Publications
137 results found
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, Peiro J, Moxey D, 2016, A variational framework for high-order mesh generation, Procedia Engineering, Vol: 163, Pages: 340-352, ISSN: 1877-7058
The generation of sufficiently high quality unstructured high-order meshes remains a significant obstacle in the adoption of high-order methods. However, there is little consensus on which approach is the most robust, fastest and produces the ‘best’ meshes. We aim to provide a route to investigate this question, by examining popular high-order mesh generation methods in the context of an efficient variational framework for the generation of curvilinear meshes. By considering previous works in a variational form, we are able to compare their characteristics and study their robustness. Alongside a description of the theory and practical implementation details, including an efficient multi-threading parallelisation strategy, we demonstrate the effectiveness of the framework, showing how it can be used for both mesh quality optimisation and untangling of invalid meshes.
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
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- Citations: 23
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
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- Citations: 19
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
The accurate computational modelling of airflows in transport tunnels is needed for regulations compliance, pollution and fire safety studies but remains a challenge for long domains because the computational time increases dramatically. We simulate air flows using the open-source code FDS 6.1.1 developed by NIST, USA. This work contains two parts. First we validate FDS6’s capability for predicting the flow conditions in the tunnel by comparing the predictions against on-site measurements in the Dartford Tunnel, London, UK, which is 1200 m long and 8.5 m in diameter. The comparison includes the average velocity and the profile downstream of an active jet fan up to 120 m. Secondly, we study the performance of the multi-scale modelling approach by splitting the tunnel into CFD domain and a one-dimensional domain using the FDS HVAC (Heating, Ventilation and Air Conditioning) feature. The work shows the average velocity predicted by FDS6 using both the full CFD and multi-scale approaches is within the experimental uncertainty of the measurements. Although the results showed the prediction of the downstream velocity profile near the jet fan falls outside the on-site measurements, the predictions at 80 m and beyond are accurate. Our results also show multi-scale modelling in FDS6 is as accurate as full CFD but up to 2.2 times faster and that computational savings increase with the length of the tunnel. This work sets the foundation for the next step in complexity with fire dynamics introduced to the tunnel.
Moura RC, Sherwin SJ, Peiro J, 2015, 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: 1090-2716
This study addresses linear dispersion–diffusion analysis for the spectral/hp continuousGalerkin (CG) formulation in one dimension. First, numerical dispersion and diffusioncurves are obtained for the advection–diffusion problem and the role of multipleeigencurves peculiar to spectral/hp methods is discussed. From the eigencurves’ behaviour,we observe that CG might feature potentially undesirable non-smooth dispersion/diffusioncharacteristics for under-resolved simulations of problems strongly dominated by eitherconvection or diffusion. Subsequently, the linear advection equation augmented withspectral vanishing viscosity (SVV) is analysed. Dispersion and diffusion characteristics ofCG with SVV-based stabilization are verified to display similar non-smooth features inflow regions where convection is much stronger than dissipation or vice-versa, owing toa dependency of the standard SVV operator on a local Péclet number. First a modificationis proposed to the traditional SVV scaling that enforces a globally constant Péclet numberso as to avoid the previous issues. In addition, a new SVV kernel function is suggestedand shown to provide a more regular behaviour for the eigencurves along with aconsistent increase in resolution power for higher-order discretizations, as measured bythe extent of the wavenumber range where numerical errors are negligible. The dissipationcharacteristics of CG with the SVV modifications suggested are then verified to be broadlyequivalent to those obtained through upwinding in the discontinuous Galerkin (DG)scheme. Nevertheless, for the kernel function proposed, the full upwind DG scheme isfound to have a slightly higher resolution power for the same dissipation levels. Theseresults show that improved CG-SVV characteristics can be pursued via different kernelfunctions with the aid of optimization algorithms.
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
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- Citations: 77
Moxey D, Ekelschot D, Keskin U, et al., 2015, High-order curvilinear meshing using a thermo-elastic analogy, Computer Aided Design, Vol: 72, Pages: 130-139, ISSN: 0010-4485
With high-order methods becoming increasingly popular in both academia and industry, generating curvilinear meshes that align with the boundaries of complex geometries continues to present a significant challenge. Whereas traditional low-order methods use planar-faced elements, high-order methods introduce curvature into elements that may, if added naively, cause the element to self-intersect. Over the last few years, several curvilinear mesh generation techniques have been designed to tackle this issue, utilising mesh deformation to move the interior nodes of the mesh in order to accommodate curvature at the boundary. Many of these are based on elastic models, where the mesh is treated as a solid body and deformed according to a linear or non-linear stress tensor. However, such methods typically have no explicit control over the validity of the elements in the resulting mesh. In this article, we present an extension of this elastic formulation, whereby a thermal stress term is introduced to 'heat' or 'cool' elements as they deform. We outline a proof-of-concept implementation and show that the adoption of a thermo-elastic analogy leads to an additional degree of robustness, by considering examples in both two and three dimensions.
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
We investigate the potential of linear dispersion–diffusion analysis in providing direct guidelines for turbulence simulations through the under-resolved DNS (sometimes called implicit LES) approach via spectral/hp methods. The discontinuous Galerkin (DG) formulation is assessed in particular as a representative of these methods. We revisit the eigensolutions technique as applied to linear advection and suggest a new perspective to the role of multiple numerical modes, peculiar to spectral/hp methods. From this new perspective, “secondary” eigenmodes are seen to replicate the propagation behaviour of a “primary” mode, so that DG's propagation characteristics can be obtained directly from the dispersion–diffusion curves of the primary mode. Numerical dissipation is then appraised from these primary eigencurves and its effect over poorly-resolved scales is quantified. Within this scenario, a simple criterion is proposed to estimate DG's effective resolution in terms of the largest wavenumber it can accurately resolve in a given hp approximation space, also allowing us to present points per wavelength estimates typically used in spectral and finite difference methods. Although strictly valid for linear advection, the devised criterion is tested against (1D) Burgers turbulence and found to predict with good accuracy the beginning of the dissipation range on the energy spectra of under-resolved simulations. The analysis of these test cases through the proposed methodology clarifies why and how the DG formulation can be used for under-resolved turbulence simulations without explicit subgrid-scale modelling. In particular, when dealing with communication limited hardware which forces one to consider the performance for a fixed number of degrees of freedom, the use of higher polynomial orders along with moderately coarser meshes is shown to be the best way to translate available degrees of freedom into resolution power.
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
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- Citations: 12
Peiro J, Rainbird JM, Ferrer E, et al., 2015, Vertical-axis wind turbine start-up modeled with a high-order numerical solver, CFD for Wind and Tidal Offshore Turbines, Publisher: Springer, ISBN: 9783319162027
Peiro J, Moxey D, Hazan M, et al., 2015, On the generation of curvilinear meshes through subdivision of isoparametric elements, New Challenges in Grid Generation and Adaptivity for Scientific Computing, Editors: Perotto, Formaggia, Publisher: Springer, ISBN: 9783319060538
This volume collects selected contributions from the “Fourth Tetrahedron Workshop on Grid Generation for Numerical Computations”, which was held in Verbania, Italy in July 2013.
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
The generation of high-order curvilinear meshes for complex three-dimensional geometries is presently a challenging topic, particularly for meshes used in simulations at high Reynolds numbers where a thin boundary layer exists near walls and elements are highly stretched in the direction normal to flow. In this paper, we present a conceptually simple but very effective and modular method to address this issue. We propose an isoparametric approach, whereby a mesh containing a valid coarse discretization comprising of high-order triangular prisms near walls is refined to obtain a finer prismatic or tetrahedral boundary-layer mesh. The validity of the prismatic mesh provides a suitable mapping that allows one to obtain very fine mesh resolutions across the thickness of the boundary layer. We describe the method in detail for a high-order approximation using modal basis functions, discuss the requirements for the splitting method to produce valid prismatic and tetrahedral meshes and provide a sufficient criterion of validity in both cases. By considering two complex aeronautical configurations, we demonstrate how highly stretched meshes with sufficient resolution within the laminar sublayer can be generated to enable the simulation of flows with Reynolds numbers of and above.
Moura RC, Sherwin S, Peiro J, 2015, Modified Equation Analysis for the Discontinuous Galerkin Formulation, 10th International Conference on Spectral and High-Order Methods (ICOSAHOM), Publisher: SPRINGER-VERLAG BERLIN, Pages: 375-383, ISSN: 1439-7358
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- Citations: 8
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
Peiro J, Moxey D, Jordi B, et al., 2015, High-Order Visualization with ElVis, IDIHOM: INDUSTRIALIZATION OF HIGH-ORDER METHODS - A TOP-DOWN APPROACH, Vol: 128, Pages: 521-534, ISSN: 1612-2909
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- Citations: 1
Moxey D, Hazan M, Sherwin SJ, et al., 2015, Curvilinear Mesh Generation for Boundary Layer Problems, IDIHOM: INDUSTRIALIZATION OF HIGH-ORDER METHODS - A TOP-DOWN APPROACH, Vol: 128, Pages: 41-64, ISSN: 1612-2909
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- Citations: 3
Keskin U, Peire J, 2014, A Level Set Method for the Construction of Boundary Conforming Voronoi Regions and Delaunay Triangulations Governed by a Spatial Distribution of Metrics, JOURNAL OF COMPUTING AND INFORMATION SCIENCE IN ENGINEERING, Vol: 14, ISSN: 1530-9827
Mengaldo G, De Grazia D, Peiro J, et al., 2014, A guide to the implementation of boundary conditions in compact high-order methods for compressible aerodynamics
The nature of boundary conditions, and how they are implemented, can have a significant impact on the stability and accuracy of a Computational Fluid Dynamics (CFD) solver. The objective of this paper is to assess how different boundary conditions impact the performance of compact discontinuous high-order spectral element methods (such as the discontinuous Galerkin method and the Flux Reconstruction approach), when these schemes are used to solve the Euler and compressible Navier-Stokes equations on unstructured grids. Specifically, the paper will investigate inflow/outflow and wall boundary conditions. In all studies the boundary conditions were enforced by modifying the boundary flux. For Riemann invariant (characteristic), slip and no-slip conditions we have considered a direct and an indirect enforcement of the boundary conditions, the first obtained by calculating the flux using the known solution at the given boundary while the second achieved by using a ghost state and by solving a Riemann problem. All computations were performed using the open-source software Nektar++ (www.nektar.info).
, 2014, A guide to the implementation of boundary conditions in compact high-order methods for compressible aerodynamics
The nature of boundary conditions, and how they are implemented, can have a significant impact on the stability and accuracy of a Computational Fluid Dynamics (CFD) solver. The objective of this paper is to assess how different boundary conditions impact the performance of compact discontinuous high-order spectral element methods (such as the discontinuous Galerkin method and the Flux Reconstruction approach), when these schemes are used to solve the Euler and compressible Navier-Stokes equations on unstructured grids. Specifically, the paper will investigate inflow/outflow and wall boundary conditions. In all studies the boundary conditions were enforced by modifying the boundary flux. For Riemann invariant (characteristic), slip and no-slip conditions we have considered a direct and an indirect enforcement of the boundary conditions, the first obtained by calculating the flux using the known solution at the given boundary while the second achieved by using a ghost state and by solving a Riemann problem. All computations were performed using the open-source software Nektar++ (www.nektar.info).
Moxey D, Ekelschot D, Keskin U, et al., 2014, A thermo-elastic analogy for high-order curvilinear meshing with control of mesh validity and quality, 23rd International Meshing Roundtable (IMR), Publisher: ELSEVIER SCIENCE BV, Pages: 127-135, ISSN: 1877-7058
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- Citations: 16
Ekelschot D, Biotto C, Peiro J, et al., 2013, P-adaption for compressible flows, Pages: 215-220
We present a p-adaptive method which takes advantage of the ability of a discontinuity sensor used to quantify the difference between the actual solution and a projected reduced order solution in order to vary the polynomial resolution in an element.
Gascons M, Blanco N, Simacek P, et al., 2012, Impact of the Fibre Bed on Resin Viscosity in Liquid Composite Moulding Simulations, APPLIED COMPOSITE MATERIALS, Vol: 19, Pages: 669-688, ISSN: 0929-189X
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- Citations: 2
Clark A, Peiró J, Cotter CJ, 2012, A reparameterisation based approach to geodesic constrained solvers for curve matching, International Journal of Computer Vision
Biotto C, Proverbio A, Ojawole O, et al., 2012, On the treatment of transient area variation in 1D discontinuous Galerkin simulations of train-induced pressure waves in tunnels, Int. J. Num. Meth. Fluids
Alastruey J, Passerini T, Formaggia L, et al., 2012, Physical determinants of the arterial pulse waveform: theoretical analysis and estimation using the 1-D formulation, Journal of Engineering Mathematics
Alastruey J, Passerini T, Formaggia L, et al., 2012, Physical determinants of the arterial pulse waveform: theoretical analysis and estimation using the 1-D formulation, Journal Engineering Mathematics
Alastruey J, Khir AW, Matthys KS, et al., 2011, Pulse wave propagation in a model human arterial network: Assessment of 1-D visco-elastic simulations against in vitro measurements, Journal of Biomechanics, Vol: 44, Pages: 2250-2258, ISSN: 1873-2380
The accuracy of the nonlinear one-dimensional (1-D) equations of pressure and flow wave propagation in Voigt-type visco-elastic arteries was tested against measurements in a well-defined experimental 1:1 replica of the 37 largest conduit arteries in the human systemic circulation. The parameters required by the numerical algorithm were directly measured in the in vitro setup and no data fitting was involved. The inclusion of wall visco-elasticity in the numerical model reduced the underdamped high-frequency oscillations obtained using a purely elastic tube law, especially in peripheral vessels, which was previously reported in this paper [Matthys et al., 2007. Pulse wave propagation in a model human arterial network: Assessment of 1-D numerical simulations against in vitro measurements. J. Biomech. 40, 3476–3486]. In comparison to the purely elastic model, visco-elasticity significantly reduced the average relative root-mean-square errors between numerical and experimental waveforms over the 70 locations measured in the in vitro model: from 3.0% to 2.5% (p<0.012) for pressure and from 15.7% to 10.8% (p<0.002) for the flow rate. In the frequency domain, average relative errors between numerical and experimental amplitudes from the 5th to the 20th harmonic decreased from 0.7% to 0.5% (p<0.107) for pressure and from 7.0% to 3.3% (p<10−6) for the flow rate. These results provide additional support for the use of 1-D reduced modelling to accurately simulate clinically relevant problems at a reasonable computational cost.
Peiro J, Galvanetto U, Chantharasenawong C, 2010, Assessment of added mass effects on flutter boundaries using the Leishman-Beddoes dynamic stall model, JOURNAL OF FLUIDS AND STRUCTURES, Vol: 26, Pages: 814-840, ISSN: 0889-9746
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- Citations: 8
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