Altered hemodynamics play a key role in cerebrovascular diseases such as aneurysms and stenosis. However, in vivo imaging lacks the spatial resolution required to resolve flow dynamics in small vessels. This study presents an experimental framework to investigate microscale hemodynamics using transparent 3D-printed vascular models and particle image velocimetry (PIV). Optically transparent microfluidic models with straight and pathological (aneurysmal and stenotic) geometries were fabricated via additive manufacturing up to a minimum diameter size of 500 µm and characterized using optical microscopy. Flow experiments were conducted under steady laminar conditions, and local velocity fields and wall shear stress (WSS) were measured using micro-PIV. Measured velocities have been compared with analytical Hagen–Poiseuille predictions, obtaining mean relative errors of 5–17%. The platform reliably captured key flow features and spatial variations in velocity. Overall, the results demonstrate that transparent 3D-printed vascular models combined with micro-PIV provide a robust experimental approach for studying microscale cerebrovascular hemodynamics.

We investigated the flow and bubble dynamics in a stopper control valve as used in continuous casting of steel under flow conditions where cavitation or quick degassing is expected to occur. We compare the flow of a typical control stopper with four archetypical stoppers. The effect of stopper geometry on cavitation dynamics is studied experimentally in a downscaled two-dimensional water model. High-speed imaging in combination with pressure data sheds light on the performance of the various stopper geometries under cavitating and non-cavitating conditions. It is found that a blunt-ended stopper shape induces, under all conditions, a strong flow separation leading to a large pressure loss coefficient, K. In return we find that the controllability of the flow improves while K changes only marginally when entering a cavitating flow regime. In contrast, more streamlined stoppers show a lower K that yet sharply increases at the onset of cavitation; possibly causing instability in valve throughput.