Imperial College London

ProfessorSpencerSherwin

Faculty of EngineeringDepartment of Aeronautics

Professor of Computational Fluid Mechanics
 
 
 
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Contact

 

+44 (0)20 7594 5052s.sherwin Website

 
 
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Location

 

359Roderic Hill BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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258 results found

Peiro J, Moxey D, Sherwin, Ekelschotet al., A p-adaptation method for compressible flow problems using a goal-based error indicator, Computers and Structures, ISSN: 1879-2243

An accurate calculation of aerodynamic force coefficients for a given geometry isof fundamental importance for aircraft design. High-order spectral/hp elementmethods, which use a discontinuous Galerkin discretisation of the compressibleNavier-Stokes equations, are now increasingly being used to improve the accuracyof flow simulations and thus the force coefficients. To reduce error in thecalculated force coefficients whilst keeping computational cost minimal, we proposea p-adaptation method where the degree of the approximating polynomialis locally increased in the regions of the flow where low resolution is identifiedusing a goal-based error estimator as follows.Given an objective functional such as the aerodynamic force coefficients, weuse control theory to derive an adjoint problem which provides the sensitivityof the functional with respect to changes in the flow variables, and assumethat these changes are represented by the local truncation error. In its finalform, the goal-based error indicator represents the effect of truncation error onthe objective functional, suitably weighted by the adjoint solution. Both flowgoverning and adjoint equations are solved by the same high-order method,where we allow the degree of the polynomial within an element to vary acrossthe mesh.We initially calculate a steady-state solution to the governing equations using a low polynomial order and use the goal-based error indicator to identify partsof the computational domain that require improved solution accuracy whichis achieved by increasing the approximation order. We demonstrate the costeffectivenessof our method across a range of polynomial orders by considering anumber of examples in two- and three-dimensions and in subsonic and transonicflow regimes. Reductions in both the number of degrees of freedom required toresolve the force coefficients to a given error, as well as the computational cost,are both observed in using the p-adaptive technique

JOURNAL ARTICLE

Xu H, Hall P, sherwin S, Effect of curvature modulation on Gortler vortices in boundary layers, 67th Annual Meeting of the APS Division of Fluid Dynamics

CONFERENCE PAPER

Xu H, Mughal MS, Sherwin S, Effect of a 3D surface depression on boundary layer transition, 68th Annual Meeting of the APS Division of Fluid Dynamics

The influence of a three-dimensional surface depression on the transitional boundary layer is investigated numerically. In the boundary layer transition, the primary mode is a Tollmien-Schlichting (TS) wave which is a viscous instability. These modes are receptive to surface roughness interacting with free stream disturbances and/or surface vibrations. In this paper, numerical calculations are carried out to investigate the effect of the depression on instability of the boundary layer. In order to implement linear analysis, two/three (2D/3D)-dimensional nonlinear Navier-Stokes equations are solved by spectral element method to generate base flows in a sufficient large domain. The linear analyses are done by the parabolic stability equations (PSE). Finally, a DNS calculation is done to simulate the boundary layer transition.

CONFERENCE PAPER

Xu H, Sherwin S, Hall P, Transmission coefficient of Tollmien-Schlichting waves undergoing small indentation/hump distortion, The 29th Congress of the International Council of the Aeronautical Sciences

CONFERENCE PAPER

Xu H, lombard J, sherwin S, Delaying natural transition of a boundary layer using smooth steps, Sixth International Symposium on Bifurcations and Instabilities in Fluid Dynamics

CONFERENCE PAPER

Lombard J-EW, Moxey D, Sherwin SJ, Hoessler JFA, Dhandapani S, Taylor MJet al., 2016, Implicit Large-Eddy Simulation of a Wingtip Vortex, AIAA JOURNAL, Vol: 54, Pages: 506-518, ISSN: 0001-1452

JOURNAL ARTICLE

Mengaldo G, De Grazia D, Vincent PE, Sherwin SJet al., 2016, On the Connections Between Discontinuous Galerkin and Flux Reconstruction Schemes: Extension to Curvilinear Meshes, Journal of Scientific Computing, Vol: 67, Pages: 1272-1292, ISSN: 0885-7474

© 2015, The Author(s). This paper investigates the connections between many popular variants of the well-established discontinuous Galerkin method and the recently developed high-order flux reconstruction approach on irregular tensor-product grids. We explore these connections by analysing three nodal versions of tensor-product discontinuous Galerkin spectral element approximations and three types of flux reconstruction schemes for solving systems of conservation laws on irregular tensor-product meshes. We demonstrate that the existing connections established on regular grids are also valid on deformed and curved meshes for both linear and nonlinear problems, provided that the metric terms are accounted for appropriately. We also find that the aliasing issues arising from nonlinearities either due to a deformed/curved elements or due to the nonlinearity of the equations are equivalent and can be addressed using the same strategies both in the discontinuous Galerkin method and in the flux reconstruction approach. In particular, we show that the discontinuous Galerkin and the flux reconstruction approach are equivalent also when using higher-order quadrature rules that are commonly employed in the context of over- or consistent-integration-based dealiasing methods. The connections found in this work help to complete the picture regarding the relations between these two numerical approaches and show the possibility of using over- or consistent-integration in an equivalent manner for both the approaches.

JOURNAL ARTICLE

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

JOURNAL ARTICLE

Moxey D, Ekelschot D, Keskin U, Sherwin SJ, Peiro Jet al., 2016, High-order curvilinear meshing using a thermo-elastic analogy, COMPUTER-AIDED DESIGN, Vol: 72, Pages: 130-139, ISSN: 0010-4485

JOURNAL ARTICLE

Serson D, Meneghini JR, Sherwin SJ, 2016, Velocity-correction schemes for the incompressible Navier-Stokes equations in general coordinate systems, Journal of Computational Physics, Vol: 316, Pages: 243-254, ISSN: 0021-9991

© 2016 The Authors. This paper presents methods of including coordinate transformations into the solution of the incompressible Navier-Stokes equations using the velocity-correction scheme, which is commonly used in the numerical solution of unsteady incompressible flows. This is important when the transformation leads to symmetries that allow the use of more efficient numerical techniques, like employing a Fourier expansion to discretize a homogeneous direction. Two different approaches are presented: in the first approach all the influence of the mapping is treated explicitly, while in the second the mapping terms related to convection are treated explicitly, with the pressure and viscous terms treated implicitly. Through numerical results, we demonstrate how these methods maintain the accuracy of the underlying high-order method, and further apply the discretisation strategy to problems where mixed Fourier-spectral/hp element discretisations can be applied, thereby extending the usefulness of this discretisation technique.

JOURNAL ARTICLE

Tzortzis KN, Roney CH, Qureshi NA, Ng FS, Lim PB, Sherwin SJ, Peters NS, Cantwell CDet al., 2016, Influence of left atrial geometry on rotor core trajectories in a model of atrial fibrillation, Pages: 481-484, ISSN: 2325-8861

© 2015 CCAL. Left atrial anatomy and myocardial architecture are known to influence rotor initiation and maintenance. However, identifying their relative contribution clinically is challenging. The present study aims to investigate in silico the effect of left atrial geometry in isolation on rotor generation and evolution through the spatiotemporal tracking of phase singularities. After meandering for a short period of time, rotors are attracted to specific areas of the chamber where there is high curvature, primarily near the base of the left atrial appendage and the junctions of the pulmonary veins. This suggests that the left atrial anatomy could play a key role in the perpetuation of fibrillatory activity.

CONFERENCE PAPER

Xu H, Sherwin SJ, Halle P, Wu Xet al., 2016, The behaviour of Tollmien-Schlichting waves undergoing small-scale localised distortions, JOURNAL OF FLUID MECHANICS, Vol: 792, Pages: 499-525, ISSN: 0022-1120

JOURNAL ARTICLE

Yakovlev S, Moxey D, Kirby RM, Sherwin SJet al., 2016, To CG or to HDG: A Comparative Study in 3D, Journal of Scientific Computing, Vol: 67, Pages: 192-220, ISSN: 0885-7474

© 2015, Springer Science+Business Media New York. Since the inception of discontinuous Galerkin (DG) methods for elliptic problems, there has existed a question of whether DG methods can be made more computationally efficient than continuous Galerkin (CG) methods. Fewer degrees of freedom, approximation properties for elliptic problems together with the number of optimization techniques, such as static condensation, available within CG framework made it challenging for DG methods to be competitive until recently. However, with the introduction of a static-condensation-amenable DG method—the hybridizable discontinuous Galerkin (HDG) method—it has become possible to perform a realistic comparison of CG and HDG methods when applied to elliptic problems. In this work, we extend upon an earlier 2D comparative study, providing numerical results and discussion of the CG and HDG method performance in three dimensions. The comparison categories covered include steady-state elliptic and time-dependent parabolic problems, various element types and serial and parallel performance. The postprocessing technique, which allows for superconvergence in the HDG case, is also discussed. Depending on the direct linear system solver used and the type of the problem (steady-state vs. time-dependent) in question the HDG method either outperforms or demonstrates a comparable performance when compared with the CG method. The HDG method however falls behind performance-wise when the iterative solver is used, which indicates the need for an effective preconditioning strategy for the method.

JOURNAL ARTICLE

Ali RL, Cantwell CD, Qureshi NA, Roney CH, Lim PB, Sherwin SJ, Siggers JH, Peters NSet al., 2015, Automated fiducial point selection for reducing registration error in the co-localisation of left atrium electroanatomic and imaging data, 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), Publisher: IEEE, Pages: 1989-1992, ISSN: 1557-170X

CONFERENCE PAPER

Cantwell C, Sherwin SJ, Moxey D, 2015, Nektar++

Nektar++ is a tensor product based finite element package designed to allow one to construct efficient classical low polynomial order h-type solvers (where h is the size of the finite element) as well as higher p-order piecewise polynomial order solvers.

SOFTWARE

Cantwell C, sherwin SJ, moxey DM, 2015, Nektar++

Nektar++ is a tensor product based finite element package designed to allow one to construct efficient classical low polynomial order h-type solvers (where h is the size of the finite element) as well as higher p-order piecewise polynomial order solvers.

SOFTWARE

Cantwell CD, Moxey D, Comerford A, Bolis A, Rocco G, Mengaldo G, de Grazia D, Yakovlev S, Lombard J-E, Ekelschot D, Jordi B, Xu H, Mohamied Y, Eskilsson C, Nelson B, Vos P, Biotto C, Kirby RM, Sherwin SJet al., 2015, Nektar++: An open-source spectral/hp element framework, Computer Physics Communications, Vol: 192, Pages: 205-219, ISSN: 1879-2944

Nektar++ is an open-source software framework designed to support the development of high-performance scalable solvers for partial differential equations using the spectral/hphp element method. High-order methods are gaining prominence in several engineering and biomedical applications due to their improved accuracy over low-order techniques at reduced computational cost for a given number of degrees of freedom. However, their proliferation is often limited by their complexity, which makes these methods challenging to implement and use. Nektar++ is an initiative to overcome this limitation by encapsulating the mathematical complexities of the underlying method within an efficient C++ framework, making the techniques more accessible to the broader scientific and industrial communities. The software supports a variety of discretisation techniques and implementation strategies, supporting methods research as well as application-focused computation, and the multi-layered structure of the framework allows the user to embrace as much or as little of the complexity as they need. The libraries capture the mathematical constructs of spectral/hphp element methods, while the associated collection of pre-written PDE solvers provides out-of-the-box application-level functionality and a template for users who wish to develop solutions for addressing questions in their own scientific domains.

JOURNAL ARTICLE

Cantwell CD, Roney CH, Ng FS, Siggers JH, Sherwin SJ, Peters NSet al., 2015, Techniques for automated local activation time annotation and conduction velocity estimation in cardiac mapping, COMPUTERS IN BIOLOGY AND MEDICINE, Vol: 65, Pages: 229-242, ISSN: 0010-4825

JOURNAL ARTICLE

Comerford A, Chooi KY, Nowak M, Weinberg PD, Sherwin SJet al., 2015, A combined numerical and experimental framework for determining permeability properties of the arterial media, BIOMECHANICS AND MODELING IN MECHANOBIOLOGY, Vol: 14, Pages: 297-313, ISSN: 1617-7959

JOURNAL ARTICLE

Jordi BE, Cotter CJ, Sherwin SJ, 2015, An adaptive selective frequency damping method, PHYSICS OF FLUIDS, Vol: 27, ISSN: 1070-6631

JOURNAL ARTICLE

Mao X, Blackburn HM, Sherwin SJ, 2015, Nonlinear optimal suppression of vortex shedding from a circular cylinder, Journal of Fluid Mechanics, Vol: 775, Pages: 241-265, ISSN: 1469-7645

This study is focused on two- and three-dimensional incompressible flow pasta circular cylinder for Reynolds number Re 6 1000. To gain insight into themechanisms underlying the suppression of unsteadiness for this flow we determinethe nonlinear optimal open-loop control driven by surface-normal wall transpiration.The spanwise-constant wall transpiration is allowed to oscillate in time, althoughsteady forcing is determined to be most effective. At low levels of control cost,defined as the square integration of the control, the sensitivity of unsteadiness withrespect to wall transpiration is a good approximation of the optimal control. Thedistribution of this sensitivity suggests that the optimal control at small magnitude isachieved by applying suction upstream of the upper and lower separation points andblowing at the trailing edge. At high levels of wall transpiration, the assumptionsunderlying the linearized sensitivity calculation become invalid since the base flowis eventually altered by the size of the control forcing. The large-magnitude optimalcontrol is observed to spread downstream of the separation point and draw the shearlayer separation towards the rear of the cylinder through suction, while blowingalong the centreline eliminates the recirculation bubble in the wake. We furtherdemonstrate that it is possible to completely suppress vortex shedding in two- andthree-dimensional flow past a circular cylinder up to Re = 1000, accompanied by70 % drag reduction when a nonlinear optimal control of moderate magnitude (withroot-mean-square value 8 % of the free-stream velocity) is applied. This is confirmedthrough linearized stability analysis about the steady-state solution when the nonlinearoptimal wall transpiration is applied. While continuously distributed wall transpirationis not physically realizable, the study highlights localized regions where discretecontrol strategies could be further developed. It also highlights the appropriate rangeof application of

JOURNAL ARTICLE

Mengaldo G, De Grazia D, Moxey D, Vincent PE, Sherwin SJet al., 2015, Dealiasing techniques for high-order spectral element methods on regular and irregular grids, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 299, Pages: 56-81, ISSN: 0021-9991

JOURNAL ARTICLE

Mengaldo G, Kravtsova M, Ruban A, SHERWIN Set al., 2015, Triple-deck and direct numerical simulation analyses high-speed subsonic flows past a roughness element, Journal of Fluid Mechanics, Vol: 774, Pages: 311-323, ISSN: 1469-7645

This paper is concerned with the boundary-layer separation in subsonic and transonic flows caused by a two-dimensional isolated wall roughness. The process of the separation is analysed by means of two approaches: the direct numerical simulation (DNS) of the flow using the Navier–Stokes equations, and the numerical solution of the triple-deck equations. Since the triple-deck theory relies on the assumption that the Reynolds number ( ) is large, we performed the Navier–Stokes calculations at Re = 4 x 10^5 based on the distance of the roughness element from the leading edge of the flat plate. This Re is also relevant for aeronautical applications. Two sets of calculation were conducted with the free-stream Mach number Ma_∞ = 0.5 and Ma_∞ = 0.87 . We used different roughness element heights, some of which were large enough to cause a well-developed separation region behind the roughness. We found that the two approaches generally compare well with one another in terms of wall shear stress, longitudinal pressure gradient and detachment/reattachment points of the separation bubbles (when present). The main differences were found in proximity to the centre of the roughness element, where the wall shear stress and longitudinal pressure gradient predicted by the triple-deck theory are noticeably different from those predicted by DNS. In addition, DNS predicts slightly longer separation regions.

JOURNAL ARTICLE

Mohamied Y, Rowland EM, Bailey EL, Sherwin SJ, Schwartz MA, Weinberg PDet al., 2015, Change of Direction in the Biomechanics of Atherosclerosis, ANNALS OF BIOMEDICAL ENGINEERING, Vol: 43, Pages: 16-25, ISSN: 0090-6964

JOURNAL ARTICLE

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

JOURNAL ARTICLE

Moxey D, Green MD, Sherwin SJ, Peiro Jet 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

JOURNAL ARTICLE

Moxey D, Hazan M, Sherwin SJ, Peiro Jet 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.

JOURNAL ARTICLE

Peiro J, Moxey D, Hazan M, Sherwin SJet 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.

BOOK CHAPTER

Peiro J, Moxey D, Jordi B, Sherwin SJ, Nelson BW, Kirby RM, Haimes Ret al., 2015, High-order visualization with ElVis, Notes on Numerical Fluid Mechanics and Multidisciplinary Design, Vol: 128, Pages: 521-534, ISSN: 1612-2909

© 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.

JOURNAL ARTICLE

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