"Measurement of the Velocity Field of a Cylinder in the Wake of a Rotor in Forward Flight"

Mavris, D.M., Liou, S-G., Komerath, N.M., and McMahon, H.M.

AIAA Paper 89-1844, 20th Fluid Dynamics, PlasmaDynamics, and Lasers Conference, Buffalo, NY, June 1989.

Abstract: The problem of predicting the flowfield around a rotorcraft in low-speed forward flight is studied using a potential-flow code, whose results are compared with surface pressure measurements and flow velocity measurements. The test case used is a 2-bladed teetering rotor above a hemisphere-cylinder airframe in a wind tunnel. The dominant features of this problem are modeled by a lifting line/lifting surface rotor model with a free wake distorting in the presence of the airframe. The airframe flowfield is modeled using a source/doublet panel method. The instantaneous flowfield is computed at specified intervals of rotor azimuth, with the effects of blade motion added to the formulation. Modeling the energy addition at the rotor using actuator segments leads to successful prediction of the time-averaged pressure field. The periodic velocity variations along the spine of the airframe are predicted successfully. When a fully unsteady potential formulation is used, however, large differences appear between measured and computed periodic velocity at the sides of the airframe. These are attributed to the inadequate understanding of interaction of the rotor tip vortices with the airframe surface, as well as to inadequate modeling of the flowfield around the rotor hub.