On turbulence production in a jet passing through a grid-type obstacle; An LES approach

Abe, Satoshi  ; Hirose, Yoshiyasu  ; Shibamoto, Yasuteru 

The interaction of turbulent jets plays a critical role in heat and mass transfer across a variety of engineering applications. In particular, the merging phenomena of jets in nuclear reactors are important for validating the credibility of the core exit temperature (CET) as an indicator of core heat-up. CET serves as a key criterion for accident management and ensuring the safe operation of the reactor. Understanding the dynamics of these jet interactions is essential for improving reactor safety and efficiency. Furthermore, in the field of containment thermal hydraulics during severe accidents, the behavior of a jet interacting with a grid-type obstacle has attracted significant attention. This study utilized Large Eddy Simulation (LES) to gain a deeper understanding of the flow characteristics of a jet affected by such an obstacle, with particular focus on the turbulence production mechanism. To improve the accuracy of turbulence modeling, the Coherent Structure Smagorinsky Model (CSM) was employed. Validation against experimental data confirmed that LES is a valuable tool for investigating jet flow behavior. The vortex structure of the jet was visualized using the Q-criterion. Additionally, the impact of the grid-type obstacle on the turbulence kinetic energy production rate was analyzed through radial profiles at various locations and its cumulative production.