Inertia effects on pulsed propulsion : Application to the study of a hydro-propulsor

The marine propulsion systems that exist at the moment rely on the product creating an almost continuous flow in which the mechanical energy is given to the liquid in a continuous fashion. Here we study an original seawater propulsor in which the mechanical energy is provided to the liquid by the alternative displacement of a fluid contact surface. The produced flow is channeled towards the back of the vehicle that has to be propelled by a system of valves, in order to create an average positive thrust. These valves are free, so their operation is linked with the flow resulting from the interaction between the surface and the fluid contained within the mechanism. The mode of surface displacement clearly shows the discontinuous character of the transmission of the mechanical energy from the engine to the fluid as well as the unsteady flow produced. Therefore we have developed a model which permits study of the technical and geometrical characteristics, the particular flow sizes (pressure and velocity), and the performance of the propulsion system (thrust and efficiency). Three basic parameters allow study of the evolution of the performance of the device in correlation to its geometry. Moreover, we show that it's possible to make the flow almost continuous by increasing the internal fluid mass of the mechanism considerably.