LES of natural convection along a side-heated vertical wall in a water cavity applied for the scale of Small Modular Reactor ($Ra \approx 10^{15}$) - CEA - Commissariat à l’énergie atomique et aux énergies alternatives Accéder directement au contenu
Article Dans Une Revue Nuclear Engineering and Design Année : 2023

LES of natural convection along a side-heated vertical wall in a water cavity applied for the scale of Small Modular Reactor ($Ra \approx 10^{15}$)

Résumé

The passive safety concept of Small Modular Reactors (SMR) is based on the transfer of residual heat from the reactor to a water pool. Since the height of the reactor vessel reaches approximately 15 m, this leads to a strong heat exchange between the wall and the water by the way of natural convection. The maximum Rayleigh number ($Ra$) reaches $10^{14}$ or $10^{15}$. Reliable heat transfer correlations exist only up to $Ra \approx 10^{12}$, still along with uncertainties in the extrapolation to higher Rayleigh number values. To improve the understanding of natural convection at high Rayleigh number values, the turbulent natural convection boundary layer (TNCBL) along a 15 m high, side-heated vertical wall in a water tank is simulated by employing the Large Eddy Simulation method with the CEA in-house code Triocfd (Angeli et al., 2015). The numerical results in terms of heat transfer correlation, mean temperature and mean velocity, second moment variables show a reasonable agreement with available experimental data in the range of $Ra < 10^{12}$. It is observed in the simulation that the powers of the heat transfer correlations in the laminar ($Nu_y = 0.56(Gr_y \cdot Pr)^{0.25}$) and the turbulent regimes ($Nu_y = 0.114(Gr_y \cdot Pr)^{1/3}$) correspond well to the classical regimes at $Ra < 2 \times 10^{12}$. A slight deviation from the classical exponent (1/3) is found at higher Rayleigh number ($2 \times 10^{12} < Ra < 1.8 \times 10^{15}$), namely $Nu_y = 0.114(Gr_y \cdot Pr)^{0.33}$. Through the analysis of turbulent kinetic energy budget, it is found that turbulent contribution from shear stress increases continuously with the increase of Rayleigh number. However, the turbulence contribution from buoyancy keeps increasing until $Ra \approx 6.6 \times 10^{13}$, then decreases gradually at higher Rayleigh number. The behavior of the maximum buoyant force shifts slowly from the inner boundary layer to the outer boundary layer may indicate the potential transition of the buoyancy-dominated regime to the shear stress dominated regime, thus confirming previous theoretical prediction (Wells Andrew and Worster, 2008). The increasing scale of the streak-like turbulent structures with the increase of Rayleigh number are clearly demonstrated through visualization process.
Fichier non déposé

Dates et versions

cea-04466640 , version 1 (19-02-2024)

Identifiants

Citer

Songzhi Yang, Ulrich Bieder, Etienne Studer. LES of natural convection along a side-heated vertical wall in a water cavity applied for the scale of Small Modular Reactor ($Ra \approx 10^{15}$). Nuclear Engineering and Design, 2023, 414, pp.112543. ⟨10.1016/j.nucengdes.2023.112543⟩. ⟨cea-04466640⟩
11 Consultations
0 Téléchargements

Altmetric

Partager

Gmail Facebook X LinkedIn More