Design and pre-evaluation of a backward facing step experiment with liquid metal coolant

This paper summarizes the efforts in designing and pre-evaluating a vertical backward facing step (BFS) experiment, with liquid sodium flow. Conducting such study is important, since sudden geometrical variations, e.g., in a flow channel, impacts the thermal-hydraulic behavior. Geometrical variations occur many times in manifolds, heat exchangers or fuel bundles. Hence, it is reasonable to investigate their influence on the flow. Up to now, the information related to backward facing steps with liquid metal coolant is sparse. The majority of investigations related to backward facing steps have been performed with fluids like air or water. Due to the fundamental differences between fluids with a Prandtl number around unity, like water and air, and fluids with a very small Prandtl number, like sodium, a one-to-one transfer of knowledge from one fluid group to another is impossible. In addition, experimental and numerical studies related to liquid metal thermal hydraulics are focusing on homogenous geometries like pipes, ducts or rod bundles, not considering the influence of geometrical variations along the flow channel. In the frame of the EU Horizon 2020 project SESAME, an extensive effort has been put forward to study the vertical BFS case. The main idea is to generate a reference database in order to validate and improve the pragmatic turbulence modelling approaches for such flow configurations. Therefore, an experimental study is foreseen to be performed with liquid sodium. In addition, a complimentary DNS of a similar geometry configuration will be performed. In the context of this study, a combined effort of the experiments, DNS, LES and RANS modelers will be put forward in order to design a vertical BFS with liquid sodium. Different aspects of the BFS design are studied to make a suitable and well-defined reference database. To name a few, the influence of the corner design of the rectangular ducts is studied. Furthermore, the estimation of the entrance length and the recirculation zone is part of this investigation, which will be valuable in placing the measurement devices at the right positions.