Boundary layer structure over standing waves

The boundary layer development and the onset and interaction of coherent structures over periodic standing waves were experimentally studied for various frequencies of wall oscillations. A customized Arduino-controlled mechanical system under a flexible wall allowed the formation of sinusoidal standing waves of 5 mm amplitude and 100 mm wavelength. The actuated wall has a section of 305 mm by 800 mm. It was placed and operated in a specially designed wind tunnel of 305 mm by 305 mm cross-section. We explored the near-wall turbulence development and large-scale coherent structure interaction for various Reynolds numbers and reduced frequency using phase-lock particle image velocimetry at different phase angles of the standing waves. We will discuss the modulation of distinct wall frequency on the turbulent energy of the flow and the coherence of energetic motions.