Fluid structure interaction in pulsatile flow through an elastic pipe segment

Fluid-structure interaction (FSI) in elastic vessels occurs in a wide range of systems in nature and technology. A difficulty in the development and validation of FSI models is the lack of quantitative measurements of vessel response to unsteady flow forcing. We here investigate the canonical case of an elastic tube subject to laminar pulsatile flow. For this purpose, we develop an experimental setup comprising a high-precision piston, a three-dimensional (3D)-printed elastic pipe, and a camera equipped with a microscope objective to determine the wall displacement. We find that for weak forcing the response is similar to a forced damped harmonic oscillator. Near resonance and for moderate forcing amplitudes, the wall motion exhibits complex dynamics, including multiple frequencies and nonaxisymmetric tube deformation. When the amplitude of the response exceeds a threshold, the tube collapses nonaxisymmetrically during parts of the cycle, thereby drastically reducing the cross-sectional area of the tube. We additionally perform fully coupled axisymmetric numerical simulations based on the solution of the Navier-Stokes equations and a thin-shell model for the tube. Our simulations agree with experimental results, except near resonance and under large amplitude forcing, where a 3D model accounting for structural damping would be necessary. Our results shed light on the rich nonlinear dynamics of this canonical system and serve as a basis to validate future models.