SUMMARY OF THE INTERACTION OF A ROTOR WAKE WITH A CIRCULAR-CYLINDER

To compute the aerodynamics of a rotorcraft in low-speed flight, the i nteraction of the strong vortices in the rotor wake with the airframe must be modeled. Using a hemisphere-cylinder airframe and a two-bladed rotor for reference, the various phenomena encountered during such in teractions are summarized, combining previous results on various confi gurations with recent experimental results. Differences between the in teraction at the front and aft portions of the wake are discussed. The precollision phase conforms to expectations from potential how and in cludes distortion of the vortex trajectory determined by the sense of rotation of the vortex. The collision phase involves complex boundary- layer interactions. The axial velocity in the vortex core causes subst antial asymmetry and influences the surface pressure distribution on t he airframe side under the advancing rotor blade, where the axial flow stagnates. The postinteraction vortex is much weaker, but still conta ins some swirl energy. Where how separation occurs due to airframe sha pes, the interaction is not modified significantly, because the vortex dominates the interaction with separated shear layers for parameter v alues of practical interest. Areas of remaining uncertainty are discus sed.