The field data acquisition and image recognition of sand streamers.

China has curbed the spread of desertification through vegetation restoration, yet in vast desert regions, the microscopic mechanisms of wind-blown sand movement remain largely unknown. This lack of detailed mechanical support hampers the design and efficient evaluation of traditional sand-control engineering.

In near-bed regions, the sediment transport process exhibits fascinating self-organizing characteristics: rather than driving sand particles uniformly, the airflow organizes them into long, winding, narrow streamers.

These unique structures, often only about 15 centimeters wide but reaching several meters in length, are the fundamental form of surface sand movement, with their spatial and temporal characteristics directly impacting the total material transport during sandstorms. However, how these sand streamers form and how their geometry changes with wind speed have long lacked precise quantitative measurements and mechanical studies.

To address these issues, Professor Zhang Yang's research group at the School of Energy and Power Engineering of Xi'an Jiaotong University (XJTU), in collaboration with a team from King's College London, has designed and established a high-resolution field-synchronous measurement system.

Using self-developed image processing algorithms, they quantified, for the first time under natural atmospheric boundary-layer conditions, the coupling between key geometric scales of sand streamers and near-surface turbulent wind fields.

They discovered three critical phenomena:

1. Sand streamers preferentially appear in high-velocity turbulent "corridors", where sediment concentration correlates positively with wind speed. This proves they are the visual footprints of large-scale, coherent atmospheric structures mapped onto the bed surface.

2. Regardless of changes in wind speed or turbulent kinetic energy, the width of streamers remains stable at approximately 15 centimeters.

3. The lateral distance between streamers increases as wind speed rises, a phenomenon that had never been quantitatively reported before.

The study further analyzed the turbulent structure spectra near the bed and provided a unified physical explanation based on the "top-down modulation" framework of wall-bounded turbulence. The constant width of streamers is attributed to the inherent scale stability of the energy footprints of large-scale coherent structures acting on the near-bed region.

Meanwhile, the increase in spacing with wind speed stems from the lateral expansion of driving vortices and the streamers' self-adaptive adjustment of spatial density within the flow field.

This research reveals the complex coupling laws between atmospheric turbulence and surface sand particles. It provides a new theoretical basis for refining wind-sand flux prediction models under wall-bounded turbulence conditions, thereby assisting in the strategic planning and layout of human-engineering facilities, such as desert photovoltaic power stations.

The research findings, titled Multiscale coupling of boundary layer flow turbulence and sand streamer dynamics, were published in Geophysical Research Letters, a prestigious international geosciences journal.