Paul R. Moran
Donald E. Thompson
David Swanson
Acoust. Program, Appl. Res. Lab., Penn State Univ., P.O. Box 30, State College, PA 16804
The passage of an airfoil through a wake is a dominant source of noise in low Mach number flows. In order to examine this phenomenon, two prediction schemes were used. The first was a thin airfoil analysis used to predict the unsteady lift response to sinusoidal transverse and longitudinal gusts [H. Naumann and H. Yeh, ASME J. Eng. Power 12, 1--10]. The strengths of these gusts are determined from the Fourier coefficients of the wake profiles. The sound was then determined from the unsteady force using a concentrated force radiation mechanism [N. Curle, Proc. R. Soc. London Ser. A 231, 451--460 (1955)]. The second method used an incompressible Navier--Stokes equation to predict the mean flow and unsteady pressure due to the passage of the wake past an airfoil. The resulting sound was then determined with a Kirchhoff solver. The pressure and sound results from both of these methods were compared with experimental data. [H. Fujita and L. S. G. Kovasznay, AIAA J. 12, 1216--1221 (1974).]