Flow pattern change and drag coefficient enhancement for non-flattened pappus models due to reversed wind direction
The architectural features of dandelion seeds contribute to their excellent flight ability.Previous studies have primarily focused on the interaction between air flow and seeds when wind passes through dandelion seeds from pappus bottom to pappus top(called'type-Ⅰ wind'hereafter).However,it is also common that wind passes through dandelion seeds from pappus top to pappus bottom(called'type-Ⅱ wind'hereafter)during abscission on the inflorescence head or flight in the air,due to the atmospheric turbulence and the diversity in architectural features.Nevertheless,the interaction between airflow and seeds in the type-Ⅱ wind has not yet been investigated.In this study,we conducted numerical investigations on the variations in drag coefficients of dandelion pappus models and flow patterns around them in both wind types,considering changes in wind speed,pappus angle,and pappus porosity.Generally,flow pattems and drag coefficients could be significantly altered due to reversing wind direction.The disturbance of pappus'filaments to air flow is moved from the leeward side to the windward side when the wind changes from type-Ⅰ to type-Ⅱ,leading to that vortex rings in the type-Ⅱ wind to be more likely to attach to the central disk of non-flattened dandelion pappus models while separation vortex rings occur in the type-Ⅰ wind.The contribution of the pressure-induced drag force to the total drag force is largely promoted when the wind changes from type Ⅰ to type Ⅱ,resulting in the enhancement of the drag coefficients of non-flattened dandelion pappus models.However,the enhancement role may be weakened as wind speed,pappus angle,and pappus porosity increase.These findings will be helpful for further quantitative prediction of seed dispersal by wind and guiding the design of micro bionic air vehicles.
Dandelion seedPappus anglePappus porosityPressure coefficientVortex ring
傅林涛、范庆、黄宗柳、陈菲
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School of Architecture and Civil Engineering,Chengdu University Chengdu 610106,China
Zhuhai Campus of Zunyi Medical University,Zhuhai 519041,China
Key Laboratory of Fluid and Power Machinery,Ministry of Education,Xihua University,Chengdu 610039,China
Dandelion seed Pappus angle Pappus porosity Pressure coefficient Vortex ring
High-Level Talent Training Program at Chengdu University
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