Unstructured grids can offer flexible and accurate geometrical approximations of reservoir models. Upscaling methods like Darcy flow-based numerical approaches can produce realistic and accurate reservoir grids. Initial flow-based upscaling approaches were developed for cartesian grids. Flow simulations were computed on groups of fine-scale grid elements covering one or many coarser elements (local, extended local, global methods). The main difficulty in flow-based methods is to define accurate fine-scale boundary conditions allowing to recover realistic coarse-scale fluxes. While cartesian grids use orthogonal directions to define vertical or horizontal pressure gradients across the simulation domain in unstructured meshes no more vertical or horizontal coarse grid alignment can be used. We investigate here fluid flow immersed boundary methods to allow incorporating cartesian-like vertical and horizontal boundary conditions for Cartesian like upscaling on unstructured meshes. I will briefly present cartesian-like flow-based upscaling approaches and then give a short review of immersed boundary methods from cartesian grids to unstructured mesh ones.