I am working on optimizing the PSWIFT parametrization of complex street canyon geometries. For that, I am currently setting up an LES simulation for a periodic street canyon (see picture) and I was wondering about the cell sizes near the walls. My university tutor told me to aim for y+ = 2 normal to the walls and y+ = 50-100 along the flow, this being valid for attached BL only. This would result in a huge mesh for me. Since my model represents a cavity and thus a detached flow, what cell sizes should I be aiming for close to walls inside my street in order to represent the flow patterns correctly? The output information I am looking for is the macrospopic flow structure, so I guess I don't need to know that much about the BL flow. My only concern is that the main flow patterns are changed significantly due to insufficient wall resolution.
Merci d'avance!
Victor