Kaplan turbines were invented by Viktor Kaplan in 1912, and are unaltered axial flow turbines.
In this turbine the speed of the blades is much greater than the speed of the water, almost double.
The big advantage of the Kaplan turbine is that even in low water speeds it still permits a high rate of blade rotation.
The Kaplan Turbine is an evolved version of the Francis Turbine, and is used in mostly low head sites where the Francis turbine was less efficient.
The Kaplan Turbine uses a specially designed propeller blade that is similar to the design of a propellor of an airplane.
The main disadvantage of a Kaplan turbine is that they are very expensive to design and construct. However, a well designed and well located Kaplan turbine can be very efficient and put out many years of quality production.
Micro-Hydro turbines that can be found in the home are usually Kaplan turbines.