The turbulent structure in the near field of heated jets was investigated at a Reynolds number of 10 000 for density ratios between 1.0 and 0.5; the corresponding mixing and entrainment of these low density jets was examined. The exit conditions of the jet were carefully controlled using extension tubes to alter the nozzle‐exit boundary layer thickness, as well as using screens to generate turbulent conditions while keeping the boundary layer thickness approximately constant. Heated jets with initially laminar exit conditions were dominated by the formation and pairing of vortex structures. Increasing the boundary layer thickness produced longer wavelength structures which saturated and paired at farther downstream distances; under these conditions jet momentum mixing was reduced, giving rise to an increase in the jet potential core length. The shear layer structures also became more organized as the jet density was reduced relative to the density of the ambient fluid, resulting in increased momentum mixing and a dramatic visual spreading of the jet. Turbulent exit conditions disrupted the formation of these large‐scale vortex structures for all of the density ratios investigated, producing smaller spreading rates and significantly lower mixing and entrainment.

中文翻译：

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加热射流中的湍流结构和夹带：初始条件的影响

的 湍流的 加热近场中的结构 喷气机 在 雷诺数密度比在1.0和0.5之间为10000; 这些低密度的相应混合和夹带喷气机被检查了。飞机的出口条件要小心受控 使用延长管改变喷嘴出口 边界层 厚度，以及使用屏幕生成 湍流的 条件，同时保持 边界层厚度大致恒定。加热的喷气机 最初的层流出口条件主要由 涡流结构。增加边界层厚度产生更长的波长结构，并在更远的下游距离处饱和并配对。在这些条件下，射流动量混合减少，导致射流电势芯长度增加。当射流密度相对于环境流体的密度降低时，剪切层结构也变得更有条理，从而导致动量混合增加，并且射流出现明显的视觉散布。湍流 出口条件扰乱了这些大规模的形成 涡流 研究了所有密度比的结构，产生了较小的铺展速率，并显着降低了混合和夹带。