referred to the type of turbine refers to the type of turbine runner. The runner of a Francis turbine consists of a twisted blade, a runner hub and a runner ring. Rely on twisted leaves to make the water flow from the radial into the axial direction.
The vortex chamber usually has two types, the metal volutes and metal tanks. Both of their role is to make the flow evenly and symmetrically into the water guide system to reduce the loss of the water head, and to ensure uniform force around the runner and work stable. Metal volute section is gradually reduced to the end, so it can ensure uniform symmetrical water supply and the formation of a certain rotation, reduce head loss. The advantage of metal tanks is simple construction and low cost. But because it does not meet the water flow, the head loss is large, so usually used for small turbines series.