The approximate deconvolution model (ADM) for the large-eddy simulation of incompressible flows is detailed and applied to turbulent channel flow. With this approach an approximation of the unfiltered solution is obtained by repeated filtering. Given a good approximation of the unfiltered solution, the nonlinear terms of the filtered Navier–Stokes equations can be computed directly. The effect of nonrepresented scales is modeled by a relaxation regularization involving a secondary filter operation. Large-eddy simulations are performed for incompressible channel flow at Reynolds numbers based on the friction velocity and the channel half-width of Reτ=180 and Reτ=590. Both simulations compare well with direct numerical simulation (DNS) data and show a significant improvement over results obtained with classical subgrid scale models such as the standard or the dynamic Smagorinsky model. The computational cost of ADM is lower than that of dynamic models or the velocity estimation model.

An alternative approach to large-eddy simulation based on approximate deconvolution (ADM) is developed. The main ingredient is an approximation of the nonfiltered field by truncated series expansion of the inverse filter operator. A posteriori tests for decaying compressible isotropic turbulence show excellent agreement with direct numerical simulation. The computational overhead of ADM is similar to that of a scale-similarity model and considerably less than for dynamic models.

A formulation of the approximate deconvolution model (ADM) for the large-eddy simulation (LES) of compressible flows in complex geometries is detailed. The model is applied to supersonic compression ramp flow where shock-turbulence interaction occurs. With the ADM approach an approximation to the unfiltered solution is obtained from the filtered solution by a series expansion involving repeated filtering. Given a sufficiently good approximation of the unfiltered solution at a time instant, the flux terms of the underlying filtered transport equations can be computed directly, avoiding the need to explicitly compute subgrid-scale closures. The effect of nonrepresented scales is modeled by a relaxation regularization involving a secondary filter operation and a dynamically estimated relaxation parameter. Results of the large-eddy simulation of the turbulent supersonic boundary layer along a compression ramp compare well with filtered DNS data. The filtered shock solution is correctly predicted by the ADM procedure, demonstrating that turbulent and nonturbulent subgrid-scales are properly modeled. We found that a computationally expensive shock-capturing technique was not necessary for stable integration. As a consequence, the computational effort for simulations with ADM is approximately as large as for a coarse-grid DNS with a hybrid compact-upwind-ENO scheme, since the additional computational cost for the subgrid-scale model is more than compensated due to the fact that in the LES flux-derivatives can be computed by linear central finite differences on the entire domain.

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Propylene glycol and triacetin are chemical compounds, commonly used as food additives. Though the usage of the pure chemicals is not considered harmful when used as dietary supplements, little is known about the nature of their thermal degradation products and the impact they may have on human health. For these reasons, in this manuscript we investigate the thermal decomposition mechanisms of both neutral propylene glycol and triacetin in the gas phase by a novel simulation framework. This is based on a free energy sampling methodology followed by an accurate energy refinement. Structures, Gibbs free energy barriers, and rate constants at 800 K were computed for the different steps involved in the two pyrolytic processes. The thermal decomposition mechanisms found theoretically for propylene glycol and triacetin were validated by a qualitative experimental investigation using gas-phase chromatography-mass spectroscopy, with excellent agreement. The results provide a validation of the novel simulation framework and shed light on the potential hazard to the health that propylene glycol and triacetin may have when exposed to high temperatures.

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The dehydration mechanism of neutral glycerol in the gas phase was investigated by means of metadynamics simulations. Structures, vibrational frequencies, Gibbs free energy barriers, and rate constants at 800 K were computed for the different steps involved in the pyrolytic process. In this article, we provide a novel mechanism for the dehydration of neutral glycerol, proceeding via formation of glycidol with a barrier of 66.8 kcal/mol. The formation of glycidol is the rate limiting step of the overall decomposition process. Once formed, glycidol converts into 3-hydroxypropanal with a barrier of 49.5 kcal/mol. 3-Hydroxypropanal can decompose further into acrolein or into formaldehyde and vinyl-alcohol with barriers of 53.9 and 35.3 kcal/mol, respectively. These findings offer new insights to available experimental data based on glycerol pyrolysis studies performed with isotopic labeling and on the interpretation of the chemistry of glycerol and sugars in pyrolytic conditions.

Spatially developing supersonic turbulent boundary layers at a Mach number of 2.5 and momentum-thickness Reynolds numbers at inflow of 4530 and 10 049, respectively, are computed with large-eddy simulation using the approximate deconvolution model [Stolz et al., Phys. Fluids 13, 2985 (2001)]. Turbulent inflow conditions are generated by rescaling the turbulent boundary layer at some distance downstream of inflow and reintroducing the rescaled mean profiles and fluctuation fields at inflow. This technique follows essentially that of Lund et al. [J. Comput. Phys. 140, 233 (1998)], albeit simplified and adapted for compressible flow. The simulations feature rather short spatial transient behavior and the results agree well with experimental data and theoretical correlations. The validity of assumptions of the strong Reynolds analogy is addressed.