Investigation of the flow field downstream of an artificial heart valve by means of PIV and PTV

摘要

Measurements of the velocity field downstream of an artificial heart valve are performed by using particle image velocimetry (PIV) and particle tracking velocimetry (PTV). The investigated field corresponds to the region immediately downstream of the valve outlet i.e. the initial ascending part of the aorta. The aim of the paper is to investigate the evolution of the flow field in time in such inhomogeneous, anisotropic, and unsteady conditions. To do this, a high-speed video camera is used to acquire images of the seeding particles illuminated by a continuous infrared laser. high seeding density conditions are investigated using PIV to perform phase-sampled Eulerian averages, whereas low seeding conditions are used to determine particle trajectories and Lagrangian statistics using PTV. Both are needed for the complete description of the magnitude and duration of the stress on blood cells. The following features are described: - The very high inhomogeneity and unsteadiness of the phenomenon - The presence of large scale vortices within the field especially in the sinuses of Valsalva and in the wake of the valve leaflets - The strong stress and strain rates at the jet-wake interface downstream of the leaflets and close to large-scale vortices - The non-negligible time spent by fluid particles in some of the high stress and strain regions. [References: 19]