Predicting fuel spray interaction with large scale vortex structures still is a major challenge for state-of-the-art CFD codes. In order to elucidate the mechanisms involved, a fundamental study has been carried out in which the interaction of water droplets with a Karman vortex street is investigated. The disperse two-phase flow around a cylinder has been computed taking into account the mass, momentum and heat transfer between both phases. Flow conditions are chosen such that large scale vortices are generated by periodic flow separations of the well known Karman vortex street. A homogeneous distribution of water droplets is injected into the hot air up-stream of the computational domain. The mixing process as well as the impact of the droplets on the gas phase instabilities is analyzed in the downstream region where large scale vortex structures are present.

The emission of jet engines is strongly affected by the fuel preparation process. Due to stringent emission standards, the development of low emission combustor concepts, like lean premixed prevaporized combustion or rich quench lean burn, is an important goal. For the design process of advanced combustors, numerical methods become more and more important. In order to provide an accurate prediction of the fuel preparation process, an exact numerical prediction of thermophysical processes is crucial. A numerically effective fuel droplet evaporation model is presented in the present paper which accounts for the description of multi-component fuels like kerosene. Fractional boiling is described by a single process variable: the molar weight. This way, the fractional distillation process during evaporation of kerosene droplets is taken into account. In addition, a novel method for modeling the properties of the fuel is provided: the property data are supplied as a function of the molar weight. Real gas effects are also taken into account, in order to achieve an accurate prediction at elevated pressures. The major advantage of this new model is that algebraic expressions are derived for the multi-component droplet vaporization. Thus, the present model combines both numerical efficiency and accuracy.

The low-pressure oxidizer preflow during start-up of an upper-stage rocket engine is analyzed computationally. An iterative Euler-Lagrange approach is used to describe the three-dimensional two-phase flow of oxidizer vapour and spray which is characterized by intense phase transfer. Multipoint injection and flash-atomization of liquid oxidizer is modelled by stochastic droplet injection according to injector locations and spray characteristics. Based on the framework of classical D²-theory, a flash-evaporation model is developed to describe heat and mass transfer between superheated liquid droplets and vapour flow. The computed transsonic flow field agrees well with experimental characteristics such as pressure level and temperature decrease and further provides detailed local information on vapour flow homogeneity and liquid wall deposit.

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.

The development of low emission aero engine combustors strongly depends on the availability of accurate and efficient numerical models. The prediction of the interaction between two-phase flow and chemical combustion is one of the major objectives of the simulation of combustor flows. In this paper, predictions of a swirl stabilized model combustor are compared to experimental data. The computational method is based on an Eulerian two-phase model in conjunction with an Eddy Dissipation (ED) and a presumed-shape-PDF (JPDF) combustion model. The combination of an Eulerian two-phase model with a JPDF combustion model is a novelty. It was found to give good agreement to the experimental data.