9,705 research outputs found
Recent Progress in the Numerical Simulation Reactor Research Project
No full text0000-0001-5444-1758Fusion plasmas are complex systems which involve a variety of physical processes interacting with each other across wide ranges of spatiotemporal scales. In the National Institute for Fusion Science (NIFS), we are utilizing the full capability of the supercomputer (Plasma Simulator) and propelling domestic and international collaborations in order to conduct the Numerical Simulation Reactor Research Project (NSRP). Understanding physical mechanisms of complex plasma phenomena for the systematization of fusion science, NSRP aims at realization of the Numerical Helical Test Reactor, which is an integrated system of simulation codes to predict behaviors of fusion plasmas over the whole machine range. In NSRP, eight task groups are organized to cover a wide range of fusion simulation subjects: plasma fluid equilibrium stability, energetic-particle physics, integrated transport simulation, neoclassical and turbulent transport simulation, peripheral plasma transport, plasma-wall interaction, multi-hierarchy physics, and simulation science basis. Verification and validation researches are in progress in these task groups collaborating with each other as well as with experimental and engineering groups. Successful examples of validations of large-scale simulations of energetic particle driven instabilities and neoclassical and turbulent transport against experimental results from tokamaks and helical systems are highlighted. In addition, recent achievements in advanced simulation studies on ion heating processes and plasma-wall interactions, as well as those in the application of Virtual-Reality (VR) technology to fusion engineering, are presented.journal articl
Numerical Simulation of a Marine Current Turbine in Turbulent Flow
No full textThe copyright of this thesis rests with the author and no quotation from it or information derived from it may be published without the prior written consent of the authorThe marine current turbine (MCT) is an exciting proposition for the extraction of renewable tidal and marine current power. However, the numerical prediction of the performance of the MCT is difficult due to its complex geometry, the surrounding turbulent flow and the free surface. The main purpose of this research is to develop a computational tool for the simulation of a MCT in turbulent flow and in this thesis, the author has modified a 3D Large Eddy Simulation (LES) numerical code to simulate a three blade MCT under a variety of operating conditions based on the Immersed Boundary Method (IBM) and the Conservative Level Set Method (CLS).
The interaction between the solid structure and surrounding fluid is modelled by the immersed boundary method, which the author modified to handle the complex geometrical conditions. The conservative free surface (CLS) scheme was implemented in the original Cgles code to capture the free surface effect.
A series of simulations of turbulent flow in an open channel with different slope conditions were conducted using the modified free surface code. Supercritical flow with Froude number up to 1.94 was simulated and a decrease of the integral constant in the law of the wall has been noticed which matches well with the experimental data.
Further simulations of the marine current turbine in turbulent flow have been carried out for different operating conditions and good match with experimental data was observed for all flow conditions. The effect of waves on the performance of the turbine was also investigated and it has been noticed that this existence will increase the power performance of the turbine due to the increase of free stream velocity
Investigating distributed simulation with COTS simulation packages: Experiences with Simul8 and the HLA
No full textCommercial-off-the-shelf simulation packages (CSPs) are used widely in industry. Several research groups are currently working towards the creation of distributed simulation with these CSPs. The motivations to do this are various and are largely unproven as there are very few good examples of this kind of distributed simulation in practice. Our goal is therefore to create a distributed simulation environment using CSPs that will allow end users to make their own decisions as to whether this technology will be useful. This paper presents continuing research in creating such an environment using the CSP Simul8 and the High Level Architecture, the IEEE 1516 standard for distributed simulation. The scope of this paper is limited to the CSPI-PDG Type I Interoperability Reference Model
Numerical simulation of drifting sand
No full textTwo-phase flows are involved in many industrial and natural flow phenomena
varying from as specific as the transport of crude oil in pipelines to as general
as the dispersion of pollutants in the atmosphere. Numerical modelling based
on Computational Fluid Dynamics (CFD), has attracted the attention of
scientists and engineers from a wide range of backgrounds over recent
decades during which these models have been extensively developed, analysed
and applied to many practical applications.
Wind blown particles such as sand or snow and their resulting accumulation
around buildings, roads, oil field installations and security fences causes
severe structural and design problems. These are traditionally addressed
based on previous experience, full-scale field investigation or using scale
model wind tunnel experiments, all of which incur high cost.
In this study, wind blown particles are considered as a two-phase flow system.
A finite volume based CFD code is developed using two-phase flow theory and
is employed to numerically simulate the drifting of sand and snow around
obstacles of different geometry. The model solves the governing transport
equations in three dimensional space. Three different approaches are
investigated to represent and solve the secondary flow phase, particles, within
the flow field; a particle tracking model, based on a Lagrangian reference
frame and the homogenous and the mixture models, based on an Eulerian
reference frame. The capabilities and limitations of each of these models are
investigated for flow fields involving drifting particles around obstacles of
different geometry.
Particles transported by wind both in suspension and saltation are modelled
based on the physical characteristic and the threshold condition of the
particle. Their effect on the flow field is incorporated through separate source
terms contributing to the particle transport equation.
The Eulerian based models are coupled with the Fractional Area/Volume
Obstacle Representation (FAVOR) as a mean of representing the solid boundary formed by deposited particles separating the flow field from the
accumulation zones. The FAVOR treatment allows the flow field to respond to
the changes in the geometry of the deposition regions and further calculations
take into account the erosion and deposition processes that have previously
occurred.
The model can be calibrated to match specific flow conditions through several
controlling parameters. These controlling parameters are identified and
analysed for four distinct case studies. Model results are compared with field
and wind tunnel observations available in the literature and with field
measurements conducted as a part of this study in the desert of the State of
Kuwait. Qualitatively good agreement between the model and the
observations is obtained in two as well as three dimensions.
Although the mixture and particle tracking models show the potential
capability to simulate such flow systems, the homogenous model is found to
be the most appropriate model due to its relative simplicity compared to the
mixture model and its lower computational cost compared to the Lagrangian
particle-tracking model.
In conclusion, a practical CFD tool has been developed and validated,
incorporating novel physical and numerical models. The tool can be utilised
by scientists and engineers to further understand the real world problem of
drifting sand and snow in urban and industrial environments
Further developments in the conflation of CFD and building simulation
No full textTo provide practitioners with the means to tackle problems related to poor indoor environments, building simulation and computational fluid dynamics can usefully be integrated within a single computational framework. This paper describes the outcomes from a research project sponsored by the European Commission, which furthered the CFD modelling aspects of the ESP-r system. The paper summarises the form of the CFD model and describes the method used to integrate the thermal and flow domains
A primer on direct numerical simulation of turbulence - methods, procedures and guidelines
No full textDirect Numerical Simulation (DNS) is the branch of CFD devoted to high-fidelity solution ofturbulent flows. DNS differs from conventional CFD in that the turbulence is explicitly resolved,rather than modelled by a Reynolds-averaged Navier-Stokes (RANS) closure. It differs fromlarge-eddy simulation (LES) in that all scales, including the very smallest ones, are captured,removing the need for a subgrid-scale model. DNS can thus be viewed as a numericalexperiment producing a series of non-empirical solutions, from first principles, for a virtualturbulent flow (see Figure 1). Its great strength is the ability to provide complete knowledge,unaffected by approximations, at all points within the flow, at all times within the simulationperiod. DNS is therefore ideal for addressing basic research questions regarding turbulencephysics and modelling. This ability, however, comes at a high price, which prevents DNS frombeing used as a general-purpose design tool.The defining characteristics of DNS stem from the distinctive characteristics of turbulence.Because turbulence is inherently unsteady and three-dimensional, DNS requires timedependentcalculations within a three-dimensional domain.? These two features are sharedwith LES (and therefore LES/RANS hybrid strategies such as detached eddy simulation(DES)). The unique feature of DNS is associated with the manner in which turbulence isaffected by viscosity. This is responsible for the two chief drawbacks of DNS – its extremecomputational cost, and severe limitation on the maximum Reynolds number that can beconsidered
Advanced rotorcraft aeromechanics studies in the French-German SHANEL project
No full textThe present paper gives an overview of the SHANEL research project (partly supported by the French DGAC and the German BMWA) which was started at the end of 2006 between the German and French
Aerospace Research Centres DLR and ONERA, the University of Stuttgart and the two national helicopter manufacturers, Eurocopter and Eurocopter Germany. This program represents the continuation of the binational CHANCE project, involving the same partners. The objective of the project is to enhance and further validate the CFD tools: the structured multi-block elsA software of Onera and the unstructured TAU
code of DLR, for computing the aerodynamics of the complete trimmed helicopter, accounting for the blade elasticity by coupling with blade dynamics and structural mechanics tools. A coupling activity between the FLOWer code of DLR and the HOST tool of Eurocopter is also completed to achieve the free flight trim of a complete helicopter. In this program particular attention is being given to wake conservation, to the modelling of elaborated complex shapes such as rotor hubs and consequently to interactional phenomena, with the global objective of improving the prediction of helicopter performance and noise. Rotorcraft noise prediction chains were rationalized, enhanced and compared. The validation activity of the flow solvers elsA and TAU is progressing from the CHANCE results and is now focussing on more complex problems such as the simulation of a rotating rotor head mounted on its fuselage, of a complete helicopter in steady mode through the use of actuator discs and engine boundary conditions, the time-accurate simulation of a complete trimmed helicopter in forward-flight, and the numerical simulation of Blade Vortex Interactions. All along the research program the updated versions of the CFD and acoustic codes are systematically delivered to industry. This approach, also followed during the former CHANCE project, is chosen to speed up the transfer of capabilities to industry and check early enough
that the products meet the expectations for applicability in the industrial environment of Eurocopter
'BioNessie(G) - a grid enabled biochemical networks simulation environment
No full textThe simulation of biochemical networks provides insight and
understanding about the underlying biochemical processes and pathways
used by cells and organisms. BioNessie is a biochemical network simulator
which has been developed at the University of Glasgow. This paper
describes the simulator and focuses in particular on how it has been
extended to benefit from a wide variety of high performance compute resources
across the UK through Grid technologies to support larger scale
simulations
3D numerical simulation of Circulating Fluidized Bed: comparison between theoretical results and experimental measurements of hydrodynamic
No full textThis work was realized in the frame of the European GAYA project supported by ADEME. This paper presents a description of the hydrodynamic into a CFB according to experimental measurements of gas pressure and solid mass flux. These experimental data are compared to three dimensional numerical simulation with an Eulerian approach. The obtained numerical results show that the applied mathematical models are able to predict the complex gas-solid behavior in the CFB and highlight the large influence of the particle wall boundary condition. Indeed,
it is shown that free slip wall boundary condition gives a good prediction a solid mass flux profile in comparison with experimental measurements nevertheless a convex shape. Moreover, the numerical solid hold-up is underestimated compared to the experimental data. On the contrary, a no-slip boundary condition improves the profile shape of solid mass flux but highly overestimates its intensity and the solid hold-up. A compromise appears to be a friction
particle-wall boundary condition such as Johnson and Jackson (1) but the model parameters have to be chosen very carefully especially the restitution coefficient
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