Studio e Controllo di Strutture Vorticose di Parete

At some flow configurations a strong vortex is standing close to the wall and creates a sliding surface which moves and prevents flow separations. In the literature this phenomenon is known as the "snow-cornice effect" . An analitycal model for steady solutions is proposed here, which is able to predict the main features of the flow control mechanism. The tools of the theory of the Hamiltonian dynamical systems are applied to determine the strength and the the position of the trapped vortex and to discuss its stability. The unsteady evolution of a distributed-vorticity region is then investigated numerically by using a high-order blob vortex method. To speed up the computations, a Fast multipole Method is used, which has been extended to general domains by a conformal mapping technique. The transient from the impulsive start to the final, on average steady, flow characterized by the trapped vortex structure is observed for a flow configuration with a single cavity ( the Ringleb Flow), for flows with periodic cavities, and for flows on rotor with N cusps and cavities.