## 4aEA6. Comparisons of approximate and exact techniques for convected acoustics.

### Session: Thursday Morning, May 16

### Time: 9:15

**Author: Laurine Leep**

**Location: Comput. Aided Eng. Dept., Ford Res. Lab., Dearborn, MI 48121**

**Author: David R. Dowling**

**Location: Univ. of Michigan, Ann Arbor, MI 48109**

**Abstract:**

In many aero- and environmental-acoustic problems, convection of sound
waves is handled by appropriately increasing or decreasing the local speed of
sound and then solving the resulting Helmholtz equation. Such solutions are
typically obtained via integral transforms or geometrical acoustics. An exact
solution technique that properly incorporates the vector character of mean-flow
convection has been found [L. Nijs and C. P. A. Wapenaar, J. Acoust. Soc. Am.
87, 1987--1998 (1987)]. Unfortunately, the formal and numerical complexity of
these techniques has prevented detailed comparisons of the acoustic field
variables with and without the standard approximation. Results and comparisons
for approximate and exact treatment of convection will be presented from a
series of simple computations made directly from the linearized time- and
space-dependent equations of inviscid fluid motion. Specifically, the
propagation of initially plane acoustic waves in a simple shear flow has been
addressed to determine how: (i) wavefront orientation and location, (ii)
acoustic-particle-velocity vector direction, and (iii) acoustic wave strength
compare when mean flow convection is handled approximately and exactly. [Work
supported by Ford Motor Company.]

from ASA 131st Meeting, Indianapolis, May 1996