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The leading-edge vortex and quasisteady vortex shedding on an accelerating plate

机译:加速板上的前沿涡旋和准稳态涡旋脱落

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摘要

A computational inquiry focuses on leading-edge vortex (LEV) growth and shedding during acceleration of a two-dimensional flat plate at a fixed 10°–60° angle of attack and low Reynolds number. The plate accelerates from rest with a velocity given by a power of time ranging from 0 to 5. During the initial LEV growth, subtraction of the added mass lift from the computed lift reveals an LEV-induced lift augmentation evident across all powers and angles of attack. For the range of Reynolds numbers considered, a universal time scale exists for the peak when α ≥ 30°, with augmentation lasting about four to five chord lengths of translation. This time scale matches well with the half-stroke of a flying insect. An oscillating pattern of leading- and trailing-edge vortex shedding follows the shedding of the initial LEV. The nondimensional frequency of shedding and lift coefficient minima and maxima closely match their values in the absence of acceleration. These observations support a quasisteady theory of vortex shedding, where dynamics are determined primarily by velocity and not acceleration. Finally, the nondimensional vortex formation time is found to be a function of the Reynolds number, but only weakly when the Reynolds number is high.
机译:一个计算研究集中在二维平板在固定的10°–60°迎角和低雷诺数的加速过程中前沿涡(LEV)的增长和脱落。板块从静止状态以从0到5的时间幂给出的速度加速。在初始LEV增长期间,从计算出的升力中减去增加的质量升力会发现LEV引起的升力在所有功率和角度上均明显增加攻击。对于所考虑的雷诺数范围,当α≥30°时,峰存在一个通用的时间标度,并且增强持续约4至5个和弦长度的平移。此时间刻度与飞行昆虫的半冲程非常吻合。最初的LEV脱落之后,前缘和后缘涡旋脱落的振荡形式。在没有加速度的情况下,脱落和升力系数最小值和最大值的无量纲频率与它们的值紧密匹配。这些观察结果支持涡流脱落的准稳态理论,其中动力学主要由速度而不是加速度决定。最后,发现无量纲涡旋形成时间是雷诺数的函数,但仅当雷诺数高时才微弱。

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