Project Details
Projekt
Hydrodynamic stability of pulsatile flow of complex fluids
Applicant
Professor Dr. Björn Hof
Subject Area
Fluid Mechanics
Term
since 2019
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 349558021
Recent experimental and theoretical advances have given rise to a near complete understanding of the onset of turbulence in steady pipe flows, yet under pulsatile flow conditions the situation is far more complicated. Here in addition to the (mean) Reynolds number also the pulsation frequency, amplitude and waveform have to be taken into account and this fundamentally changes the transition route to turbulence. The situation becomes even more complicated if we consider cardiovascular flows, where also the complex fluid properties of blood, details of the geometry (e.g. curvature, junctions, constrictions etc.) and wall compliance have to be taken into account to decide if flows are smooth and laminar or disordered and fluctuating. At the same time disordered fluid motion is believed to be a central cause of various cardiovascular diseases. The inner lining of blood vessels, the endothelium is shear sensitive and fluctuating wall shear stress levels can cause inflammation of this cell layer. This in turn can cause the development of atherosclerosis lesions. As we demonstrated during the first funding period, pulsatile flow gives rise to a specific helical instability mode and this results in a fundamentally different transition path to turbulence [P1]. Strikingly this instability persists to far lower flow rates than the ordinary transition type and hence instabilities may not only be expected in the largest blood vessels like the human aorta, but also in smaller arteries. Non-Newtonian fluid properties such as viscoelasticity or suspended particles (red blood cells are elastic and make up ~40% of the volume) are equally known to promote instability down to very low Reynolds numbers [P2,E7], whereas curvature has a stabilizing effect[E5,E6]. While the influence of these parameters on the flow’s stability is hence fairly well understood for steady pipe flow, their impact on the stability of pulsatile flow is entirely unknown and this will be the subject of A1 during this second project phase. Given the exceedingly large number of control parameters we will focus on two regimes. The first corresponds to parameter values that are typical for large blood vessels and the second to those that are encountered in small vessels. By varying one control parameter at a time we will map out the different types of instabilities that arise. This investigation will be carried out in close collaboration with the accompanying computational and theoretical projects in order to obtain a better understanding of the underlying instability mechanism. Overall the aim of this project is hence to determine the most common instability types that can occur in pulsatile flows of complex fluids.
DFG Programme
Research Units
International Connection
Austria
Partner Organisation
Fonds zur Förderung der wissenschaftlichen Forschung (FWF)
