Simulation of hydrogen auto-ignition in a turbulent co-flow of heated air with LES and CMC approach

Large-Eddy Simulations (LES) with the first order Conditional Moment Closure (CMC) approach of a nitrogen-diluted hydrogen jet, igniting in a turbulent co-flowing hot air stream, are discussed. A detailed mechanism (nine species, 19 reactions) is used to represent the chemistry. Our study covers the following aspects: CFD mesh resolution; CMC mesh resolution; inlet boundary conditions and conditional scalar dissipation rate modelling. The Amplitude Mapping Closure for the conditional scalar dissipation rate produces acceptable results. We also compare different options to calculate conditional quantities in CMC resolution. The trends in the experimental observations are in general well reproduced. The auto-ignition length decreases with an increase in co-flow temperature and increases with increase in co-flow velocity. The phenomena are not purely chemically controlled: the turbulence and mixing play also affect the location of auto-ignition. In order to explore the effect of turbulence, two options were applied: random noise and turbulence generator based on digital filter. It was found that stronger turbulence promotes ignition

Numerical simulations of hydrogen auto-ignition in a turbulent co-flow of heated air

Our research objective is the performance of Large-Eddy Simulation (LES) with the first order Conditional Moment Closure (CMC) of the test case experimentally studied by Markides and Mastorakos [1]. The experiment concerns auto-ignition of hydrogen, diluted with nitrogen, in a co-flow of heated air. A 19 step, nine species detailed mechanism is used for the reaction. Simulations reveal that the injected hydrogen mixes with co-flowing air and a diffusion flame is established. The configuration is sensitive to inlet boundary conditions, as all major turbulence effects are expected to be dominated by the inflow conditions. Preliminary LES results are presented. Stand-alone chemistry calculations are also presented to illustrate sensitivity on chemistry mechanisms

Factors associated with the continuum of care of HIV infected patients in Belgium

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Study of nanoparticles deposition in a human upper airway model using a dynamic turbulent Schmidt number

In this paper, the nanoparticles deposition in the upper portion of the human respiratory system is studied by using a dynamic turbulent Schmidt number. The flow and particle governing equations are solved using large eddy simulation (LES) with a localized dynamic subgrid scale closure of the residual stress tensor and the scalar flux term. The flow solution and the particle transport are dynamically coupled and thus, the turbulent momentum and mass diffusivity are calculated from the resolved flow and particle concentration fields. The methodology is applied to an extrathoracic oral airway model for several particle diameters ranging from 10 nm to 52 nm at a breathing rate of 30 L/min. The results are compared to the previously published RANS and experimental data. It is observed that the current methodology improves the quality of results for flow and particle deposition considerably. It is also noticed that the turbulent Schmidt number is quite different from its typically assumed values. Keywords: LES, Nanoparticles deposition, Upper airway model, Dynamic turbulent Schmidt numbe

Study of nanoparticles deposition in a human upper airway model using a dynamic turbulent Schmidt number

In this paper, the nanoparticles deposition in the upper portion of the human respiratory system is studied by using a dynamic turbulent Schmidt number. The flow and particle governing equations are solved using large eddy simulation (LES) with a localized dynamic subgrid scale closure of the residual stress tensor and the scalar flux term. The flow solution and the particle transport are dynamically coupled and thus, the turbulent momentum and mass diffusivity are calculated from the resolved flow and particle concentration fields. The methodology is applied to an extrathoracic oral airway model for several particle diameters ranging from 10 nm to 52 nm at a breathing rate of 30 L/min. The results are compared to the previously published RANS and experimental data. It is observed that the current methodology improves the quality of results for flow and particle deposition considerably. It is also noticed that the turbulent Schmidt number is quite different from its typically assumed values. Keywords: LES, Nanoparticles deposition, Upper airway model, Dynamic turbulent Schmidt numbe