Contra-rotating rotors are suitable for a small hydroturbine, because they can be expected to achieve compactification of radial direction and high performance. However, a conventional contra-rotating rotor is composed of two axial flow rotors, so it has a specification suitable for high flow rate and low head. In order to achieve a small hydroturbine suitable for low flow rate and high head, we propose a new type of contra-rotating rotor, which is composed of a hybrid rotor and a centrifugal rotor. We investigated the performance of this hydroturbine by experiment and numerical analysis. As a result, it became clear that the performance of the rear rotor was low. And we considered the cause from the internal flow conditions.
