Azipod Propulsion

Azipod propulsion offers new options in ship design. Because they remove the main driver from inside a hull they save substantial room for volume-sensitive designs. They enable almost unlimited maneuverability by yawing through a full 360 degrees. More options exist for placing, sizing, and shaping, so propeller/hull interaction can be improved. Azipods also present new challenges in hydrodynamic design.

AFT personnel have aided azipod design in a number of ways. The figure at right demonstrates a typical solution for studying tractor propellers, and shows contours of velocity on two downstream cross flow planes. RANS methods are essential for predicting performance of these units since tractor propellers shed unsteady wakes into the strut. Little previous experience exists as to how this affects vibration, acoustics, or downstream wake detail.

The application yields a classic example of how RANS can be applied to aid new concept design. Propulsor/hull interaction is traditionally addressed in terms of improving inflow or reducing thrust deduction. But in this case overall propulsive efficiency was improved by designing a strut to recapture rotational energy lost in the propeller race. This was possible only because RANS could provide the actual rotational velocities present when both the propeller and strut are operating. The new design resulted in performance gains of over 3%.

More detail about this application can be found in the paper, “Hydrodynamic Design of Integrated Propulsor/Stern Concepts by Reynolds-Averaged Navier Stokes Techniques.”