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首页> 外文期刊>Experiments in Fluids: Experimental Methods and Their Applications to Fluid Flow >Visualization and structure of confined, milliscale, unsteady impinging slot jets and associated vortices
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Visualization and structure of confined, milliscale, unsteady impinging slot jets and associated vortices

机译：受限，毫米级，非定常撞击狭缝喷嘴和相关涡流的可视化和结构

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摘要

Flow characteristics of confined, laminar milliscale slot jets are investigated from visualizations, as they impinge upon a flat target plate, with a fully developed velocity profile at the nozzle exit. The effects of Reynolds number Re and normalized nozzle-to-plate distance H/B are considered for a nozzle width B of 1.0 mm. Transition from a stable symmetric jet to an unsteady oscillating jet is observed as the Reynolds number increases (with H/B constant), where the Reynolds number associated with this transition decreases as the normalized nozzle-to-plate distance H/B increases. Instantaneous visualizations show unsteady lateral distortions of jet columns at experimental conditions corresponding to the presence of continuous sinusoidal oscillations, intermittent oscillating motion of the jet column, and jet flow fluctuation/flapping motion. Also apparent in flow visualization sequences are smoke signatures associated with instantaneous vortex structures, which form as secondary flows develop in fluid which, initially, is just adjacent to and within the jet column. Associated jet and vortex structural changes are described as different modes of unsteadiness are present, including characterization of jet column unsteadiness using jet column oscillation frequency, and lateral and streamwise extents of jet distortion.
机译：密闭的层状毫米级狭缝射流的流动特性通过可视化进行了研究，因为它们撞击在平坦的目标板上，并且在喷嘴出口处具有完全展开的速度分布。对于1.0 mm的喷嘴宽度B，考虑了雷诺数Re和归一化的喷嘴到印版距离H / B的影响。随着雷诺数增加（H / B常数），观察到从稳定的对称射流到不稳定振荡​​射流的过渡，其中，随着标准化的喷嘴到印版距离H / B的增加，与此过渡相关的雷诺数减小。瞬时可视化显示了在实验条件下射流柱的不稳定横向变形，这与连续正弦波振荡的存在，射流柱的间歇性振荡运动以及射流的波动/扑动有关。在流动可视化序列中也很明显的是与瞬时涡旋结构相关的烟雾特征，该烟雾特征是随着二次流动在流体中发展而形成的，该流体最初只是紧邻喷射柱并在喷射柱之内。由于存在不同的不稳定状态，因此描述了相关的喷射和涡旋结构变化，包括使用喷射柱振荡频率表征喷射柱不稳定的特性，以及喷射畸变的横向和沿流的程度。

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