Evaluating large eddy simulation results based on error analysis

Abstract

The quantification of the prediction accuracy in large eddy simulations (LES) is very challenging due to various interacting errors associated with this approach. When dealing with errors in LES using implicit filtering, numerical and modeling errors have drawn the interest of many researchers. Little attention has been paid to other sources of discrepancies between LES results and reference data, namely sampling errors, influence of the initial conditions, improper boundary conditions or uncertainties issuing from reference data. A framework of metrics that includes all these issues is addressed in the present paper to study subgrid-scale (SGS) models for LES and to quantify their prediction accuracy and computational costs. The method is applied to a simple wall-bounded turbulent flow at moderate Reynolds number. It turns out from the results obtained with six commonly used SGS models that wall-adapting models (WALE and SIGMA) and localized dynamic models reproduce the physics of the flow field more faithfully, reveal a superior prediction accuracy and have a similar computational cost than models using van Driest wall damping. Especially at the viscous wall region (r + < 50), wall-adapting and localized dynamic models are more accurate, reflecting the proper near wall behavior of such models. Relying on the analysis of sources of various errors, uncertainties in LES are estimated and systematically assessed, and their influence on simulation results is quantified. Finally, engineering estimations of the required averaging time to obtain basic estimates of statistical quantities with a predetermined degree of accuracy are suggested.

Combustion Characteristics of a Non-Premixed Oxy-Flame Applying a Hybrid Filtered Eulerian Stochastic Field/Flamelet Progress Variable Approach

“…Various models have been suggested in the literature (see [5,7,46]) to close these terms. In the present paper, the SGS stress tensor is postulated following the eddy viscosity approach as:…”

“…8450 cells are used for the fuel pipe jet, with minimum cell size equal to 5.31 × 10 −12 m 3 and maximum cell size located in the outlet region with 1.09 × 10 −10 m 3 . To assess the LES quality, various criteria are available, as reported in [46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65]. In the present paper we adopt the approach proposed by Hanjalic et al in [66] and Pope in [7].…”

The importance of compatible sub-grid scale and spatial discretization models on the simulation of large-scale pool fire

“…K_SGS and S_SGS were used in the pool fire simulation [21,22]. In K_SGS, the turbulent kinetic energy…”

Thermal Decomposition of a Single AdBlue® Droplet Including Wall–Film Formation in Turbulent Cross-Flow in an SCR System

“…Since the turbulent co-and cross-flow features a wall-bounded flow, a Wall-Adapting Local Eddy-Viscosity (WALE) Model [30] is considered appropriate with reasonable computational cost as pointed out in [30][31][32], among others. In which, the term τ SGS ij = u i u j −ũ iũj also called SGS stress tensor is closed as:…”

“…Further, as the LES considered do at least resolve 80% of the instantaneous carrier phase turbulence, the droplet particle dispersion and the fluctuations on the scalars are fairly considered. In LES methodology the state of turbulence at inlet and initial conditions is crucial as reported in many research contributions [23,30,32,33]. Therefore, we follow the method of Nishad et al [23] to provide realistic initial and inlet conditions for LES in the present paper.…”