Cruise Speed Characteristics of a Self--Propelled Pulsed-Jet Underwater Vehicle

Steady-jet propulsion has been widely used for air and marine vehicles. This system has a high propulsive efficiency for high vehicle velocities, but it ceases to be efficient as the vehicle velocity or Reynolds number (Re) decreases. One alternative for low Re propulsion is pulsed-jet propulsion similar to that utilized by squid and jellyfish. We have developed a self-propelled pulsed-jet underwater vehicle (``Robosquid'') to investigate the effectiveness of pulsed-jet propulsion as Re decreases. A piston-cylinder mechanism is used for generating pulsed flow. The system allows control of piston velocity program, pulsing frequency, and piston stroke-to-nozzle diameter ratio (L/D). In this preliminary study, the effects of L/D and time-averaged jet mass flow rate on the vehicle cruise speed are investigated. The results for cruise speed are presented for L/D = 3,5,{\ldots},15 at the same mass flow rate and increasing mass flow rate at the same L/D. The vehicle Re varied from 12000 to 14000 and results show that the mass flow rate is a dominant factor in vehicle cruise speed.