By means of the reverse flow theorems, results are obtained for the unsteady lift and pitching moment on two-dimensional airfoils penetrating sharp-edged traveling gusts. Both downstream and upstream traveling gusts are considered. For the incompressible case, exact results are given and are generalized numerically for any gust field by means of Duhamel superposition. Results are then given for the airloads and acoustics generated by a two-dimensional airfoil encountering a vortex convecting at different gust speed ratios. Numerical results for the traveling sharp-edged gust problem are also derived for subsonic flows by means of exact linear theory. Further results for the subsonic case are computed by means of an Euler finite-difference method. It is found that the gust speed ratio has substantial effects on the unsteady airloads and will be an important parameter to represent in helicopter rotor aeroacoustic problems.
Published in the AIAA Journal of Aircraft, Vol. 34, No. 6, Nov./Dec. 1997.
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