During recent work under DARPA and ONR sponsorship, CDI has developed substantial expertise in analysis and design of advanced marine propulsion components. This background has been applied to several projects, most recently in support of an ONR-sponsored effort on a Bio-inspired Delayed Stall Propulsor (BDSP) system. Work on this system was motivated by the fact that current propulsors are typically "steady flow" designs and that careful exploitation of unsteady mechanisms in blade design can lead to increased thrust and/or reduced acoustic signature.

Work in this area has built on the extensive recent literature on unsteady lift enhancement mechanisms identified in nature. Mechanisms such as rotational circulation, wake capture, and delayed stall due to transient wing motion play a strong role in enabling favorable changes in lift performance on lifting surfaces. Recent activity at CDI has focused on incorporating unsteady lift overshoot and delayed stall mechanisms into a conventional propulsor in a passive way. Attention has centered on the use of a specially designed stator to alter the flow angle at the rotor to transiently change angle of attack on the rotor system. This passive approach is desirable since it requires no actuation hardware on the rotor.

Modeling of a coupled rotor/stator system has been conducted with an evolved version of the CHARM model - applied to ducted propulsors as shown in Figure 1 - along with other advanced propeller modeling tools (e.g., the MIT PUF family of models). Candidate blade designs (Figure 2) are currently being evolved to enable testing in both water tunnel and wind tunnel settings, following up on promising early studies described in Usab, et al. in the July 2004 Journal of Ocean Engineering. Demonstration testing has been carried out in a wind tunnel environment, and follow-on tests in our in house water tunnel are also expected.

Figure 1: CHARM model of multi-stage ducted propulsor.

Figure 2: Stator (upper left) and rotor (upper right) blade designs generated for use in demonstrator models; sample integration of propulsor with a simple torpedo body in CHARM (bottom).

Figure 3: CDI low speed 2'x2' water tunnel (left); 1'x1' wind tunnel (with an extension housing a rotor/stator test rig).

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