134,677 research outputs found
Comparison of Subgrid-scale Viscosity Models and Selective Filtering Strategy for Large-eddy Simulations
No full textExplicitly filtered large-eddy simulations (LES), combining high-accuracy schemes with the use of a selective filtering without adding an explicit subgrid-scales (SGS) model, are carried out for the Taylor-Green-vortex and the supersonic-boundary-layer cases. First, the present approach is validated against direct numerical simulation (DNS) results. Subsequently, several SGS models are implemented in order to investigate if they can improve the initial filter-based methodology. It is shown that the most accurate results are obtained when the filtering is used alone as an implicit model, and for a minimal cost. Moreover, the tests for the Taylor-Green vortex indicate that the discretization error from the numerical methods, notably the dissipation error from the high-order filtering, can have a greater influence than the SGS models
Large eddy simulation of buoyant plumes
No full textA 3d parallel CFD code is written to investigate the characteristics of and differences
between Large Eddy Simulation (LES) models in the context of simulating a thermal
buoyant plume. An efficient multigrid scheme is incorporated to solve the Poisson
equation, resulting from the fractional step, projection method used to solve the Low
Mach Number (LMN) Navier-Stokes equations.
A wide range of LES models are implemented, including a variety of eddy models,
structure models, mixed models and dynamic models, for both the momentum stresses
and the temperature fluxes. Generalised gradient flux models are adapted from their
RANS counterparts, and also tested.
A number of characteristics are observed in the LES models relating to the thermal
plume simulation in particular and turbulence in general. Effects on transition,
dissipation, backscatter, equation balances, intermittency and energy spectra are all
considered, as are the impact of the governing equations, the discretisation scheme,
and the effect of grid coarsening. Also characteristics to particular models are
considered, including the subgrid kinetic energy for the one-equation models, and
constant histories for dynamic models.
The argument that choice of LES model is unimportant is shown to be incorrect as a
general statement, and a recommendation for when the models are best used is given
Circulation characteristics in three eddy-permitting models of the North Atlantic
No full textA systematic intercomparison of three realistic eddy-permitting models of the North Atlantic circulation has been performed. The models use different concepts for the discretization of the vertical coordinate, namely geopotential levels, isopycnal layers, terrain-following (sigma) coordinates, respectively. Although these models were integrated under nearly identical conditions, the resulting large-scale model circulations show substantial differences. The results demonstrate that the large-scale thermohaline circulation is very sensitive to the model representation of certain localised processes, in particular to the amount and water
mass properties of the overflow across the Greenland-Scotland region, to the amount of mixing within a few hundred kilometers south of the sills, and to several other processes at small or sub-grid scales. The different behaviour of the three models can to a large extent be explained as a consequence of the different
model representation of these processes
A three-dimensional inverse finite-element method applied to experimental eddy-current imaging data.
No full textEddy-current techniques can be used to create electrical conductivity mapping of an object. The eddy-current imaging system in this paper is a magnetic induction tomography (MIT) system. MIT images the electrical conductivity of the target based on impedance measurements from pairs of excitation and detection coils. The inverse problem here is ill-posed and nonlinear. Current state-of-the-art image reconstruction methods in MIT are generally based on linear algorithms. In this paper, a regularized Gauss-Newton scheme has been implemented based on an edge finite-element forward solver and an efficient formula for the Jacobian matrix. Applications of Tikhonov and total variation regularization have been studied. Results are presented from experimental data collected from a newly developed MIT system. The paper also presents further progress in using an MIT system for molten metal flow visualization in continuous casting by applying the proposed algorithm in a real experiment in a continuous casting pilot plant of Corus RD&T, Teesside Technology Centre
Large-eddy simulation of low-frequency unsteadiness in a turbulent shock-induced separation bubble
No full textThe need for better understanding of the low-frequency unsteadiness observed in shock wave/turbulent boundary layer interactions has been driving research in this area for several decades. We present here a large-eddy simulation investigation of the interaction between an impinging oblique shock and a Mach 2.3 turbulent boundary layer. Contrary to past large-eddy simulation investigations on shock/turbulent boundary layer interactions, we have used an inflow technique which does not introduce any energetically significant low frequencies into the domain, hence avoiding possible interference with the shock/boundary layer interaction system. The large-eddy simulation has been run for much longer times than previous computational studies making a Fourier analysis of the low frequency possible. The broadband and energetic low-frequency component found in the interaction is in excellent agreement with the experimental findings. Furthermore, a linear stability analysis of the mean flow was performed and a stationary unstable global mode was found. The long-run large-eddy simulation data were analyzed and a phase change in the wall pressure fluctuations was related to the global-mode structure, leading to a possible driving mechanism for the observed low-frequency motions
Large-eddy simulation of turbulent flow over a rough surface
No full textA family of wall models is proposed that exhibits more satisfactory performance than previous models for the large-eddy simulation (LES) of the turbulent boundary layer over a rough surface.The time and horizontally averaged statistics such as mean vertical profiles of wind velocity, Reynolds stress, turbulent intensities, turbulent kinetic energy and also spectra are compared with wind-tunnel experimental data. The purpose of the present study is to obtain simulated turbulent flows that are comparable with wind-tunnel measurements for use as the wind environment for the numerical prediction by LES of source dispersion in theneutral atmospheric boundary layer
Implicit large eddy simulation of ship airwakes
No full textImplicit large eddy simulations (ILES) of two different Royal Navy ships have
been conducted as part of the UK Ship/Air Interface Frame-work project using a
recently developed very high order accuracy numerical method. Time-accurate CFD
data for fourteen flow angles was produced to incorporate into flight simulators
for definition of safe helicopter operating limits (SHOLs). This paper discusses
the flow phenomenology for the different wind directions and where possible
reports on the validation of the ILES results for mean and fluctuating velocity
components and spectra against experimental data
eddy n: eddy flaw
No full texteddy nE is for eddy flaw, / Turn in the breeze, / A contrary puff / That's quick as a sneeze.eddy flawPRINTED ITEM DNE Sup[Add to DNE eddy n: eddy flaw, to 1792 quot]G.M. Story MAY 30 1988 [check] _WK_Used I and SupUsed I and SupUsed Supeddy, eddy flawChecked by Rebecca Nolan on Mon 16 Feb 201
Jurisprudence judiciaire favorable à l'exclusion: Note sous Cass. com., 9 nov. 2022, n° 20-16.454, Cass. com. 9 nov. 2022, n° 21-10.540 et Cass. com. 12 oct. 2022, n° 22-40.013
No full textDans : Sociétés et groupements [chronique], septembre 2022 – août 2023, Eddy Lamazerolles, Professeur, Directeur du DJCE, Université de Poitiers et Anne Rabreau, Professeur, Co-directeur du DJCE, CY Université Cergy Paris.International audienceNote sous :Cass. com., 9 novembre 2022, n° 20-16.454, ECLI:FR:CCASS:2022:CO00647Cass. com. 9 novembre 2022, n° 21-10.540, ECLI:FR:CCASS:2022:CO00662Cass. com. 12 octobre 2022, n° 22-40.013, ECLI:FR:CCASS:2022:CO0069
Large eddy simulation using high-resolution and high-order methods
No full textRestrictions on computing power make direct numerical simulation too expensive
for complex flows; thus, the development of accurate large eddy simulation (LES)
methods, which are industrially applicable and efficient, is required. This
paper reviews recent findings about the leading order dissipation rate
associated with high-resolution methods and improvements to the standard schemes
for use in highly turbulent flows. Results from implicit LES are presented for a
broad range of flows and numerical schemes, ranging from the second-order
monotone upstream-centered schemes for conservation laws to very high-order (up
to ninth-order) weighted essentially non-oscillatory schemes
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