A 2D simulation method for computing droplet size spectrum during the atomization of High-speeds liquid jets

Based on both experimental observations and available numerical methods, an innovative 2D approach for determining droplet size during the atomisation process has been developed. Based on experimental evidences (Sallam and Faeth (2003); Fath, Munch and Leiperzt (1997)) atomisation of turbulent high speed jets is assumed to occur in a two stage process: ligaments detachment and droplet formation. The simulation method here proposed wants to take the advantages typical of the two most effective methods in spray investigation. It joins DNS approach and the Linear Stability Analysis: the first one is used to solve the liquid-air fluid dynamics interaction and in particular the instabilities leading to ligaments formation. The second one is finally adopted to compute the droplet size spectrum from ligament breakup. Therefore dynamics of ligament formation is directly computed while droplet formation is modelled by using a Linear Stability Analysis. The numerical simulation adopts a VOF method to track liquid-gas interface. Turbulence effects on liquid surface are accounted for by adding a turbulent flow field at the nozzle exit which represents a part of the boundary condition of the computational domain. A physical criterion is then applied to detach ligaments from liquid jet surface which will reduce in diameter during simulation. The droplet formation is then computed by applying the linear stability analysis to the ligaments, assumed being circular and subject to circulation. Liquid core length, droplet size spectrum and near cone angle are the determined. Then an extensive validation and sensitivity analysis has been carried out in order to assess method advantages and limits. The experimental results of Wu et al. (1986) and Hiroyasu et al. (1974) were used as test cases. The method exhibits promising attitude in the reconstruction of the droplet size spectrum depending on injection parameter or conditions