Publication Detail

Modeling of thrust generating foils

Laura Guglielmini
141 pp.
MITSG 04-17
$10.00 DOM / $15.00 INT

The aim of this research thesis is to contribute to the comprehension of the unsteady fluid dynamics generated by flapping foils. In particular, we address the problem of the identification of the vortical structures generated by a foil in steady forward motion with constant velocity which oscillates with a combination of harmonic heaving and pitching motions. In a first approach we make the assumption of large values of the Reynolds number, so that viscous effects are significant only during the separation process. Hence, we consider an inviscid flow and the vortex structures generated by the boundary layer separation both at the leading and trailing edges of the oscillating plate are replaced by simple concentrated vortices, following the method proposed by Brown and Michael (1954). In a second part we solve numerically the governing momentum and continuity equations for the two-dimensional problem using a stream-function vorticity formulation. This approach allows to study the large scale vortical dynamics of the wake and to identify parameters corresponding to optimal propulsive performances, for moderate values of the Reynolds number.

At last, we consider the problem of the identification of the three-dimensional structure of the flow around a heaving and pitching foil of low aspect-ratio. The numerical solution is achieved by means of the code N"T r, a general purpose spectral/hp element model for solving the Navier-Stokes equations in moving domains. The simulations at Reynolds number 164 have allowed to reproduce the experiments presented in von Ellenrieder et al. (2003), to compare vorticity and velocity fields with dye visualizations and to contribute to the understanding of the mechanisms of vortical structures formation and shedding.

type: Full theses / dissertations

Parent Project

Project No.: 2001-RT-2/RD-13
Title: Biomimetic Rigid Hull Vehicle with Flapping Foils for Enhanced Agility in the Surf Zone and Cluttered Environments