Inter-species molecular attraction effect in the development of a two-species mixing layer

Abstract

Simulations of fluid mixing occurring at high-pressures mandate the use of real-fluid equations of state to capture the effect of both intermolecular repulsive forces and attractive forces which are neglected in perfect gases. Dedicated mixing rules account for these forces by providing a generic mapping of the mixture state-space onto a pure fluid domain. However, the specific inter-species molecular forces depend on the particular characteristics of the molecular pairs under consideration, and typically require the knowledge of binary interaction coefficients kαβ . The impact of kαβ on a flow field is as of now unclear; further, kαβ is unknown for many molecular pairs and when unknown, set to be null. This study addresses the impact of kαβ on the temporal evolution of a real-fluid mixing layer and uses Direct Numerical Simulation (DNS) to explore this impact. The results show differences between augmented attraction (kαβ < 0) and diminished attraction (kαβ > 0), affecting both fluid dynamics and diffusion processes. Specifically, in a binary mixing layer, it is observed that augmented attraction leads to delayed transition and mixing layer growth, manifested in the momentum layer thickness. The fractal dimension as a measure of interface corrugation likewise shows a delayed development for augmented attraction. These results provide an hitherto undocumented mechanism affecting the development of mixing layers.