Abstract

The sensitivity of the drag to the rear design of a flat-back body is investigated under different body attitudes defined by the pitch ( \(-1.5^\circ , 0^\circ , +1.5^\circ\) ) and yaw (up to \(15^\circ\) ). The rear design consists of taper angles at the top and bottom trailing edge varying from \(0^\circ\) (no taper) to \(12.5^\circ\) . Compared to the fixed optimal rear design that minimizes drag at the wind-aligned body attitude, the rear design adaptation to the change of attitude produces a noticeable drag reduction up to 5% depending on the pitch angle within a yaw range smaller than \(2^\circ\) . It is shown that this drag reduction is related to the vertical wake steady instability interfering with the rear design. For yaw larger than \(2^\circ\) and up to \(12^\circ\) , an almost constant drag reduction of 2% is found and shown to be a compromise between a beneficial pressure recovery on the flat base and a detrimental pressure drag on the tapers. At larger yaw angles and whatever the pitch angle is, there is no compromise anymore such that any taper angle different from \(0^\circ\) produces a drag increase leading eventually to the squareback rear design as the optimal design. Overall, the study emphasizes the potential of adaptive control of the top and bottom trailing edge tapers to arbitrary body attitude even at small yaw angles when the pitch is varied.

中文翻译：

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通过底部分离处的流动方向，实现可变螺距和侧风中平背 3D 钝体的自适应减阻

摘要

在由俯仰 ( \(-1.5^\circ , 0^\circ , +1.5^\circ\) ) 和偏航 (最多\(15^\circ\)）。后部设计由顶部和底部后缘的锥角组成，从\(0^\circ\)（无锥度）到\(12.5^\circ\) 不等。与在顺风车身姿态下最小化阻力的固定最优后部设计相比，适应姿态变化的后部设计可显着减少高达 5% 的阻力，具体取决于偏航范围内小于 \( 2 ^\循环\)。结果表明，这种减阻与垂直尾流稳定不稳定性干扰后部设计有关。对于大于\(2^\circ\)且高达\(12^\circ\)的偏航，发现几乎恒定的 2% 减阻，并且表明这是平底座上的有益压力恢复与对锥体产生有害的压力阻力。在较大的偏航角和无论俯仰角是多少时，不再有任何妥协，任何不同于\(0^\circ\)的锥角都会产生阻力增加，最终导致方背设计成为最佳设计。总体而言，该研究强调了即使在俯仰变化时，即使在小偏航角下，顶部和底部后缘锥度自适应控制任意身体姿态的潜力。