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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 >Modal decomposition of flow fields and convective heat transfer maps: An application to wall-proximity square ribs
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Modal decomposition of flow fields and convective heat transfer maps: An application to wall-proximity square ribs

机译：模态分解流场和对流传热图：墙壁接近方形肋的应用

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In this work the modal decomposition of convective heat transfer distributions in turbulent flows is explored. The organization and thermal footprint of the turbulent flow features generated downstream of wall-proximity two-dimensional square ribs immersed in a turbulent boundary layer are investigated experimentally. This study employs modal decomposition to investigate whether this analysis can allow identifying which characteristics of the flow topology are responsible for the Nusselt-number augmentation, aiming to uncover the underlying physics of heat-transfer enhancement. Heat transfer and flow velocity measurements are performed at a Reynolds number (based on the free-stream velocity and rib side-length) equal to 4600. Square ribs are tested for two different gap spacings from the wall (0.25 and 0.5 ribs side-length) and in wall-attached configuration. A low-thermal-inertia heat transfer sensor coupled with high-repetition-rate Infrared (IR) thermography is designed to study the unsteady variation of the convective heat-transfer coefficient downstream of the obstacles. Flow-field measurements are performed with non-time-resolved Particle Image Velocimetry (PIV). A modal analysis with Proper Orthogonal Decomposition (POD) is applied to both convective heat-transfer maps and velocity-fields. The comparison of the Nusselt-number spatial modes of the clean turbulent boundary layer configuration and of the configurations with the ribs shows a variation of the spatial pattern associated with oscillations with strong spanwise coherence, opposed to the thin elongated streaks which dominate the convective heat transfer in the clean turbulent boundary layer. In configurations where the convective heat transfer is enhanced by coherent structures located close to the wall, similar eigenspectra are observed for both flow field and convective heat transfer modes. The results of the modal analysis support a picture of a direct relation between the coherence of near-wall flo
机译：在这项工作中，探讨了湍流流动中对流传热分布的模态分解。实验研究了沉浸在湍流边界层浸没在湍流边界层的壁接近二维方形肋的下游产生的湍流功能的组织和热占地面积。本研究采用模态分解来研究该分析是否可以识别流体拓扑的哪个特征负责NUSELER号码，旨在揭示潜在的传热增强物理学。传热和流速测量在雷诺数（基于自由流速度和肋侧长度）等于4600.从墙壁（0.25和0.5肋侧长度为0.25和0.5肋骨的两个不同间隙间距测试方形肋）和墙上的配置。耦合具有高重复速率红外（IR）热成像的低温惯性传热传感器旨在研究障碍物下游的对流传热系数的不稳定变化。使用非时分粒子图像VELOCIMETRY（PIV）执行流场测量。具有适当正交分解（POD）的模态分析应用于对流传热图和速度场。清洁湍流边界层配置和肋的构造的Nusselt数空间模式的比较示出了与具有强的振荡相关的空间图案的变化，其与具有强的翼展相干的振荡，而不是占据对流热传递的薄细长条纹在清洁湍流边界层。在通过靠近壁的相干结构增强对流传热的配置中，对于流场和对流传热模式，观察到类似的Eigenspectra。模态分析的结果支持近壁浮动的连贯性之间的直接关系的图片

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