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Numerical investigation of the behaviour of circular synthetic jets for effective flow separation control

机译:圆形合成射流有效流动分离控制行为的数值研究

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摘要

The stringing regulation on greenhouse gases emissions coupled with the rising fuel price and the growth in aviation transportation have imposed increasing demands on the aircraft industry to develop revolutionary technologies to meet such challenges. Methods of delaying flow separation on aircraft high lift systems have been sought which can lead to an increase in the aircraft performance and ultimately a reduction in aircraft operational costs and its impact on the environment. Synthetic jet actuators are a promising method of delivering flow control for aircraft applications due to their ability to inject momentum to an external flow without net mass flux and their potential in being integrated in MEMS through micro-fabrication with relative ease. It has been demonstrated in many laboratory experiments that synthetic jets are capable of delaying flow separation on aerodynamic bodies of various shapes. However, currently the operating conditions of synthetic jets are mostly chosen by trial-and-error, and thus the flow control effectiveness varies from one experiment to another. In order to deliver an effective flow separation control which achieves a desired control effect at minimum energy expenditure, a better understanding of the fluid mechanics of the behaviour of synthetic jets and the interaction between synthetic jets and a boundary layer are required. The aims of the present research were to achieve such a goal through a series of purposely designed numerical simulations. Firstly, synthetic jets issued from a circular orifice into quiescent air were studied to understand the effect of dimensionless parameters on the formation and the extent of roll-up of vortex rings. The computational results confirmed that the Stokes number determines the strength of vortex roll-up of a synthetic jet. Based on the computational results, a parameter map was produced in which three different operational regimes of synthetic jets were indentified and a criterion for vortex roll-up was also established. A circular synthetic jet issued into a zero-pressure-gradient laminar boundary layer was then investigated. The capability of FLUENT in modelling the key characteristics of synthetic jets was validated using experimental data. The formation and evolution of coherent structures produced by the interaction between synthetic jets and a boundary layer, as well as their near-wall effect in terms of the wall shear stress, were examined. A parameter map illustrating how the appearance of the vortical structures and their corresponding shear stress patterns vary as the synthetic jet operating condition changes was established. In addition, the increase in the wall shear stress relative to the jet-off case was calculated to evaluate their potential separation control effect.Finally, the study moved one step forward to investigate the flow separation control effect of an array of three circular synthetic jets issued into a laminar boundary layer which separates downstream on an inclined plate. The impact of synthetic jets on the boundary layer prior to separation and the extent of flow separation delay on the flap, at a range of synthetic jet operating conditions, were examined and the correlation between them was investigated. Furthermore, the optimal operating conditions for this synthetic jet array in the current study were identified by considering both the flow control effect and the actuator power consumption. The characteristics of the corresponding vortical structures were also examined.The findings from this work have produced some further insights of the behaviour and the interaction between synthetic jets and a boundary layer, which will be useful for ensuring an effective application of synthetic jets in practical settings.
机译:严格的温室气体排放法规,加上不断上涨的燃料价格和航空运输的增长,对航空工业提出了越来越高的要求,以开发革命性的技术来应对此类挑战。已经寻求了在飞机高升力系统上延迟流分离的方法,这些方法可以导致飞机性能的提高,并最终降低飞机的运行成本及其对环境的影响。合成射流致动器是一种有希望的用于飞机应用的流量控制方法,这是因为合成射流致动器能够将动量注入到外部流中而没有净质量通量,并且具有通过相对容易地通过微细加工集成到MEMS中的潜力。在许多实验室实验中已经证明,合成射流能够延迟各种形状的空气动力体上的气流分离。然而,目前合成射流的运行条件主要是通过反复试验来选择的,因此,流量控制的有效性因一个实验而异。为了提供有效的流分离控制,以最小的能量消耗实现期望的控制效果,需要对合成射流的行为的流体力学以及合成射流与边界层之间的相互作用的更好的理解。本研究的目的是通过一系列专门设计的数值模拟来实现这一目标。首先,研究了从圆形孔口喷入静态空气的合成射流,以了解无量纲参数对涡流环形成和卷起程度的影响。计算结果证实,斯托克斯数决定了合成射流涡旋卷起的强度。根据计算结果,生成了一个参数图,其中确定了三种不同的合成射流运行方式,并建立了涡​​旋累积标准。然后研究了向零压力梯度层流边界层发出的圆形合成射流。使用实验数据验证了FLUENT对合成射流关键特性建模的能力。研究了合成射流与边界层之间相互作用产生的相干结构的形成和演化,以及它们在壁面剪切应力方面的近壁效应。建立了一个参数图,该图说明了旋涡结构的外观及其相应的切应力模式如何随着合成射流工作条件的变化而变化。此外,计算了壁剪切应力相对于喷射情况的增加,以评估其潜在的分离控制效果。最后,该研究向前迈进了一步,以研究三个圆形合成喷射器阵列的流分离控制效果扩散成层状边界层,在倾斜板上下游分开。在一系列合成射流操作条件下,研究了合成射流对分离前边界层的影响以及流分离延迟对襟翼的影响,并研究了它们之间的相关性。此外,通过同时考虑流量控制效果和执行器功耗来确定当前研究中该合成射流阵列的最佳运行条件。这项工作的发现还对合成射流和边界层之间的行为以及相互作用产生了一些进一步的见解,这对于确保合成射流在实际环境中的有效应用将是有用的。 。

著录项

  • 作者

    Zhong Shan; Zhou Jue;

  • 作者单位
  • 年度 2010
  • 总页数
  • 原文格式 PDF
  • 正文语种 English
  • 中图分类

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