Journal Article

Turbulent Flow Structures Over a Gobi Surface and Their Impact on Aeolian Sand Transport

Tan, Lihai, Wang, Hongtao, An, Zhishan, Wang, Tao, Zhao, Suping, Qu, Jianjun

2023

Overview

Here, we present the results of turbulent flow structures and their influence on aeolian sand transport over gobi surfaces based on quadrant analysis. The results show that the classified turbulent structures over gobi accounted for 43%–44% of the time frequency and contributed ∼97% to the Reynolds stress, yet the contribution rates to sand transport rate ranged from 45% to 52%. Sweeps (Quadrant 4) and ejections (Q2) were the two most frequent events and accounted for 70% of the total frequency for the classified turbulent structures. Sweeps made a major contribution of 51%–57% to sand transport rate over gobi. Outward interactions (Q1) were relatively rare, but they individually entrained as much sand as sweeps of comparable magnitude and duration. The turbulent structures over gobi show similar behaviors comparable to those of water flows over gravel riverbeds or rough seabeds yet different from those of air flow over flat sand surfaces. Plain Language Summary Turbulence is the driving factor for aeolian sand transport. Turbulence behavior over gobi, a major type of rough land surface in Asia, and its influence on sand transport are poorly understood. Quadrant analysis has been widely used to evaluate boundary layer turbulence based on the streamwise (u′) and vertical (w′) fluctuating wind speed components from the mean. Four distinct quadrants can be defined, that is, outward interactions (Q1) (u′ > 0, w′ > 0), ejections (Q2) (u′ < 0, w′ > 0), inward interactions (Q3) (u′ < 0, w′ < 0), and sweeps (Q4) (u′ > 0, w′ < 0). The quadrant analysis shows that sweeps and ejections were the two most frequent turbulent structures over gobi, accounting for a total frequency of 70%. Sweeps made the largest contribution to sand transport rate over gobi. In contrast, outward interactions were individually as effective as sweeps, and they contributed less to sand transport rate than sweeps only because they were less common. The presence of gravel on the gobi surface affects the surrounding flow field and makes the turbulent structures different from those over flat sand surfaces, highlighted by the more frequent occurrence of ejections and sweeps, whereas they show similar characteristics to those over gravel riverbeds or rough seabeds. Key Points Turbulent flow structures over a gobi surface and their impact on sand transport rate were examined Sweeps made the largest contribution to sand transport rate over gobi, while outward interactions were individually as effective as sweeps The behavior of turbulent flow over gobi surfaces shows similar turbulence characteristics to water flows over rough riverbeds or seabeds

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: aeolian sand transport / Air flow / Analysis / Boundary layer turbulence / Boundary layers / Eolian sands / Flow structures / Fluid dynamics / gobi / Gravel / Ocean floor / Periodicity / quadrant analysis / Quadrants / Reynolds stress / River beds / Riverbeds / saltation / Sand / Sand transport / Sediment transport / Transport rate / Turbulence / Turbulent flow / turbulent flow structure / Water flow / Wind speed