NUMERICAL ANALYSIS OF PROPELLER PERFORMANCE BY LIFTING SURFACE THEORY

Current trend in propeller design led to the need for complex geometry which demands numerical analysis tools expecially in off-design condition. This paper presents a lifting surface analysis method based upon Kerwin theory [1]. A totally numerical formulation has been applied to the definition of blade and wake geometry. Local phenomena as tip vortex separation and leading edge suction force are included. Viscous effect are taken into account in a semi-empirical manner, through an added viscous resistance, dependent on the local Reynolds number of the quadrilateral blade vortex element. The propeller is assumed to be operating in a prescribed axial-symmetric effective wake, which may include axial, tangential and radial components. The presence of the hull, propeller hub and free surface is ignored. Comparison are made with existing experimental and theoretical data on typical test case propeller designs whose experimental date have been obtained from tests in the cavitation tunnel of the University of Genoa. Effect of prescribed wake geometry on the predicted thrust and torque coefficients are discussed in the paper as well as the effect of the viscous corrections. In general, for the different types of benchmarks propellers, a good agreement is obtained on the predicted thrust value in a large range of the advance ratio (not only in vicinity of the design value). The difference in the calculated torques will be discussed in relation to the viscous corrections formulas adopted in the numerical method.