Measurement of turbulent flow in vascular grafts

For a smooth-walled tube, the critical Reynolds number R _c is primarily determined by the geometry of the inlet and is usually on the order of R_c=2000, although it has been measured as high as R_c=40000 in some highly refined systems. The effect of wall irregularities, such as in a fabric graft, is to lower R_c. The author reports the results of recent experiments to determine the extent of this effect. It is found that flow in the tube became intermittently unstable at R =3100 and turbulence was fully developed at R=4000. This is consistent with the results of other workers. Flow in the graft became intermittently unstable at R=1500 and was fully turbulent at R=1700. The progression from instability to full turbulence was much more rapid in the graft than in the tube, a characteristic feature of roughness-induced turbulent flow