Francis Turbine

Reaction turbines can be classified into 'radial flow' and 'Axial flow'. To type 'radial flow' there are two kinds, among others, 'Inward-radial-flow' and 'Outward-radial-flow' is often applied as a Francis turbine with the following explanation: In the turbine type 'Inward-radial-flow', the flow of incoming water from the reservoir into the runner through the penstock and spiral casing from the outside towards the center of the runner and the outgoing direction of the axis of shaft (axial). The advantage of this type is the centrifugal force caused by rotation runners will be offset by the radial flow of incoming water so that when an increase in rotation speed of the runner due to the reduction of the load tends to decrease discharge thereby setting the governor is more easily done.

In contrast to the turbine type 'Outward-radial-flow', the flow of water into the center of the runner and the runner out from the side. With a revenue stream like this then the runner will generate the centrifugal force on the flow of water thereby increasing the relative velocity result in the addition of water discharge into the runner. This situation will complicate the burden of regulation by the governor.

Example of counting rounds Francis turbine
Head, H = 30 meters
Runner inlet diameter D = 1.2 m
Runner outlet diameter d = 0.6 meters
Inlet angle alpha = 15
Runners fin angle beta = 90
This type of radial flow with velocity ratio, V / U = 0.7
Flow velocity, V = (2 * g * H) ^ 0.5
Runner speed, U = 0.7 * (2 * g * H) ^ 0.5 = 0.7 (2 * 9.81 * 30) ^ 0.5 = 17 m / sec.
Round runner, N = (N * 60) / (3.14 * D) = (17 * 60) / (3.14 * 1.2) = 270 rpm