Validation of unsteady flamelet / progress variable methodology for non-premixed turbulent partially premixed flames

This paper highlights the modeling capabilities of UFPV approach for the modeling of turbulent partially premixed lifted flames to capture the extinction and re-ignition phenomena. Large eddy simulation (LES) with the probability density function (PDF) approach provides the turbulence-chemistry interaction. All scalars are represented as a function of mean mixture fraction, mixture fraction variance, mean progress variable and scalar dissipation rate. Mixture fraction is assumed to follow a β-PDF distribution. Progress variable and scalar dissipation rate distributions are assumed to be a δ-PDF. Results are compared with experimental data of a vitiated co-flow burner with fuels like CH4/Air and H2/N2. Results of radial plots for temperature, mixture fraction and scattered data of temperature with mixture fraction at various axial locations are compared. Lift-off height for a CH4/Air flame appears to be over-predicted while the predicted lift-off height for a H2/N2 flame shows an under-prediction

Unsteady flamelet / progress variable approach for non-premixed turbulent lifted flames

The unsteady flamelet/progress variable approach has been developed for the prediction of a lifted flame to capture the extinction and re-ignition physics. In this work inclusion of the time variant behavior in the flamelet generation embedded in the large eddy simulation technique, allows better understanding of partially premixed flame dynamics. In the process sufficient simulations to generate unsteady laminar flamelets are performed, which are a function of time. These flamelets are used for the generation of the look-up table and the flamelet library is produced. This library is used for the calculation of temperature and other species in the computational domain as the solution progresses. The library constitutes filtered quantities of all the scalars as a function of mean mixture fraction, mixture fraction variance and mean progress variable. Mixture fraction and progress variable distributions are assumed to be -PDF and d-PDF respectively. The technique used here is known as the unsteady flamelet progress variable (UFPV) approach. One of the well known lifted flames is considered for the present modeling which shows flame lift-off. The results are compared with the experimental data for the mixture fraction and temperature. Lift off height is predicted from the numerical calculations and compared with the experimentally given value. Comparisons show a reasonably good agreement and the UFPV combustion model appear to be a promising technique for the prediction of lifted and partially premixed flames

Evaluation of turbulence/radiation effects using LES combustion simulation data

This paper describes the evaluation of turbulence/radiation effects on a swirl flame. The data obtained from a LES calculation in this case provides time-varying temperature field and species concentrations contributing to radiation fluctuations. In the radiation calculations demonstrated here, time varying data obtained from the LES calculations are post processed using the Discrete Transfer method incorporating a radiative property calculation algorithm to obtain radiation fluctuation statistics. The study provides an insight into how radiation fluxes, absorption coefficients and radiation intensities fluctuate in a highly turbulent complex practical flame. Simulation results show that temperature self correlation can be as high as 4 times and turbulence fluctuations has a very significant effect on source term calculations

Unsteady flamelet/progress variable approach for non-premixed turbulent lifted flames

The unsteady flamelet/progress variable approach has been developed for the prediction of a lifted flame to capture the extinction and re-ignition physics. In this work inclusion of the time variant behavior in the flamelet generation embedded in the large eddy simulation technique, allows better understanding of partially premixed flame dynamics. In the process sufficient simulations to generate unsteady laminar flamelets are performed, which are a function of time. These flamelets are used for the generation of the look-up table and the flamelet library is produced. This library is used for the calculation of temperature and other species in the computational domain as the solution progresses. The library constitutes filtered quantities of all the scalars as a function of mean mixture fraction, mixture fraction variance and mean progress variable. Mixture fraction and progress variable distributions are assumed to be β-PDF and -PDF respectively. The technique used here is known as the unsteady flamelet progress variable (UFPV) approach. One of the well known lifted flames is considered for the present modeling which shows flame lift-off. The results are compared with the experimental data for the mixture fraction and temperature. Lift off height is predicted from the numerical calculations and compared with the experimentally given value. Comparisons show a reasonably good agreement and the UFPV combustion model appear to be a promising technique for the prediction of lifted and partially premixed flames