280 results found
Alastruey J, Parker K, Peiro J, et al., Analysing the pattern of pulse waves in arterial networks: A time Domain Study, Journal of Engineering Mathematics, Vol: Submitted
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
Xu H, Mughal MS, Gowree ER, et al., Effect of a 3d indentation on boundary layer instability, ICAS 2016, 30th Congress of the International Council of the Aeronautical Sciences, Publisher: ICAS
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.
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
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
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
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
Ghim M, Alpresa P, Yang S, et al., 2017, Visualisation of three pathways for macromolecule transport across cultured endothelium and their modification by flow., Am J Physiol Heart Circ Physiol
Transport of macromolecules across vascular endothelium and its modification by fluid mechanical forces are important for normal tissue function and in the development of atherosclerosis. However, the routes by which macromolecules cross endothelium, the hemodynamic stresses that maintain endothelial physiology or trigger arterial disease, and the dependence of transendothelial transport on hemodynamic stresses are controversial. Here we visualised pathways for macromolecule transport and determined the effect on these pathways of different types of flow. Endothelial monolayers were cultured under static conditions or on an orbital shaker producing different flow profiles in different parts of the wells. Fluorescent tracers that bound to the substrate after crossing the endothelium were used to identify transport pathways. Maps of tracer distribution were compared with numerical simulations of flow to determine effects of different shear stress metrics on permeability. Albumin-sized tracers dominantly crossed the cultured endothelium via junctions between neighbouring cells, high-density-lipoprotein-sized tracers crossed at tricelluar junctions whilst low-density-lipoprotein-sized tracers crossed through cells. Cells aligned close to the angle that minimised shear stresses across their long axis. The rate of paracellular transport under flow correlated with the magnitude of these minimised transverse stresses, whereas transport across cells was uniformly reduced by all types of flow. These results contradict the long-standing two-pore theory of solute transport across microvessel walls and the consensus view that endothelial cells align with the mean shear vector. They suggest that endothelial cells minimise transverse shear, supporting its postulated pro-atherogenic role. Preliminary data show that similar tracer techniques are practicable in vivo.
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
© 2017 Cambridge University Press. 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.
Mengaldo G, Moura RC, Giralda B, et al., 2017, Spatial eigensolution analysis of discontinuous Galerkin schemes with practical insights for under-resolved computations and implicit LES, Computers and Fluids, ISSN: 0045-7930
© 2017 The Authors. 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.
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
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
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
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
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
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
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
Bao Y, Palacios R, Graham M, et 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
Bolls A, Cantwell CD, Moxey D, et 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
Chooi KY, Comerford A, Sherwin SJ, et al., 2016, Intimal and medial contributions to the hydraulic resistance of the arterial wall at different pressures: a combined computational and experimental study, JOURNAL OF THE ROYAL SOCIETY INTERFACE, Vol: 13, ISSN: 1742-5689
Lombard J-EW, Moxey D, Sherwin SJ, et al., 2016, Implicit Large-Eddy Simulation of a Wingtip Vortex, AIAA JOURNAL, Vol: 54, Pages: 506-518, ISSN: 0001-1452
Mengaldo G, De Grazia D, Vincent PE, et 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
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
Moxey D, Cantwell CD, Kirby RM, et 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
Moxey D, Ekelschot D, Keskin U, et al., 2016, High-order curvilinear meshing using a thermo-elastic analogy, COMPUTER-AIDED DESIGN, Vol: 72, Pages: 130-139, ISSN: 0010-4485
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
Turner M, Moxey D, Sherwin SJ, et al., 2016, Automatic generation of 3D unstructured high-order curvilinear meshes, Pages: 428-443
The generation of suitable, good quality high-order meshes is a significant obstacle in the academic and industrial uptake of high-order CFD methods. These methods have a number of favourable characteristics such as low dispersion and dissipation and higher levels of numerical accuracy than their low-order counterparts, however the methods are highly susceptible to inaccuracies caused by low quality meshes. These meshes require significant curvature to accuratly describe the geometric surfaces, which presents a number of difficult challenges in their generation. As yet, research into the field has produced a number of interesting technologies that go some way towards achieving this goal, but are yet to provide a complete system that can systematically produce curved high-order meshes for arbitrary geometries for CFD analysis. This paper presents our efforts in that direction and introduces an open-source high-order mesh generator, NekMesh, which has been created to bring high-order meshing technologies into one coherent pipeline which aims to produce 3D high-order curvilinear meshes from CAD geometries in a robust and systematic way.
Xu H, Mughal S, Gowree ER, et al., 2016, Effect of a 3D indentation on boundary layer instability
We are concerned about effect of a 3D surface indentation on instability and laminar-turbulent transition in a boundary layer. For natural transition in a boundary layer, the transition onset is dominated by growth of the Tollmien-Schlichting (TS) wave and its subsequent secondary instability. In the paper, both linear analysis and nonlinear calculations are carried out to address the 3D surface indentation effect on amplifying TS waves' amplitudes and prompting transition onset. By the linear analysis, we address sudden amplification of the TS modes by a separation bubble in a surface indentation region. The nonlinear calculations are implemented to validate the traditional transition criteria predicted by the linear theory when a 3D indentation is present. Finally, applicability of the traditional transition criteria is assessed.
Xu H, Sherwin SJ, Halle P, et 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
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