LES/CMC of Blow-off in a Liquid Fueled Swirl Burner

Abstract

Large Eddy Simulations of two-phase flames with the Conditional Moment Closure combustion model have been performed for flow conditions corresponding to stable and blow-off regimes in a swirl n-heptane spray burner. In the case of stable flame (i.e. low air velocity), the predicted mean and r.m.s. velocities and the location and shape of the flame agree reasonably well with experiment. In particular, the presence of localised extinctions is captured in agreement with experiment. Using model constants previously calibrated against piloted jet methane flames (Sandia F) with localised extinction, we obtain that at the experimentally determined blow-off velocity of the swirling spray flame, the predicted flame also blows off, demonstrating that the LES-CMC approach can capture the global extinction point in a realistic configuration.

Large Eddy Simulation/Conditional Moment Closure modeling of swirl-stabilized non-premixed flames with local extinction

“…Here C N = 42 is used, a constant determined through matching the computational and experimental results in Sandia flame D [21]. This has given good results for the statistics of extinction in Sandia F [21] and for capturing the global blow-off condition of a spray swirl flame [22]. The 3D-CMC equations for non-premixed combustion can be derived through filtering the equations of reactive scalars Y a [28,29] @Q a =@t |fflfflffl ffl{zfflfflffl ffl} T 0Àunsteady…”

“…Various versions of the flamelet model [16,17] and higher order Conditional Moment Closure (CMC) models and doublyconditioned CMC have also been used [18][19][20]. More recently, the first order CMC model was used to capture local extinction in Sandia F [21] and a swirl spray flame [22] in Large Eddy Simulations (LES). The Sydney swirl diffusion flames also show different levels of turbulencechemistry interactions [4].…”

Modelling of Spray Flames with Doubly Conditional Moment Closure

“…In particular, for the mixture fraction variance equation, Giusti and Mastorakos [33] pointed out that both spray source terms could have a significant effect in the inner flame region. In single-conditional CMC, the terms and are modelled either by summing ( k = 1 or 2) for all droplets in one cell [34] or, alternatively, by assuming that 〈π| η 〉 has the shape of a δ -function at the average surface mixture fraction 〈 ξ s 〉 [35]. In both cases, it is assumed that ξ s ≈ Y F ,sat , calculated for the droplet temperature T d .…”

Numerical simulation of oxy-fuel jet flames using unstructured LES–CMC

“…The constant C N is set to a value of 42, which was tuned to match experimental data in [8] and has given good agreement with experimental data in several other cases [9,10]. As there is no nitrogen present in this flame, the 16 species ARM1 chemistry was used [19].…”

“…It has also been successfully applied to other gaseous [9] and spray [10] flames. It has been seen that the combination of transport and scalar dissipation rate terms are able to capture transient extinction and reignition.…”