316 results found
Zhu H, Wang R, Bao Y, et 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
© 2019 Elsevier Ltd Three-dimensional flow past a symmetrically curved circular cylinder with the free stream parallel to the plane of curvature is numerically investigated by high-order spectral element method. The axial line of the cylinder is described in Cartesian coordinates as y=A[cosh(x∕A)−1] with A being a catenary coefficient used to scale its span ratio. In this geometry configuration, the deformed cylinder can be divided into two half segments, respectively of the convex segment in the upstream and the concave segment in the downstream. Different span ratios are investigated with respect to A=0.5∼10. It is found that four wake topologies, namely of single body, bi-stable, vortex impingement and steady wakes, are successively appeared with the increase of the span ratio. By examining the flow field quantities including mean and fluctuation of velocities and pressure along the axial line, some important characteristics of axial flow dynamics are intensively revealed. Most interestingly, the generation of axial flow along the curved surface of the cylinder is strongly influenced by not only the curvature ratio but also the wake interference effects.
Bao Y, Zhu HB, Huan P, et al., 2019, Numerical prediction of vortex-induced vibration of flexible riser with thick strip method, Journal of Fluids and Structures, ISSN: 0889-9746
© 2019 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.
© 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
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, , Gassner and Beck, Theor Comput Fluid Dyn 27(3–4):221–237, 2013, , Beck et al, Int J Numer Methods Fluids 76(8):522–548, 2014, , Wiart et al Int J Numer Methods Fluids 78:335–354, 2015, ). 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.
Winters AR, Moura RC, Mengaldo G, et al., 2018, A comparative study on polynomial dealiasing and split form discontinuous Galerkin schemes for under-resolved turbulence computations, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 372, Pages: 1-21, ISSN: 0021-9991
Buscariolo FF, Sherwin SJ, Assi GRS, et al., 2018, Spectral/hp iLES-SVV simulation methodology study on an Ahmed Body squared back
© 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) , 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)  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
Mengaldo G, Moura RC, Giralda B, et al., 2018, Spatial eigensolution analysis of discontinuous Galerkin schemes with practical insights for under-resolved computations and implicit LES, COMPUTERS & FLUIDS, Vol: 169, Pages: 349-364, ISSN: 0045-7930
Calder M, Craig C, Culley D, et al., 2018, Computational modelling for decision-making: where, why, what, who and how, ROYAL SOCIETY OPEN SCIENCE, Vol: 5, ISSN: 2054-5703
Cohen J, Marcon J, Turner M, et al., 2019, Simplifying high-order mesh generation for computational scientists, 10th International Workshop on Science Gateways, Publisher: CEUR Workshop Proceedings, ISSN: 1613-0073
Computational modelling is now tightly integrated into many fields of research in science and industry. Computational fluid dynamics software, for example, gives engineers the ability to model fluid flow around complex geometries defined in Computer-Aided Design (CAD) packages, without the expense of constructing large wind tunnel experiments. However, such modelling requires translation from an initial CAD geometry to a mesh of many small elements that modelling software uses to represent the approximate solution in the numerical method. Generating sufficiently high-quality meshes for simulation is a time-consuming, iterative and error-prone process that is often complicated by the need to interact with multiple command-line tools to generate and visualise the mesh data. In this paper we describe our approach to overcoming this complexity through the addition of a meshing console to Nekkloud, a science gateway for simplifying access to the functionality of the Nektar++ spectral/hp element framework. The meshing console makes use of the NekMesh tool in Nektar++ to help reduce the complexity of the mesh generation process. It offers a web-based interface for specifying parameters, undertaking meshing and visualising results. The meshing console enables Nekkloud to offer support for a full, end-to-end simulation pipeline from initial CAD geometry to simulation results.
Mengaldo G, De Grazia D, Moura RC, et al., 2018, Spatial eigensolution analysis of energy-stable flux reconstruction schemes and influence of the numerical flux on accuracy and robustness, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 358, Pages: 1-20, ISSN: 0021-9991
Alpresa P, Sherwin S, Weinberg P, et al., 2018, Orbitally shaken shallow fluid layers. II. An improved wall shear stress model, PHYSICS OF FLUIDS, Vol: 30, ISSN: 1070-6631
Alpresa P, Sherwin S, Weinberg P, et al., 2018, Orbitally shaken shallow fluid layers. I. Regime classification, PHYSICS OF FLUIDS, Vol: 30, ISSN: 1070-6631
De Grazia D, Moxey D, Sherwin SJ, et al., 2018, Direct numerical simulation of a compressible boundary-layer flow past an isolated three-dimensional hump in a high-speed subsonic regime, PHYSICAL REVIEW FLUIDS, Vol: 3, ISSN: 2469-990X
Xu H, Cantwell CD, Monteserin C, et al., 2018, Spectral/hp element methods: Recent developments, applications, and perspectives, JOURNAL OF HYDRODYNAMICS, Vol: 30, Pages: 1-22, ISSN: 1001-6058
Cassinelli A, Montomoli F, Adami P, et al., 2018, HIGH FIDELITY SPECTRAL/HP ELEMENT METHODS FOR TURBOMACHINERY, ASME Turbo Expo: Turbomachinery Technical Conference and Exposition, Publisher: AMER SOC MECHANICAL ENGINEERS
Bao Y, Palacios R, Graham M, et al., 2018, A Strip Modelling of Flow Past a Freely Vibrating Cable, DIRECT AND LARGE-EDDY SIMULATION X, Vol: 24, Pages: 221-227, ISSN: 1382-4309
Ghim M, Alpresa P, Yang S-W, et al., 2017, Visualization of three pathways for macromolecule transport across cultured endothelium and their modification by flow, AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY, Vol: 313, Pages: H959-H973, ISSN: 0363-6135
Serson D, Meneghini JR, Sherwin SJ, 2017, Direct numerical simulations of the flow around wings with spanwise waviness, JOURNAL OF FLUID MECHANICS, Vol: 826, Pages: 714-731, ISSN: 0022-1120
Marcon J, Turner M, Moxey D, et al., 2017, A variational approach to high-order r-adaptation
A variational framework, initially developed for high-order meshoptimisation, is being extended for r-adaptation. The method is based on theminimisation of a functional of the mesh deformation. To achieve adaptation,elements of the initial mesh are manipulated using metric tensors to obtaintarget elements. The nonlinear optimisation in turns adapts the finalhigh-order mesh to best fit the description of the target elements byminimising the element distortion. Encouraging preliminary results prove thatthe method behaves well and can be used in the future for more extensive workwhich shall include the use of error indicators from CFD simulations.
Xu H, Mughal SM, Gowree ER, et al., 2017, Destabilisation and modification of Tollmien-Schlichting disturbances by a three-dimensional surface indentation, JOURNAL OF FLUID MECHANICS, Vol: 819, Pages: 592-620, ISSN: 0022-1120
Mao X, Zaki TA, Sherwin SJ, et al., 2017, Transition induced by linear and nonlinear perturbation growth in flow past a compressor blade, Journal of Fluid Mechanics, Vol: 820, Pages: 604-632, ISSN: 0022-1120
Flow past a NACA 65 blade at chord-based Reynolds number 138 500 is studied using stability analysis, generalized (spatially weighted) transient growth analysis and direct numerical simulations (DNS). The mechanisms of transition on various sections of the blade observed in previous work by Zaki et al. (J. Fluid Mech., vol. 665, 2010, pp. 57-98) are examined, with a focus on the pressure side around the leading edge. In this region, the linearly most energetic perturbation has spanwise wavenumber 40π (five boundary-layer thicknesses) and is tilted against the mean shear to take advantage of the Orr mechanism. In a DNS, the nonlinear development of this optimal perturbation induces Λ structures, which are further stretched to hairpin vortices before breaking down to turbulence. At higher spanwise wavenumber, e.g. 120π, a free-stream optimal perturbation is obtained upstream of the leading edge, in the form of streamwise vortices. During its nonlinear evolution, this 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. This layout of streaks generates a mean shear with two inflectional points and activates secondary instabilities, namely inner and outer instabilities previously reported in the literature.
Xu H, Lombard J-EW, Sherwin SJ, 2017, Influence of localised smooth steps on the instability of a boundary layer, JOURNAL OF FLUID MECHANICS, Vol: 817, Pages: 138-170, ISSN: 0022-1120
Burovskiy P, Grigoras P, Sherwin S, et al., 2017, Efficient Assembly for High-Order Unstructured FEM Meshes (FPL 2015), ACM TRANSACTIONS ON RECONFIGURABLE TECHNOLOGY AND SYSTEMS, Vol: 10, ISSN: 1936-7406
Serson D, Meneghini JR, Sherwin SJ, 2017, Direct numerical simulations of the flow around wings with spanwise waviness at a very low Reynolds number, COMPUTERS & FLUIDS, Vol: 146, Pages: 117-124, ISSN: 0045-7930
Chooi KY, Comerford A, Sherwin SJ, et al., 2017, Noradrenaline has opposing effects on the hydraulic conductance of arterial intima and media, JOURNAL OF BIOMECHANICS, Vol: 54, Pages: 4-10, ISSN: 0021-9290
Cantwell C, Sherwin S, 2017, 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.
Ekelschot D, Moxey D, Sherwin SJ, et al., 2017, A p-adaptation method for compressible flow problems using a goal-based error indicator, COMPUTERS & STRUCTURES, Vol: 181, Pages: 55-69, ISSN: 0045-7949
Moura RC, Mengaldo G, Peiro J, et al., 2017, On the eddy-resolving capability of high-order discontinuous Galerkin approaches to implicit LES / under-resolved DNS of Euler turbulence, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 330, Pages: 615-623, ISSN: 0021-9991
Mohamied Y, Sherwin SJ, Weinberg PD, 2017, Understanding the fluid mechanics behind transverse wall shear stress, JOURNAL OF BIOMECHANICS, Vol: 50, Pages: 102-109, ISSN: 0021-9290
Serbanovic-Canic J, de Luca A, Warboys C, et al., 2017, Zebrafish Model for Functional Screening of Flow-Responsive Genes, ARTERIOSCLEROSIS THROMBOSIS AND VASCULAR BIOLOGY, Vol: 37, Pages: 130-+, ISSN: 1079-5642
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