ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

5aNS7. Numerical and analytical investigation of unsteady lift and sound due to airfoil-wake interaction.

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).]