Quantum mechanics

Turbulence

Laminar flow

Materials science

Shear (geology)

Pulsatile flow

Vortex

Cardiology

Pipe flow

Shear stress

Classical mechanics

Physics

Nonlinear system

Instability

Open-channel flow

Flow (mathematics)

Shear flow

Internal medicine

Composite material

Medicine

Mechanics

Proceedings of the National Academy of Sciences

Pulsating flows through tubular geometries are laminar provided that velocities are moderate. This in particular is also believed to apply to cardiovascular flows where inertial forces are typically too low to sustain turbulence. On the other hand flow instabilities and fluctuating shear stresses are held responsible for a variety of cardiovascular diseases. Here we report a nonlinear instability mechanism for pulsating pipe flow that gives rise to bursts of turbulence at low flow rates. Geometrical distortions of small, yet finite amplitude are found to excite a state consisting of helical vortices during flow deceleration. The resulting flow pattern grows rapidly in magnitude, breaks down into turbulence, and eventually returns to laminar when the flow accelerates. This scenario causes shear stress fluctuations and flow reversal during each pulsation cycle. Such unsteady conditions can adversely affect blood vessels and have been shown to promote inflammation and dysfunction of the shear stress sensitive endothelial cell layer.

Nonlinear hydrodynamic instability and turbulence in pulsatile flow