Turbulent Blood Flow in a Ventricular Assist Device

Application Challenge AC7-03 © copyright ERCOFTAC 2021

Test Data

Overview of Tests

An experimental validation was performed for two operation points, the partial load ( $Q=2.5~l/min$ ) and the nominal load ( $Q=4.5~l/min$ ) at a rotational speed of $n=7,900~r/min$ . The investigates VAD model was explained in section Flow Domain Geometry. This was originally created exclusively for numerical investigations. In order to enable an adequate validation of the simulated VAD flow, the following requirements were placed on the experimental model during conceptual design:

Due to the small dimensions and narrow gaps, the model to be manufactured must have tolerances in the range of $10-20~\mu m$ .
In the numerical model, the VAD has no axial gaps between rotating and stationary components. The experimental model must have axial gaps as small as possible between these components.
In the numerical model, a hydraulically smooth flow is assumed in the immediate vicinity of the wall. Also in the experimental model, a hydraulically smooth flow should be present at the walls.
No mechanical drive for the impeller is considered in the numerical model. Since the experimental model requires a drive, it must be placed as free as possible from interference for the flow.
It should be possible to measure various flow variables with the model to be produced. Thus, in the first measurement campaign, the goal is to determine the performance data, as pressure head and hydraulic efficiency. However, the model is also to be used in the future to optically measure velocities or turbulent quantities.

Fig.2.1 Fabricated acrylic model for the experimental investigations.

To meet the above points, it was decided to make the experimental model from polymethylmetacrylate (PMMA or acrylic glass). Since acrylic glass is a transparent plastic, accessibility for optical measurement techniques is ensured. Furthermore, acrylic glass can be machined well, so that all wetted components could be manufactured from solid material by milling. The fabricated components can be seen in the assembled acrylic model in Figure 2.1. The acrylic model consists of two acrylic blocks that are bolted together and sealed by an O-ring at the interface. Inside the two acrylic blocks, the VAD outside diameters and the diameters of the inlet and outlet pipes are milled. The hydraulic components of the VAD (inlet guide vane, impeller, outlet guide vane) were also made of acrylic glass. Dimensional tolerances of $10~\mu m$ were achieved for all these components. Furthermore, all components were were hand-polished to achieve hydraulically smooth flow behaviour.