Large eddy simulations of turbulent swirling flows in a dump combustor: a sensitivity study

Abstract

SUMMARYLarge eddy simulations (LES) of conÿned turbulent swirling ows in a model dump combustor are carried out. The simulations are based on a high-order ÿnite di erence method on a Cartesian grid, with the sub-grid scale stress tensor modelled using a scale-similarity model. The aims of this work are to study the physics of the ow and to evaluate the performance of LES method for simulation of the major features of turbulent swirling ows-the vortex breakdown, the highly anisotropic and fast-decaying turbulence structure. In uences of in ow=out ow conditions, combustor geometry, inlet swirl proÿle and Reynolds numbers on the vortex breakdown and turbulence structures are investigated. At very high swirl levels, the in uence of the out ow conditions and the outlet geometry is fairly signiÿcant, not only at downstream near the outlet, but also at far upstream. At low Reynolds numbers, the onset of vortex breakdown is fairly sensitive to the change of Reynolds number; however, at high Reynolds numbers it is rather insensitive to the Reynolds number. Comparisons of LES results with experimental data are made. The LES results are shown to be in reasonably good agreement with the experimental data if appropriate in ow and out ow boundary conditions are imposed.

Effect of geometrical contraction on vortex breakdown of swirling turbulent flow in a model combustor

“…Similar effects of the outlet contraction on the vortex breakdown structures have been observed in a recent experimental study of swirling isothermal and reactive flows in a combustor geometry for higher Reynolds number turbulent flows [3]. In some other studies the outlet contraction has shown low impact on the flow structures in the main chamber under a condition that the swirl number is relatively low and the chamber length to diameter ratio is relatively large [4,5].…”

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

“…For example, Wang and Bai [89] performed LES calculations of non-reacting swirling flow fields and captured complex phenomena such as recirculation, VB and precessing motion. DiMare et al [19], Kim et al [42], and Mahesh et al [55] carried out LES of combustion and simulated set-ups like simplified aero-engines.…”

Inlet Conditions for Large Eddy Simulation of Gas-Turbine Swirl Injectors

“…Running the auxiliary computation at the same time as the main calculation obviates these problem, but introduces its own programming problems. Additionally, if the flow conditions change (e.g., a different Reynolds number), then the library must be recomputed or rescaled; the latter can be shown to introduce additional problems into the simulation [5]. Integrating the auxiliary computation into the main domain in this manner, on the other hand, is much more elegant and easier to manage and generates extremely good mean and turbulent flow results.…”

“…Examples of this approach include [3,4]. However, such approaches suffer problems related to the nonphysical nature of the turbulence introduced at the inlet, leading to incorrect prediction of turbulent kinetic energy and energy spectra downstream of the inlet [5].…”

“…Having computed a library of turbulent swirling flow in this way, either as a saved precursor database or "on the fly" in parallel with the main calculation, the flow conditions from the secondary calculation can be fed into the main computation [12,13]. As an example of this, Wang and Bai [5] used Pierce and Moin's [11] method to create a 10,000 time-step library for lookup, which was then cycled through as appropriate. The library does not, however, meet the specifications for the required flow, and so the data are rescaled to meet the desired statistical properties (specified mean and variance of velocity).…”