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 (n-heptane) is injected in a hollow cone spray pattern by a simplex atomizer and is here characterized in an unconfined, non-reacting operating condition. The test rig is equipped with a two-component phase doppler laser velocimeter, enabling time-resolved measurements of the fuel droplet diameter together with two velocity components. Two features of the droplet distribution that are less commonly found in the technical literature are identified. First, the distributions of mean and Sauter mean droplet diameters exhibit non-axisymmetric patterns. The lack of symmetry in the distribution of droplet diameters is retrieved, for three types of swirlers differing by their swirl number and/or head loss.  The swirler with the highest swirl number yields a pattern that is less skewed than the others. One question that can be raised is that of the cause of the absence of symmetry of the droplet cloud. One may wonder whether this is due to imperfections in the atomizer geometry or if this is linked to the swirling flow organization that favors an asymmetric pattern. The size-conditioned velocity distribution of droplets indicates that the axial velocity distribution features a single wide peak for small droplets and becomes bimodal for the large droplets, with a first peak at low velocities, and a second at higher velocities. The analysis of the behavior of the spray is complemented by making use of high-fidelity calculations using Large Eddy Simulations based on the fully compressible, Navier-Stokes solver AVBP (developed by Cerfacs and IFPen). The droplet spray is obtained with a Lagrangian Particle Tracking. The injection of droplets is achieved using the FIMUR model, in which the atomization process is represented through empirical relationships to inject droplets in the numerical domain. Secondary atomization is not included and the Abramson and Sirignano model accounts for vaporization. The droplet cloud is found to interact with the lateral boundary of the swirler unit and requires a droplet-wall interaction model that accounts for the existence of a liquid film. The simulation including this special description yields a bimodal distribution for the axial velocity of the droplets indicating that it is important to represent the droplet-wall interaction which is not commonly found in the literature. On the other hand the skewed azimuthal distribution of the droplet diameter is not obtained indicating that the swirling flow does not induce an asymmetric droplet distribution. In conclusion, this study is focused on two features of the fuel droplet distribution having a first order impact on combustion. They are identified in the experimental data: the azimuthal diameter distribution is skewed, and the size-conditioned velocity distribution of large droplets is bimodal. The latter feature can be accounted for in a large eddy simulation if an appropriate wall modeling approach is used. On the other hand the lack of rotational symmetry is not linked to the nature of the swirling flow and appears to be due to imperfections in the atomizer geometry.


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

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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