Time-Response of Recent Prefilming Airblast Atomization Models in an Oscillating Air Flow Field

Abstract

The present study investigates the response of recent primary breakup models in the presence of an oscillating air flow and compares them to an experiment realized by Müller (2015, “Experimentelle Untersuchung des Zerstäubungsverhaltens Luftgestützter Brennstoffdüsen bei Oszillierenden Strömungen,” Ph.D. thesis, Karlsruhe Institute of Technology, Karlsruhe, Germany). The experiment showed that the oscillating flow field has a significant influence on the Sauter mean diameter (SMD) up to a given frequency. This observation highlights the low-pass filter character of the prefilming airblast atomization phenomenon, which also introduces a significant phase shift on the dynamics of SMD of the generated spray. The models are tested in their original formulations without any calibration in order to assess their robustness versus different experiments in terms of SMD and time-response to an oscillating flow field. Special emphasis is put to identify the advantages and weaknesses of theses models, in order to facilitate their future implementation in computational fluid dynamics (CFD) codes. It is observed that some models need an additional calibration of the time constant in order to match the time shift observed in the experiment, whereas some others show a good agreement with the experiment without any modification. Finally, it is demonstrated that the low-pass filter character of the breakup phenomenon can be retrieved by considering the history of the local gas velocity, instead of the instantaneous velocity. This might result in a higher simulation fidelity within CFD codes.