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In this work we present the numerical simulation of air-assisted liquid atomization at high pressure using the Smoothed Particle Hydrodynamics (SPH) method. Different post-processing tools are applied to facilitate the comparison with experimental observations. This allows to quantitatively validate the numerical method against the experiment, in terms of (i) frequency of the Kelvin-Helmholtz instability that develops on the jet surface, and (ii) statistical distribution of the jet intact length. The qualitative comparison also shows a good prediction of the jet global instability and of the fragmented liquid lumps, with regards to length and time scales. In addition, the post-processing tools also give access to the local parameters of the generated spray in the vicinity of the nozzle, which are not easily accessible in a real experiments. Using these tools, 1D profiles and 2D maps of the liquid phase properties such as the volume fraction, the droplet concentration, the Sauter Mean Diameter (SMD) and the droplet sphericity are presented. Because of the Lagrangian nature of the SPH method, it is also possible to monitor the whole atomization cascade as a causal tree, from the primary instabilities to the spray characteristics. This tree contains various information such as the fragmentation spectrum and the breakup activity, which are of great interest for researchers and engineers. Hence, the capability of the Smoothed Particle Hydrodynamics (SPH) method for simulating air-assisted atomization at high ambient pressure is demonstrated as well as its applicability to realistic configurations. This is a first step towards the development of a complete virtual spray test-rig.

In modern jet engines mostly air blast atomizers are used for the liquid fuel injection. The prediction of the spray generated by such atomizers was for a long time not feasible because of restricted computing resources. However, with modern super-computers the prediction of the atomization has come into reach. In the present paper a new approach for the numerical prediction of the primary atomization is presented. The methodology is based on the Smoothed Particle Hydrodynamics (SPH), which has originally been developed in the context of astrophysics. The numerical predictions to be presented were performed for a planar model atomizer, for which a vast amount of experimental data was collected by us previously. The major objectives of the numerical predictions are to elaborate the mechanism governing the effect of thickness of the trailing edge of the prefilmer on the size of the droplets and the temporal droplet formation rate.

In this paper, the complex two-phase flow during oil-jet impingement on a rotating spur gear is investigated using the meshless smoothed particle hydrodynamics (SPH) method. On the basis of a two-dimensional setup, a comparison of single-phase SPH to multiphase SPH simulations and the application of the volume of fluid method is drawn. The results of the different approaches are compared regarding the predicted flow phenomenology and computational effort. It is shown that the application of single-phase SPH is justified and that this approach is superior in computational time, enabling faster simulations. In the next step, a three-dimensional single-phase SPH setup is exploited to predict the flow phenomena during the impingement of an oil-jet on a spur gear for three different jet inclination angles. The oil’s flow phenomenology is described and the obtained resistance torque is presented. Thereby, a significant effect of the inclination angle on the oil spreading and splashing process as well as the resistance torque is identified.

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The formation of pollutant emissions in jet engines is closely related to the fuel distribution inside the combustor. Hence, the characteristics of the spray formed during primary breakup are of major importance for an accurate prediction of the pollutant emissions. Currently, an Euler–Lagrangian approach for droplet transport in combination with combustion and pollutant formation models is used to predict the pollutant emissions. The missing element for predicting these emissions more accurately is well defined starting conditions for the liquid fuel droplets as they emerge from the fuel nozzle. Recently, it was demonstrated that the primary breakup can be predicted from first principles by the Lagrangian, mesh-free, Smoothed Particle Hydrodynamics (SPH) method. In the present work, 2D Direct Numerical Simulations (DNS) of a planar prefilming airblast atomizer using the SPH method are presented, which capture most of the breakup phenomena known from experiments. Strong links between the ligament breakup and the resulting spray in terms of droplet size, trajectory and velocity are demonstrated. The SPH predictions at elevated pressure conditions resemble quite well the effects observed in experiments. Significant interdependencies between droplet diameter, position and velocity are observed. This encourages to employ such multidimensional interdependence relations as a base for the development of primary atomization models.

At the “Institut für Thermische Strömungsmaschinen” (ITS) a numerical method based on the the meshfree “Smoothed Particle Hydrodynamics” (SPH) approach has been developed with the objective of computing primary breakup in the vicinity of fuel spray nozzles [1, 2]. In recent publications the successful application of the code to different flow problems is demonstrated [3, 4]. In this paper we present the first application of the method to investigate a simplified, but applied fuel spray nozzle geometry of the swirl cup design in 2D. The atomization process of Jet-A1 at ambient and at high pressure conditions is compared in terms of film flow development, mixing and spray characteristics. The influence of pressure is pointed out and quantified. The study demonstrates that the SPH method is a suitable toolbox for the analysis and the design of fuel spray nozzles. Unique analysis tools that are not available in grid-based CFD methods are presented and applied. Droplet distributions are extracted, which can be considered as possible input in subsequent Euler-Lagrange computations.