The surface flow pattern characteristics of barchan dunes

doi:10.7522/j.issn.1000-694X.2022.00168

Journal of Desert Research ›› 2023, Vol. 43 ›› Issue (4): 41-54.DOI: 10.7522/j.issn.1000-694X.2022.00168

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The surface flow pattern characteristics of barchan dunes

Linyan Luo¹^,²(), Xin Gao¹^,²(), Yongcheng Zhao¹^,²

^1.National Engineering Technology Research Center for Desert-Oasis Ecological Construction，Xinjiang Institute of Ecology and Geography，Chinese Academy of Sciences，Urumqi 830011，China
^2.University of Chinese Academy of Sciences，Beijing 100049，China

Received:2022-11-27 Revised:2022-12-15 Online:2023-07-20 Published:2023-08-14
Contact: Xin Gao

Abstract

Abstract:

At present， there is a lack of comprehensive understanding of the surface flow patterns over barchan dunes， especially the complex flow structure in the vortices zone， and thus further research is needed on the influence of morphological characteristics and flow velocity on the flow structure of barchan dunes. In this paper， the airflow characteristics over the surface of barchan dunes under different geometric parameters and different inlet velocities were studied using the CFD （Computational Fluid Dynamics） numerical simulation and the RNG k-ε turbulence model， focusing on the flow characteristics of the leeward side vortices zone and the relationship between its range and the geometric parameters of the dunes and the inlet velocities. The results show that：（1） The higher the height of the barchan dune， the larger the length of the wake vortices zone is， approximately 5-7 times the height of the dune. （2） The greater the gradient of the windward slope of the barchan dune， the greater the length of the wake vortices zone is， approximately 5-7 times the height of the dune. （3） The influence of inlet velocity on the position of the reattachment point is quite limited， and the length of the vortex zone caused by different inlet velocities is about 6-7 times the height of the dune， suggesting that the larger the inlet velocity is， the shorter the length of the wake protected zone and the smaller the disturbance of the dune on the flow can be found. This study comprehensively analyzes the shaping effect of the flow patterns on the shape of barchan dunes and further confirms the cause of the formation of small barchan dunes on the downstream of the horns of the upwind barchan dunes. Collectively， the current results can deepen the understanding of the evolution mechanism of barchan dune formation， and enrich the basic theory of aeolian geomorphology.

Key words: barchan dunes, CFD, 3D flow field, inlet wind velocity, wake vortex zone

CLC Number:

P931.3

Linyan Luo, Xin Gao, Yongcheng Zhao. The surface flow pattern characteristics of barchan dunes[J]. Journal of Desert Research, 2023, 43(4): 41-54.

Figures/Tables 11

Table 1 Mesh details at five different scales

网格	第一层网格高度/m	网格数
网格1	0.05	401 813
网格2	0.025	436 577
网格3	0.0125	614 183
网格4	0.00625	825 661
网格5	0.003125	1 213 342

Fig. 1 The effect of the mesh on the calculation results

Fig. 2 Layout diagram of field anemometer and the comparison of field measurement and CFD numerical simulations

Table 2 Parameters of the CFD simulation experiments

不同沙丘高度
高度/m	迎风坡坡度/（°）	迎风坡长度/m	背风坡坡度/（°）	背风坡长度/m	翼长/m	沙丘宽度/m	摩阻风速/（m·s^-1）
1.20	15.00	6.81	34.00	1.78	4.80	12.00	0.50
1.60	15.00	9.07	34.00	2.37	6.40	16.00	0.50
2.00	15.00	11.34	34.00	2.97	8.00	20.00	0.50
2.40	15.00	13.61	34.00	3.56	9.60	24.00	0.50
2.80	15.00	15.88	34.00	4.15	11.20	28.00	0.50
3.20	15.00	18.15	34.00	4.74	12.80	32.00	0.50
3.60	15.00	20.42	34.00	5.34	14.40	36.00	0.50
4.00	15.00	22.69	34.00	5.93	16.00	40.00	0.50
4.40	15.00	24.95	34.00	6.52	17.60	44.00	0.50
4.80	15.00	27.22	34.00	7.12	19.20	48.00	0.50
不同迎风坡坡度
高度/m	迎风坡坡度/（°）	迎风坡长度/m	背风坡坡度/（°）	背风坡长度/m	翼长/m	沙丘宽度/m	摩阻风速/（m·s^-1）
3.20	8.00	22.77	34.00	4.74	12.80	32.00	0.50
3.20	10.00	18.15	34.00	4.74	12.80	32.00	0.50
3.20	12.00	15.05	34.00	4.74	12.80	32.00	0.50
3.20	14.00	12.83	34.00	4.74	12.80	32.00	0.50
3.20	16.00	11.16	34.00	4.74	12.80	32.00	0.50
3.20	18.00	9.85	34.00	4.74	12.80	32.00	0.50
3.20	20.00	8.79	34.00	4.74	12.80	32.00	0.50
不同来流风速
高度/m	迎风坡坡度/（°）	迎风坡长度/m	背风坡坡度/（°）	背风坡长度/m	翼长/m	沙丘宽度/m	摩阻风速/（m·s^-1）
3.20	15.00	18.15	34.00	4.74	12.80	32.00	0.30
3.20	15.00	18.15	34.00	4.74	12.80	32.00	0.35
3.20	15.00	18.15	34.00	4.74	12.80	32.00	0.40
3.20	15.00	18.15	34.00	4.74	12.80	32.00	0.45
3.20	15.00	18.15	34.00	4.74	12.80	32.00	0.50
3.20	15.00	18.15	34.00	4.74	12.80	32.00	0.60
3.20	15.00	18.15	34.00	4.74	12.80	32.00	0.70
3.20	15.00	18.15	34.00	4.74	12.80	32.00	0.80
3.20	15.00	18.15	34.00	4.74	12.80	32.00	0.90
3.20	15.00	18.15	34.00	4.74	12.80	32.00	1.00

Fig. 3 The horizontal wind velocity distribution of the axis of the calculation domain at 0.1 m from the barchan dune surface under different working conditions （The zero point of the x-axis coordinates is located in the leeward slope toe of the dune）. A： Different dune heights. C： Different windward slope gradients. E： Different inlet velocities. B， D and F are the relationship between vortex zone and protected zone and dune heights， windward slope gradients and inlet shear velocities， respectively

Fig. 4 Cloud map of horizontal velocity distribution of barchan dunes with different heights. A-J are horizontal velocity distribution cloud map at 0.1 m from the surface； K-T are horizontal velocity distribution cloud map at the longitudinal profile of the central axis of the dunes

Fig. 5 Cloud map of vertical velocity distribution of barchan dunes under different working conditions. A-C： Different dune heights；D-F： Different windward slope gradients；G-I： Different inlet velocities

Fig. 6 Cloud map of horizontal velocity distribution of Barchan dunes with different windward slope gradients. A-G are horizontal velocity distribution cloud map at 0.1 m from the surface； H-N are horizontal velocity distribution cloud map at the longitudinal profile of the central axis of the dunes

Fig. 7 Cloud map of horizontal velocity distribution of barchan dunes under different inlet velocities. A-J are horizontal velocity distribution cloud map at 0.1 m from the surface； K-T are horizontal velocity distribution cloud map at the longitudinal profile of the central axis of the dunes

Fig. 8 Sketch of the flow field structure over the surface of barchan dune

Fig. 9 Three-dimensional streamline of the flow field over barchan dune

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The surface flow pattern characteristics of barchan dunes

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