Project Details
Projekt
Dynamics and Instabilities of particle-laden pulsatile flows in complex pipe geometries
Applicant
Professorin Dr. Kerstin Avila
Subject Area
Fluid Mechanics
Term
since 2019
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 349558021
In a steady laminar flow through a straight pipe, particles migrate in the radial direction towards an equilibrium annulus. This effect is known as focusing and is exploited in microfluidic systems to sort particles. In a turbulent flow, on the other hand, particles are chaotically mixed and their motion cannot be predicted. Laminar flows with a time-dependent mass flux such as harmonically driven pulsatile flows fall somewhat in between, and despite their relevance for engineering and for the cardiovascular system, little is known how particles migrate in such flows. In this project, we track neutrally buoyant particles in pulsatile flows through straight pipes and a T-junction, and measure the fluid velocity field with the Shake-The-Box Algorithm yielding 4D-data. By using transparent hydrogel particles, we are able to measure in addition the instantaneous rotation velocity and axis of the particles. Our analysis resolves the particle migration during a pulsation and the particle motion averaged over several periods is compared to the one for a steady flow. This helps elucidate whether pulsation enhances or delays the particle focusing. In addition, phase-resolved measurements of the particle migration provide information about the physical mechanisms underlying migration. Our preliminary results suggest that the particle dynamics becomes most active in the low velocity pulsation phase. Here the particles have still a significant rotation, which drives a rapid radial migration. At the same time, vortices are created even several pipe diameters away from their position and trigger hydrodynamic instabilities. Special attention is dedicated to investigate the particle-flow interactions when flow reversals occur in the vicinity of the pipe wall. Such reversals are believed to contribute to diseases like intimal thickening and plaque formation in the cardiovascular system. The investigation of the particle segregation in a T-junction under pulsation will serves as a simplified model system to shed light on the path taken by blood clots in the carotid bifurcation.
DFG Programme
Research Units
