Density stratification breakup by a vertical jet: Experimental and numerical investigation on the effect of dynamic change of turbulent schmidt number

• Published in: Nuclear engineering and design Vol. 368; p. 110785
• Main Authors: Abe, Satoshi, Studer, Etienne, Ishigaki, Masahiro, Sibamoto, Yasuteru, Yonomoto, Taisuke
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.11.2020; Elsevier BV; Elsevier
• Subjects: Accuracy; Computational fluid dynamics; Computer applications; Containment; Containment vessels; Density stratification; Dynamic models; Experimental data; Fluid dynamics; Fluid flow; Fluid mechanics; Gas mixtures; Helium; Hydrodynamics; Hydrogen; Hydrogen combustion; Large eddy simulation; Mechanics; Nuclear containment vessel; Nuclear energy; Ocean engineering; Particle image velocimetry; Physics; Quadrupoles; RANS; Schmidt number; Shear stress; Turbulence; Turbulent mixing; Turbulent Schmidt number; Velocity; Velocity distribution; Vertical distribution; RANS; Density stratification; Nuclear containment vessel; Turbulent Schmidt number
• ISSN: 0029-5493; 1872-759X
• DOI: 10.1016/j.nucengdes.2020.110785

•This paper phenomenologically discusses the interaction behavior between a vertical jet and stratification by performing a small scale experiment and its CFD analysis.•The experimental and Large-Eddy Simulation (LES) results were used to validate the Reynolds-Averaged Navier-Stokes (RANS) with the dynamic modeling for turbulent Schmidt number Sct, which is developed in research on ocean engineering.•The predicted turbulence behavior around the interaction region in the case with the dynamic modeling for Sct agreed with the experimental data of the VIMES experiment and LES result.•In conclusion, the dynamic modeling for Sct is a useful and practical approach to improve the prediction accuracy on the stratification breakup behavior by a vertical jet. The hydrogen behavior in a nuclear containment vessel is one of the significant issues raised when discussing the potential of hydrogen combustion during a severe accident. Computational Fluid Dynamics (CFD) is a powerful tool for better understanding the turbulence transport behavior of a gas mixture, including hydrogen. Reynolds-averaged Navier–Stokes (RANS) is a practical-use approach for simulating the averaged gaseous behavior in a large and complicated geometry, such as a nuclear containment vessel; however, some improvements are required. In this paper, we focused on the turbulent Schmidt number Sct for improving the RANS accuracy. Some previous studies on ocean engineering mentioned that the Sct value gradually increases with the increasing stratification strength. We implemented the dynamic modeling for Sct based on the previous studies into the OpenFOAM ver 2.3.1 package. The experimental data obtained by using a small scale test apparatus at Japan Atomic Energy Agency (JAEA) was used to validate the RANS methodology. In the experiment, we measured the velocity field around the interaction region between vertical jet and stratification by using the Particle Image Velocimetry (PIV) system and time transient of gas concentration by using the Quadrupole Mass Spectrometer (QMS) system. Moreover, Large-Eddy Simulation (LES) was performed to phenomenologically discuss the interaction behavior. The comparison study indicated that the turbulence production ratio by shear stress and buoyancy force predicted by the RANS with the dynamic modeling for Sct was a better agreement with the LES result, and the gradual decay of the turbulence fluctuation in the stratification was predicted accurately. The time transient of the helium molar fraction in the case with the dynamic modeling was very closed to the VIMES experimental data. The improvement on the RANS accuracy was produced by the accurate prediction of the turbulent mixing region, which was explained with the turbulent helium mass flux in the interaction region. Moreover, the parametric study on the jet velocity indicates the good performance of the RANS with the dynamic modeling for Sct on the slower erosive process. This study concludes that the dynamic modeling for Sct is a useful and practical approach to improve the prediction accuracy.