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Instantaneous transport of a passive scalar in a turbulent separated flow.
Environmental Fluid Mechanics ( IF 1.7 ) Pub Date : 2017-12-18 , DOI: 10.1007/s10652-017-9567-3
P Ouro 1 , B Fraga 2 , N Viti 3 , A Angeloudis 4 , T Stoesser 1 , C Gualtieri 3
Affiliation  

The results of large-eddy simulations of flow and transient solute transport over a backward facing step and through a 180° bend are presented. The simulations are validated successfully in terms of hydrodynamics and tracer transport with experimental velocity data and measured residence time distribution curves confirming the accuracy of the method. The hydrodynamics are characterised by flow separation and subsequent recirculation in vertical and horizontal directions and the solute dispersion process is a direct response to the significant unsteadiness and turbulence in the flow. The turbulence in the system is analysed and quantified in terms of power density spectra and covariance of velocity fluctuations. The injection of an instantaneous passive tracer and its dispersion through the system is simulated. Large-eddy simulations enable the resolution of the instantaneous flow field and it is demonstrated that the instabilities of intermittent large-scale structures play a distinguished role in the solute transport. The advection and diffusion of the scalar is governed by the severe unsteadiness of the flow and this is visualised and quantified. The analysis of the scalar mass transport budget quantifies the mechanisms controlling the turbulent mixing and reveals that the mass flux is dominated by advection.

中文翻译:

被动标量在湍流分离流中的瞬时传输。

给出了大涡模拟的结果,表明了在向后的台阶上以及通过180°弯曲时的流动和瞬态溶质迁移。通过实验速度数据和测得的停留时间分布曲线,成功地通过流体动力学和示踪剂传输对模拟进行了验证,证实了该方法的准确性。流体力学的特征是在垂直和水平方向上进行流动分离和随后的再循环,并且溶质分散过程是对流动中明显的不稳定和湍流的直接响应。根据功率密度谱和速度波动的协方差来分析和量化系统中的湍流。模拟了瞬时无源示踪剂的注入及其在系统中的扩散。大涡模拟可以解析瞬时流场,并且证明了间歇性大型结构的不稳定性在溶质运移中起着显著作用。标量的对流和扩散受流的严重不稳定影响,这可以可视化和量化。标量运输预算的分析量化了控制湍流混合的机制,并揭示了质量通量主要由对流控制。
更新日期:2017-12-18
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