Sidewall effects and sand trap efficiency in a large wind tunnel

• Published in: Earth surface processes and landforms Vol. 43; no. 6; pp. 1252 - 1258
• Main Authors: Hong, Cheng, Yi, Fang, Sherman, Douglas J., Chenchen, Liu, Xueyong, Zou, Kaidi, Zhang, Liqiang, Kang
• Format: Journal Article
• Language: English
• Published: Bognor Regis Wiley Subscription Services, Inc 01.05.2018
• Subjects: Bed load; centerline of wind tunnel; Earth; Earth surface; Efficiency; Eolian sands; Eolian transport; Mars surface; Methods; Sampling; Sand; Sand transport; Sediment transport; Sediment traps; Sediments; shear velocity; Titan; Transport; Transport rate; Trap efficiency; Traps; vertically‐segmented trap; Weighing; Wind; wind tunnel calibration; Wind tunnel testing; Wind tunnels
• ISSN: 0197-9337; 1096-9837
• DOI: 10.1002/esp.4311

Aeolian sand transport is a widespread physical phenomenon on the surface of Earth, as well as on Mars and Titan. Accurate measurements of the components of the transport system are necessary if we are to understand the nature of the physical processes. Sand traps are typically used to measure sediment transport rates, and issues associated with the sampling efficiency of traps and the development of reliable traps have received considerable attention in recent decades. In this study, we measured aeolian transport rate at five distances from a wind tunnel sidewall using a vertically‐segmented sand trap. Total transport rates were determined by weighing the bed sediment before and after each experiment, and with and without a trap installed. The following results were obtained: (1) sand transport increased linearly with the distance away from the sidewall, and the appropriate location to measure maximum transport is within the central 20% of the wind tunnel; (2) current methods overestimate the sampling efficiency of sand traps when comparing trap data to transport rate data obtained by weighing sand moved through the entire tunnel because the effects of the sidewalls in decreasing total transport are neglected; (3) the efficiency of the vertically‐segmented trap that we tested ranged from 11.57% to 31.68% using our revised methods, whereas standard methods caused efficiency to be overestimated by 32–72% of the efficiency; (4) using either method, the efficiency of the trap increased exponentially with shear velocity for the range we used. Copyright © 2017 John Wiley & Sons, Ltd. A vertically segregated sand trap was tested in the 1 m × 1 m cross‐section wind tunnel at Beijing Normal University. After the trap efficiency was quantified, the trap was used to measure the sidewall effect on spanwise variability of sand transport. Our findings indicate that wind tunnel results of studies of sand transport may include substantial methodological bias, and suggest the importance of calibrating individual wind tunnels to account for sidewall effects.