Do Flexible Surface-Hairs Manipulate Near-Wall Turbulence?
Turbulent boundary layer flow over a flat plate with an artificial hairy coating is investigated. Flexible hairs of appropriate dimensions are chosen to achieve strong reconfiguration in streamwise direction with the mean flow such that their long cylindrical trailing bodies are placed in the buffer layer. Elasticity, anisotropic flow-opposing body forces and hydrodynamic interaction of the hairs in combination with the travelling wave-type nature of near-wall turbulence lead in sum to an energy transfer from small scale motion to a more coherent motion pattern near the wall with increased coherence in streamwise and spanwise direction. It is concluded from the experiments that appropriate geometrical arrangements of surface-hairs can be beneficial for reduction of turbulent skin friction.
KeywordsTurbulent Boundary Layer Drag Reduction Streamwise Direction Spanwise Direction Minimum Response Time
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