斑块状沙化草甸周围气流流场特性的数值风洞实验

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摘要为探讨沙化草地斑块状草甸下垫面条件下的风沙侵蚀机制，将草甸概化为多孔介质，通过附加源项改进湍流模型，以期精确表征草甸对来流的干扰作用，再基于Hesp （2019）现场试验中草甸覆盖度工况，验证Standard k-ε、RNG k-ε和Realizable k-ε模型并寻优后，结合黄河上游玛曲段近地面（2m高度处）风速，开展草甸覆盖度15.75%（稀疏）、31.05%（中度）和60.15%（稠密）和起沙风速7m/s （低）、11m/s （中）和15m/s （高）下单个斑块状草甸（1m×1m）周围正向来流条件下的流场特性数值风洞实验.结果表明：草甸水平向流场总体呈现迎风侧形成半圆形低速区、背风侧形成半椭圆遮蔽区并呈辐射状向顺风向拓展、两侧局部加速的绕流特征.垂向风速总体呈现为迎风侧风速减弱、正上方骤然加速、背风侧大范围减速规律.覆盖度一定时，草甸周围平均风速随来流风速增大而逐渐增大；来流风速一定，覆盖度增大时，草甸背风侧平均风速先增大后减小.草甸周围风速分布符合正态分布，迎风侧为高狭峰，背风侧为低阔峰；迎风侧风速分布可拟合为高斯模型的变异函数，背风侧风速变异函数与来流风速和覆盖度存在密切关系.本文提出的RNG k-ε改进湍流模型可作为精确表征柔性草甸周围复杂流场的数学模型，以期为进一步模拟中、大尺度草甸风沙流场奠定理论基础.

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关键词 ：草场沙化, 斑块状草甸, 多孔介质源项, 流场特性, 数值风洞

Abstract：In order to explore the mechanism of wind-sand erosion under the condition of patchy meadow underlying surface in desertified grassland, here in this paper, the meadow is generalized as porous medium for geometric modeling and the turbulence model is improved by additional porosity source terms in order to accurately characterize the interference effects of meadow on incoming air flow. Subsequently, based on the meadow coverage condition in the field test of Hesp (2019), the Standard k-ε, RNG k-ε and Realizable k-ε models are validated and optimized to achieve the model improvement. By referring to the wind speed near the ground (at 2m height) in the Maqu section of the Upper Yellow River, the numerical wind tunnel experiments of flow field characteristics around a single patchy meadow (1m×1m) were carried out under the conditions of meadow coverage of 15.75% (sparse), 31.05% (moderate) and 60.15% (dense) and forward threshold wind speed of 7m/s(low), 11m/s (medium) and 15m/s (high). The results show that a semi-circular low-speed zone on the windward side and a semi-elliptical shelter zone on the leeward side occur generally in the horizontal direction surrounding the meadow, the latter of which expands radially along the wind and accelerates in part on both sides. Moreover, for the vertical direction, the wind speed distribution generally shows the law of weakening on the windward side, sudden acceleration directly above, and large-scale deceleration on the leeward side. When the coverage is constant, the average wind speed around the meadow increases corresponding to the increase of the incoming wind speed. When the incoming wind speed remains constant and the coverage increases, the average wind speed on the leeward side of the meadow increases first and then decreases. The wind speed distribution around the meadow conform to the law of normal distribution, with a high narrow peak on the windward side and a low broad peak on the leeward side. The wind speed profile on the windward side can be fitted as the variogram of the Gaussian model, and the wind speed variogram on the leeward side closely relates to the incoming wind speed and coverage. The improved RNG k-ε turbulence model proposed in this paper can be used as a mathematical model to accurately characterize the complex air flow around the flexible meadow, which is also expected to provide a theoretical foundation for further numerical simulation of the wind-sand flow field for medium and large scale meadows.

Key words： grassland desertification patchy meadow porosity source air flow characteristics numerical wind tunnel

收稿日期: 2023-04-11

PACS:

X169

基金资助:国家自然科学基金资助项目（42167043，51269009）；甘肃省重点研发计划项目（20YF8ND141）

通讯作者: 王之君,副教授,wzj1159@163.com E-mail: wzj1159@163.com

作者简介: 王之君(1980-),男,甘肃武威人,副教授,博士,主要从事土壤侵蚀与水土保持研究.发表论文30余篇.wzj1159@163.com.

引用本文:

王之君, 张开和. 斑块状沙化草甸周围气流流场特性的数值风洞实验[J]. 中国环境科学, 2023, 43(11): 5687-5699. WANG Zhi-jun, ZHANG Kai-he. Numerical wind tunnel experiment on surrounding air flow field characteristics of the desertified patchy meadow. CHINA ENVIRONMENTAL SCIENCECE, 2023, 43(11): 5687-5699.

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http://www.zghjkx.com.cn/CN/ 或 http://www.zghjkx.com.cn/CN/Y2023/V43/I11/5687

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