562 research outputs found
High fidelity numerical simulations of ship and sub-marine hydrodynamics
This paper discusses the use of wall-modeled LES and hybrid RANS-LES models for the prediction of ship and submarine flows. Results from applied cases are discussed to il-lustrate the use of these methods for practical problems as well as the differences between methods. The paper then discusses the underlying theories and assumptions of wall-modeled LES and hybrid RANS-LES models. The focus of this presentation is on wall-modeled LES as these methods are theoretically more well-founded than hybrid RANS-LES models. Re-sults from both canonical and building block flows are then presented and discussed in order to provide a more firm and practical foundation for the recommendations for applied use that are provided in the final concluding remarks section
Inlet conditions for LES using mapping and feedback control
Copyright © 2009 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Computers and Fluids. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Computers and Fluids, Volume 38 Issue 6 (2009), DOI: 10.1016/j.compfluid.2009.02.001Generating effective and efficient inlet boundary conditions for large eddy simulation (LES) is a challenging problem. The most accurate way of achieving this is to run a precursor calculation to generate a library of turbulence, either prior to the simulation or concurrently with it, and to transfer the data from the library simulation to the main domain inlet. In this paper, we investigate a variant of this, in which the precursor calculation is subsumed into the main domain, its function being adopted by a mapping of data from a specified plane downstream of the inlet back to the inlet. Within this inlet section of the main domain, the flow can be affected by a number of computational manipulations, including the introduction of artificial body forces, modification of the mapped data, and direct correction of the velocity data. These modifications can be linked to feedback control algorithms to drive the solution towards specified characteristics, including mean and turbulent flow profiles, and bulk properties of the flow such as swirl. Various variants of the basic technique incorporating different levels of complexity in the control are implemented and tested on simulation of flow in a rectangular channel and in a circular pipe
Large Eddy Simulations of Fully-Developed Turbulent Pipe Flows At Moderate-To-High Reynolds Numbers
Despite the high relevance of wall-bounded turbulence for engineering and
natural science applications, many aspects of the underlying physics are still
unclear. In particular, at high Re close to many real-life scenarios, the true
nature of the flow is partially masked by the inability of numerical
simulations to resolve all turbulent scales adequately. To overcome this issue,
we aim to numerically investigate fully-developed turbulent pipe flows at
moderate-to-high Re (), employing LES. A grid
convergence study, using the WALE subgrid stress model, is presented for
. Additionally, the prediction accuracy of distinct subgrid-scale
stress models, such as WALE, SMG, OEEVM, LDKM, and DSEM, is examined using a
range of statistical measures. The results infer, as expected, that SMG and
OEEVM are too dissipative, whereas WALE, LDKM, and, more surprisingly, DSEM
perform rather well compared to experiments and results from DNS. Moreover, LES
utilizing WALE are performed and investigated in detail for six different
Reynolds numbers in the interval from to with gradually
refined grids. These computations allow an insight into what turbulence
information is retained when LES with a wall model is applied to such high
Reynolds numbers in the limit of a relatively coarse grid. Second-order
statistics for all values of exhibited excellent agreement with the
DNS data in the outer region. Surprisingly, results also revealed a dramatic
deviation from the DNS data in the sub-viscous layer region irrespective of the
, attributed to the considered scaling for mesh refinement. Overall,
the WALE model enabled accurate numerical simulations of high-Reynolds-number
wall-bounded flows at a fraction of the cost incurred if the inner layer was
temporally and spatially resolved
Industrigolv.
This paper deals with cracking in industrial concrete floars. We have restricted us to study two special cases, that is, eraeks developed by the load itself and eraeks due to shrinkage. We have of course also studied the deformation effects of the load. The effect of the load has here been studied thoroughly by two separate methods, Winklerfoundation and the more exact Elastic halfspace theory. We have also studied effects eaused by two separate loads at a distance. The shrinkage is dealt with in accordonance with a paper from Buö (11) who has studied this problem extensivly. Our purpose has been to establish designing aids for this type of pavements. These are quite extensive and are based on the regulations for concrete structures BBK 79
A Fluid-Dynamical Subgrid Scale Model for Highly Compressible Astrophysical Turbulence
We formulate and implement the Euler equations with SGS dynamics and provide
numerical tests of an SGS turbulence energy model that predicts the turbulent
pressure of unresolved velocity fluctuations and the rate of dissipation for
highly compressible turbulence. We test closures for the turbulence energy
cascade by filtering data from high-resolution simulations of forced isothermal
and adiabatic turbulence. Optimal properties and an excellent correlation are
found for a linear combination of the eddy-viscosity closure that is employed
in LES of weakly compressible turbulence and a term that is non-linear in the
Jacobian matrix of the velocity. Using this mixed closure, the SGS turbulence
energy model is validated in LES of turbulence with stochastic forcing. It is
found that the SGS model satisfies several important requirements: 1. The mean
SGS turbulence energy follows a power law for varying grid scale. 2. The root
mean square (RMS) Mach number of the unresolved velocity fluctuations is
proportional to the RMS Mach number of the resolved turbulence, independent of
the forcing. 3. The rate of dissipation and the turbulence energy flux are
constant. Moreover, we discuss difficulties with direct estimates of the
turbulent pressure and the dissipation rate on the basis of resolved flow
quantities that have recently been proposed. In combination with the energy
injection by stellar feedback and other unresolved processes, the proposed SGS
model is applicable to a variety of problems in computational astrophysics.
Computing the SGS turbulence energy, the treatment of star formation and
stellar feedback in galaxy simulations can be improved. Further, we expect that
the turbulent pressure on the grid scale affects the stability of gas against
gravitational collapse.Comment: 19 pages, 16 figures, submitted to A&
LARGE EDDY SIMULATION OF A FORWARD-BACKWARD FACING STEP FOR ACOUSTIC SOURCE IDENTIFICATION
The feasibility of using a commercial CFD code for large eddy simulation (LES) is investigated. A first test on homogeneous turbulence decay allows a fine-tuning of the eddy viscosity with respect to the numerical features of the code. Then, a flow over forward–backward facing step at Reynolds number Reh 1:7 105 is computed. The results found show good agreement with the new LDA data of Leclercq et al. [Forward backward facing step pair: aerodynamic flow, wall pressure and acoustic characterization. AIAA-2001-2249]. The acoustic source term, recorded from the LES and to be fed into a following acoustic propagation simulation, is found to be largest in the separation from the forward step. The source terms structures are similar to the vortical structures generated at the front edge of the obstacle and advected downstream. Structures generated from the backward step rapidly break down into smaller scale structures due to the background turbulence
Study of the influence of the inlet boundary conditions in a LES simulation of internal flow in a diesel injector
In this paper the study of the behavior of the fuel flow through the injector nozzle using CFD tools is presented. Large Eddy Simulation will be used to model the internal flow turbulence in a Diesel fuel injector with velocities over 500 m/s. More specifically, the influence of boundary conditions applied to the model will be studied. The article analyzes the influence of the inlet boundary condition upon activation and maintenance of turbulent flow during the calculation. Carefully assessing which inlet boundary condition is more trustworthy in reality, for this the outlet velocity, pressure, turbulence and level of stabilization will be studied.This work has been funded by UNIVERSIDAD POLITECNICA DE VALENCIA from Spain, in the framework of the project "ESTUDIO DE LA INFLUENCIA DEL LEVANTAMIENTO DE AGUJA EN EL PROCESO DE INYECCION DIESEL'', Reference No. PAID-06-10-2362.Payri MarĂn, R.; Gimeno GarcĂa, J.; Marti Aldaravi, P.; Bracho LeĂłn, GC. (2013). Study of the influence of the inlet boundary conditions in a LES simulation of internal flow in a diesel injector. Mathematical and Computer Modelling. 57(7-8):1709-1715. https://doi.org/10.1016/j.mcm.2011.11.019S17091715577-
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