On the secondary flow through bifurcating pipes

Abstract

The secondary motion induced by flow through curves and bifurcations has been subject to investigation over long time due to its importance in physiological and technological applications. In contrast to the flow in a straight pipe, curvature leads to the formation of secondary flow which is often unsteady. Streamline curvature occurs also in bifurcating pipes leading to some corresponding secondary, unsteady flow. This paper presents a detailed description of the unsteady flow in the daughter branch after a 90° bifurcation. A range of Reynolds and Womersley numbers are investigated. The results show the presence of Dean vortices and additional vortical patterns not reported in the literature. Both the streamwise (axial) and the secondary velocity components change character at larger Womersley numbers, leading to less complex secondary flow. Also, at larger Reynolds numbers, flow instabilities are observed. The secondary flow may lead to the formation of unsteady separation bubbles. This in turn yields peaks in the wall shear stress components. Such wall shear stress variations have often been related in the literature to the development process of atherosclerosis.

A computational study of the respiratory airflow characteristics in normal and obstructed human airways

“…Based on the Hagen-Poiseuille equation, which assumes a fully-developed axial flow condition, the airway resistance should be constant for the same geometry. However, because the airway geometries in our models constitute a 3-D network of conduits that are curved near the bifurcations, secondary flows were expected to develop, as reported in the literature [39]. In such a system, flow resistance does not remain constant (as expected from the Hagen-Poiseuille equation) as the secondary flow increases with an increase in the pressure drop.…”

Wall shear stress variations and unsteadiness of pulsatile blood-like flows in 90-degree bifurcations

“…The pressure values specified at the outlets are the same for all cases and do not vary with time. The values are dependent on the cross-sectional area of each branch and were chosen to validate the solver with previous studies by Evegren et al [20,21], where shorter branch lengths and a similar finite volume solver were employed. The walls are modeled as rigid, a good approximation when considering atherosclerotic arteries, but less good for arteries in young individuals.…”

“…not symmetric relative to the peak [24]. However, a welldefined temporal inflow profile is needed in order to determine the periodic pulsating character of the flow and its frequency (Womersley number) response [20,21,48]. As argued for the choice of geometry, regarding uncertainty, it is more important that the inflow profile be reproduce-able in repeated numerical experiments…”

Secondary flow structures under stent-induced perturbations for cardiovascular flow in a curved artery model

“…Strong evidence linking cellular biochemical response to mechanical factors such as shear stress on the endothelial cells lining the arterial wall has received considerable interest (Berger and Jou, 2000;Barakat and Lieu, 2003;White and Frangos, 2007;Melchior and Frangos, 2010). Secondary flow structures may affect the wall shear stress in arteries, which is known to be closely related to atherogenesis Evegren et al, 2010). Wall shear stress, especially low and oscillating wall shear stress has been shown to be important in arterial disease Weyrich et al, 2002).…”