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Effect of grid-generated turbulence on the dynamics of a flexible filament hanging in cross-flow

Abstract:

This paper describes preliminary experiments carried in a wind tunnel to study the effect of different turbulence intensities (nominally Tu=0.6,0.8 and 1.0%) on the dynamics of a flexible silicone filament (length to diameter ratio L/D=83) hanging in crossflow in the range of reduced velocities of 7 < U* < 108. The turbulence intensity inside the wind tunnel was modified by employing two different grids (porosity β=0.563 and 0.026). At low reduced velocities the filament was statically reconfigured but remained mostly rectilinear along its length. As the reduced velocity was further increased the filament started vibrating, and beyond a certain critical reduced velocity large-amplitude limit-cycle oscillation motions were observed. It is suggested that the turbulence intensity (shear velocity) affects the onset of the flapping motions and the amplitude of these. However, this behavior also depends on the turbulence integral length scale.