Flow characteristics around proximal and distal stenoses in a series of tandem stenosed vessels.

The flow characteristics around the proximal and distal stenoses in tandem vessel models are experimentally investigated with varying flow rates (Q=0.25, 0.5, 1.0L/min), interspacing distances (L=3, 6, 10 of diameter D) and severities (S=50%, 75% reduction in diameter). When the interspacing L is larger than 10 D, no fluid-dynamic interaction is observed. The flow between the proximal and distal stenoses becomes stabilized (turbulence intensity of <3%) as the interspacing distance decreases. When the severity S is 75%, the transition from laminar to turbulent flow occurs at a flow rate higher than 0.5L/min, although the interspacing distance L is 3 D. Formation of recirculation flow is restricted by the presence of distal stenosis as the interspacing distance decreases. In this case, the flow between the stenoses is focused on the central region. The center-line velocity at the neck of the distal stenosis is approximately 10-15% higher than that of the proximal stenosis with equal severity of S=50%. When the inlet flow is center-focused, the lengths of the recirculation and the jet core behind the distal stenosis increase with decrease in interspacing distance L. When the inlet flow is turbulent, the transition from laminar to turbulent flow occurs early as the interspacing distance L is reduced. When the upstream proximal stenosis exhibits increased severity, the pressure drop is measured to be 20% compared with that when the severity of the downstream distal stenosis is increased at the flow rate of Q=1.0L/min.