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Effect of Mesh Grids on the Turbulent Mixing Layer of an Axisymmetric Jet

机译：网格对轴对称射流湍流混合层的影响

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摘要

This article focuses on the effect that two different mesh grids have on the structure of the mixing layer of an axisymmetric jet. Detailed measurements of mean velocity and turbulent velocity fluctuations are made with an X hot-wire probe in the range 0.5 ≤x/d≤10, where x is the longitudinal distance from the nozzle exit plane and d is the nozzle diameter. The grids are introduced at two locations-one location just downstream of the nozzle exit plane and the other location upstream of the nozzle exit plane in order to perturb the nozzle exit boundary layer. One mesh completely covers the nozzle (full mesh or FM) and the other mesh covers the central, high-speed zone (disk mesh or DM). With reference to the undisturbed jet, FM yields a significant reduction in the turbulence intensity and width of the shear layer, whereas DM enhances the turbulence intensity and increases the width of the shear layer. Both grids suppress the formation of the Kelvin-Helmholtz instability in the mixing layer. Results are presented, mainly at x/d = 5 and 6 in both the spectral domain and physical space. In the latter context, second- and third-order structure functions associated with u (the longitudinal velocity fluctuation) and v (the lateral or radial velocity fluctuation) are presented only for the flow perturbed by placing the mesh outside the nozzle. All mesh geometries have a more significant effect on the second-order structure function of u than on that of v. The third-order energy transfer term is affected in such a way that, relative to the undisturbed jet, its peak location is shifted to a smaller scale when FM is used and to a larger scale with DM. This is consistent with our observations that FM reduces the turbulence in the shear layer while DM enhances it. It is suggested that the large-scale vortices that are formed at the edge of the grids play a significant role in the transfer of energy.
机译：本文重点介绍两个不同的网格对轴对称射流混合层结构的影响。使用X热线探针在0.5≤x/d≤10的范围内进行平均速度和湍流速度波动的详细测量，其中x是距喷嘴出口平面的纵向距离，d是喷嘴直径。在两个位置处引入栅格，一个位置在喷嘴出口平面的下游，另一个位置在喷嘴出口平面的上游，以扰动喷嘴出口边界层。一个网格完全覆盖喷嘴（全网格或FM），另一个网格覆盖中央高速区域（磁盘网格或DM）。相对于未受干扰的射流，FM使剪切层的湍流强度和宽度显着降低，而DM增强了湍流强度并增加了剪切层的宽度。两个栅格都抑制了混合层中Kelvin-Helmholtz不稳定性的形成。给出的结果主要是在光谱域和物理空间中的x / d = 5和6。在后一种情况下，与u（纵向速度波动）和v（横向或径向速度波动）相关的二阶和三阶结构函数仅针对通过将网孔放置在喷嘴外部而受到扰动的流量给出。所有网格几何形状对u的二阶结构函数的影响都比对v的影响大。对三阶能量传递项的影响是，相对于未受干扰的射流，其峰值位置移动到使用FM时规模较小，而使用DM则规模较大。这与我们的观察一致，即FM降低了剪切层的湍流，而DM增强了湍流。建议在格栅边缘形成的大规模旋涡在能量传递中起重要作用。

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  • 来源
    《Heat Transfer Engineering》 |2013年第15期|1216-1225|共10页
  • 作者

    SUNDARA RAJAGOPALAN; ROBERT ANTHONY ANTONIA; LYAZID DJENIDI;

  • 作者单位

    School of Engineering, University of Newcastle, Callaghan, New South Wales, Australia;

    School of Engineering, University of Newcastle, Callaghan, New South Wales, Australia;

    School of Engineering, University of Newcastle, Callaghan, New South Wales, Australia;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);
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  • 正文语种 eng
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