Large eddy simulation of turbulent horizontal buoyant jets
Large eddy simulation of turbulent horizontal buoyant jets
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DOI：
10.1080/14685248.2015.1008007
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发表时间：
2015-04
影响因子：
1.9
通讯作者：
N. Ghaisas;D. Shetty;S. Frankel
中科院分区：
文献类型：
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作者：
N. Ghaisas;D. Shetty;S. Frankel
采用高阶数值方法和Sigma亚网格尺度（SGS）涡粘性模型，对不同雷诺数（Re）和理查森数（Ri）下的湍流水平浮力射流进行了大涡模拟。在以前的实验流动条件（Re = 3200，24，000和Ri = 0，0.01）进行模拟，并发现定性和定量的实验结果相似，从而验证了数值方法。接下来研究改变Ri（值为2×10−4、0.001、0.005和0.01）和Re（3200和24，000）的影响。射流中心线一侧存在稳定分层，另一侧存在不稳定分层，导致水平浮力射流的不对称发展。研究发现，这种不对称性，总的径向扩展和垂直偏转显着影响由Ri，而Re只影响径向不对称性。指出需要开发改进的积分模型，以解释这种不对称性。湍流的产生和耗散率进行了研究，并发现是对称的，在水平面内，但在中间的垂直面不对称。先前提出的模型，波动标量通量矢量的垂直分量和雷诺张量的垂直互相关分量之间的相关性，修改当前LES结果的基础上。通过对瞬时标量场和速度场的分析，揭示了水平浮力射流的结构。与发展的湍流射流相似，喷嘴附近的流动在稳定和不稳定的分层区域也有明显的不同。在稳定层结区发现了持续的相干涡环，而在不稳定层结区则观察到涡环间歇性破裂成小尺度结构。讨论了水平浮力射流与横流浮力射流流场结构的异同。最后，进行了动态模态分解分析，表明不稳定层结区的流动比稳定层结区的流动更活跃，更容易出现不稳定性。
Large eddy simulations (LESs) of turbulent horizontal buoyant jets are carried out using a high-order numerical method and Sigma subgrid-scale (SGS) eddy-viscosity model, for a number of different Reynolds (Re) and Richardson (Ri) numbers. Simulations at previous experimental flow conditions (Re = 3200, 24, 000 and Ri = 0, 0.01) are carried out first, and the results are found to be qualitatively and quantitatively similar to the experimental results, thus validating the numerical methodology. The effect of varying Ri (values 2×10−4, 0.001, 0.005, and 0.01) and Re (3200 and 24, 000) is studied next. The presence of stable stratification on one side and unstable stratification on the other side of the jet centreline leads to an asymmetric development of horizontal buoyant jets. It is found that this asymmetry, the total radial spread and the vertical deflection are significantly affected by Ri, while Re affects only the radial asymmetry. The need for developing improved integral models, accounting for this asymmetry, is pointed out. Turbulent production and dissipation rates are investigated, and are found to be symmetric in the horizontal plane, but asymmetric in the mid-vertical plane. A previously proposed model, for correlation between the vertical component of the fluctuating scalar flux vector and the vertical cross-correlation component of the Reynolds tensor, is modified based on the current LES results. Instantaneous scalar and velocity fields are analysed to reveal the structure of horizontal buoyant jets. Similar to the developed turbulent jet, the flow close to the nozzle too is found to be markedly different in the stable and unstable stratification regions. Persistent coherent vortex rings are found in the stable stratification region, while intermittent breakdown of vortex rings into small-scale structures is observed in the unstable stratification region. Similarities and differences between the flow structures in the horizontal buoyant jet configuration and those in the jet in crossflow configuration are discussed. Finally, a dynamic mode decomposition analysis is carried out, which indicates that the flow in the unstable stratification region is more energetic and prone to instabilities, as compared to the flow in the stable stratification region.