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Direct Numerical Simulation (DNS) is getting more and more relevant in numerical analysis of sprays, allowing insight on breakup mechanism, granulometry studies and analysis of the turbulence field. While for more fundamental studies, the flow inlet boundary conditions are often neglected, it is mandatory for real application analysis to use reliable boundary condition in order to replicate as faithfully as possible the physical phenomena. On the other hand, the exact solution for many nozzles of engineering interest is unknown, hence there is a tendency to use simplified boundary conditions, such as the ones generating synthetic turbulence, as a simpler way to approach sprays DNS simulations without falling into the uncertainties of the nozzle flows.
In this framework, this work presents a comparison between DNS simulations in Paris-Simulator using both a digital filter based synthetic turbulence inflow boundary conditions against the mapped results generated by a Large Eddy Simulation of a periodic pipe flow. Both simulations will be carried at a Re=5050 and with physical parameters resembling the SprayA configuration given by the Engine Combustion Network. The main aim of the work is to understand how the longitudinal turbulence structures developed inside the nozzle are affecting the atomization regime and the breakup mechanism. This analysis is supported by an in-depth comparison of the resulting granulometry for both simulations, as well as an analysis of the turbulent structures developed on the spray liquid surface which trigger the primary breakup process.
After providing an in-depth analysis of the flow behavior, the conclusions will be aiming to drawn some useful considerations on what are the main implications of the two approaches and whether or not synthetic boundary conditions are feasible for engineering studies, where usually the degree of complexity of the flow features outside the nozzle is more stringent than theoretical studies.
