Fluid dynamics in helical geometries with applications for by-pass grafts

By-pass graft failure is mainly caused by progressive intimal hyperplasia at graft anastomosis and restenosis. A helical graft induces a swirl flow pattern at the outlet section of the graft, and that can reduce the effects that cause the graft failure. This paper analyses the efficiency of helical geometries in terms of helicity and vorticity. Twelve different configurations, with one, two and four turns and different values for helix amplitude were considered for numerical analysis in steady and laminar conditions, associated with Re = 151 and Re = 377. Results show that high number of turns and high amplitude induces significant variations for helicity and vorticity. We can assume, that in the conditions of our study, the most appropriate geometries for obtaining at the outlet section a swirl flow pattern, with applications for by-pass grafts, are the configurations with four-turns and amplitude of 0.3D to 0.5D, associated with helical geometry diameter D.