### 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
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*Dept. Aero. and Mech. Eng., Boston Univ., 110 Cummington St., Boston, MA
02215
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**Hafiz M. Atassi
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*Univ. of Notre Dame, Notre Dame, IN 46556
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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.