Wind tunnel experiments of air flow patterns over nabkhas modeled after those from the Hotan River basin, Xinjiang, China (I): non-vegetated |
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| Authors: | Zhizhong Li Shengli Wu Janis Dale Lin Ge Mudan He Xiaofeng Wang Jianhui Jin Rong Ma Jinwei Liu and Wanjuan Li |
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| Institution: | (1) School of Geography Science and Tourism, Xinjiang Normal University, Urumqi, 830054, China;(2) Department of Geology, University of Regina, Regina, SK, Canada, S4S 0A2 |
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| Abstract: | A nabkha is a vegetated sand mound, which is typical of the aeolian landforms found in the Hotan River basin in Xinjiang,
China. This paper compares the results of a series of wind tunnel experiments with an on-site field survey of nabkhas in the
Hotan River basin of Xinjiang. Wind tunnel experiments were conducted on semi-spherical and conical sand mounds without vegetation
or shadow dunes. Field mounds were 40 times as large as the size of the wind tunnel models. In the wind tunnel experiments,
five different velocities from 6 to 14 m/s were selected and used to model the wind flow pattern over individual sand mound
using clean air without additional sand. Changes in the flow pattern at different wind speeds resulted in changes to the characteristic
structure of the nabkha surface. The results of the experiments for the semi-spherical sand mound at all wind velocities show
the formation of a vortex at the bottom of the upwind side of the mound that resulted in scouring and deposition of a crescentic
dune upwind of the main mound. The top part of the sand mound is strongly eroded. In the field, these dunes exhibited the
same scouring and crescentic dune formation and the eroded upper surface was often topped by a layer of peat within the mound
suggesting destroyed vegetation due to river channel migration or by possible anthropogenic forces such as fuel gathering,
etc. Experiments for the conical mounds exhibit only a small increase in velocity on the upwind side of the mound and no formation
of a vortex at the bottom of the upwind side. Instead, a vortex formed on the leeward side of the mound and overall, no change
occurred in the shape of the conical mound. In the field, conical mounds have no crescentic dunes on the upwind side and no
erosion at the top exposed below peat beds. Therefore, the field and laboratory experiments show that semi-spherical and conical
sand mounds respond differently to similar wind conditions with different surface configuration and development of crescent-shaped
upwind deposits when using air devoid of additional sediment.
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Translated from Journal of Desert Research, 2007, 27(1): 9–14 译自:中国沙漠] |
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| Keywords: | nabkha sand mounds wind tunnel experiment wind flow pattern |
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