Abstract Non-circular jets, particularly elongated jets and jets with sharp corners, are of interest due to their enhanced large- and small-scale mixing and combustion stability. Non-circular jet geometries such as elliptic, triangular, rectangular, and square have been extensively studied. The non-uniform curvature and elongated design of elliptic and rectangular jets has been shown to facilitate axis switching. Additionally, jets with sharp corners have been shown to facilitate small-scale mixing and further vortex ring deformation, as has been observed in triangular, square, and rectangular jets. There are, however, currently no data on the flow characteristics of a jet that combines these two features, i.e., it enhances both large- and small-scale mixing. The jet is issuing from a nozzle shape defined by two arcs of a circle connecting at sharp corners in the shape of an eye (hereafter termed ‘lenticular’). The current study uses experimental techniques to characterize the lenticular jet and compare its behavior to previously studied circular and non-circular jets. Additionally, snapshot POD analysis was used to identify coherent structures and their dynamic features. The lenticular jet was found to have higher entrainment and stronger mixing than a traditional round jet, and comparable mixing and entrainment characteristics as previously studied non-circular jet geometries. It is particularly interesting to compare the jet behavior of the lenticular jet to an elliptic jet. The geometry of these two jets is extremely similar, the difference being sharp corners along the major axis of the lenticular jet. By comparing the lenticular jet and the elliptic jet, the effect of sharp corners, which have been shown to increase small-scale mixing and vortex ring deformation, can be observed. It was found that along the minor axis, where geometry was similar, shear layer turbulence intensity and spreading rate of the jets were also similar. Along the major axis, however, introducing corner features in the lenticular jet lowered the spread rate, resulted in a faster breakdown of turbulence in the shear layer, increased exit turbulence, and resulted in anisotropic centerline turbulence. Graphic abstract Geometry of a jet issuing from a novel exit shape defined by two arcs of a circle connecting at sharp corners. The exit shape has been termed lenticular and possesses characteristics known to increase both large- and small-scale mixing. The ensuing jet sharply contracts along the major axis and rapidly expands along the minor axis resulting in an axis switch.

中文翻译：

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透镜状射流的实验研究

摘要 非圆形射流，特别是细长射流和尖角射流，由于其增强的大尺度和小尺度混合和燃烧稳定性而受到关注。非圆形射流几何形状，例如椭圆形、三角形、矩形和正方形，已被广泛研究。椭圆形和矩形射流的非均匀曲率和细长设计已被证明有助于轴切换。此外，正如在三角形、方形和矩形射流中所观察到的那样，具有尖角的射流已被证明有助于小规模混合和进一步的涡环变形。然而，目前没有关于结合这两个特征的射流的流动特性的数据，即它增强了大尺度和小尺度混合。射流从一个喷嘴形状发出，该形状由在眼睛形状的尖角处连接的两个圆弧限定（以下称为“透镜状”）。目前的研究使用实验技术来表征透镜状射流，并将其行为与先前研究的圆形和非圆形射流进行比较。此外，快照 POD 分析用于识别连贯的结构及其动态特征。发现透镜射流比传统圆形射流具有更高的夹带和更强的混合，以及与先前研究的非圆形射流几何形状相当的混合和夹带特性。将透镜状射流与椭圆形射流的射流行为进行比较是特别有趣的。这两种喷流的几何形状极其相似，不同之处在于沿透镜状射流主轴的尖角。通过比较透镜状射流和椭圆形射流，可以观察到尖角的影响，它已被证明会增加小尺度混合和涡环变形。发现沿着短轴，几何形状相似，剪切层湍流强度和射流的扩散速率也相似。然而，沿着主轴，在透镜射流中引入角特征降低了扩散率，导致剪切层中湍流的更快分解，增加了出口湍流，并导致各向异性中心线湍流。从一个新的出口形状发出的喷气机的图形抽象几何形状，该形状由连接在尖角处的圆的两条弧线定义。出口形状被称为透镜状，具有已知可增加大尺度和小尺度混合的特性。随后的射流沿长轴急剧收缩并沿短轴迅速膨胀，导致轴切换。