Splash dynamics of aeolian sediment transport

The aeolian saltation cloud is controlled by the rebound and splash of particles upon impact with the bed. The vertical particle concentration profile and the subsequent reduction in near-bed fluid velocity are intricately linked. However, conceptual and numerical models of the fundamental interactions between the impacting and rebounding particles are often difficult to validate. Currently, sensor capabilities are limited in measuring particle-bed interactions directly. We present a series of wind tunnel experiments using Particle Tracking and Imaging Velocimetry (PTV/PIV) to overcome these measurement limitations by unobtrusively measuring particles in transport under various flow and particle concentration regimes.

Two synchronized high-speed video cameras captured the sand grains in motion. A 2 mm sheet of light from a 7-watt laser diode and an array of high-powered LEDs illuminated the particles. From the PTV data, we calculated the splash event impacts and ejections and trajectory characteristics of the particles in transport over flat and rippled beds. Additionally, a laser particle counter and sediment traps estimated sediment flux, while a pitot tube and sonic anemometer measured flow regimes. A TLS measured ripple dimensions.

We report the results from a set of wind tunnel experiments over flat and rippled beds that includes the direct observations of (1) the splash events across the stoss and lee slope, (2) the spatial variability of the vertical concentration profiles of particles in transport, (3) the impact, rebound, and ejection angles and velocities of splash events during low, moderate and high transport rates. We find the splash events change with transport rate. We find the splash event characteristics change with transport rate. We propose future models to include the transition of particle-to-bed interactions with sediment transport flux.