OBSERVATIONS OF VORTEX-INDUCED PRESSURE FORCES ACTING ON SAND GRAINS OVER RIPPLES

Two-dimensional moveable sand ripples were generated in an oscillatory flow tunnel, and high-resolution measurements of fluid-sediment interactions were made with a Particle Image Velocimetry system to assess sediment transport processes. Here we present observations of vortex-induced pressure forces acting on coarse sand grains suspended above the ripple slope, just prior to flow reversal. The sand grains were observed to move from a region of high dynamic pressure to low dynamic pressure perpendicular to the ripple slope, as would be expected from an object being impacted by a lift force. Further analyses will be conducted to calculate the lift and drag forces acting on the grains, as well as to determine the role of shear stresses and pressure gradients in mobilizing and transporting the sediment grains under these oscillatory flows.