Dragan Stankovic

Experimental and numerical study of flameless combustion in a model gas turbine combustor

Flameless combustion is an attractive solution to address existing problems of emissions and stability when operating gas turbine combustors. Theoretical, numerical and experimental approaches were used to study the flameless gas turbine combustor. The emissions and combustion stability were measured and the limits of the flameless regime are discussed. Using experimental techniques and Large Eddy Simulation (LES), detailed knowledge of the flow field and the oxidation dynamics was obtained. In particular the relation between the turbulent coherent structures dynamics and the flameless oxidation was highlighted. A model for flameless combustion simulations including detailed chemistry was derived. The theoretical analysis of the flameless combustion provides 2 non-dimensional numbers that define the range of the flameless mode. It was determined that the mixture that is ignited and burnt is composed of ∼ 50% of fresh gases and ∼ 50% vitiated gases.

A Comparison of Single and Multiphase Jets in a Crossflow Using Large Eddy Simulations

Large eddy simulations (LES) are performed for single and multiphase jets in crossflow (JICF). The multiphase JICF are compared to the single-phase case for the same momentum and mass flow, ratios but with droplets of different sizes. Multiphase JICF have stronger counterrotating vortex pairs (CVPs) than a corresponding single-phase JICF. Moreover their trajectories are higher and their induced waves weaker. The smaller the Stokes number of the droplets, the more the solution approaches the solution for single-phase flow. The computed results show the formation of a CVP and horseshoe vortices, which are convected downstream. LES also reveals the intermittent formation of upright wake vortices from the horseshoe vortices oil the ground toward the CVP. The dispersion of polydisperse spray droplets is computed using the stochastic parcel method. Atomization and droplet breakup are modeled by a combination of the breakup model by Reitz and the Taylor analogy breakup model (see Caraeni, D., Bergstrom, C., and Fuchs, L., 2000, Flow, Turbid. Combust., 65(2), pp. 223-244). Evaporation and droplet collision are also modeled. The flow solver uses two-way coupling. Averages of the velocity and gaseous fuel mass fraction are computed. The single-phase JICF is validated against experimental data obtained by PIV. Additionally, the PDFs and frequency spectra are presented.

Coherent Structures in Circular and Non-Circular Jets in Crossflow

Particle image velocimetry (PIV) and large eddy simulations (LES) are performed for jets in crossflow (JICF). It is demonstrated that the effect of nozzle shape on the flow can be accounted for using the proposed LES approach. Trajectories based on various definitions are compared. Some of these trajectories and turbulence statistics are compared for circular, elliptic, and square nozzles. In the latter cases, effects of orientation are considered. The behavior of the strength and lift-off of the counter-rotating vortices (CVP) is explained by turbulence levels introduced by these nozzles. Compared to circular nozzles, elliptic nozzles with high aspect ratio elevate turbulence whereas low aspect ratio nozzles have an attenuating effect. Square nozzles enhance turbulence most if the orientation is blunt. In case of enhanced turbulence the CVP undulates more, is weaker in the mean flow solution, and has a smaller lift-off. The near-wall turbulence downstream of the jet is clearly elevated for square nozzles with blunt orientation.

A Comparison of a Single- and Multiphase Jets in a Crossflow Using LES

Large eddy simulations are performed for a single- and multiphase jets in crossflow (JICF). The multiphase JICF are compared to the single-phase case for the same momentum and mass flow ratios but with droplets of different sizes. Multiphase JICF have stronger counter-rotating vortex pairs (CVPs) than a corresponding single-phase JICF. Moreover, their trajectories are higher and their induced wakes weaker. The smaller the Stokes number of the droplets, the more the solution approaches the solution for single-phase flow. The computed results show the formation of a CVP and horseshoe vortices which are convected downstream. LES reveals also the intermittent formation of upright wake vortices from the horseshoe vortices on the ground towards the CVP. The dispersion of polydisperse spray droplets is computed using the stochastic parcel method. Atomization and droplet breakup are modeled by a combination of the breakup model by Reitz and the Taylor analogy breakup model. Evaporation and droplet collision are also modeled. The flow solver uses two-way coupling. Averages of the velocity and gaseous fuel mass fraction are computed. The single-phase JICF is validated against experimental data obtained by PIV. Additionally, the PDFs and frequency spectra are presented. Copyright (Less)

EXPERIMENTAL INVESTIGATION OF AIRFLOW AND SPRAY STABILITY IN AN AIR-BLAST INJECTOR OF AN INDUSTRIAL GAS TURBINE

The airflow field and spray characteristics from an air blast type of injector in an industrial gas turbine (GT) combustor geometry have been investigated experimentally and numerically. The flame in the current combustor is stabilized by a highly swirling flow. The stabilization of the flame is strongly dependent on the stability of the flow field out from the injector and into the combustor. Liquid fuel spray formation in the current type of injector is highly dependent on the airflow from the internal swirler, which supplies the shear to break the liquid film, and form the spray. Experiments were performed in a Perspex model of a 12