Highly-resolved large eddy simulation of the nonreacting flow in an asymmetric vortex combustor

In this paper, we present a computational investigation of the nonreacting flow structure inside a novel asymmetric vortex combustor that was recently proposed by the authors. Large Eddy Simulation using the Smagorinsky-Lilly subgrid turbulence closure has been used to study such flow. A computational grid of 2.22×106 cells was used to ensure that the resolved turbulence kinetic energy is fairly more than 80% of the total turbulence kinetic energy budget. The flow was found to exhibit a central recirculation zone, and two secondary recirculation zones in the asymmetry regions. The vortex structure was found to be a completely forced vortex field. The effect of turbulence on the size and structure of the statistically averaged mean flow phenomena has been analyzed as discussed

Diffusive thermal instabilities of C4H10-C3H8/air laminar premixed flames

Preferential heat and mass transfer induces diffusive thermal instabilities in premixed laminar flames. Such instabilities in hydrocarbon flames are characterized by cellular structure and a tendency to promote flame extinction. We investigate the properties of such instabilities in C4H10-C3H8/air flames. The adiabatic burning velocity of the laminar premixed flame was measured at different equivalence ratios while exhibiting cellular instabilities. Direct photographs have been captured to qualitatively asses the effect of burner plate temperature on the cellular structure of the flame. The present study preliminarily suggests a normal logarithmic correlation to predict the adiabatic burning velocity of diffusive thermal instabilities in laminar premixed C4H10-C3H8/air flames

Implementation of the eddy dissipation model of turbulent non-premixed combustion in OpenFOAM

This work discusses the implementation of eddy dissipation model in OpenFOAM CFD toolbox. The code was validated in modeling of confined non-premixed Methane jet flame. The model predictions were extensively compared against published experimental results as well as ANSYS Fluent® predictions. The differences between the implemented model in OpenFOAM and Fluent were demonstrated

Integrating a simplified P-N radiation model with edmfoam1.5: model assessment and validation

This work compliments our recently published work of implementing the eddy dissipation turbulent combustion model in OpenFOAM [1]. The major update proposed herein is linking the EdmFoam1.5 solver with radiation modeling libraries in OpenFOAM. The new solver was validated against experimental data for jet and swirling Sydney flame (SM1). Each case was modeled with/without radiation modeling. The results have a fair agreement in general. In jet flame cases, the radiation modeling has a good impact on refining the predicted results. However it has not the same great effect on the swirling flame case. A review of the EDM applications in different reacting flow problems is also presented and discussed

Effect of free stream turbulence on NOx and soot formation in turbulent diffusion CH4-air flames

A two-dimensional axisymmetric RANS numerical model was solved to investigate the effect of increasing the turbulence intensity of the air stream on the NOx and soot formation in turbulent methane diffusion flames. The turbulence–combustion interaction in the flame field was modelled in a k - e/EDM framework, while the NO and soot concentrations were predicted through implementing the extended Zildovich mechanism and two transport equations model, respectively. The predicted spatial temperature gradients showed acceptable agreement with published experimental measurements. It was found that the increase of free stream turbulence intensity of the air supply results in a significant reduction in the NO formation of the flame. Such phenomenon is discussed by depicting the spatial distribution of the NO concentration in the flame. An observable reduction of the soot formation was also found to be associated with the increase of inlet turbulence intensity of air stream

Computational and experimental investigations of turbulent asymmetric vortex flames

In the present article we present computational and experimental investigations of a turbulent asymmetric vortex flame. Such flame was created in a novel asymmetric combustor, which is described for the first time in this article. The three dimensional isothermal and reacting flow fields have been described using a computational methodology that impalements the Re/k - e and the eddy dissipation turbulence and combustion models, respectively. The computational model is validated for both isothermal and reacting flows. Additionally, the visible flame structure was captured by direct photography at a wide range of equivalence ratios in order to emphasize the exceptional stability of such flame. The mechanism of flame stability and interaction with the forced vortex field is preliminarily discussed. Finally, the basic characteristics of the asymmetric vortex flames are concluded

Numerical simulation of confined vortex flow using a modified k-£ turbulence model

The turbulent flow in a tangential inlet / tangential outlet vortex tube is numerically simulated using a modified k ?? turbulence model. The results are compared to experimental measurements from literature. The modified model shows better agreement with the local tangential velocity measurements compared to the standard and RNGk ?? turbulence models. The flow structure is also demonstrated using the modified turbulence mode

Comparison of eddy dissipation model and presumed probability density function model for temperature prediction in a non-premixed turbulent methane flame

Temperature distribution is predicted through numerical simulation of a turbulent non-premixed methane flame using the standard Eddy Dissipation Model (EDM) and a model based a presumed shape of probability density function (PDF) along with an equilibrium chemistry model. Results are validated against existing experimental data. Two models are compared to each other in terms of accuracy and their advantages and disadvantages are discussed

Analyzing the effect of free stream turbulence on gaseous non-premixed flames

The effects of free stream turbulence on non-premixed flames are numerically analyzed. The Spalding eddy dissipation mathematical model is used to control the reaction rate by the large-eddy time scale. The turbulence energy production and dissipation rates are simulated by the ?-e turbulence model in order to investigate the dependence of the combustion properties on free stream turbulence. The reacting NS equations were spatially discretized and solved through a finite volume scheme and a decoupled pressure-velocity approach, respectively. The flame was assumed to be steady-state, two dimensional and axisymmetric. The reported results include the velocity, temperature and turbulent reaction rate along the flame propagation field. It is found that the increase of free stream turbulence intensity reduces the reaction zone significantly, hence, induces the flame extinction process