Bluff-body drag reduction using feedback control

最近的实验表明，对轴对称钝体后的流动进行主动开环控制，可以实现大约10%的压力阻力减少，并以脉冲射流的形式围绕钝体背面周围进行激励。虽然这种影响还没有完全被解释，但看起来喷流可以作为一个虚拟的扰流板，抑制湍流的传输和卷吸(众所周知，钝体后面的分流板通过抑制卷吸来减少压力阻力，但代价是分流板摩擦阻力)。这一效果显示出巨大的前景，开环控制调查是由法拉利公司直接资助的相关研究计划的一部分，法拉利公司打算在2012年的一款生产车型上引入脉冲喷射强迫减阻。在控制湍流从后向分离的过程中，也发现了一个密切相关的影响。这项工作有两个合乎逻辑的扩展：第一个是发展对虚拟扰流板效应的理解，这可能会在汽车、海洋和风力工程领域得到更广泛的应用。二是引入基于物理的反馈控制来实现钝体减阻。反馈控制可能会在不增加硬件复杂性的情况下提供更大的阻力减少，允许最大限度地减少执行器功率，增加净能量增益，并且可以设计为自动适应不断变化的流动条件。这些构成了这项提案的两个关键目标。我们的终极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.