Effect of wettability on the aeration characteristics of rotating thin films between EDM-prepared surfaces

Abstract. Rotating thin-film flows with small film-thickness-to-radius ratios play a critical role in various power transmission systems, such as multidisc wet clutches and limited-slip differentials. Over the past two decades, significant attention has been given to a well-documented phenomenon in wet clutch applications: the formation of two-phase Automatic Transmission Fluid (ATF)-air flow at high rotational speeds. The objective of this research is to further explore the aeration characteristics in such systems, with a focus on the impact of surface wettability due to surface topography alteration. Specifically, the study examines the progression of air bubbles into the fluid domain and the subsequent effect on drag torque, i.e., the viscous torque generated between the discs as a result of ATF’s shear stress, using a Computational Fluid Dynamics (CFD) approach. To assess this, different surface roughness profiles are achieved by varying the Electro Discharge Machining (EDM) parameters and are further characterized by measuring the contact angle. These surface textures are then correlated with aeration characteristics, revealing that oleophilicity increases aeration. This research is part of the WetSURF project, under the Basic Research Framework Programme at the National Technical University of Athens.