Abstract: Based on a concise review of state-of-the-art of the methodology for analysing the wake flows behind helicopter rotors, a novel idea for the "constrained wake model" pertaining to the conventional free wake model is proposed. The constrained wake analysis is conceived in which the wake analysis is performed under the limitation of certain constraints imposed on the wake. The essence of the idea is to lay the free wake analysis on available physical understandings, aiming at a remarkable reduction of computational efforts and a significant improvement on the reliability of the predictions.

Key words: helicopters, rotor aerodynamics, vortex theory, wakes