TY - JOUR
TI - Interface capturing simulations of bubble population effects in PWR subchannels
AU - Cambareri, Joseph J.
AU - Fang, Jun
AU - Bolotnov, Igor A.
T2 - NUCLEAR ENGINEERING AND DESIGN
AB - As the computational power of high-performance computing (HPC) facilities grows, so too does the feasibility of using first principle based simulation to study turbulent two-phase flows within complex pressurized water reactor (PWR) geometries. Direct numerical simulation (DNS), integrated with an interface capturing method, allows for the collection of high-fidelity numerical data using advanced analysis techniques. The presented research employs the massively parallel, finite-element based, unstructured mesh code, PHASTA, to simulate a set of two-phase bubbly flows through PWR subchannel geometries including auxiliary structures (spacer grids and mixing vanes). The main objective of the presented work is to analyze bubble dynamics and turbulence interactions at varying bubble concentrations to support the development of advanced two-phase flow closure models. Turbulent two-phase flows in PWR subchannels were simulated at hydraulic Reynolds numbers of 81,000 with bubble concentrations of 3%–15% by gas volume fraction (768–3928 resolved bubbles, respectively) and compared against a 1% void fraction case (262 bubbles) that had been previously simulated. The finite element mesh utilized for the study at higher bubble concentrations was composed of 1.55 billion elements, compared to the previous study which employed 1.11 billion elements, ensuring all turbulence scales and individual bubbles within the flow are fully resolved. For each case, the resolved initial bubble size was 0.65 mm in diameter (resolved with 25 grid points across the diameter). The simulations were analyzed to find flow features such as the mean velocity profile, bubble relative velocity and the effect of the bubbles on the turbulent conditions.
DA - 2020/8/15/
PY - 2020/8/15/
DO - 10.1016/j.nucengdes.2020.110709
VL - 365
SP -
SN - 1872-759X
KW - DNS
KW - Interface capturing
KW - PWR subchannel
ER -
TY - JOUR
TI - Exchange interactions and long-range magnetic order in the (Mg,Co,Cu,Ni,Zn)O entropy-stabilized oxide: A theoretical investigation
AU - Rak, Zs
AU - Brenner, D. W.
T2 - JOURNAL OF APPLIED PHYSICS
AB - The magnetic structure of the entropy-stabilized oxide (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O has been investigated using first-principles methods in combination with Monte Carlo (MC) simulations. Similar to other transition metal oxides with the rock salt structure, such as CoO and NiO, the dominant interaction in this entropic oxide is the antiferromagnetic (AFM) superexchange interaction that takes place between second nearest neighbor cations. This superexchange interaction is responsible for the long-range type-II antiferromagnetic order observed in the material, with ferromagnetic (111) planes coupled antiferromagnetically in the (111) direction. The Néel temperature (TN) is evaluated via MC simulation, where the entropic oxide is modeled by a lattice of randomly distributed strengths of magnetic exchanges obtained from the binary and ternary oxides. The composition dependence of TN suggests that the material becomes paramagnetic when the concentration of nonmagnetic species exceeds 84%. The comparison between the theoretical results and the available experimental data indicates that the magnetic interactions in the entropic oxide can be predicted from magnetic exchange parameters calculated in the binary and ternary oxides.
DA - 2020/5/14/
PY - 2020/5/14/
DO - 10.1063/5.0008258
VL - 127
IS - 18
SP -
SN - 1089-7550
ER -
TY - JOUR
TI - Simulation scaling studies of reactor core two-phase flow using direct numerical simulation
AU - Cambareri, Joseph J.
AU - Fang, Jun
AU - Bolotnov, Igor A.
T2 - NUCLEAR ENGINEERING AND DESIGN
AB - Tremendous growth in supercomputing power in recent years has resulted in the emergence of high-resolution flow analysis methods as an advanced research tool to evaluate single and two-phase flow behavior. In particular, unstructured mesh-based methods have been applied to analyze flows in complex reactor core geometries, including those of light water reactors (LWR). The finite-element based code, PHASTA, is utilized to perform large-scale simulations of two-phase bubbly flows in LWR geometries. Given the large computational cost of direct numerical simulation (DNS) coupled with interface tracking methods (ITM), typical domains encompass a portion of a single subchannel. In the presented research, the state-of-the-art analysis of turbulent two-phase flows in complex LWR subchannel geometries are demonstrated at both prototypical reactor parameters as well as scaled low pressure conditions. Three different cases are studied, a high-pressure simulation in prototypical reactor subchannel geometry, a low-pressure case in prototypical geometry and a final low-pressure case in a geometry scaled up to conserve the ratio between the bubble size and the domain pitch. Utilizing advanced statistical processing tools, these simulation conditions are compared to shed light on the relevancy of two-phase flow characteristics given the significant differences between LWR and low-pressure conditions. These findings can lead to the generation of useful guiding principles when researchers need to scale the two-phase flow behavior captured at low pressure and temperature conditions to those at reactor operating conditions.
DA - 2020/3//
PY - 2020/3//
DO - 10.1016/j.nucengdes.2019.110435
VL - 358
SP -
SN - 1872-759X
KW - DNS
KW - Interface tracking
KW - PWR subchannel
KW - Scaling studies
ER -
TY - JOUR
TI - Interface-Resolved Simulations of Reactor Flows
AU - Fang, Jun
AU - Cambareri, Joseph J.
AU - Li, Mengnan
AU - Saini, Nadish
AU - Bolotnov, Igor A.
T2 - NUCLEAR TECHNOLOGY
AB - This critical review paper outlines the recent progress in high-resolution numerical simulations of two-phase coolant flow in light water reactor–relevant geometries by resolving the water-vapor interface. Rapid development of capabilities in high-performance computing is creating exciting opportunities to study complex reactor thermal-hydraulic phenomena. Today’s advances in thermal-hydraulic analysis and interface-resolved simulations will help pave the way to the next level of understanding of two-phase flow behavior in complex geometries. This paper consists of two major parts: (1) a brief review of direct numerical simulation and interface tracking simulation and (2) several opportunities in the near future to apply cutting-edge simulation and analysis capabilities to address the nuclear-related multiphase flow challenges. The first part will discuss typical computational methods used for the simulations and provide some examples of the past work as well as computational cost estimates and affordability of such simulations for research and industrial applications. In the second part specific application examples are discussed, from adiabatic bubbly flow simulations in pressurized water reactor subchannel geometry to the modeling of nucleate boiling. The uniqueness of this study lies in the specific focus on applications with nuclear engineering interest as well as new generation modeling and analysis methodologies. Together with the ever-growing computing power, the related large-scale two-phase flow simulations will become indispensable for the improved scientific understanding of complex two-phase flow phenomena in nuclear reactors under normal operation and postulated accident conditions.
DA - 2020/2/1/
PY - 2020/2/1/
DO - 10.1080/00295450.2019.1620056
VL - 206
IS - 2
SP - 133-149
SN - 1943-7471
KW - Two-phase flow
KW - direct numerical simulation
KW - interface tracking
KW - subchannel geometry
ER -