Characterization of a diffuser flow by time-resolved PIV

Computational fluid dynamics is extensively used in the design methodology of medical devices. However, for such applications, the predictive capabilities of CFD codes are highly dependent upon geometry, which most of the time is extremely complex, and flow conditions. The study concerns a ventricular assist device (VAD) where the exit flow, generated through a diffuser, is of particular importance for blood damage predictions. The difficulty to predict the flow lies in the fact that the Reynolds number range includes the transition Reynolds number of the separated diffuser flow as well as the critical Reynolds number of pipe flows. In order to choose the appropriate CFD methodology in terms of flow hypothesis and turbulence model, an experimental setup of the diffuser was built to run PIV velocity measurements and to analyze the flow pattern with the influence of Reynolds number. The flow is described with mean and variance values of the in-plane velocity components and timeresolved results are used to visualize the development of unsteady phenomena introduced in the diffuser separated region. An optimal filter is also used to remove noise in measured velocity vector fields.