STEADY AND PULSATILE FLOWS IN A PIPE WITH A RING-TYPE CONSTRUCTION

Abstract

Numerical investigations have been carried out for laminar steady and pulsatile, turbulent steady and pulsatile flows in a pipe with a ring-type constriction. A second-order numerical method has been developed to solve the fluid flow governing equations on non-staggered grid. A mechanical pulsatile flow generator has been designed to produce and study different types of pulsatile flow. The present results are applied to bio-medical flow phenomena. The physiological, sinusoidal and non-zero mean velocity sinusoidal laminar flows are computed to study the effect of pulsating frequency. The pulsating frequency has large effect on the axial pressure gradient. Linear relations exist between the flow rate and the maximum values of velocity, vorticity and shear stress. The physiological flow, the No. I and No.2 experimental pulsatile flows have very similar properties. The amplitude has large effect on the relation between the flow rate and axial pressure gradient. The relations between the flow rate and pressure loss are approximately quadratic. The Reynolds number has small effect on pulsatile laminar flow field. Four types of k-? turbulence model are compared in the computation of turbulent flow with Reynolds number ranging from 50 to 106. The streamline curvature correction k-? turbulence model is found to have better performance in predicting the velocity and recirculation length. Steady turbulent flow is computed to study the effects of Reynolds number, constriction opening ratio and constriction thickness ratio. The Reynolds number has large effect on the recirculation length and fully developed velocity profiles, but small effect on the maximum turbulent shear stress and pressure loss. The recirculation length, pressure loss, the maximum values of turbulent shear stress and vorticity increase with the reduction of d/D. The centerline kinetic energy distribution has one peak for d/D > 0.6 and two peaks for d/D ? 0.5. The flow structures of laminar, turbulent, the transitions from laminar to turbulent and from turbulent to laminar are predicted in the numerical simulation of pulsatile turbulent flows. Elliptic relations exist between the flow rate and the axial pressure gradient. Quadratic relations exist between the flow rate and the pressure loss. Linear relations exist between the flow rate and the maximum values of velocity, vorticity. The No. 2 experimental pulsatile flow has the same flow property as the physiological flow. The property of sinusoidal flow are different from these two pulsatile flow. The pulsating amplitude has large effect on the axial pressure gradient, but small effect on the pressure loss, maximum values of vorticity, velocity, shear stress and turbulence kinetic energy. By using the mechanical pulsatile flow generator, experimental investigations reveal the relations between flow rate and the axial pressure gradient for sinusoidal flow, non-zero mean velocity sinusoidal flow and other experimental pulsatile flows. The measurement data are consistent with the present numerical results.