The outer-flow contribution to the pressure fluctuations occurring at the w
all beneath a turbulent boundary layer was studied experimentally. A moving
wall wind-tunnel facility was developed for the work. A flat test plate wa
s suspended at various heights over the movable tunnel wall such that inter
acting and noninteracting turbulent boundary layers were developed in the r
esultant channel. Mean and fluctuating velocity components were measured fo
r cases with and without wall motion. Pressure fluctuations were measured,
with pinhole microphones on the surface of the test plate forming the upper
-channel boundary, at corresponding test conditions. The data show that the
wall-pressure fluctuations are relatively insensitive to the details of th
e outer flow, even over the range of frequencies dominated by outer-flow tu
rbulence structures. (C) 1999 Acoustical Society of America. [S0001-4966(99
)02904-5].