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Mechanism of axis switching in low aspect-ratio rectangular jets

机译:低纵横比矩形射流中的轴切换机理

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In this work we systematically study one square jet (AR = 1) and four rectangular jets with an aspect ratio of width over height AR = 1.5. 2.2.5, and 3 respectively using the lattice Boltzmann method for direct numerical simulation. Focuses are on various flow properties on transverse planes downstream to investigate the correlation between the downstream velocity and secondary flow. Three distinct regions of jet development are identified in all the five jets. As the length of the PC (potential core) region maintains about the same, that of the CD (characteristic decay) region strongly depends on the jet aspect-ratio (AR) and Reynolds number (Re). The 45° and 90° axis-switching occur in the CD region, with the former followed by the latter at the early and late stages of the CD region respectively. The half-width streamwise velocity contour reveals that 45° axis-switching is mainly contributed by the corner effect, whereas the aspect-ratio (elliptic) feature affects the shape of the jet when 45° axis-switching occurs. The close examinations of flow pattern and vortic-ity contour, as well as the correlation between streamwise velocity and vorticity, indicate that 90° axis-switching results from the boundary effect. Specific flow patterns for 45° and 90° axis-switching are identified to reveal the mechanism of the axis-switchings respectively.
机译:在这项工作中,我们系统地研究了一个长方宽宽比AR = 1.5的方形射流(AR = 1)和四个矩形射流。 2.2.5和3分别使用格子Boltzmann方法进行直接数值模拟。重点是下游横向平面上的各种流动特性,以研究下游速度与二次流之间的相关性。在所有五架喷气机中都确定了三个不同的喷气机发展区域。由于PC(潜在核心)区域的长度大致保持不变,因此CD(特征衰减)区域的长度强烈取决于射流纵横比(AR)和雷诺数(Re)。 CD区域发生45°和90°轴切换,前者紧随其后,分别在CD区域的早期和晚期。半角流速度轮廓显示45°轴切换主要由转角效应引起,而纵横比(椭圆)特征会在发生45°轴切换时影响射流的形状。对流型和涡度轮廓的仔细检查以及沿流速度和涡度之间的相关性表明,90°轴转换是由边界效应引起的。确定了45°和90°轴切换的特定流型,以分别揭示轴切换的机理。

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