Experiment sheds light on dune hydrodynamics

Sand and gravel dunes can be found on beaches, deserts, and the floors of rivers and oceans. Through research on the air or water flow over these bedforms, scientists are trying to decipher the dynamics dictating the evolution of these terrains. Previous research on hydrodynamic flow over dunes has mostly focused on single-dune formation, although dunes tend to form in series in real-world scenarios.

Dey et al. experimentally studied the flow of water over a series of dunes using a 2D setup. They performed their experiments in a 15-meter-long, steel-bottomed artificial channel, with a gravel-bottom shaped into a series of dunes, and observed how the dunes changed using an Acoustic Doppler Velocimeter.

By analyzing the time-averaged and spatially-averaged data, they detailed their findings regarding the flow vorticity and turbulence structures and how these shape the dunes.

“In a fluvial environment, the near-bed flow structures provide the key mechanism of the formation and the development of bedforms. Also, an in-depth investigation of the flow quantities enabled us to comprehend the interaction between flow and dunes from the outlooks of their spatial field in a time-averaged sense, and spatiotemporally averaged distributions,” said author Subhasish Dey.

“This experimental campaign takes a major step forward in advancing the current state-of-the-science of flow over dunes and opens multiple research avenues; for instance, dynamics of bed evolution and stability of gravel streambeds,” said Dey.

Next, the authors look to expand their research by using particle image velocimetry to study the flow velocity and turbulence over a series of mobile dunes.

Source: “Hydrodynamics of flow over two-dimensional dune,” by Subhasish Dey, Prianka Paul, Hongwei Fang, and Ellora Padhi, Physics of Fluids (2020). The article can be accessed at https://doi.org/10.1063/1.5144552 .