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Polydisperse sprays in complex three dimensional flow systems are important in many technical applications. Numerical descriptions of sprays are used to achieve a fast and accurate prediction of complex two-phase flows. The Eulerian and Lagrangian methods are two essentially different approaches for the modeling of disperse two-phase flows. Both methods have been implemented into the same CFD - package which is based on a 3D body-fitted Finite Volume method. Considering sprays represented by a small number of droplet starting conditions, the Eulerian method is clearly superior in terms of computational efficiency. However, with respect to complex polydisperse sprays, the Lagrangian technique gives a higher accuracy. In addition, Lagrangian modeling of secondary effects such as spray-wall interaction enhances the physical description of the two-phase flow. Therefore, in the present approach the Eulerian and the Lagrangian methods have been combined in a hybrid method. The Eulerian method is used to determine a preliminary solution of the two-phase flow field. Subsequently, the Lagrangian method is employed to improve the accuracy of the first solution using detailed sets of initial conditions. Consequently, this combined approach improves the overall convergence behavior of the simulation. In the final section, the advantages of each method are discussed when predicting an evaporating spray in an intake manifold of an IC-engine.

Polydisperse sprays in complex three-dimensional flow systems are important in many technical applications. Numerical descriptions of sprays are used to achieve a fast and accurate prediction of complex two-phase flows. The Eulerian and Lagrangian methods are two essentially different approaches for the modeling of disperse two-phase flows. Both methods have been implemented into the same computational fluid dynamics package which is based on a three-dimensional body-fitted finite volume method. Considering sprays represented by a small number of droplet starting conditions, the Eulerian method is clearly superior in terms of computational efficiency. However, with respect to complex polydisperse sprays, the Lagrangian technique gives a higher accuracy. In addition, Lagrangian modeling of secondary effects such as spray-wall interaction enhances the physical description of the two-phase flow. Therefore, in the present approach the Eulerian and the Lagrangian methods have been combined in a hybrid method. The Eulerian method is used to determine a preliminary solution of the two-phase flow field. Subsequently, the Lagrangian method is employed to improve the accuracy of the first solution using detailed sets of initial conditions. Consequently, this combined approach improves the overall convergence behavior of the simulation. In the final section, the advantages of each method are discussed when predicting an evaporating spray in an intake manifold of an internal combustion engine.

The present study addresses the numerical prediction of the two-phase flow in the intake port of a SI-engine. Particular emphasis is put on transient phenomena, as well as secondary effects, such as droplet breakup and droplet wall interaction. These phenomena have a significant influence on the fuel air mixture characteristics and cannot be neglected in the numerical prediction. The numerical methodology, presented in this paper, is based on a 3D body-fitted Finite Volume discretization of the gas flow field and a Lagrangian particle tracking algorithm of the disperse fuel phase. The Unsteady Reynolds Averaged Navier-Stokes equations (URANS) are solved by a time-implicit three level scheme. In the Lagrangian particle tracking algorithm, the spray is modeled by superposition of a large number of droplet trajectories. Two advanced numerically effective models are presented for the prediction of droplet breakup and droplet wall interaction. Special emphasis is put on the correct reproduction of the droplet statistics. In the present study the fuel injection and spray preparation process within the intake port of a SI-engine is investigated. Spray preparation is dominated by atomization processes like droplet breakup and wall interaction which predominantly take place at the valve seat. In order to find the principal characteristics of fuel preparation in a SI-engine, a parametric study has been carried out focusing on the influence of the gap sizes of the intake valve which strongly affects the complete fuel preparation process. The study is concluded by an analysis of qualitative and quantitative results of the predicted flow field.