Measurements of the low wave number components of turbulent boundary layer wall pressure fluctuations with zero and adverse pressure gradients

Abstract

Two rectangular plates with approximately clamped boundary conditions were used as spatial filters to measure the low wave number components of the wall pressure fluctuations beneath a turbulent boundary layer. The plates were designed to provide low wave number measurements at higher frequencies and wave numbers than previous plate experiments in order to provide data comparable to measurements made using microphone arrays. Measurements were made in the lower test section wall of the MIT low turbulence subsonic wind tunnel under zero pressure gradient and adverse pressure gradient conditions. The zero pressure gradient data lies in the wave number frequency range 2.5 <ωδ*/U∞<10 and 0.5 <k1δ*<1.8 while the adverse gradient data lies in the range 4.5 <ωδ*/U∞<23 and 0.9 <k1δ*<4.6. Momentum thickness Reynolds numbers ranged from 6000 to 11 000 for the zero pressure gradient case and 11 000 to 16 000 for the adverse pressure gradient case. When normalized on outer variables the adverse gradient data do not exhibit increased levels from those of the zero pressure gradient data. [Work supported by the Sonar Technology Program, Office of Naval Research.]