Assessment of non-Boussinesq effects in a separated turbulent boundary layer with an emphasis on non-locality*

In this work, we consider a canonical separated boundary layer flow at Re_θ= 350, where a separation bubble is induced in a fully turbulent boundary layer over a flat plate. Using the macroscopic forcing method (MFM), the leading-order anisotropic eddy viscosity is quantified, and its key anisotropic directions are identified to narrow down to 5 components. A posteriori analysis demonstrates significant improvement in RANS prediction of mean flow when this leading-order eddy viscosity operator is used instead of isotropic models based on the Boussinesq approximation. However, non-negligible errors still remain due to the non-local effects which are not captured by the leading-order eddy viscosity model. We present a preliminary attempt to address the need for non-locality using a simple non-local Boussinesq model.