ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

3aEA6. An inverse acoustic problem in the presence of a mean flow.

Sheryl M. Patrick

Dept. Aero. and Mech. Eng., Boston Univ., 110 Cummington St., Boston, MA 02215

Hafiz M. Atassi

Univ. of Notre Dame, Notre Dame, IN 46556

Recent research has shown the feasibility of performing inverse aeroacoustic problems for streamlined bodies. The unsteady pressure on a flat-plate airfoil, due to a convected vortical disturbance in the mean flow, can be recovered from the far-field radiated sound. The present paper extends this analysis to oscillating airfoils in a uniform mean flow. In this case, the oscillating airfoil creates an unsteady pressure field on the airfoil surface. The inverse problem, then, is to determine the surface pressure from the radiated sound. For the oscillating airfoil problem, the normal pressure gradient does not vanish along the airfoil surface, rendering the inversion process more complex than for the gust problem, however it is still feasible. This paper also compares the oscillating airfoil application to acoustic holography. While the two problems are similar mathematically, far-field input data are, in general, not sufficient for acoustic holography applications while they are sufficient for the inverse aeroacoustic problem.