Modelling the influence of bubble dynamics on motion, mass transfer and chemical reaction

在提议的项目框架内，计划在描述气泡运动、传质和化学反应时考虑气泡动力学（即形状振荡和翻滚运动），以便通过欧拉/拉格朗日方法对反应气泡流进行数值计算。由于气泡动力学，它们将进行翻滚运动，并且它们的界面以及气泡附近的流动将不断被改变。这也会增加气泡的停留时间。因此，传质和反应速率将显著提高。迄今为止，无论是欧拉/欧拉-方法还是欧拉/拉格朗日方法，在气泡流动的数值计算中都没有考虑到气泡动力学的影响。因此，在本项目中应该发展这样的模型，从而显著提高反应性气泡流的数值计算。流体流动的数值计算将基于大涡模拟（LES），采用动态亚网格尺度（SGS）湍流模型。气泡对流体的影响将在动量方程和SGS湍流模型（即湍流耗散和气泡诱导湍流，BIT）中考虑。气泡运动的计算将考虑所有相关力（即Liao et al. 2015的基线模型）和SGS湍流对气泡的输送。此外，还将研究巴塞特力的影响，并建立一个新的气泡-壁相互作用模型。气泡动力学将在模型开发、气泡运动、传质和化学反应的所有三个层面上得到解释。动态气泡运动将通过气泡偏心和方向的随机变化来描述，并使用基于理论的气泡振荡时间尺度。对于传质和化学反应，气泡动力学将被纳入舍伍德数和增强因子的关联中。这些相关性将从理论上推导出来，由Bothe教授（达姆施塔特工业大学）工作组的直接数值模拟支持。此外，拉格朗日模拟将支持在Rzehak博士（HZD Rossendorf）提出的欧拉/欧拉方法框架下的气泡动力学模型的发展。气泡运动、传质和化学反应（其中包括Fe-NO系统）中的气泡动力学模型将在OpenFOAM中逐步开发和实现。在每个工作任务中，将根据SPP各小组进行的实验研究进行详细的验证。

In the frame of the proposed project it is planned to account for the bubble dynamics (i.e. shape oscillations and tumbling motion) in the description of bubble motion, mass transfer and chemical reaction for numerical calculations of reacting bubbly flows by the Euler/Lagrange approach. As a result of bubble dynamics they will perform a tumbling motion and their interface as well as the flow in the vicinity of the bubbles will be continuously modified. This will also yield an increase in bubble residence time. As a consequence, mass transfer and reaction rates will be remarkably improved. So far the influence of bubble dynamics was not accounted for in the numerical calculation of bubbly flows by both the Euler/Euler- and Euler/Lagrange-approach. Hence, such models shall be developed in the proposed project, whereby the numerical calculation of reactive bubbly flows will be remarkably improved.The numerical calculation of the fluid flow will be based on large eddy simulations (LES) using a dynamic sub-grid-scale (SGS) turbulence model. The influence of the bubbles on the fluid will be accounted for in the momentum equations and in SGS turbulence modelling (i.e. turbulence dissipation and bubble induced turbulence, BIT). The calculation of bubble motion will consider all relevant forces (i.e. base-line model of Liao et al. 2015) and bubble transport by SGS turbulence. In addition, the influence of the Basset force will be examined and a new bubble-wall interaction model will be developed. The bubble dynamics will be accounted for in all three levels of model development, bubble motion, mass transfer and chemical reaction. The dynamic bubble motion will be described through a stochastic variation of bubble eccentricity and orientation using a theoretically based bubble oscillation time scale. Regarding mass transfer and chemical reaction, bubble dynamics will be incorporated in the correlations of Sherwood number and enhancement factor. These correlations will be derived theoretically, supported by the direct numerical simulations of the working group Prof. Bothe (TU Darmstadt). In addition, the Lagrangian simulations will allow supporting the development of a bubble dynamics models in the frame of an Euler/Euler approach proposed by the group of Dr. Rzehak (HZD Rossendorf).The models for bubble dynamics in bubble motion, mass transfer and chemical reactions (among others for the system Fe-NO) will be stepwise developed and implemented in OpenFOAM. In each working task a detailed validation will be performed based on the experimental studies conducted in various groups of the SPP.