Bluff-body drag reduction using feedback control

最近的实验表明，对轴对称海崖体后面的流动进行主动开环控制，可以使压阻减小大约10%，其驱动形式为围绕钝体背面圆周的脉冲射流。虽然这种效应还没有得到充分的解释，但似乎射流可以表现为抑制湍流输送和卷吸的虚拟扰流器（海崖体后面的分流板通过抑制卷吸来减小压力阻力，但会带来分流板摩擦阻力的损失）。这种效果显示出巨大的前景，开环控制研究是法拉利公司直接资助的相关研究计划的一部分，他们打算在2012年的一个生产模型上引入脉冲射流强迫来减少阻力。一个密切相关的效果也已确定在控制湍流分离从一个面向后的步骤。这项工作有两个合乎逻辑的扩展：第一个是发展的虚拟扰流板效应，这是可能有更广泛的应用到汽车，船舶和风力工程部门的理解。第二个是引入基于物理的反馈控制用于海崖体减阻。反馈控制很可能在不增加硬件复杂性的情况下提供更大的阻力减小，允许致动器功率最小化，增加净能量增益，并且可以设计成自动适应变化的流动条件。这是本提案的两个主要目标。我们的最终愿景是实现汽车减阻10-15%（相当于在高速公路上节省约5-8%的燃料），减少道路运输对全球二氧化碳排放的影响。

Recent experiments have shown that active, open-loop control of the flow behind an axisymmetric bluff body can achieve roughly a 10% reduction in pressure drag with actuation in the form of a pulsed jet around the circumference of the back face of the body. Although the effect has yet to be fully explained, it appears that the jet can behave as a virtual spoiler that inhibits turbulent transport and entrainment (splitter plates behind bluff bodies are known to reduce pressure-drag via the inhibition of entrainment, but with the penalty of splitter-plate friction-drag). This effect shows significant promise and the open-loop control investigations form part of a related research programme funded directly by Ferrari S.p.A., who intend to introduce pulsed-jet forcing for drag reduction on one of their production models for 2012. A closely-related effect has also been identified in the control of turbulent separation from a backward-facing step. There are two logical extensions to this work: the first is developing an understanding of the virtual-spoiler effect which is likely to have more general application to the automobile, marine and wind-engineering sectors. The second is the introduction of physically-based feedback control for drag reduction of bluff bodies. Feedback control is likely to provide even greater reductions in drag without increasing the complexity of the hardware, allows the actuator power to be minimised, increasing the net energy gain and can be designed to automatically adapt to changing flow conditions. These form the two key objectives of this proposal. Our ultimate vision is that automotive vehicle drag-reductions of 10-15% (corresponding to fuel-savings of around 5-8% at motorway speeds) would be achievable, reducing the impact of road transportation of global CO2 emissions.