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Numerical study on the freely falling plate: Effects of density ratio and thickness-to-length ratio

机译：自由落体板的数值研究：密度比和厚度/长度比的影响

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A numerical study on two-dimensional (2D) rectangular plates falling freely in water is carried out in the range of 1.2 <= rho(s/f) <= 5.0 and 1/20 <= beta <= 1/4, where rho(s/f) is the solid-to-water density ratio and beta is the plate thickness-to-length ratio. To study this problem, the immersed boundary-lattice Boltzmann flux solver in a moving frame is applied and validated. For the numerical result, a phase diagram is constructed for fluttering, tumbling, and apparent chaotic motions of the plate parameterized using rho(s/f) and beta. The evolution of vortical structures in both modes is decomposed into three typical stages of initial transient, deep gliding, and pitching-up. Various mean and instantaneous fluid properties are illustrated and analyzed. It is found that fluttering frequencies have a linear relationship with the Froude number for all cases considered. Lift forces on fluttering plates are linearly dependent on the angle of attack alpha at the cusp-like turning point when vertical bar alpha vertical bar >= pi/5. Hysteresis of the lift force on fluttering plates is observed and explained whilst the drag forces are the same when vertical bar alpha vertical bar has the same value. Meanwhile, the drag force in the tumbling motion may have a positive propulsive effect when the plate begins a tumbling rotation from alpha = pi/2. Published by AIP Publishing.
机译：二维（2D）矩形板在水中自由下落的数值研究是在1.2 <= rho（s / f）<= 5.0和1/20 <= beta <= 1/4的范围内进行的（s / f）为固水比，β为板厚与长度之比。为了研究这个问题，应用并验证了在运动框架中浸入的边界晶格玻尔兹曼通量求解器。对于数值结果，构造了一个相位图，用于使用rho（s / f）和beta参数化的板的颤动，翻滚和明显的混沌运动。两种模式下旋涡结构的演化都被分解为初始瞬变，深滑和俯冲的三个典型阶段。示出并分析了各种平均和瞬时流体特性。发现在所有考虑的情况下，颤振频率与弗洛德数均具有线性关系。当垂直条alpha垂直条> = pi / 5时，振板上的升力线性依赖于尖点状转折点的迎角α。当垂直杆alpha垂直杆的值相同时，观察并说明了振板上的提升力的滞后现象，而曳力相同。同时，当板从α= pi / 2开始翻滚旋转时，翻滚运动中的阻力可能具有积极的推动作用。由AIP Publishing发布。

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