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首页> 外文期刊>Experimental Thermal and Fluid Science: International Journal of Experimental Heat Transfer, Thermodynamics, and Fluid Mechanics >POD analysis of momentumless trailing edge wake using synthetic jet actuation
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POD analysis of momentumless trailing edge wake using synthetic jet actuation

机译：利用合成射流驱动进行无动量后缘尾迹的POD分析

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In this work, periodic addition of momentum using a Trailing Edge Synthetic Jet Actuation (TESJA) was used as an open-loop forcing mean to control the wake of an elongated plate. Two synthetic jet actuators were positioned at the trailing edges, spanning the width of the plate, to provide either in-phase or out-of-phase simultaneous actuation. The actuation frequency was fixed to 75% of the natural vortex shedding frequency, while a high momentum addition coefficient of C_μ=24% was applied to balance momentum deficit in the wake. Two component velocity measurements had been recorded using Particle Image Velocimetry (PIV) at mid span around the plate. These measurements allowed the flow dynamic investigation of both natural and actuated wakes at Reynolds number, based on the model height h, Re=U_∞ h/ν of 7200.The measurements revealed that the application of TESJA changes the wake flow topology, reduces the extent of the recirculation bubble and redistributes energy among the Reynolds stresses. Coherent structures and their dynamics in the wake were evaluated for both simultaneous actuation strategy (in-phase and out-of-phase). Axial velocity fluctuations spectra showed that these modifications are caused by suppressing the natural vortex shedding and generating new structures which are locked-in on the actuation frequency.The Proper Orthogonal Decomposition (POD) was used to identify the most energetic modal contributions and extract the effect of the actuation on the spatial structure of the corresponding modes. POD modes were found to be associated in pairs corresponding to the downstream convection of flow structures. Actuation affected especially the first mode pairs; i.e. the initial symmetric alternate-signed structures present in the natural case were converted into two anti-symmetric parallel rows of alternate-signed structures in the in-phase actuation, while for out-of-phase actuation modes have the same alignment of structures as the natural case.The most energetic POD modes and the phase-averaged approach are used to reconstruct low-dimensional evolution. The low-order reconstruction highlights the actuation mechanism and exemplifies the key roles of actuation structures. This is evidenced by the fact that the redistribution of the injected momentum is mainly controlled by these generated structures.
机译：在这项工作中，使用后缘合成射流驱动（TESJA）定期添加动量作为开环强迫手段来控制细长板的尾流。两个合成射流执行器位于后缘，横跨板的宽度，以提供同相或异相同时驱动。激励频率固定为自然涡旋脱落频率的75％，而高动量相加系数C_μ= 24％用于平衡尾流中的动量不足。在平板周围的中跨处使用粒子图像测速（PIV）记录了两个分量速度测量值。这些测量结果允许根据模型高度h（Re =U_∞h /ν为7200）对雷诺数下的自然和促动尾流进行流动动力学研究。这些测量表明，TESJA的应用改变了尾流拓扑结构，减少了尾流拓扑。循环气泡的范围，并在雷诺应力之间重新分配能量。针对同时的致动策略（同相和异相），评估了尾流中的相干结构及其动力学。轴向速度波动谱表明，这些变化是由于抑制了自然涡旋脱落并产生了新的结构而导致的，这些结构被锁定在驱动频率上。正确的正交分解（POD）用于识别最有能量的模态贡献并提取作用驱动对相应模式的空间结构的影响。发现POD模式成对关联，与流结构的下游对流相对应。致动尤其影响第一模式对;即，在自然情况下存在的初始对称交替符号结构在同相驱动中被转换为交替排列的两个反对称平行行，而对于异相驱动模式，结构的对齐方式与最有活力的POD模式和相位平均方法用于重构低维演化。低阶重建突出了致动机制，并举例说明了致动结构的关键作用。事实证明，注入动量的重新分布主要受这些生成的结构控制。

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