Eulerian Stochastic Field Method Research Articles

LES-pdf simulation of a spark ignited turbulent methane jet

A spark ignited turbulent jet flame is simulated using Large Eddy Simulation (LES) in conjunction with the filtered probability density function (pdf) equation approach, which is solved using the Eulerian stochastic field method. The spark energy deposition is mimicked by a gaussian distributed source term in the enthalpy equation. A dynamic model for the sub-grid stresses together with a simple gradient diffusion approximation for the scalar fluxes is adopted. The chemistry is represented by a global 4-step chemistry involving seven species. The different stages of the ignition sequence, namely the flame kernel growth, the triple flame propagation against the flow and the stabilisation were in good agreement with the experimental data.

Large Eddy Simulation of the Sandia Flame Series (D–F) using the Eulerian stochastic field method

Three turbulent piloted methane jet flames with increasing levels of local extinction (Sandia Flames D–F) have been computed using Large Eddy Simulation. The smallest unresolved scales of the flow, in which combustion occurs, are represented using the filtered probability density function method where the corresponding evolution equation is solved directly. A dynamic model for the sub-grid stresses together with a simple gradient diffusion approximation for the scalar fluxes is applied in conjunction with the linear mean square estimation closure for sub-filter scale mixing. An augmented reduced mechanism (ARM) derived from the full GRI 3.0 mechanism is incorporated to describe the chemical reaction. The results demonstrate the ability of the method in capturing quantitatively finite rate effects such as extinction and re-ignition in turbulent flames.

Numerical Study of n-Heptane Auto-ignition Using LES-PDF Methods

This work deals with pre-vaporized n-heptane auto-ignition in turbulent flows. The paper applies the Eulerian Stochastic Field method to the solution of the sub-grid joint-scalar probability density function (PDF) of the reacting scalars in the Large Eddy Simulations (LES) context. A reduced mechanism of 22 species and 18 reactions is used to model n-heptane chemical kinetics. The method is able to reproduce the different regimes observed experimentally and studies the influence of inflow temperature fluctuations.

Study of hydrogen auto-ignition in a turbulent air co-flow using a Large Eddy Simulation approach

Large Eddy Simulation (LES) is applied to the auto-ignition of an hydrogen jet issuing into a turbulent co-flowing air stream. A 19 step, 9 species detailed mechanism is used for modelling the chemical reactions. The influence of sub-grid fluctuations is accounted for by a sub-grid joint probability density function (PDF) for the reactive scalars. A Eulerian Stochastic Field method is used to solve the modelled form of the PDF transport equation. The model is able to reproduce ignition lengths and different regimes observed experimentally without adjustment of the sub-grid scale model parameters.

Large eddy simulation of autoignition with a subgrid probability density function method

This paper applies the Eulerian stochastic field method to the solution of the subgrid joint probability density function (PDF) of the reacting scalars in a large eddy simulation (LES) of a jet of hydrogen issuing into a co-flow of vitiated air. The hot co-flow induces autoignition of the mixture and a lifted flame results downstream of the nozzle exit. The simulations were performed using a detailed H 2–air mechanism. The results were found to be sensitive to the co-flow temperature even with temperatures varied within the experimental uncertainty. The results obtained were in excellent agreement with the experimental data, both quantitatively and qualitatively. The method was able to capture partially premixed and partially extinguish zones with a relatively small number of stochastic fields. The radical HO 2 was found to be the trigger for autoignition. The fact that no large-scale premixed flame propagation was observed suggests that the stabilization mechanism is associated mainly with the chemistry.

A probability density function Eulerian Monte Carlo field method for large eddy simulations: Application to a turbulent piloted methane/air diffusion flame (Sandia D)

The Eulerian stochastic field method is applied to the solution of the modeled evolution equation for the subgrid joint probability density function (JPDF) of the reacting scalars in a large eddy simulation (LES) of a piloted methane/air diffusion flame (Sandia Flame D). A simple model for subgrid scale (SGS) stresses and fluxes and a global four-step mechanism for combustion are combined in the formulation. Test cases with varying mesh sizes and numbers of stochastic fields were completed. The differences in the results obtained with the two grids were very small and this indicates that the mesh resolution was sufficient. However, incorporation of the JPDF, via the stochastic field solution method, improved the quality of predictions significantly, particularly those quantities related to reaction, such as temperature. Eight stochastic fields were shown to be enough to characterize the influence of SGS fluctuations on filtered species formation rate to reasonable accuracy and at moderate computational cost. With the exceptions of H 2 and CO, good agreement between measured and computed mean and RMS profiles of velocity, composition, and temperature was achieved. The discrepancies in H 2 and CO concentrations are attributable to limitations in the global chemistry mechanism used in the LES. Overall the results serve to highlight the potential of the Eulerian stochastic field method in LES.