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.