The isothermal mixing of a heavy and a light liquid of different physical properties is numerically investigated by means of Large Eddy Simulations. The validation is based on experimental data held in a system reproducing various components of a pressurized water nuclear reactor, during a scenario of cold water injection at a low Atwood number of 0.05. The flow has two distinct stages: first a buoyancy-driven phase is characterized by a fluid front development in the cold leg and gives rise to Kelvin–Helmholtz whorls under the action of density changes. Then, the heavy liquid discharges into the downcomer filled with light liquid, which causes a turbulent mixing. These phenomena are analyzed through a single-phase approach where the density of the working fluid is either variable or modeled by the Boussinesq approximation. The influence of grid refinement is deeply examined, which shows that the mesh convergence is well achieved for the main flow quantities, unlike the low-magnitude spanwise components. Overall, the numerical solutions are found to reproduce the experimental measurements with a fair accuracy for both physical models used. These latter exhibit similar trends, due to the small density difference under consideration. The predictions in the downcomer appear to be more challenging owing to a strongest turbulence than in the cold leg, some flow features being not properly captured. However, the experimental data in the downcomer are found to be incomplete and somewhat dubious for a strict validation of the numerical simulations. Lastly, the flow distribution in the dowcomer is investigated, providing further insight on the mixing process.

通过大涡模拟对不同物理性质的重液体和轻液体的等温混合进行了数值研究。该验证基于在以低阿特伍德数0.05注入冷水的情况下，在再现压水核反应堆各个组件的系统中保存的实验数据。流动具有两个截然不同的阶段：首先，浮力驱动阶段的特征是冷段中的流体锋面发育，并在密度变化的作用下引起开尔文-亥姆霍兹涡旋。然后，重液体排放到充满轻液体的降液管中，这导致湍流混合。通过单相方法分析这些现象，在该方法中，工作流体的密度可变或通过Boussinesq逼近建模。深入研究了网格细化的影响，结果表明，与低幅度展向分量不同，对于主流流量，网格收敛很好。总体而言，对于所使用的两种物理模型，数值解均能以相当准确的精度再现实验测量结果。由于考虑中的较小的密度差异，后者表现出相似的趋势。由于湍流最强，因此降液管中的预测似乎比冷腿中的预测更具挑战性，某些流动特征未得到正确捕获。但是，在下降管中的实验数据被发现是不完整的，并且对于严格的数值模拟验证有些怀疑。最后，研究了陶氏混合器中的流量分布，从而提供了有关混合过程的进一步见解。