A novel predictive dual scale model to accurately and efficiently simulate phase interfaces in turbulent flows

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Turbulent flows with phase interfaces occur in almost every aspect of our daily lives, ranging from energy systems using liquid fuels to pharmaceutical sprays. Many of these flows involve atomizing a liquid into small-scale drops forming a spray. The performance of the overall system depends strongly on the quality of this spray. For example, in aircraft or internal combustion engines improvements in the quality of the spray can result in efficiency gains and reduction in pollutant production. In medical sprays, precisely controlling the spray drop sizes of aerosols can significantly improve the delivery of pharmaceuticals into the lung. Unfortunately, no efficient model derived from first principle currently exists that can predict and simulate the complex process of spray formation in turbulent flows. Thus an incremental design improvement philosophy is prevalent in many applications because experiments of radically new designs are very costly and numerical simulations lack a predictive model for turbulent atomization processes and thus require tuning with existing experimental data. The goal of this project is to develop an efficient predictive model to simulate atomization processes in turbulent flows. Such a model has the potential to initiate a bold new design philosophy that targets radically new designs because the cost of pre-selection feasibility studies using the new model would be significantly lower than experimental studies. The project also incorporates significant educational activities, including involvement of undergraduate researchers and outreach targeting local Title-One schools through on-campus activities and off-campus classroom visits.The new model is based on the idea of a dual scale approach, circumventing the limitations of classical modeling approaches for turbulent flows that rely on the existence of a cascade process from large to small scales. Such a cascade is likely not dominant for atomizing phase interfaces since surface tension forces that are dominant on the small scale can both generate and annihilate small scale interface structures. The proposed dual scale approach takes this into account by employing a multi-scale decomposition that combines features of direct numerical simulations resolving the small scales with large eddy simulation for the larger scales in an efficient way. This approach inherently incorporates the interaction and competition between different forces and atomization mechanisms acting on multiple length and time scales and enables the explicit closure of terms requiring modeling on the larger scales by applying explicit filters to the resolved scale phase interface geometry.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.