LOCAL MOMENTUM THEORY AND ITS APPLICATION TO THE ROTARY WING

A new momentum theory, named the local momentum theory, has been developed and applied to study rotary wing aerodynamics. The theory is based on the instantaneous momentum balance of the fluid with the blade elemental lift at a local station in the rotar rotational plane. A rotor blade is considered to be decomposed into a series of wings, each of which has an elliptical circulation distribution. The elliptical wings are so arranged that a tip of each wing is aligned to the blade tip. By neglecting the upwash flow outside the wings and by introducing an attenuation coefficient to represent the timewise variation of the local induced velocity following an impact of blade passage, the induced velocity distribution and the spanwise aerodynamic loading along the blade span can be obtained easily. Applying the proposed theory to both steady and unsteady aerodynamic problems leads to fruitful results with much less computational time than that required in the vortex theory, in which complexity of calculation and difficulty of convergence usually are unavoidable. © 1979 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.