## 4aPAb7. Two-dimensional effects in the edge noise of vortices and dipoles.

### Session: Thursday Morning, December 5

### Time: 11:30

**Author: Gerrit Schouten**

**Location: Aerosp. Dept., Delft Univ. of Tech., Kluyverweg 1, 2629 HS Delft, The Netherlands**

**Abstract:**

Expressions for the edge noise of 2-D moving vortices and 3-D moving
dipoles (ringvortices) are presented. The integrals, involving Green's functions
in the time domain, are approximated in the far field in terms of the halved
derivative of the near-field pseudosound. Attention is paid to the transition
from near-field pseudosound to far-field wave behavior, e.g., in the closed form
response to a triangular pulse. In 2D the edge sound due to a moving vortex has
two components of equal order of magnitude. One is retarded pseudosound from the
edge, the other is due to the motion along the trajectory as if the vortex moved
in free space. The latter component is deformed as the halfth derivative of
free-space pseudosound. In 3D the pressure wave generated by the motion of a
dipole near an edge is a factor (r/c)[sup 1/2] times stronger than the pressure
of the pseudosound. The free motion of a dipole in 3D generates quadrupole
sound, the proximity of an edge amplifies it to dipole sound. The vortex sound
in 2D does not show this amplification in the edge effect. The time-domain
analysis is efficient and illustrative, and seems more attractive than methods
using the frequency domain.

ASA 132nd meeting - Hawaii, December 1996