SECONDARY BREAK-UP OF LIQUID DROPLETS: EXPERIMENTAL INVESTIGATION FOR A NUMERICAL DESCRIPTION

In order to analyze secondary break-up of single droplets usually image-forming systems are used. These allow detailed time-resolved investigations of the droplet deformation and disintegration processes. However, in real sprays, due to a superposition of multiple droplets of different sizes and due to high volume fluxes in the center of the spray, the use of image-forming systems is problematical. For that reason, experimental results are in genera] not comparable to the results of numerical computations. Therefore, in the present study a Phase-Doppler-Anemometer (PDA) is used for the spray analysis, knowing the limitations of the system measuring non-spherical droplets. This PDA-system provides a very good spatial resolution of the data and allows detailed comparisons between measured data and numerical calculations.

For the experiments a rectangular flow duct made of acrylic glass is used, so an excellent accessibility for all optical measuring systems is obtained. By a full analysis of the experimental data, areas are detected, where due to secondary break-up non-spherical droplets occur and consequently the droplet size cannot be determined correctly. Therfore, a criterion is developed to determine a demarcation of these areas. Considering this criterion, comparisons of the experimental results with numerical calculations are carried out. The calculations using a new developed break-up model reveal a significant improvement by the use of break-up correlations in contrast to calculations where secondary break-up is not taken into account.