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首页> 外文期刊>Flow, turbulence and combustion >Effects of Nozzle Geometry on Turbulent Characteristics and Structure of Surface Attaching Jets
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Effects of Nozzle Geometry on Turbulent Characteristics and Structure of Surface Attaching Jets

机译：喷嘴几何形状对表面附着喷射湍流特性及结构的影响

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摘要

The effects of nozzle exit geometry on the characteristics of a surface attaching jet were investigated experimentally. Three different types of nozzle geometries were studied, including a circular, square and rectangular nozzle with the same exit area. The jets were discharged with an offset height of two nozzle width at a Reynolds number of 5500. A particle image velocimetry system was used to measure the flow. Instantaneous visualizations revealed that the largest enhancements in the near field mixing and entrainment occur in the minor plane of the rectangular nozzle compared to the square and circular nozzles resulting in more rapid expansion of the shear layer. This also caused a faster deflection of the jet towards the free surface, maximum velocity decay and spread rates of the rectangular jet with minor axis orientation. The jet-surface interaction was examined using surface velocity, vorticity thickness and surface turbulence intensities. It was found that the damping of the surface-normal velocity fluctuations at the free surface is more severe in the minor plane of the rectangular jet than the square and circular nozzles. The influence of the free surface was also felt in the profiles of mean velocity and Reynolds stresses. The attenuation of Reynolds shear stress due to confinement was more dramatic in the minor plane of the rectangular nozzle than the other geometries. To quantify the influence of nozzle geometry on the coherent structures in the interaction region, two-point correlations of the velocity fluctuations and swirling strength; and proper orthogonal decomposition were performed.
机译：实验研究了喷嘴出口几何形状对表面附着射流特性的影响。研究了三种不同类型的喷嘴几何形状，包括具有相同出口区域的圆形，方形和矩形喷嘴。在雷诺数为5500的雷诺数的两个喷嘴宽度的偏移高度排出射流。颗粒图像速度系统用于测量流量。瞬时可视化表明，与正方形和圆形喷嘴相比，在矩形喷嘴的次要平面中发生近场混合和夹带中的最大增强，导致剪切层的较快膨胀。这也导致射流朝向自由表面，最大速度衰减和具有短轴取向的矩形射流的扩展速率的更快偏转。使用表面速度，涡度厚度和表面湍流来检查喷射表面相互作用。发现在比方形和圆形喷嘴的矩形射流的小平面中，自由表面的表面正常速度波动的阻尼更严重。在平均速度和雷诺应力的曲线上也感觉到自由表面的影响。由于限制引起的reynolds剪切应力的衰减在比其他几何形状的矩形喷嘴的次要平面中更显着。为了量化喷嘴几何形状对相互作用区域相干结构的影响，速度波动的双点相关性和旋转强度;并进行适当的正交分解。

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