117 results found
Marcon J, Peiró J, Moxey D, et al., 2019, A semi-structured approach to curvilinear mesh generation around streamlined bodies
We present an approach for robust high-order mesh generation speciallytailored to streamlined bodies. The method is based on a semi-sructuredapproach which combines the high quality of structured meshes in the near-fieldwith the flexibility of unstructured meshes in the far-field. We utilise medialaxis technology to robustly partition the near-field into blocks which can bemeshed coarsely with a linear swept mesher. A high-order mesh of the near-fieldis then generated and split using an isoparametric approach which allows us toobtain highly stretched elements aligned with the flow field. Special treatmentof the partition is performed on the wing root juntion and the trailing edge--- into the wake --- to obtain an H-type mesh configuration with anisotropichexahedra ideal for the strong shear of high Reynolds number simulations. Wethen proceed to discretise the far-field using traditional robust tetrahedralmeshing tools. This workflow is made possible by two sets of tools: CADfix,focused on CAD system, the block partitioning of the near-field and thegeneration of a linear mesh; and NekMesh, focused on the curving of thehigh-order mesh and the generation of highly-stretched boundary layer elements.We demonstrate this approach on a NACA0012 wing attached to a wall and showthat a gap between the wake partition and the wall can be inserted to removethe dependency of the partitioning procedure on the local geometry.
Winters AR, Moura RC, Mengaldo G, et al., 2018, A comparative study on polynomial dealiasing and split form discontinuous Galerkin schemes for under-resolved turbulence computations, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 372, Pages: 1-21, ISSN: 0021-9991
Turner M, Peiro J, Moxey D, 2018, Curvilinear mesh generation using a variational framework, COMPUTER-AIDED DESIGN, Vol: 103, Pages: 73-91, ISSN: 0010-4485
Green MD, Peiro J, 2018, Long duration SPH simulations of sloshing in tanks with a low fill ratio and high stretching, COMPUTERS & FLUIDS, Vol: 174, Pages: 179-199, ISSN: 0045-7930
Eichstadt J, Green M, Turner M, et al., 2018, Accelerating high-order mesh optimisation with an architecture-independent programming model, COMPUTER PHYSICS COMMUNICATIONS, Vol: 229, Pages: 36-53, ISSN: 0010-4655
Mengaldo G, Moura RC, Giralda B, et al., 2018, Spatial eigensolution analysis of discontinuous Galerkin schemes with practical insights for under-resolved computations and implicit LES, COMPUTERS & FLUIDS, Vol: 169, Pages: 349-364, ISSN: 0045-7930
Cohen J, Marcon J, Turner M, et al., Simplifying high-order mesh generation for computational scientists, 10th International Workshop on Science Gateways, Publisher: CEUR Workshop Proceedings, ISSN: 1613-0073
Computational modelling is now tightly integrated into many fields of research in science and industry. Computational fluid dynamics software, for example, gives engineers the ability to model fluid flow around complex geometries defined in Computer-Aided Design (CAD) packages, without the expense of constructing large wind tunnel experiments. However, such modelling requires translation from an initial CAD geometry to a mesh of many small elements that modelling software uses to represent the approximate solution in the numerical method. Generating sufficiently high-quality meshes for simulation is a time-consuming, iterative and error-prone process that is often complicated by the need to interact with multiple command-line tools to generate and visualise the mesh data. In this paper we describe our approach to overcoming this complexity through the addition of a meshing console to Nekkloud, a science gateway for simplifying access to the functionality of the Nektar++ spectral/hp element framework. The meshing console makes use of the NekMesh tool in Nektar++ to help reduce the complexity of the mesh generation process. It offers a web-based interface for specifying parameters, undertaking meshing and visualising results. The meshing console enables Nekkloud to offer support for a full, end-to-end simulation pipeline from initial CAD geometry to simulation results.
Marcon J, Turner M, Peiro J, et al., 2018, High-order curvilinear hybrid mesh generation for CFD simulations
© 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. We describe a semi-structured method for the generation of high-order hybrid meshes suited for the simulation of high Reynolds number flows. This is achieved through the use of highly stretched elements in the viscous boundary layers near the wall surfaces. CADfix is used to first repair any possible defects in the CAD geometry and then generate a medial object based decomposition of the domain that wraps the wall boundaries with partitions suitable for the generation of either prismatic or hexahedral elements. The latter is a novel distinctive feature of the method that permits to obtain well-shaped hexahedral meshes at corners or junctions in the boundary layer. The medial object approach allows greater control on the “thickness” of the boundary-layer mesh than is generally achievable with advancing layer techniques. CADfix subsequently generates a hybrid straight-sided mesh of prismatic and hexahedral elements in the near-field region modelling the boundary layer, and tetrahedral elements in the far-field region covering the rest of the domain. The mesh in the near-field region provides a framework that facilitates the generation, via an isoparametric technique, of layers of highly stretched elements with a distribution of points in the direction normal to the wall tailored to efficiently and accurately capture the flow in the boundary layer. The final step is the generation of a high-order mesh using NekMesh, a high-order mesh generator within the Nektar++ framework. NekMesh uses the CADfix API as a geometry engine that handles all the geometrical queries to the CAD geometry required during the high-order mesh generation process. We will describe in some detail the methodology using a simple geometry, a NACA wing tip, for illustrative purposes. Finally, we will present two examples of application to reasonably complex geometries proposed by NASA as CFD val
Rainbird J, Peiro J, Graham JM, 2017, Poststall Airfoil Performance and Vertical-Axis Wind Turbines, JOURNAL OF PROPULSION AND POWER, Vol: 33, Pages: 1053-1062, ISSN: 0748-4658
Marcon J, Turner M, Moxey D, et al., 2017, A variational approach to high-order r-adaptation
A variational framework, initially developed for high-order meshoptimisation, is being extended for r-adaptation. The method is based on theminimisation of a functional of the mesh deformation. To achieve adaptation,elements of the initial mesh are manipulated using metric tensors to obtaintarget elements. The nonlinear optimisation in turns adapts the finalhigh-order mesh to best fit the description of the target elements byminimising the element distortion. Encouraging preliminary results prove thatthe method behaves well and can be used in the future for more extensive workwhich shall include the use of error indicators from CFD simulations.
Ekelschot D, Moxey D, Sherwin SJ, et al., 2017, A p-adaptation method for compressible flow problems using a goal-based error indicator, COMPUTERS & STRUCTURES, Vol: 181, Pages: 55-69, ISSN: 0045-7949
Moura RC, Mengaldo G, Peiro J, et al., 2017, On the eddy-resolving capability of high-order discontinuous Galerkin approaches to implicit LES / under-resolved DNS of Euler turbulence, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 330, Pages: 615-623, ISSN: 0021-9991
Moura RC, Peiro J, Sherwin SJ, 2017, On the accuracy and robustness of implicit LES/under-resolved DNS approaches based on spectral element methods
We present a study on the suitability of under-resolved DNS (uDNS)-also called implicit LES (iLES)-approaches based on spectral element methods (SEM), with emphasis on high-order continuous and discontinuous Galerkin (i.e. CG and DG) schemes. Broadly speaking, these are model-free eddy-resolving approaches to turbulence which solve the governing equations in unfiltered form and rely on numerical stabilization techniques for small-scale regularization. Model problems in 1D, 2D and 3D are used in the assessment of solution quality and numerical stability. A rationale for the excellent potential of these methods for transitional and turbulent flows is offered on the basis of linear dispersion-diffusion analysis.
Turner M, Moxey D, Peiro J, et al., 2017, A framework for the generation of high-order curvilinear hybrid meshes for CFD simulations, 26th International Meshing Roundtable (IMR), Publisher: ELSEVIER SCIENCE BV, Pages: 206-218, ISSN: 1877-7058
Bianchini A, Balduzzi F, Rainbird JM, et al., 2016, An Experimental and Numerical Assessment of Airfoil Polars for Use in Darrieus Wind Turbines-Part I: Flow Curvature Effects, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME, Vol: 138, ISSN: 0742-4795
Bianchini A, Balduzzi F, Rainbird JM, et al., 2016, An Experimental and Numerical Assessment of Airfoil Polars for Use in Darrieus Wind Turbines-Part II: Post-stall Data Extrapolation Methods, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME, Vol: 138, ISSN: 0742-4795
Moxey D, Ekelschot D, Keskin U, et al., 2016, High-order curvilinear meshing using a thermo-elastic analogy, COMPUTER-AIDED DESIGN, Vol: 72, Pages: 130-139, ISSN: 0010-4485
Moura RC, Sherwin SJ, Peiro J, 2016, Eigensolution analysis of spectral/hp continuous Galerkin approximations to advection-diffusion problems: Insights into spectral vanishing viscosity, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 307, Pages: 401-422, ISSN: 0021-9991
Ang CDE, Rein G, Peiro J, et al., 2016, Simulating longitudinal ventilation flows in long tunnels: Comparison of full CFD and multi-scale modelling approaches in FDS6, TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY, Vol: 52, Pages: 119-126, ISSN: 0886-7798
Turner M, Peiro J, Moxey D, 2016, A variational framework for high-order mesh generation, 25TH INTERNATIONAL MESHING ROUNDTABLE, Vol: 163, Pages: 340-352, ISSN: 1877-7058
Rainbird JM, Bianchini A, Balduzzi F, et al., 2015, On the influence of virtual camber effect on airfoil polars for use in simulations of Darrieus wind turbines, ENERGY CONVERSION AND MANAGEMENT, Vol: 106, Pages: 373-384, ISSN: 0196-8904
Moura RC, Sherwin SJ, Peiro J, 2015, Linear dispersion-diffusion analysis and its application to under-resolved turbulence simulations using discontinuous Galerkin spectral/hp methods, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 298, Pages: 695-710, ISSN: 0021-9991
Rainbird JM, Peiro J, Graham JMR, 2015, Blockage-tolerant wind tunnel measurements for a NACA 0012 at high angles of attack, JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS, Vol: 145, Pages: 209-218, ISSN: 0167-6105
Bianchini A, Balduzzi F, Rainbird JM, et al., 2015, AN EXPERIMENTAL AND NUMERICAL ASSESSMENT OF AIRFOIL POLARS FOR USE IN DARRIEUS WIND TURBINES. PART 2-POST-STALL DATA EXTRAPOLATION METHODS, ASME Turbo Expo: Turbine Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS
Bianchini A, Balduzzi F, Rainbird JM, et al., 2015, AN EXPERIMENTAL AND NUMERICAL ASSESSMENT OF AIRFOIL POLARS FOR USE IN DARRIEUS WIND TURBINES. PART 1-FLOW CURVATURE EFFECTS, ASME Turbo Expo: Turbine Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS
Moxey D, Green MD, Sherwin SJ, et al., 2015, On the generation of curvilinear meshes through subdivision of isoparametric elements, Pages: 203-215, ISBN: 9783319060521
© 2015, Springer International Publishing Switzerland. Recently, a new mesh generation technique based on the isoparametric representation of curvilinear elements has been developed in order to address the issue of generating high-order meshes with highly stretched elements. Given a valid coarse mesh comprising of a prismatic boundary layer, this technique uses the shape functions that define the geometries of the elements to produce a series of subdivided elements of arbitrary height. The purpose of this article is to investigate the range of conditions under which the resulting meshes are valid, and additionally to consider the application of this method to different element types. We consider the subdivision strategies that can be achieved with this technique and apply it to the generation of meshes suitable for boundary-layer fluid problems.
Rainbird JM, Ferrer E, Peiro J, et al., 2015, Vertical-Axis Wind Turbine Start-Up Modelled with a High-Order Numerical Solver, Editors: Ferrer, Montlaur, Publisher: SPRINGER INT PUBLISHING AG, Pages: 37-48, ISBN: 978-3-319-16201-0
Moxey D, Hazan M, Sherwin SJ, et al., 2015, Curvilinear mesh generation for boundary layer problems, Notes on Numerical Fluid Mechanics and Multidisciplinary Design, Vol: 128, Pages: 41-64, ISSN: 1612-2909
© Springer International Publishing Switzerland 2015. In this article, we give an overview of a new technique for unstructured curvilinear boundary layer grid generation, which uses the isoparametric mappings that define elements in an existing coarse prismatic grid to produce a refined mesh capable of resolving arbitrarily thin boundary layers. We demonstrate that the technique always produces valid grids given an initially valid coarse mesh, and additionally show how this can be extended to convert hybrid meshes to meshes containing only simplicial elements.
© Springer International Publishing Switzerland 2015. Accurate visualization of high-order meshes and flow fields is a fundamental tool for the verification, validation, analysis and interpretation of high-order flow simulations. Standard visualization tools based on piecewise linear approximations can be used for the display of highorder fields but their accuracy is restricted by computer memory and processing time. More often than not, the accurate visualization of complex flows using this strategy requires computational resources beyond the reach of most users. This chapter describes ElVis, a truly high-order and interactive visualization system created for the accurate and interactive visualization of scalar fields produced by high-order spectral/hp finite element simulations. We show some examples that motivate the need for such a visualization system and illustrate some of its features for the display and analysis of simulation data.
Moxey D, Green MD, Sherwin SJ, et al., 2015, An isoparametric approach to high-order curvilinear boundary-layer meshing, COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING, Vol: 283, Pages: 636-650, ISSN: 0045-7825
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