SIMULATION OF THE PISTON DRIVEN FLOW INSIDE A CYLINDER WITH AN ECCENTRIC PORT

grid-free Lagrangian approach is applied to simulate the high Reynolds number unsteady flow inside a three-dimensional domain with moving bo undaries. For this purpose, the Navier-Stokes equations are expressed in terms of the vorticity transport formulation. The convection and st retch of vorticity are obtained using the Lagrangian vortex method, wh ile diffusion is approximated by the random walk method. The boundary- element method is used to solve a potential flow problem formulated to impose the normal flow condition on the boundary of the domain. The n o-slip condition is satisfied by a vortex the generation mechanism at the solid boundary which takes into account the time-varying boundary surfaces due to, e.g., a moving piston. The approach is entirely grid- free within the fluid domain, requiring only meshing of the surface bo undary, and virtually free of numerical diffusion. The method is appli ed to study the evolution of the complex vortical structure forming in side the time-varying semi-confined geometry of a cylinder equipped wi th an eccentric inlet port and a harmonically driven piston. Results s how that vortical structures resembling those observed experimentally in similar configurations dominate this unsteady flow. The roll-up of the incoming jet is responsible for the formation of eddies whose axes are nearly parallel to the cylinder axis. These eddies retain their c oherence for most of the stroke length. instabilities resembling conve ntional vortex ring azimuthal nodes are found to be responsible for th e breakup of these toroidal eddies near the end of the piston motion. The nondiffusive nature of the numerical approach allows the predictio n of these essentially inviscid phenomena without resorting to a turbu lence model or the need for extremely fine, adaptive volumetric meshes .