Flow topology in the wake of a cyclist and its effect on aerodynamic drag
Flow topology in the wake of a cyclist and its effect on aerodynamic drag
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骑自行车者尾随的流动拓扑及其对空气动力阻力的影响
DOI：
10.1017/jfm.2013.678
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发表时间：
2014
影响因子：
3.7
通讯作者：
John Sheridan
中科院分区：
文献类型：
--
作者：
Timothy Crouch;D. Burton;Nicholas A. T. Brown;Mark C. Thompson;John Sheridan
摘要对全尺寸自行车运动员人体模型的三维绕流进行了实验研究，以解释当腿部位于360 °曲柄循环周围时测得的气动阻力的大变化。据发现，影响阻力的主要机制是不是在踏板行程的正面表面积的小变化，而是由于在曲柄循环的流动结构的大变化。一系列详细的速度场尾流调查和表面摩擦流动可视化清楚地表明了这一点。识别两个特征流态，对应于对称的低阻力和不对称的高阻力制度，其中所示的主要特征的唤醒是一个大的拖尾流向涡对，在人体模型的中心平面不对称取向。尾流中的这些主流结构是驱动整个踏板行程中阻力变化的主要机制。拓扑临界点已被确定的吸力面上的人体模型的背部，并与速度场测量进行了讨论，以阐明时间平均流的拓扑结构，显示的主要流动结构的低和高阻力流制度。建议的流动拓扑结构，然后与测量的表面压力作用在人体模型的背部的吸力面。这些测量结果表明，阻力的变化大部分是由于作用在下背部的压力分布的变化，其中大尺度流动结构对阻力的影响最大。
Abstract Three-dimensional flows around a full-scale cyclist mannequin were investigated experimentally to explain the large variations in aerodynamic drag that are measured as the legs are positioned around the $360^\circ $ crank cycle. It is found that the dominant mechanism affecting drag is not the small variation in frontal surface area over the pedal stroke but rather due to large changes in the flow structure over the crank cycle. This is clearly shown by a series of detailed velocity field wake surveys and skin friction flow visualizations. Two characteristic flow regimes are identified, corresponding to symmetrical low-drag and asymmetrical high-drag regimes, in which the primary feature of the wake is shown to be a large trailing streamwise vortex pair, orientated asymmetrically in the centre plane of the mannequin. These primary flow structures in the wake are the dominant mechanism driving the variation in drag throughout the pedal stroke. Topological critical points have been identified on the suction surfaces of the mannequin’s back and are discussed with velocity field measurements to elucidate the time-average flow topologies, showing the primary flow structures of the low- and high-drag flow regimes. The proposed flow topologies are then related to the measured surface pressures acting on the suction surface of the mannequin’s back. These measurements show that most of the variation in drag is due to changes in the pressure distribution acting on the lower back, where the large-scale flow structures having the greatest impact on drag develop.