### ASA 125th Meeting Ottawa 1993 May

## 2pEA10. Spacing effects in large-area hydrophone arrays.

**Richard N. Brown
**

**
E. F. Berkman
**

**
**
*Systems and Technol. Div., Bolt Beranek and Newman, Inc., 70 Fawcett St.,
Cambridge, MA 02138
*

*
*
It has long been known that large hydrophones filter out the high-wave
number, convective components of turbulent boundary layer (TBL) noise. A
two-dimensional array constructed of NxM hydrophones might be expected to
increase the filtering by a factor of NxM, but, in practice, inter-hydrophone
spaces (``gaps'') diminish this benefit. An analysis, based on a wave-vector
approach, has been done to study the effect of gaps in two-dimensional arrays.
It is shown that the effect of gaps is to allow leakage into the array response
function at wave numbers corresponding to aliasing lobes. This leakage can
extend to moderately high wave numbers, although the details of the leakage are
sensitive to the exact gap size. Numerical estimates of array self-noise due to
flow noise are made using models of the TBL wall pressure wave-vector spectrum.
It is shown that, at low values of k[sub 0]L (k[sub 0] is the acoustic wave
number and L is characteristic array length), the leakage from the convective
and subsonic components of the TBL can be substantial, even for relatively
small gaps.