Gordon Fru

Direct Numerical Simulation of highly turbulent premixed flames burning methane

The last century has witnessed soaring gas prices, deteriorating air quality and alarming global climate changes. In recent years, increasing concerns have been raised with respect to the environmental impacts of energy consumption via the combustion of fossil fuels, for instance in stationary power generation and transportation, emitting greenhouse gases and air pollutants. As a result, governments now set more and more stringent standards. Hence, it is essential to understand and improve combustion processes, in order to reduce fuel consumption and pollutant emissions as much as possible.

Direct Numerical Simulations of the Impact of High Turbulence Intensities and Volume Viscosity on Premixed Methane Flames

Parametric direct numerical simulations (DNS) of turbulent premixed flames burning methane in the thin reaction zone regime have been performed relying on complex physicochemical models and taking into account volume viscosity (). The combined effect of increasing turbulence intensities () and on the resulting flame structure is investigated. The turbulent flame structure is marred with numerous perforations and edge flame structures appearing within the burnt gas mixture at various locations, shapes and sizes. Stepping up from 3 to 12 m/s leads to an increase in the scaled integrated heat release rate from 2 to 16. This illustrates the interest of combustion in a highly turbulent medium in order to obtain high volumetric heat release rates in compact burners. Flame thickening is observed to be predominant at high turbulent Reynolds number. Via ensemble averaging, it is shown that both laminar and turbulent flame structures are not modified by . These findings are in opposition to previous observations for flames burning hydrogen, where significant modifications induced by were found for both the local and global properties of turbulent flames. Therefore, to save computational resources, we suggest that the volume viscosity transport term be ignored for turbulent combustion DNS at low Mach numbers when burning hydrocarbon fuels.

Direct Numerical Simulations of turbulent flames to analyze flame/acoustic interactions

Direct Numerical Simulations (DNS) are becoming increasingly important as a source of quantitative information to understand turbulent reacting flows. For the present project DNS have been mainly used to investigate in a well-defined manner the interaction between turbulent flames and isolated acoustic waves. This is a problem of fundamental interest with practical applications, for example for a better understanding of combustion instabilities. After developing a specific version of the well-known Rayleigh’s criterion, allowing to investigate local amplification or damping of an acoustic pulse interacting with a reaction front, extensive investigations have been carried out. The present publication summarizes the main findings of all these studies and describes in detail the underlying numerical and physical models, in particular those used to describe chemical reactions. Post-processing of DNS data in the light of turbulent combustion modeling is also discussed. The results illustrate the complexity of the coupling between reaction fronts and acoustics, since amplification and damping appear mostly side by side, as alternating layers. The influence of individual reactions and species on the damping process can also be quantified in this manner. This publications concludes with perspectives towards higher turbulence levels and effects of differential diffusion.

Direct Numerical Simulations of Turbulent H_2-Air Pre-mixtures and Analysis Towards Safety-Relevant Ignition Prediction

The energy requested to obtain a stable ignition in a turbulent gas mixture has been investigated extensively during many decades [1], mostly through experiments or reduced (zero- or one-dimensional) simulation models [2].

Sparse representation and visualization for direct numerical simulation of premixed combustion

Direct Numerical Simulations of premixed combustion produce terabytes of raw data, which are prohibitively large to be stored, and have to be analyzed and visualized. A simultaneous and integrated treatment of data storage, data analysis and data visualization is required. For this, we introduce a sparse representation tailored to DNS data which can directly be used for both analysis and visualization. The method is based on the observation that most information is located in narrow‐band regions where the chemical reactions take place, but these regions are not well defined. An approach for the visual investigation of feature surfaces of the scalar fields involved in the simulation is shown as a possible application. We demonstrate our approach on multiple real datasets.

The Influence of Differential Diffusion in Turbulent Oxygen Enhanced Methane Flames

For conventional combustion processes one of the most common oxidizers is air, mainly because it is cheap and readily available compared to other oxidizers.

3D Direct Simulation of a Nonpremixed Hydrogen Flame with Detailed Models

We present a three-dimensional direct simulation of a turbulent nonpremixed H2/air flame described with a complete chemical scheme and a multicomponent transport model. When analyzing for example the local flame structure with a flame index, various burning regimes (nonpremixed, partially-premixed, premixed) are shown to coexist and to contribute to fuel oxidation. Nevertheless, nonpremixed combustion globally dominates the process, as expected for such a configuration. The distribution of mixture fraction can be quite accurately reconstructed using a β-function approximation based on mean and variance. A γ-function approximation leads always to a higher error level. Furthermore, the evolution of scalar dissipation rate versus mixture fraction is investigated, revealing a highly non-symmetrical distribution.