PIV and PTV measurements downstream an artificial heart valve by A. Balducci (1) , M. Grigioni (2) , G. Querzoli (3) , G.P. Romano (1) , C. Daniele (2) , G. D’Avenio (2), V. Barbaro (2) (1) Dept. Mechanics and Aeronautics, University "La Sapienza", Roma, Italy romano@dma.ing.uniroma1.it (2) Istituto Superiore di Sanita’, Roma, Italy grigioni@iss.it (3) Dip. Ingegneria del Territorio, University of Cagliari, Italy querzoli@unica.it ABSTRACT 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 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. The investigated field corresponds to the region immediately downstream of the artificial valve outlet i.e. the initial ascending part of the aorta. An example of the bi-leaflet valve used in the experiments is given in figure 1, together with the velocity field measured by PIV 50 ms after the opening of the valve (descending part of the systolic peak). The investigated flow field is extremely complex and the amount of acquired data is very high. A preliminary inspection of such data reveals the following features: - the very high inhomogeneity and unstationarity of the phenomenon; - the presence of large scale vortices within the field especially in the Valsalva sinuses and in the wake of the valve leaflets (as the one on the right part of figure 1); - the strong stresses at the jet-wake interface downstream of the leaflets and close to large-scale vortices. a b Fig.1. An example of the flat bi-leaflet artificial heart valve (a) and the measured velocity vector field (t = 220 ms) with overlapped vortex detection (b). Peak Reynolds number equal to 3200 (D is the valve diameter).