A Joint Experimental and LES Characterization of the Liquid Fuel Spray in a Swirl Injector

Abstract

Abstract The quality of liquid fuel spray injection determines to a large extent the steady state performance and dynamics of gas turbine and aero-engine combustors. The present investigation is focused on the detailed characterization of the liquid fuel spray in a single sector test rig targeted at aero-engine applications. The liquid fuel (heptane) is injected in a hollow cone spray pattern by a simplex atomizer and the injector comprises a radial swirler. Two features of the droplet distribution that are less commonly found in the technical literature are identified. First, the distributions of mean droplet diameters exhibit non-axisymmetric patterns, a lack of symmetry that is investigated for three types of swirlers differing by their swirl number and/or head loss. Second, it is found that the size-conditioned velocity distributions feature a single wide peak for small droplets and become bimodal for the largest droplets, with a first peak at low velocities, and a second one at higher velocities. The spray behavior analysis is complemented by making use of Large Eddy Simulations with Lagrangian Particle Tracking. Droplet injection is achieved with a model in which the initial size and velocity distributions are specified from experimental data in the atomizer near field. The initial spray interacts with the lateral injector surface and requires a droplet-wall interaction model accounting for the existence of a liquid film. Simulations do not retrieve the lack of rotational symmetry that is found experimentally indicating that this is not linked to the nature of the swirling flow. This is also consistent with further experiments with a different atomizer confirming that this is due to imperfections in the initial atomizer geometry. Another result is that certain swirler designs appear to be more robust to these atomizer imperfections. Simulations accounting for the liquid film yield a bimodal distribution for the droplets’ axial velocity distribution which would not be obtained without this model indicating that it is important to represent the droplet-wall interaction, a feature that is not commonly found in the literature.