Francis turbine is a reaction turbine. The water flow of Francis turbine enters the runner radially and leaves the runner axially, pushes the runner when passing through the blades in the axial direction, and also pushes the runner when passing downwards through the blades. That is to say, the water does work when passing through the blades in the radial and axial directions, so it is called a Francis turbine, also known as a radial axial flow turbine.
Francis turbine can be used in a wide range of heads, and there are corresponding products for use with heads ranging from 30m to 300m.
The principal parts of the structure of Francis water turbine as follows:
- Spiral case; 2) Distributor; 3) Rotating parts (Francis turbine runner); 4) Inlet tube; 5) Draft tube
The main parts of the turbine are assembled around the stay ring, There is a bottom ring and draft tube under the stay ring, and a head cover above the stay ring, A spiral case is installed on the outside of the stay ring, A number of guide vanes are installed on the inside of the stay ring, A runner is installed in the middle. The guide bearing of the runner is installed on the head cover. There is a shaft sealing device under the guide bearing to prevent water from leaking into the head cover along the shaft.
The structure of the runner of the Francis turbine
The following figure is a 3D structure diagram of the Francis runner model. Multiple blades are fixed on the cone under the upper crown, and the lower end of the blade is fixed on the inner side of the lower ring.
The following figure is a 3D view of the axial section of the Francis turbine runner. There is a drain cone under the upper crown. The upper crown and the drain cone form a smooth curved surface to allow water to flow smoothly.
Water flows horizontally from all sides into the Francis turbine runner
Working principle of Francis runner
In a hydraulic turbine, the water flow enters the runner through movable guide vanes, which are distributed around the runner, as shown in the following Figure. The guide vanes control the size and direction of the water flow.
The shape of the blades of the Francis turbine runner is such that all the water flowing through the blade can push the runner to rotate, which conforms to the lift force principle of the airfoil.