Blade Element Momentum Method for Propeller Under Nonaxial Flow

This paper presents a three-dimensional blade element momentum method to estimate aerodynamic forces and moments of a propeller under nonaxial flow. In the momentum theory part, the axial and normal elements in the velocity change are included for the estimation of the thrust and the normal force, and the rotating elements are introduced for the estimation of the counter-torque and the p-factor moment. In the blade element part, multiple coordinate systems are introduced to compute the local velocity and the angle-of-attack at the blade element. Then the forces and moments are averaged during the one revolution of the element, to be compared to those computed in the momentum theory. An iterative numerical method is applied to match the two parts to compute the resulting forces and moments.