Numerical simulation of a supersonic ejector for vacuum generation with explicit and implicit solver in openfoam

Supersonic ejectors are used extensively in all kind of applications: compression of refrigerants in cooling systems, pumping of volatile fluids or in vacuum generation. In vacuum generation, also known as zero-secondary flow, the ejector has a transient behaviour. In this paper, a numerical and experimental research of a supersonic compressible air nozzle is performed in order to investigate and to simulate its behaviour. The CFD toolbox OpenFOAM 6 was used, with two density-based solvers: explicit solver rhoCentralFoam, which implements Kurganov Central-upwind schemes, and implicit solver HiSA, which implements the AUSM+up upwind scheme. The behaviour of the transient evacuation ranges between adiabatic polytropic exponent at the beginning of the process and isothermal at the end. A model for the computation of the transient polytropic exponent is proposed. During the evacuation, two regimes are encountered in the second nozzle. In the supercritic regime, the secondary is choked and sonic flow is reached. In the subcritic regime, the secondary flow is subsonic. The final agreement is good with the two different solvers, although simulation tends to slightly overestimate flow rate for large values region.Peer ReviewedPostprint (published version

Quantification of the influence of drugs on zebrafish larvae swimming kinematics and energetics

The use of zebrafish larvae has aroused wide interest in the medical field for its potential role in the development of new therapies. The larvae grow extremely quickly and the embryos are nearly transparent which allows easy examination of its internal structures using fluorescent imaging techniques. Medical treatment of zebrafish larvae can directly influence its swimming behaviours. These behaviour changes are related to functional changes of central nervous system and transformations of the zebrafish body such as muscle mechanical power and force variation, which cannot be measured directly by pure experiment observation. To quantify the influence of drugs on zebrafish larvae swimming behaviours and energetics, we have developed a novel methodology to exploit intravital changes based on observed zebrafish locomotion. Specifically, by using an in-house MATLAB code to process the recorded live zebrafish swimming video, the kinematic locomotion equation of a 3D zebrafish larvae was obtained, and a customised Computational Fluid Dynamics tool was used to solve the fluid flow around the fish model which was geometrically the same as experimentally tested zebrafish. The developed methodology was firstly verified against experiment, and further applied to quantify the fish internal body force, torque and power consumption associated with a group of normal zebrafish larvae vs. those immersed in acetic acid and two neuroactive drugs. As indicated by our results, zebrafish larvae immersed in 0.01% acetic acid display approximately 30% higher hydrodynamic power and 10% higher cost of transport than control group. In addition, 500 μM diphenylhydantoin significantly decreases the locomotion activity for approximately 50% lower hydrodynamic power, whereas 100 mg/L yohimbine has not caused any significant influences on 5 dpf zebrafish larvae locomotion. The approach has potential to evaluate the influence of drugs on the aquatic animal’s behaviour changes and thus support the development of new analgesic and neuroactive drugs

Numerical Simulation of Selected Two-Dimensional and Three-Dimensional Fluid-Structure Interaction Problems Using OpenFOAM Technology

Fluid-structure interaction (FSI) problems are increasing in various engineering fields. In this thesis, different cases of FSI in two- and three-dimensions (2D and 3D) are simulated using OpenFOAM and foam-extend. These packages have been used to create a coupling between fluid and solid. The vortex-induced vibration (VIV) phenomenon of flow past a circular cylinder is studied using PIMPLE algorithm for pressure-velocity coupling. This VIV study is restricted to incompressible flow simulation at a Reynolds number (Re) of 100. The changes of drag and lift coefficient values depend on the study case and the spring-mass-damper system for the flow past a free oscillatory cylinder. The free vibrating cylinder examined in one-degree-of-freedom (1DOF) and two-degrees-of-freedom (2DOF) systems with linear damping and spring properties. Both will affect the behaviour of the cylinder within the flow with some noticeable differences. The response time of the cylinder and the drag coefficient are the most affected by the spring and damper. Besides the vortex-induced vibration test cases, the two-dimensional and three-dimensional fluid-structure interaction benchmarking is also studied. A partitioned solution method for strongly coupled solver with independent fluid and solid meshes for transient simulation has been applied. The fluid domain dynamics is governed by the incompressible Navier-Stokes equations; however, the structural field is described by the nonlinear elastodynamic equations. Fluid and solid domains are discretised by finite volume method (FVM) in space and time. A strong coupling scheme for partitioned analysis of the thin-walled shell structure exposed to wind-induced vibration (WIV) is presented. The achievement of the 3D membrane roof coupling scheme is studied by applying the 2D model. Additionally, numerical models for the slender shell structures coupling and the 3D flows indicate possible applications of the presented work. The computational fluid dynamics (CFD) simulation results revealed that even the flow is considered as a laminar, turbulence modelling or more refined meshes should be used to capture the generation and release of vortices. A partitioned solution procedure for FSI problems in the building aeroelasticity area is also studied. An illustrative real-world model on the coupled behaviour of membrane structure under wind flow influence is given. A four-point tent subjected to wind motion is a typical application of this work applying with various physical factors that are a necessity for the thin membrane structure. The fluid domain is described by the incompressible Navier-Stokes equations at a Reynolds number of Re = 3,750. However, the motion of the solid field is modeled by total Lagrangian strategy for nonlinear elastic deformation. The FSI simulation, particularly 3D problems require in very long calculation time. Some limitations of the FSI solver in foam-extend package called fsiFoam is discussed. All solvers that used in this thesis are considered to be applied to a wide use of the implementation of FSI models, despite some problems in parallelisation, particularly in the latest FSI solver version. The analysis results are presented to demonstrate accuracy, convergence, and stability

Developing a 3D incompressible vof based multiphase solver using OpenFOAM libraries

In the recent past open source analysis software have been on the demand for studying various phenomenon related to uids and solids. To counter act the booming prices of commercial CFD and FEM toolkits, open source software pro- vide the key. In the eld of computational uid dynamics, open source cfd toolkit , OpenFOAM (Open source Field Operation And Manipulation) is a viable al- ternative to commercial cfd toolkits like FLUENT, StarCCM+, etc. In the following thesis, an attempt has been made to address standard droplet breakup problem using OpenFOAM. The thesis aims at developing an incom- pressible multiphase vof (volume of uid) based solver which works on a SMAC algorithm, using the native OpenFoam libraries. The native vof solver of OpenFOAM and the newly developed explicit solver are tested against standard benchmark cases like 3D lid driven cavity, vortex in a box, dual vortex stretching, spurious currents, square bubble to circle, cubical bubble to sphere, dual vortex stretching and droplet splashing and compared in terms of accuracy and computational time. This knowledge led to deciding upon optimum case setup parameters which was then used to address the problem at hand: droplet breakup. For the droplet breakup analysis, two droplets with di erent diameters ratios were allowed to collide for di erent Reynolds number and Weber numbers. The collisions were also studied for di erent o sets parameters. Apart from above standard cases, other important features of OpenFOAM such as di erent linear solvers, numerical schemes, multicore operational capabilities, dynamic mesh re nement and static mesh re nement were also tested and re- ported

multiRegionFoam -- A Unified Multiphysics Framework for Multi-Region Coupled Continuum-Physical Problems

This paper presents a unified framework, called multiRegionFoam, for solving multiphysics problems of the multi-region coupling type within OpenFOAM (FOAM-extend). This framework is intended to supersede the existing solver with the same name. The design of the new framework is modular, allowing users to assemble a multiphysics problem region-by-region and coupling conditions interface-by-interface. The present approach allows users to choose between deploying either monolithic or partitioned interface coupling for each individual transport equation. The formulation of boundary conditions is generalised in the sense that their implementation is based on the mathematical jump/transmission conditions in the most general form for tensors of any rank. The present contribution focuses on the underlying mathematical model for these types of multiphysics problems, as well as on the software design and resulting code structure that enable a flexible and modular approach. Finally, deployment for different multi-region coupling cases is demonstrated, including conjugate heat, multiphase flows and fuel-cells

Using the generalized interpolation material point method for fluid-solid interactions induced by surface tension

This thesis is devoted to the development of new, Generalized Interpolation Material Point Method (GIMP)-based algorithms for handling surface tension and contact (wetting) in fluid-solid interaction (FSI) problems at small scales. In these problems, surface tension becomes so dominant that its influence on both fluids and solids must be considered. Since analytical solutions for most engineering problems are usually unavailable, numerical methods are needed to describe and predict complicated time-dependent states in the solid and fluid involved due to surface tension effects. Traditional computational methods for handling fluid-solid interactions may not be effective due to their weakness in solving large-deformation problems and the complicated coupling of two different types of computational frameworks: one for solid, and the other for fluid. On the contrary, GIMP, a mesh-free algorithm for solid mechanics problems, is numerically effective in handling problems involving large deformations and fracture. Here we extend the capability of GIMP to handle fluid dynamics problems with surface tension, and to develop a new contact algorithm to deal with the wetting boundary conditions that include the modeling of contact angle and slip near the triple points where the three phases -- fluid, solid, and vapor -- meet. The error of the new GIMP algorithm for FSI problems at small scales, as verified by various benchmark problems, generally falls within the 5% range. In this thesis, we have successfully extended the capability of GIMP for handling FSI problems under surface tension in a one-solver numerical framework, a unique and innovative approach.Chapter 1. Introduction -- Chapter 2. Using the generalized interpolation material point method for fluid dynamics at low reynolds numbers -- Chapter 3. On the modeling of surface tension and its applications by the generalized interpolation material point method -- Chapter 4. Using the generalized interpolation material point method for fluid-solid interactions induced by surface tension -- Chapter 5. Conclusions

Fluid-structure interaction models on the hydroelastic analysis of containerships in waves

Commercial vessels have recently been increasing in size to meet the fast-growing demand for transportation and operations. However, this trend may result in more flexible or "softer" hulls. The flexible hull structure and high operational speed requirements bring the ship's natural frequency closer to the wave encounter frequency, increasing the probability of resonance or high-frequency vibrations. Therefore, hydroelastic effects and relevant loads should be considered when designing wave loads and evaluating the strength of large ships. A robust numerical model is in search of ship designers and regulators, intended to predict the impact of hydroelasticity in the initial stages of design as per the design regulations, where there exists a greater opportunity to make modifications and utilise high-fidelity tools to verify the performance of advanced designs. This study aims to fill this gap by performing robust numerical investigations based on open-source software on the seakeeping and hydroelastic analysis of a monohull under wave excitations. Firstly, a detailed literature review is presented to overview the previous theoretical and numerical methods for ship hydroelasticity. This review also includes a general comparison between these hydroelastic techniques and discusses the differences. Following this, two fully coupled CFD-based unsteady FSI numerical frameworks are established: coupled CFD-FEA and CFD-DMB methods, respectively. The physical principle of these FSI models is to treat a ship’s surface hull as an elastic body and interact with its surrounding flow field to form a fully coupled system. Taking advantage of the present numerical models, the hydroelastic behaviours of a containership, such as its vertical bending displacement and corresponding bending moment, can be quantified, and the “springing” and “whipping” behaviour can be measured. It is believed that the present FSI model will exhibit more advantages over the traditional rigid-body method in the ship seakeeping field. Later, the presented CFD-DMB model is further extended for its application to irregular extreme waves and damaged ship conditions. The results achieved from these studies could also help to assess the structural integrity and longitudinal strength of a ship (intact or damaged), which serves as an improved technique for regulations to evaluate conventional ship designs. Finally, the results drawn from each chapter of this thesis are summarised and discussed, and recommendations are made for future research.Commercial vessels have recently been increasing in size to meet the fast-growing demand for transportation and operations. However, this trend may result in more flexible or "softer" hulls. The flexible hull structure and high operational speed requirements bring the ship's natural frequency closer to the wave encounter frequency, increasing the probability of resonance or high-frequency vibrations. Therefore, hydroelastic effects and relevant loads should be considered when designing wave loads and evaluating the strength of large ships. A robust numerical model is in search of ship designers and regulators, intended to predict the impact of hydroelasticity in the initial stages of design as per the design regulations, where there exists a greater opportunity to make modifications and utilise high-fidelity tools to verify the performance of advanced designs. This study aims to fill this gap by performing robust numerical investigations based on open-source software on the seakeeping and hydroelastic analysis of a monohull under wave excitations. Firstly, a detailed literature review is presented to overview the previous theoretical and numerical methods for ship hydroelasticity. This review also includes a general comparison between these hydroelastic techniques and discusses the differences. Following this, two fully coupled CFD-based unsteady FSI numerical frameworks are established: coupled CFD-FEA and CFD-DMB methods, respectively. The physical principle of these FSI models is to treat a ship’s surface hull as an elastic body and interact with its surrounding flow field to form a fully coupled system. Taking advantage of the present numerical models, the hydroelastic behaviours of a containership, such as its vertical bending displacement and corresponding bending moment, can be quantified, and the “springing” and “whipping” behaviour can be measured. It is believed that the present FSI model will exhibit more advantages over the traditional rigid-body method in the ship seakeeping field. Later, the presented CFD-DMB model is further extended for its application to irregular extreme waves and damaged ship conditions. The results achieved from these studies could also help to assess the structural integrity and longitudinal strength of a ship (intact or damaged), which serves as an improved technique for regulations to evaluate conventional ship designs. Finally, the results drawn from each chapter of this thesis are summarised and discussed, and recommendations are made for future research