This work is concerned with the study of the flow around a stream tidal turbine andthe wake behavior behind it. Two methods are used in this study, the first is the Multiple Reference Frame (MRF) method and the second is the Actuator Disk Method (ADM). The effects of the tidal turbine on the fluid flow in the radial and in the longitudinal axis are studied, as well as the forces on the turbine blade. Different turbulence intensity conditions are investigated. The computational effort for the two
methods is approximately the same.

Heat transfer is a known challenge in many industrial as well as everyday applications. Commonly the heating or cooling processes are required to be implemented in a compact manner due to various process and/or design constraints. To achieve an augmentation in the heat transfer rate in compact heat exchangers, vortex generators (VGs) such as winglets, wings, ribs or grooves are frequently employed. VGs disrupt the formation of boundary layers by introducing longitudinal as well as transverse vortices and cause enhanced flow mixing, thereby increasing the heat transfer rate at the cost of pressure loss.
In this work a numerical investigation of the influence of winglet configurations in a rectangular duct on the flow and heat transfer characteristics is carried out. The winglets considered in the study are delta and three new winglets namely arrow, delta-cut and X winglet. Nandana and Janoske studied the heat transfer characteristics of a single arrow, delta-cut and X winglet placed in a rectangular duct for laminar flow (Reynolds number of channel flow, Re = 300 − 1200) regime in a previously examined study. Here the study is extended to turbulent regime for Re ranging from 4000 to 12000 and for multiple winglets in the duct. The arrangements of multiple winglets are defined in terms of longitudinal distances between each other. For all the simulations, the flow attack angle (α) and the inclination angle (β) of winglets are chosen to be constant 45° and 90°, respectively. The study focuses on the influence of various aforementioned winglet and flow configurations on the vortex expansions and flow structure as well as heat transfer rate, pressure loss and thermal enhancement factor. The results are compared with the heat transfer rate in a plain rectangular duct without winglets. The RANS k-ω-SST model is employed to calculate turbulence in the flow domain.

At present, the Portuguese footwear industry is considered one of the most important internationalized sectors of the Portuguese economy. Recent developments in the shoe market induced some adaptations on this industrial sector, in order to maintain its reference in the footwear industry, with high technical and innovative solutions, able to offer high‑quality products [1]. To achieve this goal, the Portuguese footwear industry has been investing in research and technological development of new materials, products and processes, to obtain better solutions that result in high end added-value products [2].

Toecaps are one of the most important components in safety footwear, but the currently available ones have a significant contribution to the total part weight, mainly because they are made of steel, due to its high mechanical resistance. This limitation has been motivating efforts to replace steel toecaps by polymeric ones, since they are lighter, insulated and insensitive to magnetic fields. Nevertheless, polymeric toecaps require larger volumes, when compared with their metallic counterparts, which has a negative impact in aesthetics and design.

This work is part of a PhD project, which aims the development of a new composite toecap design with improved mechanical behavior. The toecap design should be defined with the support of the computational modelling open source library, OpenFOAM. In order to accomplish this goal, two different case studies that simulate the laboratory mechanical test conditions will be prepared, one regarding compressive behavior (up to 15 kN) and another a free-falling weight with an impact energy of 200 J [3]. In this work, the free-falling weight case is presented, being the solid mechanics toolbox, developed by P. Cardiff [4-5], the solver selected for modelling purposes. After implementation and validation, different toecap designs will be simulated aiming to identify the geometry that accomplishes the toecap specifications, with the minimum possible amount of material.

References:

[1] APICCAPS, “Statistical Report, Portugal - Footwear, Components and Leather Goods.”, 2017.

[2] CTCP, “Inovação”, 2019 [Online], Available: https://www.ctcp.pt/inovacao/inovacao.asp?op=0&idmp=Ng==&idms=NDU=&lista=todos [Accessed: 17-Jun-2019].

[3] “Personal protective equipment – Safety Footwear”, prEN ISO 20345, 2011.

[4] P. Cardiff et al. (2016), DOI: 10.1002/nme.5345

[5] P. Cardiff et al. (2018), arXiv:1808.10736.

Nuclear power plant operators should conduct in-service testing (IST) to verify the safety functions of safety-related pumps and valves and to monitor the degree of vulnerability over time during reactor operation. The system to which the pump and valve to be tested are installed has various sizes of orifices for flow control and decompression. Rapid flow acceleration and accompanying pressure drop may cause cavitation inside the orifice, which may induce many detrimental effects, such as vibration and damage of the piping system integrity.

Currently, there is no Computational Fluid Dynamics (CFD) software licensed from nuclear regulatory agency in Korea, but license applicants use specific CFD software to revise licensing documents for facility improvements and submit analysis results as licensing documents. In case of CFD software currently being used for licensing, modeling and numerical techniques for single-phase flow have reached a certain level, but significant uncertainty may be involved in the analysis results for especially multi-phase flow due to the technical limitations of CFD software. Therefore, from the nuclear regulatory perspective, it is necessary to perform the systematic assessment and prepare the domestic regulatory guideline for checking whether valid CFD software and the numerical modeling is used for IST-related problems. Under these circumstances, CFD simulation for the cavitating flow inside a square-edged orifice was conducted using OpenFOAM v6 and the predicted results were compared to those of commercial CFD software, ANSYS CFX R.18.

Acknowledgement

This work was supported by the Nuclear Safety Research Program through the Korea Foundation Of Nuclear Safety (KOFONS) using the finiancial resource granted by the Nuclear Safety and Security Commision (NSSC) of the Republic of Korea (No. 1805007)

CFD Simulation is difficult for small and medium-sized enterprises(SMEs) to apply to their process. Nevertheless CFD simulation must be an efficient way to reduce the cost of developing SME products and processes. That is why 'High-performance Engineering MOdeling & Simulation(HEMOS)' has been developed. HEMOS is a general-purpose CAE software which can conduct both structural and CFD analyses. Various open-source libraries are used to develop HEMOS. Especially, we used OpenFOAM as a CFD solver. Preprocessor and postprocessor have been also developed on HEMOS. Preprocessor has been developed with OpenCasCade library which is a CAD kernel based on OpenGL. Postprocessor for structural analysis has been developed with self-developed code which is also based on OpenGL, while Paraview is utilized for postprocessing of CFD analysis. CFD part of HEMOS is called HEMOS-Fluid. HEMOS-Fluid has some features for CFD analysis. It is related with some solvers in OpenFOAM which consists of simpleFoam, porousSimpleFoam, pisoFoam and pimpleFoam. In addition, HEMOS-Fluid deals with MRF functions, too. The main purpose of developing HEMOS is to supply very easy and user-friendly CAE software for SMEs engineers. As a result, workflow system has been developed to use it easily for beginners. And the workflow of HEMOS-fluid is designed with standard process of CFD. Few inputs are needed to make a complete case to have a simulation. Most of mandatory inputs do not need to be determined in HEMOS. They are completely automatically determined in HEMOS. HEMOS-Fluid can generate hybrid meshes on arbitrary geometry. HEMOS-Fluid only supports STEP and IGES formats of CAD file. It also provides fluid domain extraction function which can make inner fluid domain or outer fluid domain. Fluid domain extraction algorithms were self-developed based on OpenCasCade functions. HEMOS-Fluid generates OpenFOAM input files and their file structure automatically with user inputs from graphic user interface (GUI). This paper presents how HEMOS-Fluid is designed and how it works by process.

Fine bubble diffusers are often used for aeration systems in large wastewater treatment works. The bubbles created are a source of momentum for mixing and provide oxygen required for the micro-organisms to feed on the organic matter and nitrogen in the wastewater. The energy needed to aerate the system can account for 25-60% of the total energy consumption; therefore, large savings can be gained with an energy efficient aeration system. Biokinetic models have been developed (ASMs, ADMs, etc.) that describe the growth and decay of micro-organisms and their dependence on oxygen in wastewater treatment systems and are a useful tool for understanding the biological processes. However, a critical assumption made by these models is that the reactors are well-mixed such that the parameter concentrations are uniform throughout the reactor. If we reduced the aeration, this would reduce the amount of available oxygen for the reactions and also affect the mixing flow regime. In many cases, the optimal reactor design would be one that uses the least amount of energy to mix while not hindering the desired reactions. By coupling the biokinetic growth models with the hydrodynamics using computational fluid dynamics, we can analyse the impact of the hydrodynamics on the biokinetic growth models in the case of reduced aeration. These enhanced predictions can aid in improved operating conditions of the aeration systems, leading to more efficient processes which reduce the overall cost of the systems.

To achieve this, a multiphase Eulerian-Eulerian approach has been adopted which includes the bubble dynamics and oxygen mass transfer to simulate the hydrodynamics under a range of initial conditions. An experimental large scale transparent aeration reactor has been modelled that is a 2/3 replica of a working pilot-plant. Ultrasonic techniques, dissolved oxygen probes and other experimental methods have been used to take measurements to validate the CFD model which has shown that it can reliably reproduce the hydrodynamics and oxygen distribution over time. The biokinetic models can then be coupled in to the model to investigate the affect of the initial aeration conditions on the biological performance of the pilot-plant reactor.

Since 1886, the Hall-Héroult process developed by Charles Martin Hall and Paul Héroult is the main process for the industrial production of aluminum. Liquid metal instabilities in aluminium cells are a common problem due to high currents (100 – 800 kA) required for production. The induced magnetic field from the current carrying busbars together with high current in liquid metal leads to high Lorentz force. This force results in the movement of the liquid, which can result in a Metal Pad Rolling (MPR) instability. Since the experimental investigation of MPR inside a Hall-Héroult cell is impractical, numerical simulations are essential to examine the fluid flow and magnetic field.

This work focuses on the development of a multi-phase, multi-region solver to predict liquid metal instabilities. The solver is implemented in the open source framework OpenFOAM®. The volume of fluid method with a phase-fraction based reconstruction approach is used to solve the multi-phase system. The magnetic field is implemented using three different methods, the induction equation, Biot-Savart law and the magnetic potential formulation. These three methods were compared in terms of calculation speed and accuracy for a single-phase test case. Additionally, the performance of the magnetic potential formulation is improved by the usage of the Barnes-Hut method, to reduce the original problem from n² to n log(n), where n is the number of computational elements. The solver is validated with an experiment from literature. While the angular frequencies obtained from the simulation are in good agreement with the experiment, further work is needed for the validation of the amplitude.

The OpenFOAM service begin in May at KISTI NURION supercomputer. NURION has a total 570,020 cores consisting of Intel KNL architecture (8305 nodes) and Skylake architecture (132 nodes) in Cray CS500 cluster system. NURION’s theoretical peak(Rpeak) is 25.7PF and Linpack performance(Rmax) is 13.9PF, which marked the 13th place in the list of Supercomputer Top500 in November 2018.

OpenFOAM version 5.x was compiled by comparing optimization options for the installation of KNL compute nodes. GNU C++ compile options of ‘-std=c11 -march=knl -O3 -mavx512f - mavx512pf -mavx512er -mavx512cd -mfma –malign-data=cacheline -finline-functions’ and Intel C++ compile options of ‘-std=c11 -O3 -xMIC-AVX512 -fma -align -finline-functions’ was applied. And some libraries have been included or changed to improve OpenFOAM’s computing performance. The Libhbm library, a wrapper library for handling high bandwidth memory when run in KNL’s flat memory mode, was included. This library was written specifically for running OpenFOAM in the flat memory mode. Smoothers for KNL was also updated. In this treatment, the library libKNL.so was included in the system/controlDict of OpenFOAM which need to be appended in the library lists. We then changed GaussSeidel to GaussSeidelKNL and sysGaussSeidel to symGaussSeidelKNL in system/fvSolution of OpenFOAM.

Parallel execution was tested by the Intel MPI or Open MPI after these installation test. In Open MPI, options of ‘-mca pml cm –mca mtl psm2’ must additionally be included. The combination of the three types (compile options, libraries and MPIs) yielded the best parallel execution time or parallel speed-up depending on the nature of each problem.

Using KISTIFOAM, the pre-processing GUI tool developed as a linux platform, users can create and deliver input files to NURION easily and conveniently. KISTIFOAM will play an important role in increasing the number of OpenFOAM users on the NURION supercomputer.