Seminars

The burning rate in a spherically expanding turbulent premixed flame is explored using direct numerical simulations, and a model of ordinary differential equations is proposed. Direct numerical simulations are performed of confined spherical flames in isotropic turbulence over a range of Reynolds numbers. The model assumes a thin flame and a two-fluid approach, with burning rate found to be controlled by surface area effects of turbulent wrinkling and a correction factor that is later shown to be representative of flame stretch effects and is able to be accurately modeled as such. A Reynolds scaling hypothesis for the flame turbulent wrinkling from a previous work, in conjunction with linear Markstein theory completes the model, which shows predictions of flame radius and chamber pressure in good agreement with the numerical data within expected variances.  Working towards studying these Reynolds number scaling effects in shear-driven turbulence, we employ large scale Direct Numerical Simulations (DNS) of turbulent flames in the turbulent swirling von Kármán flow. The reaction model features a single passive reactive scalar, allowing for focused studies on the evolution of turbulent flame surfaces with only three dimensionless parameters, i.e. a large-scale Reynolds number, a Damköhler number, and the Schmidt number. Such a single scalar combustion model coupled with DNS of reactive turbulence is computationally affordable, enabling simulations at much higher Reynolds numbers than would otherwise be possible. The Reynolds number is increased by up to a factor of 4 across three configurations, holding the other parameters constant.  The flame Surface Density Function (SDF) is shown to scale in time according to a common function shared across configurations, exhibiting self-similarity. The peak of the SDF is scaled by a power law of the Reynolds number with exponent nearly identical to that reported in recent numerical and experimental studies of turbulent spherically expanding flames, indicating the robustness of turbulent flame surface wrinkling, minimally affected by the nature of turbulence, variable density, variable transport properties, and chemistry model.