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 and coworkers in 2008. 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 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. * geoffroy.chaussonnet@kit.edu † Dr. A. Müller is currently Team leader for sensor systems at JENOPTIK Robot GmbH

Influence of the ambient pressure on the liquid accumulation and on the primary spray in prefilming airblast atomization

“…Hence, the discrepancy comes from the calibration constants. This model was already compared to an experiment similar to the present one in a previous publication (Chaussonnet et al 2017) and it was also found to deliver too small droplets. This is because in the bimodal PDF used by this model, one peak is overestimated compared to the other.…”

“…This is because in the bimodal PDF used by this model, one peak is overestimated compared to the other. After recalibration, it delivered a good prediction of the SMD (Chaussonnet et al 2017). For all correlations, the dependency on the ambient pressure is represented by the gas density, whose exponent is given in Table 8.…”

“…However, it predicts the current experiment with a remarkable good agreement. As pointed out in (Chaussonnet et al 2017), this can be explained by the fact that the model first overestimates the mean droplet size, and then reduces it by using the TAB model. The correlation from Eckel et al (2013) was calibrated using the experiment by Gepperth et al (2012).…”

“…Then, the author use a Taylor Analogy Breakup (TAB) model to mimic the secondary breakup that occurs between the atomizing edge and the measurement distance. The interested reader is referred to (Inamura et al 2012) for further details, and to (Chaussonnet et al 2017) for a concise explanation of how to implement the model. The correlation from Eckel et al (2013) is a model that predicts a bimodal drop size distribution downstream the atomizing edge.…”

“…It also supposes two different instabilities on the film surface. Further details can be found in (Eckel et al 2013) and a condensed description of implementation can be found in (Chaussonnet et al 2017). The correlation from Gepperth et al (2013) was derived from the same experimental setup as in this work, based on a previous campaign (Gepperth et al 2012) with a different atomizing edge.…”