On the optimum performance of oscillating foil propulsors

The design of oscillating foil propulsors is considerably more complex than that of conventional propellers due to the large amount of geometric and kinematic parameters involved in the problem. No general use of such promising propulsion concept is made routinely yet since many open questions remain to be solved. One of such questions is the sensitivity of the propulsor efficiency to foil chord length that is much larger than for conventional propellers. Our focus is on this particular problem. A potential flow theory that estimates the main force components affecting the global performance of such devices is presented. The theory is applied to oscillating foils with heaving and pitching motions and to wheel propellers with foils describing trochoidal paths. Added mass terms that usually are neglected in efficiency analyses and that play an important role in determining the global performance are included. A parameter optimization procedure is introduced in this context. Comparison to experimental data and RANS computations is made.