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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259 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

Bao Y, Palacios R, Graham M, Sherwin Set al., 2016, Generalized thick strip modelling for vortex-induced vibration of long flexible cylinders, Journal of Computational Physics, Vol: 321, Pages: 1079-1097, ISSN: 0021-9991

© 2016 The Authors.We propose a generalized strip modelling method that is computationally efficient for the VIV prediction of long flexible cylinders in three-dimensional incompressible flow. In order to overcome the shortcomings of conventional strip-theory-based 2D models, the fluid domain is divided into "thick" strips, which are sufficiently thick to locally resolve the small scale turbulence effects and three dimensionality of the flow around the cylinder. An attractive feature of the model is that we independently construct a three-dimensional scale resolving model for individual strips, which have local spanwise scale along the cylinder's axial direction and are only coupled through the structural model of the cylinder. Therefore, this approach is able to cover the full spectrum for fully resolved 3D modelling to 2D strip theory. The connection between these strips is achieved through the calculation of a tensioned beam equation, which is used to represent the dynamics of the flexible body. In the limit, however, a single "thick" strip would fill the full 3D domain. A parallel Fourier spectral/hp element method is employed to solve the 3D flow dynamics in the strip-domain, and then the VIV response prediction is achieved through the strip-structure interactions. Numerical tests on both laminar and turbulent flows as well as the comparison against the fully resolved DNS are presented to demonstrate the applicability of this approach.

JOURNAL ARTICLE

Bolls A, Cantwell CD, Moxey D, Serson D, Sherwin SJet al., 2016, An adaptable parallel algorithm for the direct numerical simulation of incompressible turbulent flows using a Fourier spectral/hp element method and MPI virtual topologies, COMPUTER PHYSICS COMMUNICATIONS, Vol: 206, Pages: 17-25, ISSN: 0010-4655

JOURNAL ARTICLE

Chooi KY, Comerford A, Sherwin SJ, Weinberg PDet al., 2016, Intimal and medial contributions to the hydraulic resistance of the arterial wall at different pressures: a combined computational and experimental study., J R Soc Interface, Vol: 13

The hydraulic resistances of the intima and media determine water flux and the advection of macromolecules into and across the arterial wall. Despite several experimental and computational studies, these transport processes and their dependence on transmural pressure remain incompletely understood. Here, we use a combination of experimental and computational methods to ascertain how the hydraulic permeability of the rat abdominal aorta depends on these two layers and how it is affected by structural rearrangement of the media under pressure. Ex vivo experiments determined the conductance of the whole wall, the thickness of the media and the geometry of medial smooth muscle cells (SMCs) and extracellular matrix (ECM). Numerical methods were used to compute water flux through the media. Intimal values were obtained by subtraction. A mechanism was identified that modulates pressure-induced changes in medial transport properties: compaction of the ECM leading to spatial reorganization of SMCs. This is summarized in an empirical constitutive law for permeability and volumetric strain. It led to the physiologically interesting observation that, as a consequence of the changes in medial microstructure, the relative contributions of the intima and media to the hydraulic resistance of the wall depend on the applied pressure; medial resistance dominated at pressures above approximately 93 mmHg in this vessel.

JOURNAL ARTICLE

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

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, Cantwell CD, Kirby RM, Sherwin SJet al., 2016, Optimising the performance of the spectral/hp element method with collective linear algebra operations, Computer Methods in Applied Mechanics and Engineering, Vol: 310, Pages: 628-645, ISSN: 0045-7825

© 2016 The Author(s)As computing hardware evolves, increasing core counts mean that memory bandwidth is becoming the deciding factor in attaining peak performance of numerical methods. High-order finite element methods, such as those implemented in the spectral/hp framework Nektar++, are particularly well-suited to this environment. Unlike low-order methods that typically utilise sparse storage, matrices representing high-order operators have greater density and richer structure. In this paper, we show how these qualities can be exploited to increase runtime performance on nodes that comprise a typical high-performance computing system, by amalgamating the action of key operators on multiple elements into a single, memory-efficient block. We investigate different strategies for achieving optimal performance across a range of polynomial orders and element types. As these strategies all depend on external factors such as BLAS implementation and the geometry of interest, we present a technique for automatically selecting the most efficient strategy at runtime.

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

JOURNAL ARTICLE

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

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

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