Mechanical heart valves implanted in mitral position have a great effect on the ventricular flow. Changes include alteration of the dynamics of the vortical structures generated during the diastole and the onset of turbulence, possibly affecting the efficiency of the heart pump or causing blood cell damage. Modifications to the hemodynamics in the left ventricle, when the inflow through the mitral orifice is altered, were investigated in vitro using a silicone rubber, flexible ventricle model. Velocity fields were measured in space and time by means of an image analysis technique: feature tracking. Three series of experiments were performed: one with a top hat inflow velocity profile (schematically resembling physiological conditions), and two with mechanical prosthetic valves of different design, mounted in mitral position—one monoleaflet and the other bileaflet. In each series of runs, two different cardiac outputs have been examined by changing the stroke volume. The flow was investigated in terms of phase averaged velocity field and second order moments of turbulent fluctuations. Results show that the modifications in the transmitral flow change deeply the interaction between the coherent structures generated during the first phase of the diastole and the incoming jet during the second diastolic phase. Top hat inflow gives the coherent structures which are optimal, among the compared cases, for the systolic function. The flow generated by the bileaflet valve preserves most of the beneficial features of the top hat inflow, whereas the monoleaflet valve generates a strong jet which discourages the permanence of large coherent structures at the end of the diastole. Moreover, the average shear rate magnitudes induced by the smoother flow pattern of the case of top hat inflow are nearly halved in comparison with the values measured with the mechanical valves. Finally, analysis of the turbulence statistics shows that the monoleaflet valves yield higher turbulence intensity in comparison with the bileaflet and, with top hat inflow, there is not a complete transition to turbulence.

An experimental study of inclined negatively buoyant jets released from a sharp-edged orifice was carried out to better understand the re-entrainment phenomenon, i.e. the mixing of jet fluid with itself instead with external fluid, and how it biases the jet behaviour. Experiments reproducing an orifice in the lateral wall of an outfall pipe on the sea bottom were conducted using light-induced fluorescence. The mean and variance of the concentration field have been determined to study the hydrodynamic features along the jet axis, including turbulent mixing and entrainment as the densimetric Froude number varies. The re-entrainment phenomenon tends to appear as the angle exceeds 75° with respect to the horizontal, and its onset occurs for lower angles as the Froude number increases. The re-entrainment biases the behaviour of the jet trajectory, making it bend on itself, and causing a reduction of both the maximum height and distance at the location where entrainment of external fluid reaches the jet axis.