scholarly journals Analysis and Modelling of the Commutation Error

Fluids ◽  
2020 ◽  
Vol 6 (1) ◽  
pp. 15
Author(s):  
Markus Klein ◽  
Massimo Germano
Keyword(s):  
Channel Flow ◽  
A Priori ◽  
Dynamic Modelling ◽  
Turbulent Channel Flow ◽  
First Order ◽  
Scale Similarity ◽  
Germano Identity ◽  
A Priori Analysis ◽  
Filtering Approach ◽  
Modelling Approach

A multiscale dynamic analysis of the commutation error, based on the filtering approach is performed. The similarity multiscale hypothesis proposed by Bardina (1983) and extended by Geurts and Holm (2006) to the commutation error is examined in detail and an extension of the Germano identity to the analysis and the modelling of the commutation error is proposed. For a detailed analysis under controlled condition the method is first applied to synthetic turbulence and subsequently to the a-priori analysis of a turbulent channel flow at Reτ=590. The results illustrate the flexibility of the dynamic modelling approach. Combined with a scale similarity assumption for the commutation error very satisfactory results have been obtained for first order derivatives and reasonable results for second order derivatives. In all cases the modelling of the commutation error resulted in smaller errors than the error obtained by neglecting the commutation error.

Subgrid Scale Modeling of Turbulence for the Dynamic Procedure Using Finite Difference Method and Its Assessment on the Thermally Stratified Turbulent Channel Flow

2005 ◽  
Vol 73 (3) ◽  
pp. 382-390 ◽  
Author(s):  
Makoto Tsubokura
Keyword(s):  
Heat Flux ◽  
Finite Difference ◽  
Channel Flow ◽  
A Priori ◽  
Turbulent Channel Flow ◽  
Eddy Diffusivity ◽  
Subgrid Scale ◽  
Eddy Simulation ◽  
Scale Modeling ◽  
Subgrid Scale Modeling

Previously proposed methods for subgrid-scale (SGS) stress modeling were re-investigated and extended to SGS heat-flux modeling, and various anisotropic and isotropic eddy viscosity/diffusivity models were obtained. On the assumption that they are used in a finite-difference (FD) simulation, the models were constructed in such a way that they are insensitive to numerical parameters on which calculated flows are strongly dependent in the conventional Smagorinsky model. The models obtained, as well as those previously proposed, were evaluated a priori in a stably stratified open channel flow, which is considered to be a challenging application of large eddy simulation and suitable for testing both SGS stress and heat-flux models. The most important feature of the models proposed is that they are insensitive to the discretized test filtering parameter required in the dynamic procedure of Germano et al. (1991, Phys. Fluids, 3, pp. 1760–1765) in FD simulation. We also found in SGS heat-flux modeling that the effect of the grid (resolved)-scale (GS) velocity gradient plays an important role in the estimation of the streamwise heat flux, and an isotropic eddy diffusivity model with the effect of the GS velocity is proposed.

scholarly journals Prediction of Combustion and Heat Release Rates in Non-Premixed Syngas Jet Flames Using Finite-Rate Scale Similarity Based Combustion Models

Energies ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 2464 ◽  
Author(s):  
Ali Shamooni ◽  
Alberto Cuoci ◽  
Tiziano Faravelli ◽  
Amsini Sadiki
Keyword(s):  
Heat Release ◽  
A Priori ◽  
Local Extinction ◽  
Release Rates ◽  
Finite Rate ◽  
Jet Flame ◽  
Flame Instability ◽  
Combustion Models ◽  
Scale Similarity ◽  
Filtering Approach

Generating energy from combustion is prone to pollutant formation. In energy systems working under non-premixed combustion mode, rapid mixing is required to increase the heat release rates. However, local extinction and re-ignition may occur, resulting from strong turbulence–chemistry interaction, especially when rates of mixing exceed combustion rates, causing harmful emissions and flame instability. Since the physical mechanisms for such processes are not well understood, there are not yet combustion models in large eddy simulation (LES) context capable of accurately predicting them. In the present study, finite-rate scale similarity (SS) combustion models were applied to evaluate both heat release and combustion rates. The performance of three SS models was a priori assessed based on the direct numerical simulation of a temporally evolving syngas jet flame experiencing high level of local extinction and re-ignition. The results show that SS models following the Bardina’s “grid filtering” approach (A and B) have lower errors than the model based on the Germano’s “test filtering” approach (C), in terms of mean, root mean square (RMS), and local errors. In mean, both Bardina’s based models capture well the filtered combustion and heat release rates. Locally, Model A captures better major species, while Model B retrieves radicals more accurately.

scholarly journals Dynamic slip wall model for large-eddy simulation

2018 ◽  
Vol 859 ◽  
pp. 400-432 ◽  
Author(s):  
Hyunji Jane Bae ◽  
Adrián Lozano-Durán ◽  
Sanjeeb T. Bose ◽  
Parviz Moin
Keyword(s):  
Boundary Layer ◽  
Boundary Condition ◽  
Channel Flow ◽  
A Priori ◽  
Wall Stress ◽  
Turbulent Channel Flow ◽  
Slip Boundary Condition ◽  
Wall Model ◽  
Slip Boundary ◽  
Eddy Simulation

Wall modelling in large-eddy simulation (LES) is necessary to overcome the prohibitive near-wall resolution requirements in high-Reynolds-number turbulent flows. Most existing wall models rely on assumptions about the state of the boundary layer and require a priori prescription of tunable coefficients. They also impose the predicted wall stress by replacing the no-slip boundary condition at the wall with a Neumann boundary condition in the wall-parallel directions while maintaining the no-transpiration condition in the wall-normal direction. In the present study, we first motivate and analyse the Robin (slip) boundary condition with transpiration (non-zero wall-normal velocity) in the context of wall-modelled LES. The effect of the slip boundary condition on the one-point statistics of the flow is investigated in LES of turbulent channel flow and a flat-plate turbulent boundary layer. It is shown that the slip condition provides a framework to compensate for the deficit or excess of mean momentum at the wall. Moreover, the resulting non-zero stress at the wall alleviates the well-known problem of the wall-stress under-estimation by current subgrid-scale (SGS) models (Jiménez & Moser, AIAA J., vol. 38 (4), 2000, pp. 605–612). Second, we discuss the requirements for the slip condition to be used in conjunction with wall models and derive the equation that connects the slip boundary condition with the stress at the wall. Finally, a dynamic procedure for the slip coefficients is formulated, providing a dynamic slip wall model free of a priori specified coefficients. The performance of the proposed dynamic wall model is tested in a series of LES of turbulent channel flow at varying Reynolds numbers, non-equilibrium three-dimensional transient channel flow and a zero-pressure-gradient flat-plate turbulent boundary layer. The results show that the dynamic wall model is able to accurately predict one-point turbulence statistics for various flow configurations, Reynolds numbers and grid resolutions.

Subgrid Scale Modeling of Turbulence for the Dynamic Procedure Using FDM and Its Assessment on the Thermally Stratified Turbulent Channel Flow

2003 ◽  
Author(s):  
Makoto Tsubokura
Keyword(s):  
Heat Flux ◽  
Channel Flow ◽  
A Priori ◽  
Turbulent Channel Flow ◽  
Eddy Diffusivity ◽  
Subgrid Scale ◽  
Scale Modeling ◽  
Flux Model ◽  
Subgrid Scale Modeling ◽  
Heat Flux Model

The objective of this study is to develop the SGS stress and heat-flux models that are suitable for the dynamic procedure using FDM. The models are derived with taking the consistency of the numerical error in the procedure under consideration [1]. They are assessed a priori using the DNS data of the stably stratified turbulent channel flow. It was found that for the SGS heat-flux modeling, effect of the GS velocity gradient plays an important role for the estimation of especially the streamwise heat-flux. Therefore for the SGS heat-flux model, isotropic eddy diffusivity together with the effect of the GS velocity was finally proposed. The proposed models were also found to be insensitive to the discretized test filtering operation.

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