Direct numerical simulation of primary break-up in swirling liquid jet

The development and fragmentation of a conical swirled liquid jet has been numerically predicted implementing a multi-phase flow model according to the VOF (Volume Of Fluid) methodology. Direct numerical simulations (DNS) have been performed using the in-house FS3D (Free Surface 3D) code. Two operating conditions, corresponding to typical test cases for an aircraft engine, have been investigated under isothermal and non reacting environment. The inlet boundaries of the numerical problem, corresponding to the characteristics of the annular liquid lamella at the nozzle exit and the internal air core, have been provided by previous internal nozzle flow calculations based on LES (Large Eddy Simulation) methodology. The main features of the jet evolution and fragmentation are analysed, evaluating the lamella instability characteristics in terms of fastest growing wavelength and break-up length. The break-up outcomes are liquid ligaments, which shape and size were evaluated and statistically described. Comparison with available analytical models are reported and discussed.