Protoplanetary Disks (PPD) are sheet-like, large scale astrophysical vortices that rotate around central massive object such as young stars. These disks are mainly composed of cold gas with a small portion of dust. Though PPD are believed to be the birthplace of planets, no mechanism has been identified so far to explain the aggregation of dust into planets on timescales shorter than the lifespan of the disks themselves, of order of magnitude one million years. The generation of local, small scale vortices in the flow could promote aggregation of a planetesimal by confining dust. In this talk, we consider the potentiality of vortex generation in a PPD: we investigate the stability of a quasi- Keplerian, non magnetic flow in the vicinity of its equatorial plane by means of a multiscale analysis which yields a family of reduced systems of equations for the dynamics of perturbations. We will focus on one of these models that features potentiality for instability: we will discuss analytical results about linear stability, along with direct numerical simulations of the fully non linear viscous equations.