ON THE MAXIMUM EFFICIENCY OF SOME MARINE PROPULSORS IN OPEN WATER

Article type: Research Article

Authors: Brockett,, Terry E.

Affiliations: Maumee Bay R&D LTD., Curtice, Ohio, USA

Abstract: Available performance data of selected open, contra-rotating and ducted propulsors operating in a uniform onset field are assembled to display the maximum efficiency as a function of thrust-loading coefficient, C_T = T/(½ρV^2R_{R^2}). Satisfactory correlation is presented between this observed best efficiency and estimates from a numerical method based on an inviscid lifting-line representation of the rotor, or other blade row, plus, when appropriate, an axi-symmetric panel-method analysis of the duct and hub surfaces. Viscous drag is added empirically as a local blade-section friction coefficient. For the open-propeller series and various sets of conventional accelerating ducted propulsors, the maximum efficiency of the ducted propulsors is greater by several percent at a C_T = 1 and by about 5 percent (straight difference in values) at a C_T approaching 10. The contra-rotating configuration displays a greater increase in the observed maximum efficiency at reduced C_T values compared to the accelerating ducted propulsor but at C_T > 2 the accelerating ducted units develop greater efficiency. Only at reduced thrust levels is there an indicated beneficial interaction between the blade rows of a contra-rotating propulsor compared to a simple thrust division without interactions.

Journal: International Shipbuilding Progress, vol. 50, no. 1-2, pp. 147-169, 2003