INVESTIGATION OF A PREFILMING AIRBLAST ATOMIZER WITH RESPECT TO SURFACE STRIPPING

One commonly used injection system in gas turbines is the prefilming airblast atomizer which creates a fuel film that should disintegrate at the end of the prefilmer. But under certain conditions droplets are separated from the film before reaching the end of the prefilmer. This phenomenon is called surface stripping. For the investigation of those conditions both an experimental and numerical setup are defined. The experiment measures the film thickness on the prefilmer with the help of the planar laser-induced fluorescence technique. For the numerical investigation the volume of fluid method together with a large eddy simulation of OpenFOAM (R) 2.1.1 is used. After the validation of the numerical model with the experimental data, the dependency of the mean film thickness from the relative velocity of air and water is investigated. It is shown that first the momentum flux ratio is not sufficient in describing the behavior of the film on the prefilmer and second a critical relative velocity has to be exceeded so that surface stripping can take place. Three flow regimes are observed by increasing the relative velocity: smooth film surface, wavy film surface and surface stripping. Due to the surface stripping the transferred fuel mass into the gas phase is increased rapidly.