Large-scale structure in the far field of byoyant jets
Large-scale structure in the far field of byoyant jets
复制标题
射流远场中的大型结构
DOI：
10.1017/s002211208900306x
复制
发表时间：
1989
影响因子：
3.7
通讯作者：
E. J. List
中科院分区：
文献类型：
--
作者：
Dimitrios A. Papantoniou;E. J. List
利用激光诱导荧光（LIF）光学技术对圆形垂直浮力射流远场的流动结构和卷吸机理进行了实验研究。大量的基本上是瞬时示踪剂浓度分布记录为每个实验运行相结合的LIF与线性光电二极管阵列成像和高速数字数据采集。由此产生的高分辨率流图像的分析表明，远场区域是由跨越整个径向流范围的结构的周期性通道占主导地位。周围流体被旋涡运动夹带，并被输送到深入流动内部的区域。相关分析表明，结构的通过频率与当地平均流速和流宽成比例。有条件的平均数据表明，该结构的下游正面区域是很好的混合，并在更高的浓度水平比后面和侧面的区域，周围的流体是间歇性存在的。这导致结构内的轴向浓度梯度，类似于先前在加热空气射流中观察到的斜坡状图案。与动量驱动的流动相比，当体积力是驱动机制时，流动内部存在的环境流体大大增加。这似乎是由于浮力的影响，在生产中的湍流旋涡在积分尺度。动量驱动和浮力驱动的流动研究的一个重要特征是浓度场的强间歇性。这就提出了梯度扩散理论描述这种流动的适当性的问题。
The flow structure and entrainment mechanisms in the far field of a round vertical buoyant jet have been studied experimentally by use of an optical technique based on laser-induced fluorescence (LIF). A large number of essentially instantaneous tracer concentration profiles were recorded for each experimental run by combining LIF with linear photodiode array imaging and high-speed digital data acquisition. Analysis of the resulting high-resolution flow images indicates that the far-field region is dominated by the periodic passage of structures spanning the entire radial flow extent. Ambient fluid is entrained by vortical motions and is transported to regions deep into the flow interior. Correlation analysis discloses that the passage frequency of the structures scales with the local mean velocity and flow width. Conditional averaging of the data indicates that the downstream frontal region of the structure is well mixed and at higher concentration level than the back and side regions where ambient fluid is intermittently present. This results in an axial concentration gradient within the structure, analogous to the ramp-like pattern previously observed in heated air jets. In comparison to the momentum-driven flow the ambient fluid presence in the flow interior is greatly increased when body forces are the driving mechanism. This appears to result from the influence of buoyancy forces in the production of turbulent vortices at the integral scale. An important feature of both the momentum-driven and buoyancy-driven flows investigated is the strongly intermittent character of the concentration field. This raises the issue of the appropriateness of gradient-diffusion theories for the description of such flows.