## 4pEA13. Computations of acoustic wave strength and vorticity in shear flow.

### Session: Thursday Afternoon, December 5

### Time: 5:00

**Author: Laurine Leep-Apolloni**

**Location: CAE Dept., Ford Res. Lab., Dearborn, MI 48121**

**Author: David R. Dowling**

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

**Abstract:**

While exact techniques are available for plane-wave propagation in uniform
flow, acoustic propagation in nonuniform flow has proven much less tractable. A
numerical technique has been developed to treat the simplest possible case:
acoustic plane waves launched into a uniform shear. The computations are based
on the Euler and continuity equations, using only the standard linearization for
small acoustic amplitudes. When nondimensionalized, these equations produce a
single governing parameter: m/f, where m is the flow's shear rate, and f is the
acoustic frequency. Numerical solution for acoustic fluctuation velocity and
density at each grid point allows wavefront location and orientation as well as
wave strength to be determined. The results for wavefront location and
orientation from the current numerical method are compared to a WKB solution
obtained from the simplest nonuniform flow approximation which uses a nonuniform
speed of sound in lieu of a nonuniform background flow. Gradients of acoustic
field variables along the wavefronts, which are not predicted by the standard
approximation, are also presented. The acoustic vorticity field is examined to
study the rotational nature of the plane waves after interaction with the shear.

ASA 132nd meeting - Hawaii, December 1996