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J. Hoffman 《国际流体数值方法杂志》2009,59(11):1241-1258
General Galerkin (G2) is a new computational method for turbulent flow, where a stabilized Galerkin finite element method is used to compute approximate weak solutions to the Navier–Stokes equations directly, without any filtering of the equations as in a standard approach to turbulence simulation, such as large eddy simulation, and thus no Reynolds stresses are introduced, which need modelling. In this paper, G2 is used to compute the drag coefficient cD for the flow past a circular cylinder at Reynolds number Re=3900, for which the flow is turbulent. It is found that it is possible to approximate cD to an accuracy of a few percent, corresponding to the accuracy in experimental results for this problem, using less than 105 mesh points, which makes the simulations possible using a standard PC. The mesh is adaptively refined until a stopping criterion is reached with respect to the error in a chosen output of interest, which in this paper is cD. Both the stopping criterion and the mesh‐refinement strategy are based on a posteriori error estimates, in the form of a space–time integral of residuals times derivatives of the solution of a dual problem, linearized at the approximate solution, and with data coupling to the output of interest. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
23.
Direct or large eddy simulation of a turbulent flow field is strongly influenced by its initial or inflow boundary condition. This paper presents a new stochastic approach to generate an artificial turbulent velocity field for initial or inflow boundary condition based on digital filtering. Each velocity component of the artificial turbulent velocity field is generated by linear combination of individual uncorrelated random fields. These uncorrelated random fields are obtained by filtering random white‐noise fields. Using common elements in these linear combinations results in multi‐correlation among different velocity components. The generated velocity field reproduces locally desired Reynolds stress components and integral length scales including cross‐integral length scales. The method appears to be simple, flexible and more accurate in comparison with previously developed methods. The accuracy and performance of the method are demonstrated by numerical simulation of a homogeneous turbulent shear flow with high and low shear rates. To assess the accuracy and performance of the method, simulation results are compared with a reference simulation. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
24.
This paper describes the first steps in the development of a large eddy simulation (LES) code able to compute combustion instabilities
in gas turbines. This code was used to compute the forcing of an experimentally investigated premixed dump combustor. It is
shown that the main effect of acoustic waves entering the combustion chamber is to create large vortices and unsteady heat
release when these vortices burn. Another effect of waves entering the combustor is to modulate the fuel and air flow rates
produced by the feeding lines. In this case the equivalence ratio of the mixture entering the combustor may also vary. This
was investigated in a “chemical effect” simulation where the inlet equivalence ratio fluctuates but the total flow rate remains
constant. For perturbations from stoichiometric burning, this mechanism was shown to induce less destabilizing effects than
the purely aerodynamical mechanism due to vortex formation and combustion. It is shown that the LES methodology developed
is able to reproduce the experimentally observed phase shift between acoustic excitation and total reaction rate in the chamber.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
25.
The interaction of turbulence, temperature fluctuation, liquid fuel transport, mixing and evaporation is studied by using
Large Eddy Simulations (LES). To assess the accuracy of the different components of the methods we consider first isothermal,
single phase flow in a straight duct. The results using different numerical methods incorporating dynamic Sub-Grid-Scale (SGS)
models are compared with DNS and experimental data. The effects of the interactions among turbulence, temperature fluctuation,
spray transport, evaporation and mixing of the gaseous fuel are studied by using different assumptions on the temperature
field. It has been found that there are strong non-linear interactions among temperature-fluctuation, evaporation and turbulent
mixing which require additional modeling if not full LES is used. The developed models and methods have been applied to a
gas turbine burner into which liquid fuel is injected. The dispersion of the droplets in the burner is described.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
26.
A high-temperature turbulent jet in a cold crossflow is investigated with the help of two scale-resolving simulation approaches. This work aims at improving the methodologies used to predict the thermal footprint of exhaust gases issuing from helicopter engines onto the fuselage. Specific attention is brought to the capability of scale resolving simulations to correctly reproduce flow dynamics and turbulent mixing. Mean flow features, turbulent quantities and temperature fields are compared and validated against wind tunnel test measurements. In addition, the present work highlights the importance of synthetic turbulence injection at pipe inlet to obtain a fair prediction of both flow dynamics and temperature field. 相似文献
27.
Large-Eddy Simulation is performed for a single day from the Cooperative Atmosphere-Surface Exchange Study (CASES-99) field program. This study investigates an observed case of evening transition boundary layer over land. Parameters of the ambient atmosphere in the LES-decay studies conducted so far were typically prescribed in an idealized form. To provide suitable data under the wide range of the PBL weather conditions, the LES should be able to adequately reproduce the PBL turbulence dynamics including–if possible–baroclinicity, radiation, large scale advection and not only be related to a decreasing surface heating. In addition LES-decay studies usually assume that the sensible heat flux decreases instantaneously or with a very short time scale. The main purpose of this investigation is to study the decay of boundary-layer average turbulent kinetic energy at sunset with Large-Eddy Simulation that is forced with realistic environment conditions. This allows investigating the Turbulent Kinetic Energy decay over the realistic time scale that is observed in the atmosphere. During the intermediate and last stage of decay of the boundary-layer average Turbulent Kinetic Energy the exponents of the decay power law t−n go from 2 to 6, as evidenced by experimental results and recent analytical modeling in the surface layer. 相似文献
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David K Bisset 《国际流体数值方法杂志》2002,39(10):961-977
Turbulent flow simulation methods based on finite differences are attractive for their simplicity, flexibility and efficiency, but not always for accuracy or stability. This paper demonstrates that a good compromise is possible with the advected grid explicit (AGE) method. Starting from the same initial field as a previous spectral DNS, AGE method simulations of a planar turbulent wake were carried out as DNS, and then at three levels of reduced resolution. The latter cases were in a sense large‐eddy simulations (LES), although no specific sub‐grid‐scale model was used. Results for the two DNS methods, including variances and power spectra, were very similar, but the AGE simulation required much less computational effort. Small‐scale information was lost in the reduced resolution runs, but large‐scale mean and instantaneous properties were reproduced quite well, with further large reductions in computational effort. Quality of results becomes more sensitive to the value chosen for one of the AGE method parameters as resolution is reduced, from which it is inferred that the numerical stability procedure controlled by the parameter is acting in part as a sub‐grid‐scale model. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献