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

 

313BCity and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

346 results found

Marcon J, Castiglioni G, Moxey D, Sherwin SJ, Peiro Jet al., 2020, rp-adaptation for compressible flows, International Journal for Numerical Methods in Engineering, ISSN: 0029-5981

We present an rp-adaptation strategy for high-fidelity simulation of compressible inviscid flows with shocks. The mesh resolution in regions of flow discontinuities is increased by using a variational optimiser to r-adapt the mesh and cluster degrees of freedom there. In regions of smooth flow, we locally increase or decrease the local resolution through increasing or decreasing the polynomial order of the elements, respectively. This dual approach allows us to take advantage of the strengths of both methods for best computational performance, thereby reducing the overall cost of the simulation. The adaptation workflow uses a sensor for both discontinuities and smooth regions that is cheap to calculate, but the framework is general and could be used in conjunction with other feature-based sensors or error estimators. We demonstrate this proof-of-concept using two geometries at transonic and supersonic flow regimes. The method has been implemented in the open-source spectral/hp element framework Nektar++, and its dedicated high-order mesh generation tool NekMesh. The results show that the proposed rp-adaptation methodology is a reasonably cost-effective way of improving accuracy.

Journal article

Reavette RM, Sherwin SJ, Tang M, Weinberg PDet al., 2020, Comparison of arterial wave intensity analysis by pressure-velocity and diameter-velocity methods in a virtual population of adult subjects., Proceedings of the Institution of Mechanical Engineers Part H: Journal of Engineering in Medicine, ISSN: 0954-4119

Pressure-velocity-based analysis of arterial wave intensity gives clinically relevant information about the performance of the heart and vessels, but its utility is limited because accurate pressure measurements can only be obtained invasively. Diameter-velocity-based wave intensity can be obtained noninvasively using ultrasound; however, due to the nonlinear relationship between blood pressure and arterial diameter, the two wave intensities might give disparate clinical indications. To test the magnitude of the disagreement, we have generated an age-stratified virtual population to investigate how the two dominant nonlinearities 'viscoelasticity and strain-stiffening' cause the two formulations to differ. We found strong agreement between the pressure-velocity and diameter-velocity methods, particularly for the systolic wave energy, the ratio between systolic and diastolic wave heights, and older subjects. The results are promising regarding the introduction of noninvasive wave intensities in the clinic.

Journal article

Yan Z-G, Pan Y, Castiglioni G, Hillewaert K, Peiró J, Moxey D, Sherwin SJet al., 2020, Nektar++: Design and implementation of an implicit, spectral/hp element, compressible flow solver using a Jacobian-free Newton Krylov approach, Computers & Mathematics with Applications, ISSN: 0898-1221

At high Reynolds numbers the use of explicit in time compressible flow simulations with spectral/ element discretization can become significantly limited by time step. To alleviate this limitation we extend the capability of the spectral/ element open-source software framework, Nektar++, to include an implicit discontinuous Galerkin compressible flow solver. The integration in time is carried out by a singly diagonally implicit Runge–Kutta method. The non-linear system arising from the implicit time integration is iteratively solved by the Jacobian-free Newton Krylov (JFNK) method. A favorable feature of the JFNK approach is its extensive use of the explicit operators available from the previous explicit in time implementation. The functionalities of different building blocks of the implicit solver are analyzed from the point of view of software design and placed in appropriate hierarchical levels in the C++ libraries. In the detailed implementation, the contributions of different parts of the solver to computational cost, memory consumption and programming complexity are also analyzed. A combination of analytical and numerical methods is adopted to simplify the programming complexity in forming the preconditioning matrix. The solver is verified and tested using cases such as manufactured compressible Poiseuille flow, Taylor–Green vortex, turbulent flow over a circular cylinder at and shock wave boundary-layer interaction. The results show that the implicit solver can speed-up the simulations while maintaining good simulation accuracy.

Journal article

Moxey D, Cantwell CD, Bao Y, Cassinelli A, Castiglioni G, Chun S, Juda E, Kazemi E, Lackhove K, Marcon J, Mengaldo G, Serson D, Turner M, Xu H, Peiró J, Kirby RM, Sherwin SJet al., 2020, Nektar++: Enhancing the capability and application of high-fidelity spectral/hp element methods, Computer Physics Communications, Vol: 249, ISSN: 0010-4655

Nektar++ is an open-source framework that provides a flexible, performant and scalable platform for the development of solvers for partial differential equations using the high-order spectral/hp element method. In particular, Nektar++ aims to overcome the complex implementation challenges that are often associated with high-order methods, thereby allowing them to be more readily used in a wide range of application areas. In this paper, we present the algorithmic, implementation and application developments associated with our Nektar++ version 5.0 release. We describe some of the key software and performance developments, including our strategies on parallel I/O, on in-situ processing, the use of collective operations for exploiting current andemerging hardware, and interfaces to enable multi-solver coupling. Furthermore, we provide details on a newly developed Python interface that enable more rapid on-boarding of new users unfamiliar with spectral/$hp$ element methods, C++ and/or Nektar++. This release also incorporates a number of numerical method developments - in particular: the method of moving frames, which provides an additional approach for the simulation of equations on embedded curvilinear manifolds and domains; a means of handling spatially variable polynomial order; and a novel technique for quasi-3D simulations to permit spatially-varying perturbations to the geometry in the homogeneous direction. Finally, we demonstrate the new application-level features provided in this release, namely: a facility for generating high-order curvilinear meshes called NekMesh; a novel new AcousticSolver for aeroacoustic problems; our development of a 'thick' strip model for the modelling of fluid-structure interaction problems in the context of vortex-induced vibrations. We conclude by commenting some directions for future code development and expansion.

Journal article

Moura RC, Peiró J, Sherwin SJ, 2020, Under-Resolved DNS of Non-trivial Turbulent Boundary Layers via Spectral/hp CG Schemes, ERCOFTAC Series, Pages: 389-395

© Springer Nature Switzerland AG 2020. This study assesses the suitability of spectral/hp continuous Galerkin (CG) schemes [1] for model-free under-resolved simulations of a non-trivial turbulent boundary layer flow. We consider a model problem proposed by Spalart in [2] that features a rotating free-stream velocity and admits an asymptotic solution with significant crossflow effects. Note this test case is substantially more complex than typical turbulent boundary layer canonical problems owing to its unsteadiness and enhanced small-scale anisotropy. Reported LES-based solutions to this problem are known to require sophisticated modelling and relatively fine grids to achieve meaningful results, with traditional models exhibiting poor performance. The model-free CG-based approach advocated, on the other hand, yields surprisingly good results with considerably less degrees of freedom for higher order discretisations. Usefully accurate results for the mean flow quantities could even be obtained with half as many degrees of freedom per direction (in comparison to reference LES solutions). Usage of high-order spectral element methods (CG in particular) is therefore strongly motivated for wall-bounded turbulence simulations via under-resolved DNS (uDNS), sometimes called implicit LES (iLES), approaches.

Book chapter

Moura RC, Fernandez P, Mengaldo G, Sherwin SJet al., 2020, Viscous diffusion effects in the eigenanalysis of (hybridisable) dg methods, Pages: 371-382, ISSN: 1439-7358

© 2020, The Author(s). We present the first eigenanalysis of hybridisable discontinuous Galerkin (HDG) schemes for the advection-diffusion equation in one dimension. This study is also one of the first to include viscous diffusion effects in the eigenanalysis of discontinuous spectral element methods. The interplay between upwind dissipation and viscous diffusion is discussed and preliminary insights deemed relevant to (under-resolved) turbulence computation approaches are presented.

Conference paper

Sherwin SJ, Moxey D, Peiró J, Vincent PE, Schwab Cet al., 2020, Preface, ISBN: 9783030396466

Book

Buscariolo FF, Sherwin SJ, Assi GRS, Meneghini JRet al., 2020, Spectral/hp methodology study for iles-svv on an ahmed body, Pages: 297-311, ISSN: 1439-7358

© 2020, The Author(s). The Ahmed Body is one of the most widely studied bluff bodies used for automotive conceptual studies and Computational Fluid Dynamics (CFD) software validation. With the advances of the computational processing capacity and improvement in computing costs, high-fidelity turbulence models, such as Detached Eddies Simulation (DES) and Large Eddies Simulation (LES), are becoming a reality for industrial cases, as studied by Buscariolo et al. (Analysis of turbulence models applied to CFD drag simulations of a small hatchback vehicle. SAE Paper 2016-36-0201, Society of Automotive Engineers, 2016), evaluating DES models to automotive applications.

Conference paper

Marcon J, Kopriva DA, Sherwin SJ, Peiro Jet al., 2019, A high resolution PDE approach to quadrilateral mesh generation, Journal of Computational Physics, Vol: 399, Pages: 1-17, ISSN: 0021-9991

We describe a high order technique to generate quadrilateral decompositions and meshes for complex two dimensional domains using spectral elements in a field guided procedure. Inspired by cross field methods, we never actually compute crosses. Instead, we compute a high order accurate guiding field using a continuous Galerkin (CG) or discontinuous Galerkin (DG) spectral element method to solve a Laplace equation for each of the field variables using the open source code Nektar++. The spectral method provides spectral convergence and sub-element resolution of the fields. The DG approximation allows meshing of corners that are not multiples of pi/2 in a discretization consistent manner, when needed. The high order field can then be exploited to accurately find irregular nodes, and can be accurately integrated using a high order separatrix integration method to avoid features like limit cycles. The result is a mesh with naturally curved quadrilateral elements that do not need to be curved a posteriori to eliminate invalid elements. The mesh generation procedure is implemented in the open source mesh generation program NekMesh.

Journal article

Moura RC, Aman M, Peiró J, Sherwin SJet al., 2019, Spatial eigenanalysis of spectral/hp continuous Galerkin schemes and their stabilisation via DG-mimicking spectral vanishing viscosity for high Reynolds number flows, Journal of Computational Physics, Pages: 109112-109112, ISSN: 0021-9991

Journal article

Vymazal M, Moxey D, Cantwell CD, Sherwin SJ, Kirby RMet al., 2019, On weak Dirichlet boundary conditions for elliptic problems in the continuous Galerkin method, Journal of Computational Physics, Vol: 394, Pages: 732-744, ISSN: 0021-9991

We combine continuous and discontinuous Galerkin methods in the setting of a model diffusion problem. Starting from a hybrid discontinuous formulation, we replace element interiors by more general subsets of the computational domain – groups of elements that support a piecewise-polynomial continuous expansion. This step allows us to identify a new weak formulation of Dirichlet boundary condition in the continuous framework. We show that the boundary condition leads to a stable discretization with a single parameter insensitive to mesh size and polynomial order of the expansion. The robustness of the approach is demonstrated on several numerical examples.

Journal article

Buscariolo FF, Hoessler J, Moxey D, Jassim A, Gouder K, Basley J, Murai Y, Assi GRS, Sherwin SJet al., 2019, Spectral/hp element simulation of flow past a Formula One front wing: validation against experiments, Publisher: arXiv

Emerging commercial and academic tools are regularly being applied to thedesign of road and race cars, but there currently are no well-establishedbenchmark cases to study the aerodynamics of race car wings in ground effect.In this paper we propose a new test case, with a relatively complex geometry,supported by the availability of CAD model and experimental results. We referto the test case as the Imperial Front Wing, originally based on the front wingand endplate design of the McLaren 17D race car. A comparison of differentresolutions of a high fidelity spectral/hp element simulation usingunder-resolved DNS/implicit LES approach with fourth and fifth polynomial orderis presented. The results demonstrate good correlation to both the wall-boundedstreaklines obtained by oil flow visualization and experimental PIV results,correctly predicting key characteristics of the time-averaged flow structures,namely intensity, contours and locations. This study highlights the resolutionrequirements in capturing salient flow features arising from this type ofchallenging geometry, providing an interesting test case for both traditionaland emerging high-fidelity simulations.

Working paper

Chun S, Marcon J, Peiro J, Sherwin SJet al., 2019, Numerical study on the effect of geometric approximation error in the numerical solution of PDEs using a high-order curvilinear mesh, Publisher: arXiv

When time-dependent partial differential equations (PDEs) are solved numerically in a domain with curved boundary or on a curved surface, mesh error and geometric approximation error caused by the inaccurate location of vertices and other interior grid points, respectively, could be the main source of the inaccuracy and instability of the numerical solutions of PDEs. The role of these geometric errors in deteriorating the stability and particularly the conservation properties are largely unknown, which seems to necessitate very fine meshes especially to remove geometric approximation error. This paper aims to investigate the effect of geometric approximation error by using a high-order mesh with negligible geometric approximation error, even for high order polynomial of order p. To achieve this goal, the high-order mesh generator from CAD geometry called NekMesh is adapted for surface mesh generation in comparison to traditional meshes with non-negligible geometric approximation error. Two types of numerical tests are considered. Firstly, the accuracy of differential operators is compared for various p on a curved element of the sphere. Secondly, by applying the method of moving frames, four different time-dependent PDEs on the sphere are numerically solved to investigate the impact of geometric approximation error on the accuracy and conservation properties of high-order numerical schemes for PDEs on the sphere.

Working paper

Marcon J, Kopriva DA, Sherwin SJ, Peiro Jet al., 2019, Naturally curved quadrilateral mesh generation using an adaptive spectral element solver, 28th International Meshing Roundtable and User Forum, Publisher: arXiv

We describe an adaptive version of a method for generating valid naturally curved quadrilateral meshes. The method uses a guiding field, derived from the concept of a cross field, to create block decompositions of multiply connected two dimensional domains. The a priori curved quadrilateral blocks can be further split into a finer high-order mesh as needed. The guiding field is computed by a Laplace equation solver using a continuous Galerkin or discontinuous Galerkin spectral element formulation. This operation is aided by using p-adaptation to achieve faster convergence of the solution with respect to the computational cost. From the guiding field, irregular nodes and separatrices can be accurately located. A first version of the code is implemented in the open source spectral element framework Nektar++ and its dedicated high order mesh generation platform NekMesh.

Conference paper

Cooke EE, Mughal MS, Sherwin S, Ashworth R, Rolston Set al., 2019, Destabilisation of Stationary and Travelling Crossflow Disturbances Due to Steps over a Swept Wing, AIAA Aviation 2019 Forum, Publisher: American Institute of Aeronautics and Astronautics

Destabilization effects of forward facing steps, backward facing steps and bumps on stationary and travelling crossflow disturbances are investigated computationally for a 40° infinite swept wing. Step and bump heights range from 24% to 53% of the boundary layer thickness and are located at 10% chord. The spectral/hp element solver, Nektar++, is used to compute base flow profiles with an embedded swept wing geometry. Parabolized Stability Equations (PSE) and Linearized Harmonic Navier-Stokes (LHNS) models are used to evaluate growth of convecting instabilities. The paper describes derivations of the PSE and LHNS models which accurately solve for the perturbed field over the very localized and rapid variations imposed by the surface step-features. Unlike the PSE, which suffer from a stream-wise numerical step size restriction, the LHNS are a fully elliptic set of equations which may use arbitrarily fine grid resolution. Unsurprisingly, the PSE codes fail to capture the effect of abrupt changes in surface geometry introduced by the steps features. Results for the LHNS and roughness incorporating LHNS are given for the varying step types. Comparisons are made between the LHNS model and direct numerical simulations involving the time-stepping linearized Navier-Stokes solver in the Nektar++ software suite. Most previous work in the topic area has focused on Tollmien-Schlichting perturbations over two-dimensional flat plate flows or airfoils, the novelty of this work lies with analyzing crossflow instability over a swept wing boundary-layer flow with step features.

Conference paper

Cookson AN, Doorly DJ, Sherwin SJ, 2019, Efficiently Generating Mixing by Combining Differing Small Amplitude Helical Geometries, FLUIDS, Vol: 4, ISSN: 2311-5521

Journal article

Zhu H, Wang R, Bao Y, Zhou D, Ping H, Han Z, Sherwin SJet al., 2019, Flow over a symmetrically curved circular cylinder with the free stream parallel to the plane of curvature at low Reynolds number, JOURNAL OF FLUIDS AND STRUCTURES, Vol: 87, Pages: 23-38, ISSN: 0889-9746

Journal article

Bao Y, Zhu HB, Huan P, Wang R, Zhou D, Han ZL, Palacios R, Graham M, Sherwin Set al., 2019, Numerical prediction of vortex-induced vibration of flexible riser with thick strip method, Journal of Fluids and Structures, ISSN: 0889-9746

We present numerical prediction results of vortex-induced vibration (VIV) of a long flexible tensioned riser subject to uniform currents. The VIV model of long length-to-diameter ratio is considered and ‘thick’ strip technique based on high-order spectral/hp element method is employed for computational simulation. The model parameter of the riser for the simulation is chosen according to the dimensional counterparts used in the experimental tests in Lehn (2003). The numerical results are displayed in terms of motion responses, hydrodynamic forces and wake patterns as well and compared and discussed with the available data in the literature.

Journal article

Buscariolo FF, Meneghini JR, da Silva Assi GR, Sherwin SJet al., 2019, Diffuser study on a squared-back ahmed body considering ILES-SVV

© 2019 International Symposium on Turbulence and Shear Flow Phenomena, TSFP. All rights reserved. The Ahmed Body is one of the most studied 3D bluff bodies used for automotive research and was first proposed by Ahmed et al. (1984). Due to the variation of the slant angle of the read upper surface, it can generate different flow behaviours, similar to a standard road vehicles. In this study we also use the Ahmed body to evaluate the performance of the introduction of a rear underbody diffuser which are commonly applied in high performance and race cars to improve downforce. As a default body we consider the Ahmed Body with Squared-Back or 0° slant angle to perform a parametric study of the rear diffuser angle. We employing a high-fidelity CFD based on Spectral/hp element discretisation that combines classical mesh refinement with polynomial expansions in order to achieve both better accuracy. The diffuser length was fixed at the same length that the top slant angle has previously been studies of 222mm and the angle was changed from 0° to 50° in increments of 10°. An additional case considering the diffuser angle of 5° was also evaluated. It was observed that peak values for drag and negative lift (downforce) coefficient were achieved at 30° diffuser angle, in which the topology indicates flow fully attached with two streamwise vortical structures, similar to results obtained from Ahmed et al. (1984), but in this case with the the body flipped upside down.

Conference paper

Yakhot A, Feldman Y, Moxey D, Sherwin S, Karniadakis GEet al., 2019, Near-wall turbulence in a localized puff in a pipe, Pages: 15-20, ISSN: 0930-8989

© Springer Nature Switzerland AG 2019. We have performed direct numerical simulations of a transitional flow in a pipe for Rem=2250 when turbulence manifests in the form of fleshes (puffs). From experiments and simulations, Rem ≈ 2250 has been estimated as a threshold when the average speeds of upstream and downstream fronts of a puff are identical (Song et al. in J Fluid Mech 813:283–304, 2017, [1]). The flow regime upstream of its trailing edge and downstream of its leading edge is almost laminar. To collect the velocity data, at each time instance, we followed a turbulent puff by a three-dimensional moving window centered at the location of the maximum energy of the transverse (turbulent) motion. In the near-wall region, despite the low Reynolds number, the turbulence statistics, in particular, the distribution of turbulence intensities and Reynolds shear stress becomes similar to a fully-developed turbulent pipe flow.

Conference paper

Mao X, Zaki T, Sherwin S, Blackburn Het al., 2019, Bypass transition induced by free-stream noise in flow past a blade cascade

© Open Archives of the 16th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery, ISROMAC 2016. All rights reserved. Flow past a NACA 65 blade cascade at Reynolds number 138, 500 is studied through weighted transient growth and Direct Numerical Simulations (DNS). The mechanism of bypass transition on the pressure side around the leading edge observed in a previous work [1] is examined. The weighted optimal initial perturbations have spanwise wavenumber 40π and are amplified via the Orr mechanism. At higher spanwise wavenumber, e.g. 120π, a free-stream optimal initial perturbation, upstream of the leading edge in the form of streamwise vortices, is obtained. In nonlinear evolution, this high-wavenumber optimal perturbation tilts the mean shear and generates spanwise periodic high and low-speed streaks. Then through a nonlinear lift-up mechanism, the low-speed streaks are lifted above the high-speed ones and generate a mean shear with inflectional points. This layout of streaks activates secondary instabilities and both inner and outer instabilities addressed in literature are observed.

Conference paper

Moura RC, Peiró J, Sherwin SJ, 2019, Implicit LES approaches via discontinuous galerkin methods at very large reynolds, ERCOFTAC Series, Pages: 53-59

© Springer Nature Switzerland AG 2019. We consider the suitability of implicit large-eddy simulation (iLES) approaches via discontinuous Galerkin (DG) schemes. These are model-free eddy-resolving approaches which solve the governing equations in unfiltered form and rely on numerical stabilization techniques to account for the missing scales. In DG, upwind dissipation from the Riemann solver provides the baseline mechanism for regularization. DG-based iLES approaches are currently under rapid dissemination due to their success in predicting complex transitional and turbulent flows at moderate Reynolds numbers (Uranga et al, Int J Numer Meth Eng 87(1–5):232–261, 2011, [1], Gassner and Beck, Theor Comput Fluid Dyn 27(3–4):221–237, 2013, [2], Beck et al, Int J Numer Methods Fluids 76(8):522–548, 2014, [3], Wiart et al Int J Numer Methods Fluids 78:335–354, 2015, [4]). However, at higher Reynolds number, accuracy and stability issues can arise due the highly under-resolved character of the computations and the suppression of stabilizing viscous effects.

Book chapter

Cassinelli A, Xu H, Montomoli F, Adami P, Diaz RV, Sherwin SJet al., 2019, ON THE EFFECT OF INFLOW DISTURBANCES ON THE FLOW PAST A LINEAR LPT VANE USING SPECTRAL/HP ELEMENT METHODS, ASME Turbo Expo: Turbomachinery Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Buscariolo FF, Meneghini JR, da Silva Assi GR, Sherwin SJet al., 2019, Diffuser study on a squared-back ahmed body considering ILES-SVV

© 2019 International Symposium on Turbulence and Shear Flow Phenomena, TSFP. All rights reserved. The Ahmed Body is one of the most studied 3D bluff bodies used for automotive research and was first proposed by Ahmed et al. (1984). Due to the variation of the slant angle of the read upper surface, it can generate different flow behaviours, similar to a standard road vehicles. In this study we also use the Ahmed body to evaluate the performance of the introduction of a rear underbody diffuser which are commonly applied in high performance and race cars to improve downforce. As a default body we consider the Ahmed Body with Squared-Back or 0° slant angle to perform a parametric study of the rear diffuser angle. We employing a high-fidelity CFD based on Spectral/hp element discretisation that combines classical mesh refinement with polynomial expansions in order to achieve both better accuracy. The diffuser length was fixed at the same length that the top slant angle has previously been studies of 222mm and the angle was changed from 0° to 50° in increments of 10°. An additional case considering the diffuser angle of 5° was also evaluated. It was observed that peak values for drag and negative lift (downforce) coefficient were achieved at 30° diffuser angle, in which the topology indicates flow fully attached with two streamwise vortical structures, similar to results obtained from Ahmed et al. (1984), but in this case with the the body flipped upside down.

Conference paper

Yakhot A, Feldman Y, Moxey D, Sherwin S, Karniadakis GEet al., 2019, Turbulence in a Localized Puff in a Pipe, Flow, Turbulence and Combustion, ISSN: 1386-6184

© 2019, Springer Nature B.V. We have performed direct numerical simulations of a spatio-temporally intermittent flow in a pipe for Rem = 2250. From previous experiments and simulations of pipe flow, this value has been estimated as a threshold when the average speeds of upstream and downstream fronts of a puff are identical (Barkley et al., Nature 526, 550–553, 2015; Barkley et al., 2015). We investigated the structure of an individual puff by considering three-dimensional snapshots over a long time period. To assimilate the velocity data, we applied a conditional sampling based on the location of the maximum energy of the transverse (turbulent) motion. Specifically, at each time instance, we followed a turbulent puff by a three-dimensional moving window centered at that location. We collected a snapshot-ensemble (10000 time instances, snapshots) of the velocity fields acquired over T = 2000D/U time interval inside the moving window. The cross-plane velocity field inside the puff showed the dynamics of a developing turbulence. In particular, the analysis of the cross-plane radial motion yielded the illustration of the production of turbulent kinetic energy directly from the mean flow. A snapshot-ensemble averaging over 10000 snapshots revealed azimuthally arranged large-scale (coherent) structures indicating near-wall sweep and ejection activity. The localized puff is about 15-17 pipe diameters long and the flow regime upstream of its upstream edge and downstream of its leading edge is almost laminar. In the near-wall region, despite the low Reynolds number, the turbulence statistics, in particular, the distribution of turbulence intensities, Reynolds shear stress, skewness and flatness factors, become similar to a fully-developed turbulent pipe flow in the vicinity of the puff upstream edge. In the puff core, the velocity profile becomes flat and logarithmic. It is shown that this “fully-developed turbulent flash” is very narrow being about t

Journal article

Cassinelli A, Adami P, Sherwin S, Montomoli Fet al., 2018, High Fidelity Spectral/hp Element Methods for Turbomachinery, ASME IGTI 2018

Conference paper

Buscariolo FF, Sherwin SJ, Assi GRS, Meneghini JRet al., 2018, Spectral/hp iLES-SVV simulation methodology study on an Ahmed Body squared back, 2018 SAE Brasil Congress & Exhibition

© 2018 SAE International. All Rights Reserved. The Ahmed Body is one of the most widely studied bluff bodies used for automotive conceptual studies and Computational Fluid Dynamics - CFD software validation. With the advances of the computational processing capacity and improvement in cluster costs, high-fidelity turbulence models, such as Detached Eddies Simulation - DES and Large Eddies Simulation - LES, are becoming a reality for industrial cases, as studied by BUSCARIOLO et al. (2016) [4], evaluating DES models to automotive applications. This work presents a correlation study between a computational and physical model of an Ahmed Body with slant angle of 0 degree, also known as a squared back. Physical results are from a wind tunnel test, performed by STRACHAN et al. (2007) [11] considering moving ground and Reynolds number of 1.7M, based on the length of the body. CFD simulations were performed by the code Nektar++, which is an open source spectral/hp element high-order solver, which methodology combine both mesh refinement (h), with higher polynomial order (p) for lower error propagation and better convergence. It employs a high-fidelity turbulence model known as Spectral Vanish Viscosity - iLES-SVV model, which works as a filter for high frequencies. Same physical test conditions and tunnel test section were considered, with a total time of 4 convective lengths. The 4 cases studies consider high-order mesh of 6 th order, divided in two polynomial orders: 5 th and 6 th for two different mesh setups: one base mesh setup with around 95,000 elements corresponding to 6.3Million of DOFs and a second mesh considering a refinement (h) with around 310,000 elements, corresponding to 19.8 Million of DOFs. Meshes were generated by NekMesh, which works with Nektar++ for high-order mesh generation. In order to improve the computational costs, only half of the model is simulated, considering symmetric condition. Considering the converged drag coefficient values for c

Conference paper

Mengaldo G, Moura RC, Giralda B, Peiró J, Sherwin SJet al., 2018, Spatial eigensolution analysis of discontinuous Galerkin schemes with practical insights for under-resolved computations and implicit LES, Computers and Fluids, Vol: 169, Pages: 349-364, ISSN: 0045-7930

The study focusses on the dispersion and diffusion characteristics of discontinuous spectral element methods - specifically discontinuous Galerkin (DG) - via the spatial eigensolution analysis framework built around a one-dimensional linear problem, namely the linear advection equation. Dispersion and diffusion characteristics are of critical importance when dealing with under-resolved computations, as they affect both the numerical stability of the simulation and the solution accuracy. The spatial eigensolution analysis carried out in this paper complements previous analyses based on the temporal approach, which are more commonly found in the literature. While the latter assumes periodic boundary conditions, the spatial approach assumes inflow/outflow type boundary conditions and is therefore better suited for the investigation of open flows typical of aerodynamic problems, including transitional and fully turbulent flows and aeroacoustics. The influence of spurious/reflected eigenmodes is assessed with regard to the presence of upwind dissipation, naturally present in DG methods. This provides insights into the accuracy and robustness of these schemes for under-resolved computations, including under-resolved direct numerical simulation (uDNS) and implicit large-eddy simulation (iLES). The results estimated from the spatial eigensolution analysis are verified using the one-dimensional linear advection equation and successively by performing two-dimensional compressible Euler simulations that mimic (spatially developing) grid turbulence.

Journal article

Winters A, Moura RC, Mengaldo G, Gassner G, Walch S, Peiro J, Sherwin Set al., 2018, A comparative study on polynomial dealiasing and split form discontinuous Galerkin schemes for under-resolved turbulence computations, Journal of Computational Physics, ISSN: 0021-9991

Journal article

Calder M, Craig C, Culley D, de Cani R, Donnelly CA, Douglas R, Edmonds B, Gascoigne J, Gilbert N, Hargrove C, Hinds D, Lane DC, Mitchell D, Pavey G, Robertson D, Rosewell B, Sherwin S, Walport M, Wilson Aet al., 2018, Computational modelling for decision-making: where, why, what, who and how, Royal Society Open Science, Vol: 5, ISSN: 2054-5703

In order to deal with an increasingly complex world, we need ever more sophisticated computational models that can help us make decisions wisely and understand the potential consequences of choices. But creating a model requires far more than just raw data and technical skills: it requires a close collaboration between model commissioners, developers, users and reviewers. Good modelling requires its users and commissioners to understand more about the whole process, including the different kinds of purpose a model can have and the different technical bases. This paper offers a guide to the process of commissioning, developing and deploying models across a wide range of domains from public policy to science and engineering. It provides two checklists to help potential modellers, commissioners and users ensure they have considered the most significant factors that will determine success. We conclude there is a need to reinforce modelling as a discipline, so that misconstruction is less likely; to increase understanding of modelling in all domains, so that the misuse of models is reduced; and to bring commissioners closer to modelling, so that the results are more useful.

Journal article

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