The transient response of propellers to changes in rotation rate and forward speed is analyzed using a general unsteady vortex lattice method. This method is an extension of the well-known vortex lattice technique used for incompressible aerodynamics. The method described in this paper is not limited by aspect ratio, twist, camber or angle of attack as vortex breakdown does not occur near the surface of the propeller and separation occurs only along sharp edges of the blades. It is fully three-dimensional. Moreover, the position of and the vorticity distribution in the wake are obtained numerically at discrete time steps during the rotation. Steady flow can be treated by giving the propeller an impulsive start and allowing it to run under constant conditions until a steady-state emerges. The accuracy of the procedure was verified by comparing the predicted torque and thrust to known experimental results for a steady case. Unsteady results are given for varying rotation rates and forward speeds. It is demonstrated that the present version of the vortex-lattice method has the potential for handling a number of arbitrary maneuvers and transient conditions.

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