Influence of Particle Migration in Blood and Particulate Blood Analog Fluids in Gap Flows and Annular Gap Flows at Technically Relevant Reynolds Numbers

• Applicants: Professorin Dr.-Ing. Jeanette Hussong; Professor Dr.-Ing. Frank-Hendrik Wurm
• Subject Area: Hydraulic and Turbo Engines and Piston Engines
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 469384587

Ventricular assist devices (VADs) are implanted in people with severe heart failure to maintain blood circulation. The most implanted VADs are turbomachines. The rotation of the impeller in these machines causes supraphysiological stresses of several hundred pascals, which can damage blood cells. The highest stresses are present in the gaps of the VAD. These gaps are often only a few hundred micrometers in size and blood flow into this region has been little studied. It is known from the literature that blood cells flowing through vessels of a few hundred micrometers tend to migrate to the center of the vessel. A cell-free layer (CFL) is formed at the wall due to this migration. Cell migration also occurs in VAD gaps. But, its extend and effect on the resulting stress field has not been investigated in the literature to date. In the first phase of the project, cell migration in microchannels was therefore characterized under flow conditions and geometric dimensions of a VAD gap without rotation. From these results, new central questions arose, which will be answered in a follow-up project: How does a CFL develop at different volume fractions at high Reynolds numbers and how can this be numerically modeled? How do additional shear flow and centrifugal forces, as they occur in rotating VAD gaps, affect cell migration and the stress field? Since optical accessibility to the VAD gaps is limited, the geometric parameters and flow conditions of VAD gaps are mimicked in microchannels and rotating annular gap flows perfused by animal blood and refractive index matched, particulate blood analog fluid. Optical flow investigations by astigmatism particle tracking velocimetry (APTV) are performed to characterize the particle migration in blood and blood analog fluid. In addition, mechanical measurement methods, such as direct wall shear stress measurement and pressure loss measurements will be used. The investigations allow detailed comparisons between blood and particulate blood analog fluid at different volume fractions. Numerical modeling of blood flow will be used to capture cell migration extending the currently developed fluid model that accounts for cell migration at high Reynolds numbers. This flow model will be validated against experimental data. The investigations form the basis for a better understanding of blood flow in VAD gaps under the action of shear forces and centrifugal forces and will help to improve numerical blood modeling in VAD flows.

• DFG Programme: Research Grants