Investigation of the stable interaction of a passive compliant surface with a turbulent boundary layer

The near-wall flow structure of a zero-pressure-gradient flat-plate turbulent boundary layer with a single-layer viscoelastic compliant surface was visualized using the hydrogen-bubble technique. The compliant materials were made by mixing silicone elastomer with silicone oil. The flow-visualization experiments indicated low-speed wall streaks with increased spanwise spacing and elongated spatial coherence compared to those obtained on a rigid surface. More interestingly, an intermittent relaminarization-like phenomenon was observed at low Reynolds numbers for the particular compliant surface investigated. Apparently, the observed changes in the near-wall flow structure over the compliant surface are caused by the stable interaction between the compliant surface and the turbulent flow-field. Optical holographic interferometry and laser Doppler velocimetry were also employed to obtain the basic parameters of the turbulent boundary layers and the flow-induced compliant-surface displacements to better understand the physics of the interaction between a turbulent boundary layer and a passive compliant surface.