Two-Phase Structures in High-Reynolds-Number Sand-Laden Wall-Bounded Turbulence

Sandstorms, a high Reynolds number gas-solid two-phase wall turbulence, occur on the erodible sandy surfaces. The quantitative analysis of the nonstationary stages of sandstorms can help us better understand their occurrence and development, and provide scientific basis for optimally designing the prevention measures. It also contributes to quantitative research on the nonstationary sandstorms process, which is a open issue with multiphase modulation, multiphysical coupling, multiscale and highly nonlinear interlacing. In this study, a nonstationary signal processing method is proposed based on the empirical mode decomposition and adaptive segmentation. Then it is used to analyze the sandstorm data obtained from the occurrence and evolution process of sandstorms. Results revealed that the competitive evolutionary process of the main driving factors in the early, middle and late stages of sandstorms, as shear turbulence becomes dominant and is then suppressed by enhanced thermal stability. This results in some different characteristics and rules of turbulent motions between the nonstationary and stationary stages during the sandstorms. Even in the steady stage of sandstorms, the turbulence exhibits significant differences with the sand-free flow due to the present of dust/sand particles. Additionally, studies based on sandstorm data originally revealed that in addition to flow filed, the dust field is also found to exist coherent structures with streamwise scales larger than 5 times the surface layer thickness. The difference and connection between the dust concentration and the flow field structure is also revealed.