Effect of blade number on optimum rotor performance in axial flow with swirl

Dynamic inflow theory is used to develop an analytical formulation for the general performance of the lifting rotor in axial flow with finite blade number and improved swirl correction. The theory incorporates conventional blade-element theory for blade lift and provides the integrated loads and the induced power of the rotor in terms of an arbitrary number of blades. A finite-state model of the rotor provides the basis for a classical quadratic optimization with realistic constraints that is applied to determine the minimum induced power for a variety of available control combinations, rotor trim constraints, number of blades, and operating conditions. The findings show relative agreement to the classical propeller solutions predicted by Golstein at moderate to high inflow ratios. Swirl vortices - due to finite number of blades - significantly reduce the non-ideal induced power increment. New insights are given for some of the factors that prevent practical rotors from achieving Golstein's predicted efficiency. Improvements to the swirl correction give greater understanding to the nature of this puzzling phenomenon. Limited comparisons with previous research corroborate the earlier results and demonstrate the versatility of the present formulation.