NUMERICAL-STUDIES OF TRANSITIONAL TURBULENT PULSATILE FLOW IN PIPES WITH RING-TYPE CONSTRICTIONS

Pulsatile flows in the vicinity of mechanical ring-type constrictions in pipes were studied for transitional turbulent flow with a Reynolds number (Re) of the order of 10(4). The Womersley number (Nw) is in the range 30-50, with a corresponding Strouhal number (St) range of 0.014 3-0.0398. The pulsatile flows considered are a pure sinusoidal flow, a physiological flow and an experimental pulsatile flow profile for mec hanical aortic valve flow simulations. Transitional laminar and turbul ent flow characteristics in an alternating manner within the pulsatile flow fields were studied numerically It was observed that fluid accel erations tend to suppress the development of flow disturbances. All th e instantaneous maximum values of turbulent kinetic energy, turbulent viscosity and turbulent shear stress are smaller during the accelerati on phase than during the deceleration period. Various parametric equat ions have been formulated through numerical experimentation to better describe the relationships between the instantaneous flow rate (Q), th e pressure loss (Delta P), the maximum velocity (V-max), the maximum v orticity (zeta(max)), the maximum wall vorticity (zeta(w,max)), the ma ximum shear stress (tau(max)) and the maximum wall shear stress (tau(w ,max)) for turbulent pulsatile flow in the vicinity of constrictions i n the vascular tube. An elliptic relationship has been found to exist between the instantaneous flow rate and the instantaneous pressure gra dient. Other linear and quadratic relations between various flow param eters were also obtained.