Zhi Shang - Academia.edu (original) (raw)

Papers by Zhi Shang

Acta Physica Sinica, 2012

In this paperan improved dissipative particle dynamics(DPD) method was applied to simulate drople... more In this paperan improved dissipative particle dynamics(DPD) method was applied to simulate droplet motion in a grooved microchannel. The improved DPD method adopted a recently proposed combination of short-range repulsive and long-range attractive interaction, which can simulate fluid flows with free surfaces, such as droplet motions. The static contact angle between the droplet and the solid wall was simulated with the new potential function, andstatic contactangle～awf/af curve was obtained by Polynomial fit of the 2nd order. The influences ofwall wettability, flow field force, droplet temperature on the flow pattern of droplet in the grooved microchannel were investigated. The results showed that wall wettability and flow field force have large affectson the flow pattern of the droplet, whiledroplet temperature have little affectson it. This article is helpful to understand the fluid flow behavior with free surfaces on rough surfaces.

Proceedings of the Practice and Experience in Advanced Research Computing 2017 on Sustainability, Success and Impact, 2017

Multiphase flow in porous media is an important component in petroleum reservoir research. During... more Multiphase flow in porous media is an important component in petroleum reservoir research. During the processing of oil exploration, the gas, liquid and solid particles may flow through porous media in a reservoir. A novel solver, named MPPICmultiphaseInterFoam1, was developed using OpenFOAM to simulate multiphase flows in the porous media of a reservoir. This solver is realized by coupling DPM (discrete particle modeling) and VOF (volume of fluid) with CFD (computational fluid dynamics) based on the MP-PIC (multiphase particle-in-cell) method. After validation, this solver was used to simulate multiphase flows in oil and gas reservoirs. The Intel Xeon Phi KNL (Knights Landing) processors on an HPC (high performance computing) system were employed to carry out the numerical simulations. Optimal performance was realized by parallel programming with MPI and vectorization based on the Intel Xeon Phi KNL processors. It was found that Intel Xeon Phi Knights Landing processors are good to perform the large-scale simulations of multiphase flow in porous media.

Bulletin of the American Meteorological Society, 2021

The development of high-resolution, fully-coupled, regional Earth system model systems is importa... more The development of high-resolution, fully-coupled, regional Earth system model systems is important for improving our understanding of climate variability, future projections, and extreme events at regional scales. Here we introduce and present an overview of the newly-developed Regional Community Earth System Model (R-CESM). Different from other existing regional climate models, R-CESM is based on the Community Earth System Model version 2 (CESM2) framework. We have incorporated the Weather Research and Forecasting (WRF) model and Regional Ocean Modeling System (ROMS) into CESM2 as additional components. As such, R-CESM can be conveniently used as a regional dynamical downscaling tool for the global CESM solutions or/and as a standalone high-resolution regional coupled model. The user interface of R-CESM follows that of CESM, making it readily accessible to the broader community. Among countless potential applications of R-CESM, we showcase here a few preliminary studies that illus...

International Journal of Aerospace and Lightweight Structures (IJALS), 2013

Bubbly flow is widely encountered in many engineering applications, such as those in chemical and... more Bubbly flow is widely encountered in many engineering applications, such as those in chemical and nuclear systems, bubble column reactors and oil transportation pipes. Therefore, understanding of bubbly flow in a bubble-liquid flow system is extremely important. In this paper, bubbly flow involved with thousands of bubbles in a vertical pipe is numerically simulated. The motions of the bubbles are tracked using a Discrete Phase Model (DPM) and bubble-bubble interactions are simulated through the model of discrete element method (DEM). The effects of bubble diameter on the bubble flow trajectories are studied. Comparisons are made on the flow field with and without considering bubble-bubble collision.

Open Journal of Applied Sciences, 2013

An open source Direct Simulation Monte Carlo (DSMC) code, called as dsmcFoam in OpenFOAM, is used... more An open source Direct Simulation Monte Carlo (DSMC) code, called as dsmcFoam in OpenFOAM, is used to study a blunt body with the shape of a space crew capsule return vehicle. The rarefied gas has the Knudsen number with 0.03. The flow with a Mach number 4.35 over the capsule was simulated by DSMC. The distributions of velocity field and temperature around the capsule were calculated. This study may provide some useful information for the reentry of the return vehicle.

Nuclear Engineering and Design, 2011

The commercial CFD code STAR-CD 4.02 is used as a numerical simulation tool for flows in the supe... more The commercial CFD code STAR-CD 4.02 is used as a numerical simulation tool for flows in the supercritical water-cooled nuclear reactor (SCWR). The basic heat transfer element in the reactor core can be considered as round tubes and tube bundles. Reactors with vertical or horizontal flow in the core can be found. In vertically oriented core, symmetric characters of flow and heat transfer can be found and two-dimensional analyses are often performed. However, in horizontally oriented core the flow and heat transfer are fully three-dimensional due to the buoyancy effect. In this paper, horizontal tubes and tube bundles at SCWR conditions are studied. Special STAR-CD subroutines were developed by the authors to correctly represent the dramatic change in physical properties of the supercritical water with temperature. From the study of single round tubes, the Speziale quadratic non-linear high-Re k-ε turbulence model with the two-layer model for near wall treatment is found to produce the best results in comparison with experimental data. In tube bundle simulations, it is found that the temperature is higher in the top half of the bundle and the highest tube wall temperature is located at the outside tubes where the flow rate is the lowest. The secondary flows across the bundle are highly complex. Their main effect is to even out the temperature over the area within each individual recirculating region. Similar analysis could be useful in design and safety studies to obtain optimum fuel rod arrangement in a SCWR.

Journal of Engineering, 2013

In order to run CFD codes more efficiently on large scales, the parallel computing has to be empl... more In order to run CFD codes more efficiently on large scales, the parallel computing has to be employed. For example, in industrial scales, it usually uses tens of thousands of mesh cells to capture the details of complex geometries. How to distribute these mesh cells among the multiprocessors for obtaining a good parallel computing performance (HPC) is really a challenge. Due to dealing with the massive mesh cells, it is difficult for the CFD codes without parallel optimizations to handle this kind of large-scale computing. Some of the open source mesh partitioning software packages, such as Metis, ParMetis, Scotch, PT-Scotch, and Zoltan, are able to deal with the distribution of large number of mesh cells. Therefore they were employed as the parallel optimization tools ported into Code_Saturne, an open source CFD code, for testing if they can solve the issue of dealing with massive mesh cells for CFD codes. Through the studies, it was found that the mesh partitioning optimization so...

Journal of Nuclear Science and Technology, 2008

A compact supercritical water-cooled fast reactor (superfast reactor) core with a power of 700 MW... more A compact supercritical water-cooled fast reactor (superfast reactor) core with a power of 700 MWe is designed by using a three-dimensional neutronics thermal-hydraulic coupled method. The core consists of 126 seed assemblies and 73 blanket assemblies. In the seed assemblies, 251 fuel rods, consisting of MOX pellets, stainless steel (SUS304) cladding, and fission gas plenum are arranged into a tight triangle lattice along with 19 guide tubes for control rods and instrumentation. A zirconium hydride (ZrH) layer is employed in the blanket assemblies to reduce void reactivity. The results of the coupling three-dimensional neutronics and thermal hydraulic calculations show that this core has a high power density of 158.8 W/cm 3 with a maximum linear heat generation rate (MLHGR) less than 39 kW/m, that an average coolant outlet temperature of 500 C is achieved with a maximum cladding surface temperature (MCST) less than 650 C, and that void reactivity coefficients are negative throughout the cycle. Since the thermal-hydraulic part of the core design is based on single-channel analyses, subchannel analyses are also performed on all the seed assemblies to clarify the influence of cross-flow.

hector.ac.uk

The move towards petaflop computing will require scientific software to run efficiently on many t... more The move towards petaflop computing will require scientific software to run efficiently on many thousands of processors. For computational fluid dynamics, this imposes new challenges. We need to be able to generate very large computational grids, in excess of one billion computational cells, to ensure the processors have enough work. In addition, we need to partition these large computational meshes for efficient execution on these large scale facilities. As most grid generation codes are serial and proprietary, there is little the user can do. However, the majority of mesh partitioning software is available open-source and this study aims to understand how these codes perform when we need to create an extremely large number of computational domains. In particular, we seek to run our fluid dynamics software on a petascale system with more than 100,000 cores. This work focuses on the open-source software, Code_Saturne, and investigates the issues associated with pre-processing. The mesh partitioning software considered in this report has been restricted to open-source packages such as Metis, ParMetis, PT-Scotch and Zoltan. Today, Metis is the de facto standard but is a sequential code and is therefore limited by memory requirements. Parallel mesh partitioning software, such as ParMetis and PT-Scotch, can overcome this limitation provided the quality of the partition (edges cut, load balance) remains good. During our study, we found that the time required to perform the partition of 121M tetrahedral elements varied with the package and found that Metis consistently required the least amount of time. However, in all cases, the time to perform the partition was always modest and was not found to be a significant issue. In contrast, the memory constraints did vary with the package and PT-Scotch could generate mesh partitions in parallel (up to 131072 domains) using only 16 cores whereas ParMetis 3.1.1 required a minimum of 512 cores to create the 131072 domains. An analysis of the metrics suggests that the larger number of cores required by ParMetis results in a partition with a poor load balance. In practice, however, the simulation run time did not reflect this observation and, for up to 1024 cores, ParMetis produced the lower time to solution. Above 1024 cores, and up to 8192 cores, the sequential version of Metis showed the best speed-up. For 2048 and 4096 cores, PT-Scotch provided a better performance than ParMetis. In general, all packages did a reasonable job and it is difficult to identify any specific trends that would lead to one package being clearly superior to the others.

Chemical Engineering Science, 2013

ABSTRACT A novel Lagrangian algebraic slip mixture model (LASMM) has been developed to study mult... more ABSTRACT A novel Lagrangian algebraic slip mixture model (LASMM) has been developed to study multiphase flows. In this model, the slip velocity between continual and dispersed phases was developed through the bubble Lagrangian movement equation. According to the Lagrangian equation, the various interfacial forces at interface of the continual and dispersed phases were considered. Through the connection of the slip velocity, the Lagrangian equation was induced into the governing Eulerian equations of the two-phase mixture flow. This model therefore realized the connection between Eulerian model and Lagrangian model. Through the comparisons of the numerical simulations to the experiments in horizontal pipe, this model was validated.

Chemical Engineering Science, 2004

A mathematical model of multi-phase turbulent flow based on the diffusion flux model and the nume... more A mathematical model of multi-phase turbulent flow based on the diffusion flux model and the numerical simulation method to analyze the gas-particle flow structures have been developed. The diffusion flux model in which the accelerations due to various forces are taken into account for the calculation of the diffusion velocity of the particles enables its application to the analysis of multi-dimensional gas-particle two-phase flow. In order to verify the accuracy and efficiency of the numerical simulations, an experimental study of gas-particle flow in a suspension bed has been conducted. The numerical analysis results by using the diffusion flux model agree reasonably well with the experimental investigation. It is confirmed that the diffusion flux model has the capacity of correctly simulating the multi-dimensional gas-particle two-phase flow.

Applied Thermal Engineering, 2011

The diameter effect on the heat transfer of supercritical water (SCW) flows in horizontal round t... more The diameter effect on the heat transfer of supercritical water (SCW) flows in horizontal round tubes has been studied using computational fluid dynamics (CFD) technique. The numerical simulations are carried out by the STAR-CD solver combined with the user developed subroutines that control the numerical calculation procedures. Through the tests it is found that the discretization scheme using CD, LUD or MARS will not affect the accuracy of the numerical simulations. Through the diameter effect studies, it is found that the heat transfer of supercritical water flows in the horizontal round tube is strongly affected by the buoyancy especially for the large diameter tube. The large diameter (D=10mm) tube will have the high risk to have the strong heat transfer deterioration that can introduce 180 o C wall temperature difference between the top and bottom surfaces due to the buoyancy effects. The magnitudes of the effects can be quantificationally expressed by a ratio of Grashof number over Reynolds number square. Under the high mass flux regime, the heat transfer deterioration will disappear for all the diameters from 5mm to 10mm. The different secondary flow patterns at different tube diameters are also studied.

Journal of Fluids, 2014

A multidimensional diffusion flux mixture model was developed to simulate water jet two-phase flo... more A multidimensional diffusion flux mixture model was developed to simulate water jet two-phase flows. Through the modification of the gravity using the gradients of the mixture velocity, the centrifugal force on the water droplets was able to be considered. The slip velocities between the continuous phase (gas) and the dispersed phase (water droplets) were able to be calculated through multidimensional diffusion flux velocities based on the modified multidimensional drift flux model. Through the numerical simulations, comparing with the experiments and the simulations of traditional algebraic slip mixture model on the water mist spray, the model was validated.

Tongji Daxue Xuebao/Journal of Tongji University

Considering the cell subdivision method and the modified velocity-Verlet algorithm,the implementa... more Considering the cell subdivision method and the modified velocity-Verlet algorithm,the implementation of Lees-Edwards boundary conditions for DPD method was investigated.The simulated results show that the profiles of velocities,densities,temperatures,pressures and stresses agree well with the expected.Furthermore,when dissipative coefficient γ was increased to 100,the velocity profile in the system was homogeneous,indicating that the LE boundary conditions still valid for higher dissipation rate.Viewpoints different from Ref are proposed.

Chemical Engineering Science, 2008

The system pressure effect on heat transfer of supercritical water (SCW) flows in a horizontal ro... more The system pressure effect on heat transfer of supercritical water (SCW) flows in a horizontal round tube has been studied by using computational fluid dynamics (CFD) technique, aiming for extending previous researches on the buoyancy effect by further investigating the coupling effects of the system pressure and the buoyancy. A commercial CFD software STAR-CD v4.02 has been used for this purpose. Simulation starts with the sensitive study of key issues, i.e. the mesh dependency, the turbulence model influence, and the near-wall treatments. It was found that on baseline mesh of 477 000 elements with near-wall grid resolution of y + = 0. 2, the simulation using the Speziale nonlinear high Reynolds k-turbulence model and the Hassid and Poreh near-wall treatment gives the best predictions in comparison with the experimental data. After the validation, further simulations continued to study the system pressure effect on heat transfer characteristics of SCW flows in a horizontal round tube. It was found that when the buoyancy effect is negligible, the system pressure change has significant effects on the heat transfer of the flow. This implied that the SCW physical property variations due to the system pressure change could play some dominate roles on the heat transfer. However, when the buoyancy effect was considerably strong, the system pressure change has less effect on the heat transfer due to the strong influences of the buoyancy force. This finding has indicated that the heat transfer of SCW flows in a horizontal round tube was primarily governed by the buoyancy effect as observed by previous researchers, but the system pressure changes could also have some effects that cannot be simply ignored.

Tsinghua Science & Technology, 2005

A modified diffusion flux model (DFM) was developed to analyze turbulent multi-dimensional gas-pa... more A modified diffusion flux model (DFM) was developed to analyze turbulent multi-dimensional gas-particle two-phase flows. In the model, the solid particles move in a modified acceleration field, ′′ g , which includes the effects of various forces on the particles as if all the forces have the same effect on the particles as the gravity. The accelerations due to various forces are then taken into account in the calculation of the diffusion velocities of the solid particles in the gas-particle two-phase flow. The DFM was used to numerically simulate the gas-solid two-phase flow behind a vertical backward-facing step. The numerical simulation compared well with experimental data and numerical results using both the k-ε-A p and k-ε-k p twofluid models available in the literature. The comparison shows that the modified diffusion flux model correctly simulates the turbulent gas-particle two-phase flow.

Volume 2: Fuel Cycle and High Level Waste Management; Computational Fluid Dynamics, Neutronics Methods and Coupled Codes; Student Paper Competition, 2008

CFD investigation of heat transfer in supercritical water-cooled flow through fuel rod bundles ha... more CFD investigation of heat transfer in supercritical water-cooled flow through fuel rod bundles has been carried out, using commercial software STAR-CD 4.02 with specific ad hoc user routines for modeling physical property of supercritical water. The configuration considered is a typical core assembly of 3×3 fuel rod (round tube) bundles inside solid square box, as seen in the nuclear reactor. After priori mesh convergence studies, investigations are focused on key characteristics of flow and heat transfer performance, notably the wall temperature distributions, the mass flux and the secondary flow patterns in the cross-section. It is found that the rod wall temperature distributions exhibit highly non-uniform feature near the domain exit with very high wall temperatures: about 625°C observed on the corner rod and about 562.5°C on the border rod, respectively. It is believed that the appearance of the extremely wall temperature may be related to the non-uniform distributions of mass ...