Experimental investigation of the steady flow downstream of the St. Jude bileaflet heart valve: a comparison between laser Doppler velocimetry and particle image velocimetry techniques.

This study investigates turbulent flow, based on high Reynolds number, downstream of a prosthetic heart valve using both laser Doppler velocimetry (LDV) and particle image velocimetry (PIV). Until now, LDV has been the more commonly used tool in investigating the flow characteristics associated with mechanical heart valves. The LDV technique allows point by point velocity measurements and provides enough statistical information to quantify turbulent structure. The main drawback of this technique is the time consuming nature of the data acquisition process in order to assess an entire flow field area. Another technique now used in fluid dynamics studies is the PIV measurement technique. This technique allows spatial and temporal measurement of the entire flow field. Using this technique, the instantaneous and average velocity flow fields can be investigated for different positions. This paper presents a comparison of PIV two-dimensional measurements to LDV measurements, performed under steady flow conditions, for a measurement plane parallel to the leaflets of a St. Jude Medical (SJM) bileaflet valve. Comparisons of mean velocity obtained by the two techniques are in good agreement except for where there is instability in the flow. For second moment quantities the comparisons were less agreeable. This suggests that the PIV technique has sufficient temporal and spatial resolution to estimate mean velocity depending on the degree of instability in the flow and also provides sufficient images needed to duplicate mean flow but not for higher moment turbulence quantities such as maximum turbulent shear stress.