A fibre sensor based frequency analysis of surface waves at hollow cone nozzles

The characterization of the disintegration process caused by sheet break up, e.g. at hollow cone nozzles (HCN) is of fundamental importance for a better understanding of the drop formation process. This paper introduces our new measuring device capable of resolving surface wave formation and propagation on the sheet along main streamlines of the flow. Furthermore, it reveals the development of adapted algorithms for the data and image evaluation. Two different frequency ranges are found for the oscillations on the sheet at higher viscosities, showing a superposition of different spectra in each case. The wave bands in the lower frequency range 10<f _low<80 s⁻¹ are considered to be irrelevant for the disintegration process. Surface waves with higher energy content at given conditions are found within a range 300<f _high<1,500 s⁻¹ probably leading to sheet disintegration. Results obtained from a photo-based evaluation show good agreement compared to the frequency analysis.