Scarifying and fingering surfaces of plunging jets
Scarifying and fingering surfaces of plunging jets
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DOI：
10.1016/j.coastaleng.2009.08.007
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发表时间：
2009-11
影响因子：
4.4
通讯作者：
A. Saruwatari;Yasunori Watanabe;D. Ingram
中科院分区：
文献类型：
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作者：
A. Saruwatari;Yasunori Watanabe;D. Ingram
使用三维大涡模拟，计算了柱状水射流倾斜冲击引起的局部表面变形，作为破碎波翻转射流的模型。已检查了二次射流从初始射流正面的出现，并表征了射流内涡流的组织。当二次射流出现时，在射流表面下方的强剪切作用下，涡量场变得不稳定，并形成沿射流投影方向拉伸的纵向反向旋转涡对。这些纵向涡流对的存在产生会聚表面流，导致在突出射流的背面形成纵向疤痕。随着其上表面和下表面上的疤痕显着增长，喷射流解耦成指状。纵向涡流的横向宽度提供了手指尺寸的最小测量值。定义了水平弗劳德数 Frh，代表重力主导的冲击流中水平剪切强度的量度，其表征剪切流中发生的纵向涡流的组织以及由此形成的疤痕和指状物。对于较高的 Frh，在较长的横向间隔处会形成更强的纵向涡流和更深的疤痕，从而增强飞溅事件期间的指法过程。射流表面附近物质传输的基本特征（例如穿过海面的气体传输）与纵向涡流对表面流体的夹带有关，因此也可以用 Frh 来表征。
The local surface deformation resulting from the oblique impact of a columnar water jet has been computed, using a three-dimensional large eddy simulation, as a model of the overturning jet of a breaking wave. The emergence of the secondary jet from the front face of the initial jet has been examined and the organisation of the vortices within the jet characterised. As the secondary jet emerges, the vorticity field becomes unstable under the action of the strong shear beneath the jet surface and pairs of longitudinal counter-rotating vortices stretched along the direction of the jet projection are formed. The presence of these longitudinal vortex pairs creates convergent surface flows, resulting in the formation of longitudinal scars on the rear face of the projecting jet. Following significant growth of the scars on both its upper and lower surfaces, the jet decouples into fingers. The lateral widths of the longitudinal vortices provide a minimum measure of the finger size. A horizontal Froude number Frh, representing a measure of strength of horizontal shear in a gravity-dominated impacting flow is defined, which characterises the organisation of the longitudinal vortices occurring in the shear flow, and the resultant formation of scars and fingers. For higher Frh, stronger longitudinal vortices and deeper scars are formed at longer lateral intervals, enhancing the fingering process during the splashing event. Fundamental features of material transport in the vicinity of the surface of jets (e.g. gas transfer across a sea surface) are related to the entrainment of surface fluid by the longitudinal vortices, and is thus also characterised by Frh.