Boundary layer analysis of nonlinear reaction-diffusion equations in a polygonal domain

We propose a boundary layer analysis which fits a domain with corners. In particular, we consider nonlinear reaction-diffusion problems posed in a polygonal domain having a small diffusive coefficient ε>0. We present the full analysis of the singular behaviours at any orders with respect to the parameter ε where we use a systematic nonlinear treatment initiated in Jung et al. (2016). The boundary layers are formed near the polygonal boundaries and two adjacent ones overlap at a corner P and the overlapping produces additional layers, the so-called corner layers. It is noteworthy that the boundary layers are also degenerate due to the singularities of the solutions involving a negative power of the radial distance to the corner P which are present in the Laplace operator on a sector (sector corresponding to the part of the polygon near the corner). The corner layers are then designed to absorb both the singularities and the interaction of the two boundary layers at P.