A direct numerical simulation has been conducted for a laminar flow in a constricted tube with an immiscible droplet in order to investigate the phenomena which an viscoelastic object such as a thrombus causes when it passes through a stenosed vessel. An immersed-boundary method is used for simulating the flow inside the constricted tube, while the PLIC-VOF algorithm is used for tracking the droplet interface. We have focused on a neutrally buoyant droplet of a fixed size. It is found that the droplet shape strongly depends on the capillary number, while the droplet velocity mainly depends on the viscosity ratio between two phases. The drag force (or fluid resistance) associated with the flow inside the tube is found to increase due to the presence of the droplet at low capillary numbers and at high viscosity ratios. The drag fluctuates when the droplet passes through the constricted area. This is triggered by a relatively large fluctuation in the pressure drag.

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