Large Eddy Simulations of Swirling Non-premixed Flames With Flamelet Models: A Comparison of Numerical Methods

Abstract

This work investigates the application of large eddy simulation (LES) to selected cases of the turbulent non-premixed Sydney swirl flames. Two research groups (Loughborough University, LU and Imperial College, IC) have simulated these cases for different parameter sets, using two different and independent LES methods. The simulations of the non-reactive turbulent flow predicted the experimental results with good agreement and both simulations captured the recirculation structures and the vortex breakdown without major difficulties. For the reactive cases, the LES predictions were less satisfactory, and using two independent simulations has helped to understand the shortcomings of each. Furthermore one of the flames (SMH2) was found to be exceptionally hard to predict, which was supported by the lower amount of turbulent kinetic energy that was resolved in this case. However, the LES has identified modes of flame instability that were similar to those observed in some of the experiments.

Transported scalar PDF calculations of a swirling bluff body flame (‘SM1’) with a reaction diffusion manifold

“…Further downstream all the calculations correctly predict the tangential velocity. In general, agreement with experimental data is quite good, comparable to what was obtained with LES in [20]. As already observed in similar simulations of the non-swirling Sydney bluff-body flames [27,28], the differences in mean density between the three different calculations do not strongly affect the mean flow field.…”

“…Unfortunately no detailed study of turbulence-chemistry interaction is reported. LES results of non-reacting and reacting cases have been presented with flamelet chemistry in [20][21][22][23] and with FGM chemistry in [24]. A comparable quality of flow and mixing field results is obtained here with axisymmetric steady RANS calculations with a non-linear k-model [25].…”

Burning syngas in a high swirl burner: Effects of fuel composition

“…The predictive capabilities of numerical models is advancing rapidly, and future research will further increase the accuracy and efficiency of these computational tools, ultimately leading over the next decade to the generalisation of computer-aided design and optimisation as a fundamental engineering tool. The large eddy simulation (LES) technique is widely accepted as a potential numerical tool to simulate turbulent combustion problems corresponding to laboratory and practical scale configurations [16][17]. In LES, the large scale turbulence structures are directly computed and small dissipative structures are modelled.…”

Identification and analysis of instability in non-premixed swirling flames using LES

“…In earlier studies, we have shown that LES predicts different isothermal swirling flow fields of the Sydney swirl flame series with a good degree of success [44] and later extended the work to the reacting cases [45]. We have also investigated flame comparisons based on two different independent LES codes [46] and found good agreement especially for capturing the vortex breakdown, recirculation, turbulence and basic swirling flame structures. Despite these contributions and validation studies, a systemic study of flow instabilities associated with the Sydney swirling flames is essential and timely.…”