Evaluating the Importance of Nonlocal Eddy Diffusivity for Rayleigh Taylor Instability

In this work, we investigate the importance of the nonlocality of the eddy diffusivity operator in RANS models for Rayleigh-Taylor Instability (RTI) using the macroscopic forcing method (MFM). With this method, we measure the moments of the eddy diffusivity in RTI, including the zeroth order moment, which is purely local, and higher order moments in space and time, which characterize nonlocality. We show that the nonlocal effects cannot be ignored when constructing a RANS model, as omission of the terms corresponding to higher order moments results in erroneous predictions. Finally, we present a framework for constructing a nonlocal model for RTI based on our MFM measurements.