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

在拟议项目的框架内，计划通过欧拉/拉格朗日方法对反应泡状流进行数值计算，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）。作为气泡动力学的结果，它们将执行翻滚运动，并且它们的界面以及气泡附近的流动将被连续地修改。这也将导致气泡停留时间的增加。因此，传质和反应速率将显著提高。目前，在用Euler/Euler和Euler/Lagrange方法对泡状流进行数值计算时，都没有考虑气泡动力学的影响。因此，在拟议项目中应开发此类模型，从而显著改善反应泡状流的数值计算。流体流动的数值计算将基于使用动态亚网格尺度（SGS）湍流模型的大涡模拟（LES）。气泡对流体的影响将在动量方程和SGS湍流建模（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等人2015年的基线模型）和SGS湍流的气泡输送。此外，Basset力的影响将被检查和一个新的气泡壁相互作用模型将被开发。气泡动力学将在所有三个层次的模型开发，气泡运动，传质和化学反应。动态气泡运动将通过使用基于理论的气泡振荡时间尺度的气泡偏心率和取向的随机变化来描述。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式中。这些相关性将从理论上推导出来，并得到工作组Bothe教授（达姆施塔特工业大学）直接数值模拟的支持。此外，拉格朗日模拟将支持由Rzehak博士（HZD Rossendorf）小组提出的欧拉/欧拉方法框架内的气泡动力学模型的开发。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逐步开发并在OpenFOAM中实施。在每个工作任务中，将根据SPP各组中进行的实验研究进行详细验证。

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.