SBIR-STTR Award

It is proposed to investigate and develop innovative propeller blade section geometry which will result in improved acoustic and powering performance of surface ships through the attainment of higher cavitation inception speeds and reduce blade drag. These sections are characterized by a blunt trailing edge with a separated, non- cavitating wake. The expect of the blunt trailing edge, when coupled with an appropriate section profile, is twofold: 1) the low pressure on the blade surface is relieved which results in a delay of the onset of cavitation; 2) the thickened trailing edge increases the section modulus which can lead to a reduction in drag for a given strength requirement. The proposed Phase I work is divided into two tasks: task 1 will be directed to exploratory development through parametric studies aimed at determining the most suitable profiles with regard to cavitation inception, strength, and drag. This data will be analyzed to identify desirable foil characteristics and trends. Task 2 will quantify the potential gains in efficiency and/or cavitation inception speed in actual ship applications. It is proposed to carry out design studies for two representative Navy ships which provide an established baseline. We have tentatively selected the AO 177 as representative of a moderate speed auxiliary, and the Ddg 51Fflight Iii as representative of a modern combatant.

In Phase I of this SBIR project, HRA performed computational studies of blunt base sections which promise potential for delaying cavitation inception on hydrofoils and marine propellers. Example calculations are presented for a representative naval surface combatant to demonstrate how blade surface cavitation can be delayed by up to 5 knots compared with conventional designs. This analysis is based on a new second-order airfoil theory which includes singularity distributions downstream of the foil section to represent the separated water-filled wake. In the design procedure, blunt trailing edges are combined with optimal chordwise distributions of loading and thickness specifically chose to operate over a range of incidence. The Phase II work continues the development of the blunt base concept through more refined analytical/numerical study and urgently needed experimental confirmation. Water tunnel tests are planned to measure the forces, wake flow, and cavitation performance of a specially designed (two-dimensional) hydrofoil section and to evaluate the hydrodynamic performance of a demonstration propeller design. In combination with these experiments, parametric design calculations will be undertaken in order to illustrate the benefit of blunt base section propellers in a wide variety of ship applications.