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Wind tunnel experiments of air flow patterns
over nabkhas modeled after those from the Hotan River basin, Xinjiang,
China (I): non-vegetated |
| LI Zhizhong1, WU Shengli1, GE Lin1, HE Mudan1, WANG Xiaofeng1, JIN Jianhui1, MA Rong1, LIU Jinwei1, LI Wanjuan1, DALE Janis2 |
| 1.School of Geography Science and Tourism, Xinjiang Normal University; 2.Department of Geology, University of Regina; |
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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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Issue Date: 05 September 2008
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|
| 1 |
Hasi. , Wang G Y, Dong G R (2000). Geomorphological significance ofair low over reticulate dunes of the southeastern Tengger desert. Journal of Desert Research, 20(1): 30–34 (in Chinese)
|
| 2 |
Hesp P A (1981). The formation of shadow dune. Journal of Sedimentary Petrology, 51: 101–112
|
| 3 |
Hu M C, Zhao A G, Li N (2002). Sand-trapping efficiency of railwayprotective system in Shapotou tested by wind tunnel. Journal of Desert Research, 22(6): 598–602 (in Chinese)
|
| 4 |
Li Z Z, Chen G T (1995). Experimentalstudy on the structure of wind-tunnel flow pattern for Pyramid dune:giving consideration to a model for Pyramid dune formation. Journal of Desert Research, 15(3): 227–233 (in Chinese)
|
| 5 |
Li Z Z, Guan Y Z (1996). Experimentalstudy on imitative flow pattern of longitudinal and transverse dunes. Journal of Desert Research,16(4): 360–363 (in Chinese)
|
| 6 |
Ling Y Q, Liu S Z, Wu Z et al (1997). Analysis on dynamics conditions ofPyramid dunes formation. Journal of DesertResearch, 17(2): 112–118 (in Chinese)
|
| 7 |
Ling Y Q, Qu J J, Jin J (2003). Influence of sparse natural vegetationon sand-transporting quantity. Journalof Desert Research, 23(1): 12–18 (in Chinese)
|
| 8 |
Liu X P, Dong Z B (2002). Windtunnel tests of the roughness and drag partition on vegetated surfaces. Journal of Desert Research, 22(1): 82–88 (in Chinese)
|
| 9 |
Liu X P, Dong Z B (2003). Aerodynamicroughness of gravel beds. Journal of DesertResearch, 23(1): 38–46 (in Chinese)
|
| 10 |
Liu X W (1995). Experimental physics and engineer of wind-sand experiment. Beijing: Science Press, 66–68 (in Chinese)
|
| 11 |
Qu J J, Lin Y Q, Zhang W M et al. (1992). Preliminary observation and study on the formation mechanism of Pyramiddune. Journal of Desert Research, 12(4): 19–27 (in Chinese)
|
| 12 |
Stam J M T (1997). On the modeling of two-dimensional Aeolian dunes. Sedimentlogy, 44: 127–141.
doi:10.1111/j.1365‐3091.1997.tb00428.x
|
| 13 |
Tseo G (1993). Two types of longitudinal dune fields and possible mechanismsfor their development. Earth Surface Processesand Landforms, 18: 627–643.
doi:10.1002/esp.3290180706
|
| 14 |
Walker I J (1999). Secondary airflow and sediment transport in the leeof a reversing dune. Earth Surface Processesand Landforms, 24: 437–448.
doi:10.1002/(SICI)1096‐9837(199905)24:5<437::AID‐ESP999>3.0.CO;2‐Z
|
| 15 |
Wang X M, Dong Z B, Zhao A G (2004). Air flow and particle-size distributionsand their significance on the dynamic process of a simple transversedune. Journal of arid land resources &environment, 18(4): 29–34 (in Chinese)
|
| 16 |
Wiggs G F S, Livingstone I, Wancen A (1996). The role of streamline curraturein sand dune dynamics: evidence form field and wind tunnel measurements. Geomorphology, (17): 29–46
|
| 17 |
Wu Z (2003). Geomorphology of wind-drift sands and their controlledengineering. Beijing: Science Press, 400–404 (in Chinese)
|
| 18 |
Zhang W M, Li X Z, Qu J J, et al. (1998). The flow field and its dynamicsprocess of pyramidal dune. Journal of desertresearch, 18(3): 215–220 (in Chinese)
|
| 19 |
Zhang J W, Chen G T (1999). The surfacedynamics process of linear dune in central area of Taklimakan desert. Journal of desert research, 19(2): 128–134 (in Chinese)
|
| 20 |
Zhu Z D, Wu Z (1981). Studyon sand landform in Taklimakan desert. Beijing: Science Press, 41–48 (in Chinese)
|
| 21 |
Zhu Z D, Chen G T, Wang T et al. (1994). Sandy desertification in China. Beijing: Science Press, 24–25 (in Chinese)
|
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