The destabilization of an erodible sediment bed by a reproducible impulsive phenomenon is studied experimentally.For this,a specific setup is designed to produce a well-controlled isolated vortex,advected over a unifo...The destabilization of an erodible sediment bed by a reproducible impulsive phenomenon is studied experimentally.For this,a specific setup is designed to produce a well-controlled isolated vortex,advected over a uniform sand bed.Particle image velocimetry(PIV)measurements are performed to get fluid flow information;suspended particles images are also recorded.A new measurement technique,based on a stereo-correlation method,provides a precise reconstruction of the bedform morphology over time.Strong turbulent structures(namely sweep events)are evidenced in a near-wall region,where particles are mainly dislodged.The sediment plume follows the vortex:in particular,the upward velocity inside maintains the suspension phenomenon.However,the dispersion process seems to be not dependent on the vortex parameters.Then,the bed morphology is investigated:a scour hole is dug as the vortex hits the granular layer.Its dynamics is described by a typical scour law,even if the initial perturbation is transient.Another area,where the particles settled,can be observed:it behaves like a ripple,with a logarithmic growth of its crest.This deposition region has a specific geometry,studied here by a Fourier contour approach.Finally,a pickup rate is also derived from the morphological data:it appears independent of the vortex and bedform features.展开更多
文摘The destabilization of an erodible sediment bed by a reproducible impulsive phenomenon is studied experimentally.For this,a specific setup is designed to produce a well-controlled isolated vortex,advected over a uniform sand bed.Particle image velocimetry(PIV)measurements are performed to get fluid flow information;suspended particles images are also recorded.A new measurement technique,based on a stereo-correlation method,provides a precise reconstruction of the bedform morphology over time.Strong turbulent structures(namely sweep events)are evidenced in a near-wall region,where particles are mainly dislodged.The sediment plume follows the vortex:in particular,the upward velocity inside maintains the suspension phenomenon.However,the dispersion process seems to be not dependent on the vortex parameters.Then,the bed morphology is investigated:a scour hole is dug as the vortex hits the granular layer.Its dynamics is described by a typical scour law,even if the initial perturbation is transient.Another area,where the particles settled,can be observed:it behaves like a ripple,with a logarithmic growth of its crest.This deposition region has a specific geometry,studied here by a Fourier contour approach.Finally,a pickup rate is also derived from the morphological data:it appears independent of the vortex and bedform features.
