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Linear feedback control for form-drag reduction on bluff bodies with a blunt trailing edge

机译:线性反馈控制,用于在具有钝后缘的钝体上进行形状减阻

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摘要

The work described in this thesis is a computational investigation applying linear feedbackudcontrol to reduce form-drag on bluff bodies with a blunt trailing edge. For such bodies, audlarge portion of the aerodynamic drag is associated with an unsteady separated region or wakeuddownstream of the body. The development of tractable feedback strategies to control unsteadyudwakes promises strong benefits, both in terms of industrial applications and for furthering ourudunderstanding of the flow mechanisms at play.udFor this purpose, large-eddy simulations are carried out where a linear feedback controllerudtargets an increase in the mean pressure force on the rear (base) of the body. The flows overudtwo distinct geometries are examined: a backward-facing step and a bluff body with a roundedudleading edge, often referred to as a D-shaped body. The control is effected by zero-net-mass-flux slot jets, responding to sensors located on the body base. Open-loop characterization providesudinformation on the effects of actuation and some physical insight into the relation between theudbase pressure and wake dynamics. System identification is used to obtain a low-order modeludof the flow's response to actuation that can be used for control.udThe control strategy is based on the premise that reducing the fluctuations in the near-wakeudwill cause an increase in the mean base pressure, hence a reduction in form-drag. Theudcontrollers are designed with classical frequency-domain methods, using a sensitivity transferudfunction to attenuate the size of the pressure force fluctuations.udThe influence of parameters such as the Reynolds number and the location and type ofudactuators is studied. For all cases, low-order linear feedback controllers successfully reduceudthe pressure force fluctuations and achieve sensible drag reductions. They do so with higher efficiency than the open-loop forcing considered. Uncertainties in the model and flow conditionsudcan be to some extent mitigated by the robustness of the controller. The results support theudconjecture linking the fluctuating and mean base pressure, although it is observed that furtherudwork is needed before such an approach can be used for optimization.
机译:本文描述的工作是应用线性反馈 udcontrol来减少具有钝后缘的钝体上的形式阻力的计算研究。对于这样的车身,空气阻力的很大一部分与车身的不稳定的分离区域或尾流相关。易于控制的反馈策略的发展,无论是在工业应用方面,还是在进一步深化我们对运动机理的理解上,都有望带来巨大的好处。为此,在线性反馈的情况下进行了大涡模拟。控制器 ud以增加车身后部(底部)的平均压力为目标。检查 ud两个不同几何形状上的流动:向后的台阶和带有圆形 udlead边缘的钝体,通常称为D形体。该控制由零净质量通量槽式射流完成,响应位于车身底座上的传感器。开环表征提供了有关驱动效果的信息,并提供了一些物理洞察力,以了解基础压力与尾流动力学之间的关系。系统识别用于获得流对驱动响应的低阶模型 ud,该模型可用于控制。 ud控制策略基于以下前提:减小近苏醒的波动 ud将导致流量增加。平均基本压力,因此减少了形式阻力。 udcontroller采用经典的频域方法设计,使用灵敏度传递 udfunction来减小压力波动的大小。 ud研究了诸如雷诺数以及 ductuator的位置和类型等参数的影响。在所有情况下,低阶线性反馈控制器都能成功地减小/消除压力波动并实现合理的减阻。它们以比考虑的开环强制更高的效率进行操作。控制器的鲁棒性可以在一定程度上缓解模型和流动条件的不确定性。尽管可以观察到在将这种方法用于优化之前还需要进一步的工作,但结果支持将波动和平均基本压力联系在一起的“猜想”。

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    Dahan Jeremy;

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  • 年度 2013
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  • 原文格式 PDF
  • 正文语种 eng
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