Comparison of viscous and inviscid numerical simulations of the start-up vortex issuing from a semi-infinite flat plate

Subject of the present work is the start-up vortex issuing from a sharp trailing edge accelerated from rest in still air. A numerical simulation of the flow has been performed in case of a semi-infinite flat plate by solving the Navier-Stokes equations in the Psi-Omega formulation. The new numerical algorithm is based on a fast multigrid implicit integration of the difference equations in an unstructured mesh that is dynamically built to minimize the computational costs. The results, compared with inviscid lumped-vortex simulations, show the appearance of instabilities that quickly destroy the regular structure of the spiral vortex. This analysis gives a contribution to the understanding of a physical problem still discussed in the literature and raises the question whether the application of numerical regularization procedures can tend to stabilize a phenomenon even when its physical nature is unstable