@article{bao_feng_dinh_zhang_2021, title={Deep learning interfacial momentum closures in coarse-mesh CFD two-phase flow simulation using validation data}, volume={135}, ISSN={["1879-3533"]}, DOI={10.1016/j.ijmultiphaseflow.2020.103489}, abstractNote={Multiphase flow phenomena have been widely observed in the industrial applications, yet it remains a challenging unsolved problem. Three-dimensional computational fluid dynamics (CFD) approaches resolve of the flow fields on finer spatial and temporal scales, which can complement dedicated experimental study. However, closures must be introduced to reflect the underlying physics in multiphase flow. Among them, the interfacial forces, including drag, lift, turbulent-dispersion and wall-lubrication forces, play an important role in bubble distribution and migration in liquid-vapor two-phase flows. Development of those closures traditionally rely on the experimental data and analytical derivation with simplified assumptions that usually cannot deliver a universal solution across a wide range of flow conditions. In this paper, a data-driven approach, named as feature-similarity measurement (FSM), is developed and applied to improve the simulation capability of two-phase flow with coarse-mesh CFD approach. Interfacial momentum transfer in adiabatic bubbly flow serves as the focus of the present study. Both a mature and a simplified set of interfacial closures are taken as the low-fidelity data. Validation data (including relevant experimental data and validated fine-mesh CFD simulations results) are adopted as high-fidelity data. Qualitative and quantitative analysis are performed in this paper. These reveal that FSM can substantially improve the prediction of the coarse-mesh CFD model, regardless of the choice of interfacial closures. It demonstrates that data-driven methods can aid the multiphase flow modeling by exploring the connections between local physical features and simulation errors.}, journal={INTERNATIONAL JOURNAL OF MULTIPHASE FLOW}, author={Bao, Han and Feng, Jinyong and Dinh, Nam and Zhang, Hongbin}, year={2021}, month={Feb} }
 @article{feng_bolotnov_2018, title={Effect of the wall presence on the bubble interfacial forces in a shear flow field}, volume={99}, ISSN={["1879-3533"]}, DOI={10.1016/j.ijmultiphaseflow.2017.10.004}, abstractNote={Understanding the interactions between the bubbles and solid walls is important for predicting how the bubbly flow characteristics, such as void fraction and statistical distribution of bubble sizes, are affected by the presence of solid boundaries. In the present research, the numerical simulations with interface tracking method are performed to evaluate the interfacial forces’ closures in shear flow field under well-controlled conditions. The proportional-integral-derivative bubble controller is adopted to keep a single bubble at fixed position near the wall by balancing the forces in all three directions. This allows the extraction of the interfacial forces and the calculation of the corresponding coefficients. Validation tests have previously been conducted by the authors to compare the interfacial closures’ results against the experimental data. In this work, the influence of wall distance, relative velocity and bubble deformation on the interfacial forces are investigated. The results show that as the bubble approaches the wall, it experiences a transition from attractive force to repulsive force normal to the wall. The bubble Reynolds number also has significant impact on the interfacial forces: the net lateral force changes direction at Reb=35. The coupled phenomenon of bubble deformation and wall effect is investigated as well. The net lift sign change is observed at Eo=2.3 when the dimensionless wall distance (the ratio between the distance from the bubble center to the wall and the bubble diameter) is equal to 1. The presented studies complement the state-of-the-art knowledge and those are aimed to help improve the closure laws for interfacial forces and contribute to the multiphase computational fluid dynamics (M-CFD) closure model development.}, journal={INTERNATIONAL JOURNAL OF MULTIPHASE FLOW}, author={Feng, Jinyong and Bolotnov, Igor A.}, year={2018}, month={Feb}, pages={73–85} }
 @article{feng_bolotnov_2017, title={Evaluation of bubble-induced turbulence using direct numerical simulation}, volume={93}, ISSN={["1879-3533"]}, DOI={10.1016/j.ijmultiphaseflow.2017.04.003}, abstractNote={The presented research evaluates the interaction between a single bubble and homogeneous turbulent flow using direct numerical simulation (DNS) approach. The homogeneous single-phase turbulence is numerically generated by passing a uniform flow through grid planes. The turbulence decay rate is compared with experiment-based correlation. The single phase turbulence is then used as an inflow boundary condition for a set of single bubble studies. By estimating the turbulent field around the fully resolved bubble, the effects of bubble deformability, turbulent intensity and relative velocity on the bubble-induced turbulence are investigated. The existence of bubble creates new vortices in the wake region and the enhancement of turbulence is observed in the region behind the bubble. The results show that the magnitude of the turbulence enhancement would increase as the bubble encounters larger liquid turbulent intensity or higher relative velocity. Set of bubble Weber numbers from 0.34 to 3.39 are used to investigate the effect of bubble deformability. The more deformable bubble is the higher the increase in the magnitude of the turbulence enhancement behind the bubble. This research provides systematic insight on the bubble-induced turbulence (BIT) mechanism and is important for multiphase computational fluid dynamics (M-CFD) closure model development.}, journal={INTERNATIONAL JOURNAL OF MULTIPHASE FLOW}, author={Feng, Jinyong and Bolotnov, Igor A.}, year={2017}, month={Jul}, pages={92–107} }
 @article{feng_bolotnov_2017, title={Interfacial force study on a single bubble in laminar and turbulent flows}, volume={313}, ISSN={["1872-759X"]}, DOI={10.1016/j.nucengdes.2016.12.034}, abstractNote={Two-phase flows are present in various industrial processes in engineering fields ranging from light water reactor engineering to petrochemical engineering. In this paper, we conduct the interfacial force study on a single bubble under both laminar and turbulent flow scenarios. Advanced finite-element based flow solver (PHASTA) with level-set interface tracking method is used to perform the studies. The interface tracking approach is verified and validated by analyzing the interfacial forces, i.e., drag and lift forces, and comparing the results with the experiment-based data and correlations. The sign change of transverse migration direction is observed at Eo=3.4 which is close to the experimental observations. A set of parametric studies, including relative velocity, bubble deformability and turbulent intensity, are performed to analyze the impact of homogeneous turbulent flow on the drag force. A new drag coefficient closure model is proposed which agrees well with the DNS data considering both laminar and turbulent flow. Those studies can complement the experimental database to obtain improved closure laws for interfacial forces and are important contribution to the multiphase computational fluid dynamics (M-CFD) closure model development.}, journal={NUCLEAR ENGINEERING AND DESIGN}, author={Feng, Jinyong and Bolotnov, Igor A.}, year={2017}, month={Mar}, pages={345–360} }
 @article{thomas_fang_feng_bolotnov_2015, title={ESTIMATION OF SHEAR-INDUCED LIFT FORCE IN LAMINAR AND TURBULENT FLOWS}, volume={190}, ISSN={["1943-7471"]}, DOI={10.13182/nt14-72}, abstractNote={Abstract The goal of the present study is to demonstrate that direct numerical simulations (DNS) coupled with interface tracking methods can be used to estimate interfacial forces in two-phase flows. Current computational multiphase fluid dynamics codes model interfacial forces utilizing closure laws that are heavily dependent on limited experimental data and simplified analytical approximations. In the present work, a method for improving the current interfacial force database has been developed by using DNS to quantify the lift and drag forces on a single bubble in laminar and turbulent shear flows. A proportional-integral-derivative–based controller was implemented into the finite element–based, multiphase flow solver [PHASTA (Parallel, Hierarchic, higher-order accurate, Adaptive, Stabilized, finite element method Transient Analysis)] to control the bubble position. This capability allowed for utilization of a steady-state force balance on the bubble to determine lift and drag coefficients in various shear flows. Specifically, for low shear flows (2.0 s−1), the effect of the wall presence is analyzed, and for high shear flows, the effect of turbulence is studied. A number of uniform shear (10.0 to 470.0 s−1) laminar flows were simulated to assess lift and drag force behavior as the kinetic energy of the flow increased. Two high shear (236.0 and 470.0 s−1) turbulent flows were simulated to understand bubble-turbulence interaction influence on the drag and lift phenomena. Two uniform shear rates (20.0 and 100 s−1) were simulated utilizing pressurized water reactor fluid properties. The lift and drag coefficients estimated in this work are in agreement with models developed for low shear laminar flows, whereas for high shear laminar and turbulent flows, bubble-turbulence interaction became a dominating influence in the lift and drag coefficient estimation. The novel results and method presented in this paper offer a path to simulating full-fledged reactor coolant environments where the lift and drag forces on a single bubble can be studied.}, number={3}, journal={NUCLEAR TECHNOLOGY}, author={Thomas, Aaron M. and Fang, Jun and Feng, Jinyong and Bolotnov, Igor A.}, year={2015}, month={Jun}, pages={274–291} }