构树叶在风中的形态重构

Reconfiguration of paper mulberry leaves in wind

通过风洞实验研究垂直于来流悬挂的构树叶在0~25m/s风速段的形态重构现象.根据构树叶分裂情况将其分成心形、单侧分裂、双侧分裂3种,迎风面正、反面各半.在实验风速段内,构树叶存在3类形态(飞翼形、锥形、薄三角翼形),主要有3种卷缩方式(U形、ω形和σ形).统计数据表明,树叶分裂情况会在发生概率上影响重构的形态和卷缩方式,但不会从根本上决定某一形态或卷缩方式的出现.与正面迎风比较,反面迎风的失稳重构次数减少,气动性能更佳.叶片角在风速小于6m/s时随风速增加锐减,然后变化速度减缓,最后风速大于14m/s后在0°附近几乎不变;随着雷诺数增加,构树叶的阻力系数减小,最后稳定于0.05附近.

Reconfiguration of paper mulberry leaves hanged to the flow in the 0～25 m/s wind were studied. The leaves were divided into three kinds according to lobed bases, heart shape, unilateral fissure and symmetric fissure. The number of front or back surface facing wind was equal. There were three types in steady status, wing shape, conical shape and thin delta wing. There were three main rolling up ways： U,w and б type in the range of wind speed 0～25 m/s. The shape of lamina affected the proportions of three steady status of the whole and three ways of rolling up, but it did not fundamentally decide the status and way of rolling up as was shown by the statistics of the results. Compared with the front, the back surface was better in aerodynamic performance with few vibrations. The blade angles increased sharply when the wind speed was less than 6 m/s, then slowed down, and almost were stable near 0°after 14 m/s. With the increasing of the flow Reynolds number, the coefficient of drag decreased, and it was in the vicinity of 0.05 finally.