Large Eddy Simulation Predictions Research Articles

LES of lock-exchange compositional gravity currents: a brief review of some recent results

Three-dimensional 3-D Large eddy simulation (LES) has become a powerful tool to investigate evolution and structure of gravity currents, especially for cases (e.g., high Reynolds number flows, flows with massive separation) where 3-D Direct numerical simulation using non-dissipative viscous solvers is computationally too expensive. In this paper we briefly review some important results obtained based on high-resolution 3-D LES of bottom-propagating compositional Boussinesq currents in lock-exchange configurations. LES was used to provide a detailed description of the structure of the current, to discuss the role of the large-scale coherent structures, and to predict the evolution of the front velocity over the different stages of the current propagation. Three main types of lock-exchange flows are considered: (1) currents with a high volume of release (HVR) and a low volume of release (LVR) propagating in a channel with a smooth horizontal bed; (2) HVR and LVR currents propagating in a horizontal channel containing a porous layer; and (3) currents propagating in a horizontal channel containing an array of bottom obstacles (2-D dunes and ribs). The simulations are performed using non-dissipative numerical algorithms and sub-grid scale models that predict a zero eddy viscosity in regions where the turbulence is negligible. Experimental data is used to validate LES predictions. LES results show that in most cases the evolution of the front velocity is consistent with that predicted based on shallow-flow theory. LES flow fields are then used to estimate important quantities (e.g., bed friction velocity, sediment entrainment capacity) that are very difficult to obtain from experiments and to understand how the structure and evolution of the current change because of the additional drag induced by obstacles present within the channel or at the channel bed. The paper also discusses how the evolution and structure of the current change as the Reynolds number is increased to values that are relevant for gravity currents encountered in geosciences and environmental engineering applications.

Large-Eddy Simulation for Turbulent Heat Transfer

The paper gives an overview of different components of conducting large-eddy simulations (LES) for convective heat transfer in practical applications. Subgrid stress models, wall models, and the generation of inlet turbulent boundary conditions are highlighted. For application to complex high Reynolds number flows, a two-layer LES wall model is used together with a synthetic eddy method (SEM) for generating turbulent inlet conditions for developing flows. Representative results highlighting LES predictions are given in a dimpled fin arrangement relevant to compact heat exchangers, in a simulated leading edge film cooling geometry, and in a developing ribbed duct and 180 deg turn relevant to turbine blade cooling. The use of LES wall modeling with the SEM is shown in an experimental can combustor with swirl, and finally a simulation which combines Reynolds-averaged Navier–Stokes (RANS) with wall modeled LES and SEM to predict combustor linear heat transfer is highlighted. It is shown that the combined use of these techniques can reduce computational time by at least an order of magnitude for developing flows. In all cases, predictions of mean turbulent quantities and heat transfer coefficients compare favorably with experiments.

DNS, LES and RANS of turbulent heat transfer in boundary layer with suddenly changing wall thermal conditions

The objectives of this study are to investigate a thermal field in a turbulent boundary layer with suddenly changing wall thermal conditions by means of direct numerical simulation (DNS), and to evaluate predictions of a turbulence model in such a thermal field, in which DNS of spatially developing boundary layers with heat transfer can be conducted using the generation of turbulent inflow data as a method. In this study, two types of wall thermal condition are investigated using DNS and predicted by large eddy simulation (LES) and Reynolds-averaged Navier–Stokes equation simulation (RANS). In the first case, the velocity boundary layer only develops in the entrance of simulation, and the flat plate is heated from the halfway point, i.e., the adiabatic wall condition is adopted in the entrance, and the entrance region of thermal field in turbulence is simulated. Then, the thermal boundary layer develops along a constant temperature wall followed by adiabatic wall. In the second case, velocity and thermal boundary layers simultaneously develop, and the wall thermal condition is changed from a constant temperature to an adiabatic wall in the downstream region. DNS results clearly show the statistics and structure of turbulent heat transfer in a constant temperature wall followed by an adiabatic wall. In the first case, the entrance region of thermal field in turbulence can be also observed. Thus, both the development and the entrance regions in thermal fields can be explored, and the effects upstream of the thermal field on the adiabatic region are investigated. On the other hand, evaluations of predictions by LES and RANS are conducted using DNS results. The predictions of both LES and RANS almost agree with the DNS results in both cases, but the predicted temperature variances near the wall by RANS give different results as compared with DNS. This is because the dissipation rate of temperature variance is difficult to predict by the present RANS, which is found by the evaluation using DNS results.

A Cumulus Cloud Microphysics Parameterization for Cloud-Resolving Models

Abstract A microphysical parameterization for shallow cumulus and boundary layer stratocumulus clouds has been developed. Similar to the Khairoutdinov and Kogan parameterization for stratocumulus clouds, the new parameterization is based on an explicit microphysical large-eddy simulation (LES) model as a data source and benchmark for comparison. The predictions of the bulk model using the new parameterization were tested in simulations of shallow cumulus and boundary layer stratocumulus clouds; in both cases the new parameterization matched the predictions of the explicit microphysics LES quite accurately. These results show the importance of the choice of the dataset in parameterization development and the need for it to be balanced by realistic dynamic conditions. The strong sensitivity to representation of rain evaporation is also demonstrated. Accurate formulation of this process, tuned for the case of cumulus convection, has substantially improved precision of rain production.

Assessment of stretched vortex subgrid‐scale models for LES of incompressible inhomogeneous turbulent flow

The physical space version of the stretched vortex subgrid scale model [Phys. Fluids 12, 1810 (2000)] is tested in large eddy simulations (LES) of the turbulent lid driven cubic cavity flow. LES is carried out using a higher order finite-difference method [J. Comput. Phys. 229, 8802 (2010)]. The effects of different vortex orientation models and subgrid turbulence spectrums are assessed through comparisons of the LES predictions against direct numerical simulations (DNS) [Phys. Fluids 12, 1363 (2000)]. Three Reynolds numbers 12000, 18000, and 22000 are studied. Good agreement with the DNS data for the mean and fluctuating quantities is observed.

An explicit algebraic model for the subgrid-scale passive scalar flux

AbstractIn Marstorpet al. (J. Fluid Mech., vol. 639, 2009, pp. 403–432), an explicit algebraic subgrid stress model (EASSM) for large-eddy simulation (LES) was proposed, which was shown to considerably improve LES predictions of rotating and non-rotating turbulent channel flow. In this paper, we extend that work and present a new explicit algebraic subgrid scalar flux model (EASSFM) for LES, based on the modelled transport equation of the subgrid-scale (SGS) scalar flux. The new model is derived using the same kind of methodology that leads to the explicit algebraic scalar flux model of Wikströmet al. (Phys. Fluids, vol. 12, 2000, pp. 688–702). The algebraic form is based on a weak equilibrium assumption and leads to a model that depends on the resolved strain-rate and rotation-rate tensors, the resolved scalar-gradient vector and, importantly, the SGS stress tensor. An accurate prediction of the SGS scalar flux is consequently strongly dependent on an accurate description of the SGS stresses. The new EASSFM is therefore primarily used in connection with the EASSM, since this model can accurately predict SGS stresses. The resulting SGS scalar flux is not necessarily aligned with the resolved scalar gradient, and the inherent dependence on the resolved rotation-rate tensor makes the model suitable for LES of rotating flow applications. The new EASSFM (together with the EASSM) is validated for the case of passive scalar transport in a fully developed turbulent channel flow with and without system rotation. LES results with the new model show good agreement with direct numerical simulation data for both cases. The new model predictions are also compared to those of the dynamic eddy diffusivity model (DEDM) and improvements are observed in the prediction of the resolved and SGS scalar quantities. In the non-rotating case, the model performance is studied at all relevant resolutions, showing that its predictions of the Nusselt number are much less dependent on the grid resolution and are more accurate. In channel flow with wall-normal rotation, where all the SGS stresses and fluxes are non-zero, the new model shows significant improvements over the DEDM predictions of the resolved and SGS quantities.

Large-Eddy Simulation of Turbulent Flow with Heat Transfer in a Rod Bundle

To assess the accuracy of large-eddy simulation (LES) predictions for flow without and with heat transfer in a rod bundle, analyses were performed with a constant-coefficient Smagorinsky LES model, and numerical predictions were compared with experimental measurements in a heated triangular rod array. First, flow simulations without heat transfer were performed with one and two channels at the central region of the bundle, and simulation predictions were compared with the experimental data. For the normalized mean axial velocity and the axial component of the turbulent intensity, the predictions of the one-channel model are nearly identical with those of the two-channel model. For the other turbulence parameters, the predictions of the one-channel model are either identical or are mostly in good agreement with those of the two-channel model. LES predictions for the mean axial velocity agree well with experimental measurements. Predictions of the axial component of the turbulent intensity agree well with experimental measurements for most of the points of measurement. Predictions of the other parameters of turbulence agree well to reasonably well with measurements. Because LES simulations are computationally very demanding, the LES simulation of heat transfer was performed only with the one-channel model. LES predicts the temperature of the rod surface within the range of the experimental error. The profile (log law) of the dimensionless fluid temperature T+ predicted by LES has the same slope as that derived from the measurements, but it has a significantly higher constant. The turbulent intensity of temperature is predicted well to reasonably well. The turbulent heat flux in the axial direction and the radial direction is predicted well at points away from the wall, but there is significant discrepancy between predictions and measurements close to the wall. The predicted turbulent heat flux in the azimuthal direction agrees very well to quite well with measurements.

Numerical simulation of convective heat transfer coefficients at the external surfaces of building arrays immersed in a turbulent boundary layer

The convective heat transfer is an important component in the total energy balance for arrays of buildings immersed in a turbulent boundary layer. This study examines convective heat transfer coefficients (CHTC) at the external windward, leeward, lateral and top surfaces of buildings. This study uses Large Eddy Simulations (LES) with Smagorinsky–Lily model to predict CHTC and then compares the simulation results with experimental data. In addition, steady RANS including the realizable k–ε and the shear stress transport k–ω turbulence models are also validated with the experimental data. However, both of these RANS models overestimated CHTC values for arrays of buildings in contrast to LES predictions. Regular arrays of cubic buildings are modeled to investigate CHTC in an urban environment, which are arranged according to different plan area densities (λp=0.44, 0.25, 0.16, 0.11, 0.063 and 0.04). This morphological parameter (λp) represents different urban neighborhoods and it is used to characterize different flow regimes in an urban environment. The CHTC distributions are independent of the Reynolds number based on different incoming wind velocities at a height of 10m above the ground (U10) for windward, leeward, lateral and top building surfaces. Furthermore, CHTC distributions for different λp and U10=5m/s are compared with flow characteristics in building arrays. Finally, the CHTC correlations as a function of λp and U10 were obtained, where λp varies from 0.04 to 0.25 and the Reynolds number ranges from 7×105 to 5×106. With the increase of the plan area densities from 0.04 to 0.25, CHTCs increases 15% for the leeward surface and decreases 16% for the lateral surfaces. Consequently, a total energy balance and the energy consumption predictions for a building need to take into account the urban density of the building surroundings.

Large-Eddy Simulations of a Cylindrical Film Cooling Hole

Large-eddy simulations are used to explore the unsteady jet-in-crossflow interactions arising from discrete hole film cooling from a cylindrical hole. The numerical grids are created using GridPro and solved in OpenFOAM. A recycling-rescaling technique is used to generate a realistic turbulent incoming boundary layer upstream of injection. The simulations match the conditions of an experiment in the open literature for the robust validation of the numerical solution and turbulence modeling. The current study tests the ability of large-eddy simulations in predicting film cooling flows using detailed experimental measurements. The large-eddy simulation results compared favorably with the experimental data except in areas close to the injection site and close to the wall. Grid resolution is discussed in terms of the percent turbulent kinetic energy resolved and related to the success of the large eddy simulation predictions in different regions of the jet. No substantial benefit was seen by using a dynamic Smagorinsky model for the subgrid turbulent heat fluxes instead of a constant subgrid Prandtl number. The trajectories, spreading rates, and large turbulent structures of the jet are discussed in terms of the hydrodynamic parameters such as velocity ratio and momentum ratio.

Numerical prediction of turbulent flows using Reynolds‐averaged Navier–Stokes and large‐eddy simulation with uncertain inflow conditions

SUMMARYNumerous comparisons between Reynolds‐averaged Navier–Stokes (RANS) and large‐eddy simulation (LES) modeling have already been performed for a large variety of turbulent flows in the context of fully deterministic flows, that is, with fixed flow and model parameters. More recently, RANS and LES have been separately assessed in conjunction with stochastic flow and/or model parameters. The present paper performs a comparison of the RANS k − ε model and the LES dynamic Smagorinsky model for turbulent flow in a pipe geometry subject to uncertain inflow conditions. The influence of the experimental uncertainties on the computed flow is analyzed using a non‐intrusive polynomial chaos approach for two flow configurations (with or without swirl). Measured quantities including an estimation of the measurement error are then compared with the statistical representation (mean value and variance) of their RANS and LES numerical approximations in order to check whether experiment/simulation discrepancies can be explained within the uncertainty inherent to the studied configuration. The statistics of the RANS prediction are found in poor agreement with experimental results when the flow is characterized by a strong swirl, whereas the computationally more expensive LES prediction remains statistically well inside the measurement intervals for the key flow quantities.Copyright © 2012 John Wiley & Sons, Ltd.

Large Eddy Simulations of Supersonic Impinging Jets

Supersonic impinging jet flow fields contain self-sustaining acoustic feedback features that create high levels of tonal noise. These types of flow fields are typically found with short takeoff and landing military aircraft as well as jet blast deflector operations on aircraft carrier decks. The United States Navy has a goal to reduce the noise generated by these impinging jet configurations and is investing in computational aeroacoustics to aid in the development of noise reduction concepts. In this paper, implicit large eddy simulation (LES) of impinging jet flow fields are coupled with a far-field acoustic transformation using the Ffowcs Williams and Hawkings (FW-H) equation method. The LES solves the noise generating regions of the flow and the FW-H transformation is used to predict the far-field noise. The noise prediction methodology is applied to a Mach 1.5 vertically impinging jet at a stand-off distance of five nozzle throat diameters. Both the LES and FW-H acoustic predictions compare favorably with experimental measurements. Time averaged and instantaneous flow fields are shown. A calculation performed previously at a stand-off distance of four nozzle throat diameters is revisited with adjustments to the methodology including a new grid, time integrator, and longer simulation runtime. The calculation exhibited various feedback loops which were not present before and can be attributed to an explicit time marching scheme. In addition, an instability analysis of the heated jets at both stand-off distances is performed. Tonal frequencies and instability modes are identified for the sample problems.

LES and RANS simulations of cryogenic liquid nitrogen jets

Turbulent flows of liquid nitrogen jets at near-critical and supercritical pressures are investigated by turbulence models (RANS) and a large eddy simulation (LES). To consider real-fluid effects, two real-fluid equations of state (EOS) are implemented into the numerical procedure and the normalized static enthalpy is introduced to describe the turbulent mixing under supercritical conditions. The pressure–velocity–density coupling is obtained by the modified PISO algorithm. The relative performance of six convection schemes and the predictions of four turbulence models for the different EOSs are compared with the available data. From the results, the suitable adoption of real-fluid EOS is more significant than the selection of turbulence model for the numerical performance. Additionally, the effects of SGS models are examined for the LES predictions using the different EOSs. The importance of real-fluid EOS is similarly found in the LES results. The coherent structures are strongly dependent on the different EOSs than SGS models. The results display that the selected RANS models need to be extended for supercritical fluid flows. Finally, the effects of turbulence models and SGS models on the jet spreading rate are discussed.

Calibration of a new very large eddy simulation (VLES) methodology for turbulent flow simulation

Following the idea of Speziale's Very Large Eddy Simulation (VLES) method, a new unified hybrid simulation approach was proposed which can change seamlessly from RANS (Reynolds-Averaged Navier-Stokes) to LES (Large Eddy Simulation) method depending on the numerical resolution. The model constants were calibrated in accordance with other hybrid methods. Besides being able to approach the two limits of RANS and LES, the new model also provides a proper VLES mode between the two limits, and thus can be used for a wide range of mesh resolutions. Also RANS simulation can be recovered near the wall which is similar to the Detached Eddy Simulation (DES) concept. This new methodology was implemented into Wilcox's k-omega model and applications were conducted for fully developed turbulent channel flow at Re (tau) = 395 and turbulent flow past a square cylinder at Re = 22000. Results were compared with LES predictions and other studies. The new method is found to be quite efficient in resolving large flow structures, and can predict satisfactory results on relative coarse mesh.

LES prediction of space-time correlations in turbulent shear flows

We compare the space-time correlations calculated from direct numerical simulation (DNS) and large-eddy simulation (LES) of turbulent channel flows. It is found from the comparisons that the LES with an eddy-viscosity sub-grid scale (SGS) model over-predicts the space-time correlations than the DNS. The overpredictions are further quantified by the integral scales of directional correlations and convection velocities. A physical argument for the overprediction is provided that the eddy-viscosity SGS model alone does not includes the backscatter effects although it correctly represents the energy dissipations of SGS motions. This argument is confirmed by the recently developed elliptic model for space-time correlations in turbulent shear flows. It suggests that enstrophy is crucial to the LES prediction of space-time correlations. The random forcing models and stochastic SGS models are proposed to overcome the overpredictions on space-time correlations.

Effects of free-stream turbulence on high pressure turbine blade heat transfer predicted by structured and unstructured LES

Recent developments and demonstrations for the prediction of turbulent flows around blades point to Large Eddy Simulations (LES) as a very promising tool. Indeed and despite the fact that this numerical method still requires modeling and intense computing effort compared to Reynolds Average Navier–Stokes (RANS), this fully unsteady simulation technique provides valuable information on the turbulent flow otherwise inaccessible. Theoretical limits and scales of wall bounded flows are now well mastered in simple cases but complex industrial applications usually introduce unknowns and mechanisms that are difficult to apprehend beforehand especially with LES which is usually computationally intensive and bounded to code scalability, mesh quality, modeling performances and computer power. In this specific context, few studies directly address the use of fully structured versus unstructured, implicit versus explicit flow solvers and their respective impact for LES modeling of complex wall bounded flows. To partly address these important issues, two dedicated structured and unstructured computational solvers are applied and assessed by comparing the predictions of the heat transfer around the experimental high pressure turbine blade profile cascade of Arts et al. [6]. First, both LES predictions are compared to RANS modeling with a particular interest for the accuracy/cost ratio and improvement of the physical phenomena around the blade. LES’s are then detailed and further investigated to assess their ability to reproduce the inlet turbulence effect on heat transfer and the development of the transitioning boundary layer around the blade. Quantitative comparisons against experimental findings show excellent agreement especially on the pressure side of the profile. Detailed analysis of the flow predictions provided by both the structured and unstructured solvers underline the importance of long stream-wise streaky structures responsible for the augmentation of the heat transfer and leading to the transition of the suction-side boundary layer.

Assessing the predictive capabilities of isotropic, eddy viscosity Reynolds‐averaged turbulence models in a natural‐like meandering channel

The predictive capabilities of an isotropic, eddy viscosity turbulence model for closing the unsteady Reynolds‐averaged Navier‐Stokes (RANS) equations are systematically investigated by simulating turbulent flow through a field‐scale meandering channel and comparing the computed results with the large‐eddy simulation (LES) of the same flow recently reported by Kang and Sotiropoulos (2011). To facilitate the comparison of the two turbulence models, both RANS simulation and LES are carried on exactly the same grid with the same numerical method. The comparisons show that while the RANS model captures the curvature‐driven secondary flow within the bend, it fails completely to predict other key flow features in the channel, which are predicted by the LES and also observed in flow visualization experiments. These features include the inner and outer bank shear layers, the outer bank secondary cell, and the inner bank horizontal recirculation zone. By analyzing the results of the LES, we conclusively show that flow features not predicted by the RANS calculation are located in regions of the flow with high levels of turbulence anisotropy. The extent of these regions and, consequently, the degree of disagreement between the RANS and LES predictions are shown to depend on the stream geometry and the flow rate. Our results underscore the major challenges confronting the computationally expedient, isotropic RANS models, which are widely used today in three‐dimensional hydrodynamic and morphodynamic simulations.

The Role of the Combustion Submodel for Large Eddy Simulation of Transient Premixed Flame-Vortex Interactions in Gas Explosions

In this paper, the sensitivity of large eddy simulation (LES) to the presence of the combustion submodel was investigated for transient interactions between premixed flame fronts and toroidal vortex structures generated at the wake of a circular orifice. To this end, LES computations were run, with and without the combustion submodel, for two orifice diameters: 40 mm and 20 mm. Nonuniform unstructured grids with a cell characteristic length varying in the range of 0.5-1 mm were used. In going from the 40-mm orifice to the 20-mm orifice, both the size and velocity of the vortex increase, leading to a different regime of interaction with the flame: the vortex only wrinkles the flame front in the 40-mm case (wrinkled regime) and also disrupts the continuity of the front, giving rise to the formation of separate reaction zones (i.e., flame pockets that leave the main front), in the 20-mm case (breakthrough regime). It has been found that the impact of the combustion submodel on LES predictions is strongly dependent on the regime of interaction. Results for the 40-mm orifice are substantially the same, regardless of the presence of the combustion submodel. Conversely, at the wake of the 20-mm orifice, the intensity of the flame-vortex interaction is such that the combustion submodel is strictly needed to reproduce both the qualitative (evolution of the pockets formed and their interaction with the main front) and quantitative (flame speed) characteristics of the flame propagation correctly.

Numerical Investigations of Passive Scalar Transport in Turbulent Taylor-Couette Flows: Large Eddy Simulation Versus Direct Numerical Simulations

The highly turbulent flow occurring inside (electro)chemical reactors requires accurate simulation of scalar mixing if computational fluid dynamics (CFD) methods are to be used with confidence in design. This has motivated the present paper, which describes the implementation of a passive scalar transport equation into a hybrid spectral/finite-element code. Direct numerical simulations (DNS) and large eddy simulation (LES) were performed to study the effects of gravitational and centrifugal potentials on the stability of incom-pressible Taylor-Couette flow. The flow is confined between two concentric cylinders with an inner rotating cylinder while the outer one is at rest. The Navier-Stokes equations with the uncoupled convection–diffusion–reaction (CDR) equation are solved using a code named spectral/finite element large eddy simulations (SFELES) which is based on spectral development in one direction combined with a finite element discretization in the remaining directions. The performance of the LES code is validated with published DNS data for channel flow. Velocity and scalar statistics showed good agreement between the current LES predictions and DNS data. Special attention was given to the flow field, in the vicinity of Reynolds number of 68.2 with radii ratio of 0.5. The effect of Sc on the concentration peak is pointed out while the magnitude of heat transfer shows a dependence of the Prandtl number with an exponent of 0.375.

LES of turbulent wind and gas dispersion in a city

We have conducted LES (large eddy simulation) for turbulent wind flows and dispersion of hazardous gas emitted from a point source on the ground in a large city, Tokyo. Also, for numerical validation, wind tunnel tests using a Dynamic Particle Image Velocimetry (DPIV) and tracer gas measurement system are performed to estimate turbulence statistics of wind and gas concentration in between the compacted tall buildings. We elucidate the predictive accuracy of LES based on the wind tunnel test data. Finally, we discuss the meaning and the potential of LES prediction for dispersion problems in a complex urban area, taking into consideration the limitation of the predicted results by Reynolds Averaged Navier–Stokes (RANS) modeling.

Explicit filtering to obtain grid-spacing-independent and discretization-order-independent large-eddy simulation of compressible single-phase flow

AbstractIn large-eddy simulation (LES), it is often assumed that the filter width is equal to the grid spacing. Predictions from such LES are grid-spacing dependent since any subgrid-scale (SGS) model used in the LES equations is dependent on the resolved flow field which itself varies with grid spacing. Moreover, numerical errors affect the flow field, especially the smallest resolved scales. Thus, predictions using this approach are affected by both modelling and numerical choices. However, grid-spacing-independent LES predictions unaffected by numerical choices are necessary to validate LES models through comparison with a trusted template. First, such a template is created here through direct numerical simulation (DNS). Then, simulations are conducted using the conventional LES equations and also LES equations which are here reformulated so that the small-scale-producing nonlinear terms in these equations are explicitly filtered (EF) to remove scales smaller than a fixed filter width; this formulation is called EFLES. First, LES is conducted with four SGS models, then EFLES is performed with two of the SGS models used in LES; the results from all these simulations are compared to those from DNS and from the filtered DNS (FDNS). The conventional LES solution is both grid-spacing and spatial discretization-order dependent, thus showing that both of these numerical aspects affect the flow prediction. The solution from the EFLES equations is grid independent for a high-order spatial discretization on all meshes tested. However, low-order discretizations require a finer mesh to reach grid independence. With an eighth-order discretization, a filter-width to grid-spacing ratio of two is sufficient to reach grid independence, while a filter-width to grid-spacing ratio of four is needed to reach grid independence when a fourth- or a sixth-order discretization is employed. On a grid fine enough to be utilized in a DNS, the EFLES solution exhibits grid independence and does not converge to the DNS solution. The velocity-fluctuation spectra of EFLES follow those of FDNS independent of the grid spacing used, in concert with the original concept of LES. The reasons for the different predictions of conventional LES or EFLES according to the SGS model used, and the different characteristics of the EFLES predictions compared to those from conventional LES are analysed.